Infrared spectra of four isotopic species of azulene

Spectrorlknicn dcta, 1963,Vol. 19,pp. 1495to 1530.PergamonPressLtd. Pritltedin NorthernIreland

Infrared

spectra of four isotopic species of azulene* A. VAN TETS and Hs. H. G~~NTHARD

Physical

Chemistry

Laboratory,

(Received

ETH,

2 January

Ziirich,

Switzerland

1963)

Abstract-The infrared spectra of azulene and its isotopic modifications d,(1,3), c&(2,4,5,6,7,8) and d, have been measured between 4000 and 280 cm- I. Both polarized and unpolarized crystal spectra, in addition to solution spectra, were investigated. Based on these spectra, vibrational assignments are discussed for all four isotopic species. For the A, and B, fundamentals the assignments suggested are complete and satisfactorily obey the sum and product rules. An assignment is also proposed for the B, fundamentals, which is considered to be complete for the light molecule d,, but includes two estimated fundamentals for the deuterated species in the far-infrared region. Finally, a tentative and incomplete assignment for the A, fundamentals is given, as well as a plausible interpretation of the remaining parts of the infrared spectra in terms of combination tones. 1. INTRODUCTION THE infrared spectrum of azulene has been investigated by several authors. By far the most complete experimental study of azulene, itself, in solution as well as a single crystal, has recently been reported by HUNT and ROSS [Z]. This work includes an assignment of a number of fundamentals and combination tones, based mainly on polarization measurements in the frequency range 2000-450 cm-l. These authors have also studied the vapor spectrum between 4000 and 700 cm-l. They used the vapor-crystal intensity ratio for the assignment of the A, vibrations. A partial assignment for the CH stretching vibrations of azulene and azulene-d,(1,3) based on solut#ion spectra has been given by BAUDER and G~~NTHARD [3]. In addition infrared solution spectra of azulene-d,-( 1) [4], azulene-d,-( 1,3) (3,5), azulened,-(2,4,5,6,7,8) (5) and azulene-d8 [5] have been reported. In this paper polarization measurements on single crystals of azulene and its heavy modifications d&1,3), d,-(2,4,5,6,7,8) and d, (hereafter these isotopic species will be designated for convenience as d,, d,, dG and d, respectively) are reported for the 3000, 2300 and 1700-450 cm-l regions, as well as unpolarized crystal and solution spectra in the frequency range 4000-280 cm-l. A complete assignment for the A,, B, and B, fundamentals is suggested, which explains the observed spectra satisfactorily. The sum and product rules are well satisfied and most of the nonfundamental bands can be reasonably explained. In addition an incomplete and rather tentative assignment for the A, fundamentals is given. From a spectroscopic point of view the azulene crystal represents a rather particular case [6]. Crystal structure studies of azulene have shown the lattice to be

* For detailed [I] [2] [3] [4] [5] [6]

information

see Ref. [l].

A. VAN TETS, Thesis ETH. Prom. No. 3400. To be published. G. R. HUNT and I. G. Ross, J. Mol. Spectrosc. 3, 604 (1959). A. BAUDER and Hs. H. G~~NTHARD, HA. Chim. Acta 41, 889 (1958). A. VAN TETS and Hs. H. GeNTHARD, Helv. Chim. Acta 44, 692 (1961). A. VAN TETS and Hs. H. GBNTHARD, Helv. Ohim. Acta 45, 457 (1961). J. M. ROBERTSON, H. IN. M. SHEARER, G. A. SIM and D. G. WATSON, Acta Cryst. (1962). 1495

15, 1

1496

,4.

VAX

TETS and Hs. H. G~~NTHARD

disordered.* The crystal at room temperature belongs to the class C,, with space group Csh5. The unit cell contains two molecules (Z = 2) and has very similar Therefore the symmetry of the sites of both dimensions to that of napthalene. molecules is C,?. The symmetry group of the free molecule is believed to be CZV, but the crystal field is expected to disturb this molecular symmetry and reduce it to C,. However, the crystal field may be assumed to be weak as as a consequence, the deviation from C,, for the molecular symmetry should be small. Nevertheless this perturbation might allow A, type vibrational transitions in the crystal spectra. Indeed this seems to be the case. It is difficult, however, to predict the intensity Only small dichroic splitting of the A,, B, and polarization of the A, transitions. and B, type transitions is expected under the assumption of a weak crystal field. The disorder, which seems to exist in the lattice, is of such a nature that the polarizations of the A,, B, and B, transitions in the crystal spectra should obey the same selection rules as for an ordered lattice. 2. EXPERIMENTAL The isotopic azulenes used in this work were prepared and purified by the methods [3-51 previously reported. With regard to isotopic purity of the samples used in this investigation a few remarks seem to be adequate. The d, sample was found by direct deuterium determination to contain 24.9 & O-2 atomic y0 D. Nevertheless a few very strong d,- and cl,- absorption bands have been observed in the infrared spectrum of this dz sample. The d, samples showed a content of approximately 90 per cent of mass 134 (de), the isotopic impurities were essentially the d,, d, and d4 forms. Only a very few of the observed bands seem to originate from these isotopic contaminations. In the case of the d, isotope the mass spectroscopic investigation of the samples are not too reliable, due to exchange of deuterium by protium in I- and S-positions Since the d, isotope samples were prepared from I&, in the mass spectrometer. we conclude that the isotopic impurities of our d, samples do not exceed IO per cent. As a consequence no strong bands from lower isotopic substituents should Owing to the above mentioned uncertainties with be observed in the spectra. regard to isotopic purity of our d,, cl, and d, isotopes, an additional precaution was made. Several samples of each isotope obtained by different preparations were checked for the identity of the absorption spectra. Crystals The single crystals were grown by slow sublimation from 20 mg aliquots of the isotopic azulenes. The growing process was carried out in narrow necked ampules of Pyrex glass (70 mm diameter, 120 mm length), which were filled to 200 mm Hg with dry nitrogen. The temperature gradient was kept as low as possible during the growing process, which was started at about 60°C. After a day, the containers were cooled slowly to room temperature. In most cases this process was repeated several times in an ordinary oven until satisfactory results were obtained. The specimens obtained in this way were proved to be single crystals by the * The disorder originates from the possibility of inversion of t,he molecules in their sites. t The site co-ordinates are O,O,O; I/2, l/2. 0.

Infrared

spectra

of four isotopic

1497

species of azulene

They appear in thin plates (approximately 10 ,u thick) of polarizing microscope. about 2 cm2 area. The shiny faces were invariably parallel to the (001) lattice plane, whereas the ot’her faces often were irregular. However (1 IO), (010) and other Identification of the crystallographic a and faces were sometimes well developed. b axes by the polarizing microscope was not always possible due to the high absorption in the visible region. Spectra infrared Unpolarized crystal spect’ra (Fi g. 1) were measured on a Perkin-Elmer spectrometer model 221! using slit program 9.27 and recording speed 3 (scan time

Fig.

1. Nonpolarized

crystal

spectra

(4000-650

cm-l)

Perkin-Elmer

Model

221.

1 hr). For these measurements between 4000 and 650 cm-l the sample, which sometimes was composed of several crystals, was placed between rocksalt plates. The light was normal to the ab faces. Polarized crystal spectra (Figs. 2-6) were measured on a Perkin-Elmer infrared monochrometer model 99 using double-pass operation and a silver chloride plate polarizer (4 plates) in front of the entrance slit. The polarized spectra were taken on single crystals of sufficient size (1.5 x 0.7 cm2 area) cut from larger specimens and placed between CsBr plates inside a suitably shaped lead spacer of 100 y thickness. The whole sandwich was mounted in

A. VAN TETS and Hs. H. G~~NTHARD

1498

Solution

Crystal

8

7, ,I-.\.< ,-\ ,^l_ __‘~.__ : (~,’ .l,, ” e,;*., ;‘?, I \..,,-,i: : {F:;I ,,. .’ ,,’ .’ f _’ _’ ~bf?j QO ;

Fig. 2. C-H stretching region (3100-2950 cm-r). On the left: single crystal spectra _,----

unpolarized polarized //b polarized I b

Perkin-Elmer, Model 99, LiF prism; spectral half width 261.9 cm-l. On the right: 10% solution in CS,, thickness 0.2 mm for d, and d,; 5% solution in Ccl,, thickness 0.5 mm for d,; Perkin-Elmer Model 221.

2950

cm-’

3100

$? ’ Fig. 3. C-D stretching region (2350-2200 cm-l). On the left: spectral half-width 1.6-1.3 cm-r

----- . -

-----

Nonpolarized polarized [( b polarized 1 b

-

I

,

I---- ~.

2 _ z ‘c

On the right: 5% solution in 2 2 Ccl,, thickness 0.5 mm; PerkinIElmer, Model 221.

---

_

235;

_I1_i___-i_l_--l_

c m-’

2200

Infrared

spectra

of four isotopic

1499

species of aznlcne

Fig. 4. Polarized crystal spectra (17001250 cm-l). NaCl prism, spectral halfwidth 44-1.8 cm-l. Other conditions as in crystal spectra of Fig. 2. _~__

Nonpolarized 11b - - polarized I_ b

t ~- polarized

1300

8

Fig. 5. Polarized crystal spectra (1300-660 cm-l). Spectral half width 3.0-1.5 cm-l. Other conditions as in Fig. 4.

i

.-0

.-2

___ _-

Nonpolarized polarized j/ b - - - - polarized 1 b

E

F 0

c

1300

cm-’

1000

700

cm-’

-

1500

il. VAN TETS and Hs. H. G~~NTHARD

600

560

460

360

cm-’

Fig. 6. Polarized crystal spectra (670-280 cm-l). Oni Lhe left: KBr prism, spectral half-width 3.2-1.1 cm-l. On the right: CsBr prism, spectral half-width 5.5-2.1 cm-l. Other conditions as in Fig. 4. Nonpolarized - polarized 11b - - -- - polarized 1 b

an evacuated low-temperature cell. A special mirror system was used to focus the global source on the single crystal and the single crystal on to the entrance slit of the monochromator. To prevent sublimation of the crystal and improve heat conduction the sample space was filled with helium to approximately 20 mm Hg pressure and the whole sandwich was cooled to about 0°C. By this procedure the crystals kept long enough to allow all the required measurements on the same single crystal between 3100 and 280 cm- l. It should be mentioned that in some cases these measurements were disturbed by the appearance of interference fringes originating from the sample cell, from the crystal plate and from the dummy cell used to measure the background intensity. The spectra were corrected for this disturbance as much as possible. The large breadth of the interference fringes (period about 50 cm-l) compared to the half width of the absorption bands and the lack of the polarization of the fringes permitted a reliable correction in general. Spectra in Ccl, and CS, solutions were measured on the Perkin-Elmer model 221 in the 4000-650cm-l region (Figs. 2,3 and 7)and on the model-99 single beam, double pass between 660 and 280 cm-l (Fig. 8). Ordinate and abscissa expanded spectra have been recorded with very low

1501

Infrared spectra of four isotopic species of azulcnc

4000

3000

2000

1000,

cm-’

Fig. 7. Solution spectra (4000-500 cm-l). Perkin-Elmer, Model 221. l 5% solution in Ccl,, thickness 0.5 mm. * 0.5% solution in Ccl,, thickness 0.5 mm. 0 5% solution in CS,, thickness 0.2 mm for d,, d, and d, or 0.25 mm for

d,.

recording speed and are partly given in Figs. 2 and 3. These spectra were taken to obtain detailed information on envelopes of bands occurring in the v(C-H) and v(C-D) region, around 3000 and 2300 cm-l respectively, as well as on the band envelopes occurring in the region of solvent absorption near 1500 cm-l. Measurements of far infrared spectra on Nujol mulls of d, have been made by MILLER and FATELEY* between 640 and 100 cm-i. The results have been kindly communicated to us by the authors and will be ut’ilized in the discussion below. Their measurements agree satisfactorily with those reported here for most bands in the region 640-280 cm-i. For the discussion of the spectra, only those absorption bands have been considered whose intensities exceeded the noise level and which were detected in all spectra of a given isotopic molecule taken under fixed conditions. In the case of * We express our gratitude to Dr. MILLER and Dr. FATELEY for their kindness in making the measurements and informing us about the results.

A. VAN TETS and Hs. H. G~NTHARD

1502

~~ i:i

:-

Fig.

~. ,.

500

600

~~ J-

~._,

300

400

cm-’

8. Solution

spectra (600-280 cm-l). Perkin-Elmer, Model For KBr prism spectral half-width 3.3-1.3 cm-l. For CsBr prism spectral.half-width 5.5-2.1 cm-l. thickness

solution prism 1 2 3 4 5 6 7 8 9 10

=KBr =KBr = KBr = CsBr = CsBr =KBr = KBr =KBr =KBr = KBr

99.

(mm)

% 5 1.7 0.6 5 2.5 3.3 3.3 0.8 0.4 5

in in in in in in in in in in

Ccl, Ccl, Ccl, CCI, Ccl, Ccl, CS, Ccl, CS, Ccl,

1 1 1 0.5 0.5 1 1 1 0.5 0.5

the d, species, a small number of bands were found, which show different intensities For such bands the possibility of originating from in different preparations. isotopic impurities was considered and their assignment is rather uncertain. 3. RESULTS The spectra are shown in Figs. 1-8 in Tables l-4.

and DISCUSSION and the observed

frequencies

are collected

Infrared Table

spectra

1. Observed

V16

iaTBU C&,, (W4,)

,‘tccc,

VS6

v43y

VMB,)

y20y

(a2) (b,‘(B,)

y4ay AICCC,

v42y ylgy

180+ m, p.n.m. 319 vs,p.n.m. 333 xv, p.n.m. 401 VW, p.n.m. 483 m /I

(al)(B,) (WA,)

(h’(4) W(B’,,) @a’(%) (WA,,)

%s

+

v45

$)(B,,)?

y14

+

v47

(B,)(B,)

y12

-

v47

VI5 + V46 N(C--Cl 1'13

(BdB,) (B,)(B,) (alHB,)

v18y

(a21

Yll

-

v47

(B,)(Bt,)

%I

-

Y48

(B,)(B,)

(cm-‘)

170+ 6, p.n.m.

(b,‘(-%) @A(B,) W(B,) (U(B,’

V21 AICCCI 2’15 AK!CC, V38 AfCCC, VS? AtCCC, VI1

1503

bands of azulene*

(crystal) v vacuum

VP8 ,‘(CCCl VP7 rICCCI VP6 r,ccc, V45 AICCCI v17 A.cCCC, 1’39

AfCCC)

infrared

species of azulene

Wln. Ccl,) v

Assignment l-,CCC,

of four isotopic

1

484 s 1

531 VW 11 558 vs i\ 566 vs 11I 596 s 11 671 VW? p.n.0. 708m i? 722 w, sh? I 730 vs _I 744 m _i~? 765 “S, p.n.0. 795 s 1 826 w jL 858 U’ I/ n.0. 899 w i

nm. n.m. 311 vs, b 330 w, sh 403 m 478 m 492 s ll.0.

559 vs 593 s 671 m 702 w 721* s Il.0.

764* “S n.0. 821* s 853 VW 869 VW? 899 8

908 U’ 11

n.0.

940 VW. sh i/

940 sh

1

V41Y

(b,)(h)

954 vs, p.n.0.

v40y

(b2H-U

966 X’S I/?

946 “S 960 vs

9SG m ;I

97G m

W(A,)

y35* y14

+

V46

2

x

V16

y43

+

V46

v44

+

v4.5

'15

+

'16

'38

+

'39

6 y34

V126

(B,)(B,)

(,4,)(%) (WA,) (MB,) (a,)(&) (;3,)(B,) (f&H%) (al)(%)

I 1014 1 1

%I6 y20

+

VI7

v42

+

'39

'42

+

'16

v33* y326

'8

-

v44

YBCUUm

(cm-l)

'47 +

v15

%)I BU) (&‘U (WA,) (A,) U-W)) (B.&B,) (B,HRJ

VIOS

(al)(&)

V316

WkL)

%9

+

V21

b‘M%)?

'42

+

'15

(B,H%)

m 11 n.0.

1035 w

1046 VU’ I

1046 w

1056 VW A. 1115 VW, b? i ? 1140 w. sh A_ 1154 m 11

1054 vs

1208vs 6 ? 1250 VW, p.n.0.

1117 VW n.0. 1151 w 1205 s n.o.

1266 VW 1.

1267 w, sh

1292 sh 1 1301 s //

1294s

i

1

1007 m

n.o.

1301 s 1320 VW, sh

1504

A. VAN TETS and Hs. H. G~~NTH~RD Table 1 (COY&I.)

(Soln. Ccl,)

Assignmont

(Crystal) hcuum 1352 VW’, b I 1397 m i

(B,)(B,) (a,)(%)

v2s -

v47

(A,)? (A,)

v~~c=fov14 Vl3 NK!=C) VW3 pc=o 88

@,K‘L)

v34 + v39

(A,)(K)

v41

+

v15

(B,)(B,)

v12

+

V16

(A,)(&,)

v33

+

v17

(W(A,)

1408 w I/

(b,)(4)

(B,)(A,)

y12 +

(Al)(%)

v15

(B,)(A,)

'32 + v17 N(C=Cj V%

(al)(%)

y35

+

v14

(B,WL)

%2

+

v37

(WA,)

v40

+

v44

(Al)(%) (A,)(W

%l + VI5 N(C=C, VW

1

v17 v13

(Al)(%)

'32

+

'37

(Al)(%)

2

'

'18

v43

+

v38

2 v40 '8

x

v21(AlHBu)

v13

(B,)(B,)

V16

(A,)(%)

(A,)(%) (MB,)

'1G v39

(Al)(%)

'32

v36

(MB,)

VI3 +

V46

(B,)(B,)

y9

+

v15

(Al)(%)

+

y13

(A,)(%)

+

v45

(B,)(B,)

+

v14

(A,)(%)

'8

+

'15

(Al)(%)

2

x

y9

+

%4

2

x

v12

Y6

1628 w, b J_

1638 m

1649 w I/

1650 w. sh

n.0.

1670 w

Ij

1694 m 1742 VW? 1769 VW?

11.0.

1799 w

I

1815w I

(Al)(B,)

V4l

+

%o

1617 m

J_?

1820 s

/I?

1858 w

1864~~

1884 VW, p.n.o.

1889 w

1907 vw, p.n.0.

1908 m

1926 m 1

1930 m

(B,)(B,)

2130 +

%2

1580 vs

1618 VW, sh? p.n.o.

1697w

(A,)(%) +

+v41

+

1493 m 1518 VW, sh? 1537 m n.0. n.0.

(Al)(%)

+ x

+v45

1479vs

n.0. 1770 VW?

2

y7

1453 s

vs, p.n.0. vw? p.n.0. w // w 1 w jl ? w 11?

1

W(A,)

y9

+

1454 s I/ 1478 1495 1516 1535 1555 1563

1

n.R.

y9

1443 vs

1581 1588 mm 1111

n.a.

2140 +

1351 w, sh

1392 vs

1448 s iI?

(MB,) (bl)(A,)

bsCUUm

(cm-l)

no.

1

(4(%)

v34 + v15 NlC=C) V7 NlC=Cl VW

(cm+)

n.a.

?

I

1948 m I

1959 m jj ? 1968 m

I

n.0.

2004 VW

(Al)(%)

n.0.

(Al)(%)

n.0.

2065 VW 2115 m

n.0.

2135 VW, sh

(MB,)

v34

I

1

Infrared spect.ra of four isotopic species of azulene

1505

Table 1 (Contd.)

(Crystal) ~"a,,",(cm-l)

Assignment

n.0.

n.a. y27 + y39

(Al)(%)

v33 + y34

(B,)(K)

v33 + p12

(WA,)

Y28 + %4

(B&A,)

v27 + %

(BlWL)

'32 +- '12

(WA,)

(,4,)(B,)

2 x v32

W(%) (B,)(A,)

y30 + %2 2 x v31

Ph)(%)

n.a. n.a. n.a. n.a. n.a. n.a. n.a.

2 x v29 v7 +ve

“(C--H) VU “,C_-H, 16 “,C_-H, rq “(C--H, %6 “(c--II, r3 “,C_-H, r, “,C--H, r24 “,C_II) VI V6 + y30 2 x v7

(A,)(%

(14,)(&J (WA,) (al)(K) j;‘;;;“,’ (&R:) (Q(K) WA,) (Q(G) (BlWJ (A,)(%)

'27 + '29

(A,)(%)

-t v13

v4 + v13

2210 vw, p.n.m.

2210 VW

2259 w, p.n.m.

2257 m

n.0. 2299 w, p.n.m. n.0. n.0. 2509 w, p.n.m. n.0. n.0. 2686 VW, p.n.m. 2733 VW, p.n.m. 2780 VW, b, p.n.m. 2820 vw, b, p.n.m. 2850 VW, p.n.m. 2868 VW, p.n.m. 2961 m 11 2966 s I 2991 w ]I 3002 m I 3013 s _L 3032 m jl 3041 s 1 3057 s 1 3070 s 11 3075 s i_ 3086 w 11

2265 VW, sh 2299 w 2351 w 2398 m 2505 w 2601 w 2631 VW n.0. 2748 VW, b 2780 VW, b n.0. 2840 VW 2880 VW, b 2958* m 2971* m 3007* vs 3024* 3044* 3059* 3074* 3083*

s, b s s b, sh vs

3091*

sh

(A,)(%)

'28

v5 + y13

2165 w

I

(Bl)(A,)

y32 + y33

%6

n.0. I

n.a.

+ %4

2 ’

2152 VW, sh

(A,)(%)

Yll + %2

%a

(Soln. Ccl,) Y,,,,,, (cm-l)

;Zg::3

2 x v2g + v40$2iiE$l

n.0.

3174 w, b

I

3896 w, p.n.m.

3896 w

3925 w, b, p.n.m.

3911 VW, sh

* For the polarization in the 2000-670 cm-l region of azulene reference is made to the work of HUNT and-Ross [2]. v(C-H) C-H stretching v(C-D) C-D stretching N(C=C) aromatic ring stretching N(C-C) aliphatic C-C stretching s light atom planar bending A skeletal planar bending light atom nonplanar bending Y iskelet)al nonplanar bending

8

A. VAN TETS and Hs. H. GWTHARD

1509

Table 1 (Contd.) absorption expected mainly )I crystal b-axis absorption expected mainly //crystal b-axis polarization 11b-axis polarization 1 b-axis not assigned not measured not, observed polarization not measured polarization not observed broad shoulder uncertain Nujol spectra from MILLER and PATELEY (sol.CS,)

(A,) (BtA (! I na. n.m. n.o. p.n.m.

p.n.0. b sh ? + * For the conventional

notations

see Ref. [7].

The interpretation of the crystal spectra is based on the lattice model represented by Fig. 9. This model is derived from the work of ROBERTSON et al. [6] (Table 3c), where the co-ordinates of the carbon atoms are given. Although the Azulen - Krl S~OII (001)

Lottfce

Projection

Fig.

9. Azulene

(010)

crystal.

Inversion monads are centered between screw diads and glide planes. Molecular sites are identical with the positions of half of the inversion monads. Alternative molecular arrangement is given in each site separately by broken and unbroken lines respectively. For conventional not,ations see: International tables for X-ray cryst,allography Vol. I (1952) (The Kynoch Press, Birmingham, England) Tables 4.1.6 and 4.1.7 (pp. 49950) [7] 0. HERZBEKG, York (1947).

Molecular Spectra

and Molecular

Structure

Vol.

II.

Van

Sostrand,

Sew

Infrared spect,ra of four isotopic species of azulene

1507

Table 2

tsol.

Assignment

-_____ r1ccc1 ‘48 I‘ICCC, VP? ,‘,CCC) v&e ,‘COCCI VP6 ,~,‘CCC’ LSICCC) VSU AICCC) V18

v44

-

(b,)(k)

c. (-155)

n.m.

(U( B,)

c. (-lG;j)

n.m.

(M( B,)

327 vs, p.n.m.

(W( B,)

320 sh, p.n.m.

(al)(&)

398 vw, p.n.m.

(b,)(-%)

457m,b

(a,)(&)

479,

ccccb

@e)?\

(b,HA,)

d,-fundamental do-fundamental

I

(hl)b~,) (%)?I

impurity ? v44y

2 x v45 AICCC, V.36

I (bJ( Bu) I

v19v

d-fundamental 1’4??

-fundamental

y47

+

‘46

VI5

+

V46

v:i(i

+

“48

*38

+

y:5

VI5

+-

v?s

VYI

WC-C, V’, 3

“47

n.0. 500 1-s

531s

526 m

1 VW

I?

558 x-w 583 s

598 w, p.n.o.

n.0

0’43 \‘S _L

636* “S

G64 w, b i/

653 m

b,HB,) (B,KB,) (B,)(B,) (A,)(&)? (b,)(B,) (&H-4,)? (%?)?I

691 m _L 704 w, b 1 718 w, b .L n.0. 73X “S /I 763 w // 771 m /I

684 m 696* w n.0. 731* sh 7.3X* vs 765* m 771* w, sh

lb& Bu’I

780 vs 1)

774* vs

797

796*

VWU~ I

(A,HBJ~

+

485 w, b, sh?

5X6 s, p.n.0.

(b,)(4)

‘38

401 nl 452 VW, b, sh?

503 vs i I 50.5 s, sh li(

563

%oY

y44

n.m. ,308 s 315 sh

(R,WW)

v47

,AW321 3,

Ylli + Y?S PIA + Y16

1

n.m.

(AlHB,!? (aI)

d,

II?

vvwxum

(cm-l)

491 w, sh 1

(A,)?

y47

v4s + y47 AICCCI VIS l,A’CCCI 38

VI7 +

cc14)

(cm-‘)

kcoum

(A,)(h)?

‘48

VT36 -

(crystal)

I

(B,)(B,)\

(WB,)I

(o,H B,

) ((13) ((A,)( B,,) (tq(B,) (‘$1 (t~,J(A,)

I/?

808 w, b !I

(A,HB,)? (8,) (B,)(B,) (il,)? (A,) (B,I(B,) (il,)?

“W

VW?

808* VW

818 w, b 1

n.0.

835

n.0.

I VW

1

1 854 s i X57 s, p.n.0. XXX sh L? X91 P jl 91.7 w, sh 1 954 vs 11

860 vs n.0. 893 “S 899 x’s 11.0.

947 “S

1508

A. VAN TETS and Hs. H. G~~NTHARD Table 2 (Con&.)

Assignment

(crystal) vvacuum (cm-l)

$36 + V46

(A,)

'15

(WA,)

+ 1'

'39

I

(b,)(B,)

y40 %l

+

y39

(B,)(B,)?

v37

+

v17

(B,NB,)

v43

f

v45

v43

+

V46

v44

+

v17

pa1

+

v47

'32

-

v4!3 @,)(A,)

%BB %I6 v35

+

y47

la'YuJ 2?

y43

+

%7

(B,)(B,) (A,)

v44

+

V38

'13

+

'46

(B,)(B,)

V36

+

V38

(A,)(B,)

2

x

v37

(A,)(&)

YIOd

(a,)(B,)

'32'

(W‘U

v43

+

v15

(B,HB,)

'9

-

'47

(B,HB,)?

'18

-" '17

(A,)

V33 d

+ x

(B,)(B,)?

Y48 vq4

n.0. 980 m

1007 vs i

1003 s

1054 w, b 1

1046 m

1087 s, p.n.0. 1093 s 1. 1119 VW I/ 1140m 1 1151 m, sh

1088 s 1092 sh

1161 m 1

1162 w

1175 VW, sh, p.n.0. 1208 w, p.n.0. 1236 m 1_

1186 m 1213 w 1227 m

n.0. 1138 w n.0.

I

I

I

(AlHB,)

1247 sh 1 11252 w (( i n.0.

n.0. 1271 m

(W%)

y31* VI2

+

v17

(AI)

y41

+

%7

(B,HB,)

'42

+

'38

(A,)

y14

+

V20

(A,)?

'29

-

V47

(A,)?

'13

+

'39

(Wb‘L)

v34

+

y45

(A,)

'34

+

'46

(A,)

y43

+

y37

(A,) I

%3

+

Pl6

(Al)(&)

y43

+

v20

(f&HA,)?

y12

+

y39

(B,WL)

%o

f

y47

(B,HB,)?

'12

+

'16

Ml)(B,)

y13

i- %5

(A,)(&)

v43

+

(A,)(B,.)

y44

2 xv14 NtC=CI V9 y42

968 w I/ 978 s [I? 984 s 1

v346

(sol. ccl,) VW%C”“rn (cm-l)

+

y44

(A,)(b)

1288 sh i ( 1295 X’S [I

1%94 vs

I

1312 VW, sh I?

n.0.

1323 VW _L

n.0.

i

1336 VW I

1331 m

1342 w 1 ( 1346 w 111

1347 VW, sh?

I

I

1360w,b

I

I

1371 m 1381 w, p.n.0.

I

1402 m J_

(a,)(B,) (A,)(B,) (A,)(B,)

1

1394 vs

n.0.

1409 sh

I

v3.5 + v39 YIc=c, Vi,

kW‘L)

1428 w 11

1420 sh

NIC=C, VbJ

b,)(B,)

7449 s _L

1452 s

Infrared

spectra

of four isotopic Table

species of azulene

1509

2 (Contd.)

Assignment NCc?=C1

WL‘L) (A,)(%) (B,)(B,)

v29 2

x

y40

v43

i- v15

(B,)(B,)?

y35

+

%l

%3

+

y44

(WB,)

y35

-I- y37

y&~~

y41

+

y44

L&B:)

v;~y:c~~,y16 V? N,C=C, V28

(adB,)

+

VI7

1I jh$))($))

'8 + pC'C, cl

'48

(Bl,)(BI)‘!

y32

2 x v12 +

y14

2

x

v41

'43

+

'21

'31

+

'38

'35

+

'18

%o

+

v44

'32

+

'20

'8

+

'17

+

'38

n.a. y34

+

%2

y31

+

%o

v9

+

%

y7

+"a5

'8

+

'16

v29

+

y39

'30

+

'38

Y6

+

y45

'8

+

'15

Yll

+

1113

y31

+

836

v34

+

1'35

Y6

+

v45

ma. n.a. n.a. n.a. '28

+

'37

'32

+

'35

'28

+

'36

y7

+

V36

VlO

+

v33

(A,)(B,) (-4&B,) (AdB,,) (A,)(B,)? (JWB,) (B,)(B,) (B,)(B,) (B,)(K)? (-4,)(B,)

(B,)(B:) (A,)(%)

1530 sh

1566 w, sh 1

1570 sh?

1586 s L

1586 V8

1600 VW, sh, b Ii

1614 w

168.3 VW /I? n.0.

1631 m 1640 VW, sh 1689 m 1712 VW

n.0.

1779 s

n.0.

1796 VW, sh

i

1811 w, p.n.m.

1812 w

1841 vw, p.n.m. n.0.

1846 m 1858 VW

1882 VW, p.n.m.

1892 VW

1902 w, p.n.m.

1909 m

1926 m, p.n.m.

1930 m

1

(WA,) I (%W,~f~ (~4,)(%) (B,)(B,) I (AI) (~41)(B,) (WB,) 1 (B&(%) (A,)(B,) (A,)(B,,) I $$E”; J

2 x vqO

1530 w 1

n-0.

n.a. Yll

1494 VW?

163s w 1

(MB,,) L4,NBJ WA,,)

*41 f V4? v,c=c1 . y'z?

1497 VW, sh 1

1

(WB,) 1 (WB,) (A,)(B,) (B&4,) (B,)(A,,) I

r 1969 s 1959 m, p.n.m.

II949

m

n.0. n.0. n.0. n.0.

2015 2044 2061 2141

n.0.

2164 m

n.0.

2232 w

2257 VW, p.n.m.

VW, b VW VW sh

2258 w

1510

A. VAN TETS and Hs. H. G~~NTHARD Table

(sol. ccl,) %cuum

Assignment

(crystal)

.___ “CC--D)

Vl

UC--Dl

V24 v31

+

v33

v7

+

v13

y30

n.a.

-t %I

v30

+

y31

-t T'32

v33

'28

+

'34

2 x VQ1 n.a. n.a. n.a. n.a. ma. 2 x vss

“,LkPQ VI6 V6“IC--H) &C--H1 V4 "(C--H, VZ5 vtc-n) V3 "(C-H, v2 '24

+

'42

'27

+

'9

'27

+

'30

Y6

+

v29

1'27 + 2

x

:! x

vs

VZ8

V6

+

v7

V26

+

v13

V5

+

%3

1'4 +

v13

%

y13

+

2 x

V2Q

+

v40

c. = calculated d, = azulene-dl-(1) For other notations

vyaCUUm

(cm-l)

~--__--

(cm-l)

(4(&J

3296 s

(b,W,) (AI)

2306 m II? n.0. n.o. n.0.

2299 2308 2389 2425 2441

2505 W, p.n.o.

2.503 w

(A,)(B,) (B&L) (A,)(K) (B,)(K) (A,)(%) (A,)(%)

_L

s m w VW, sh m

I 1

no. no. 2680 VW, b, p.n.m. n.0. n.o. n.0.

(A,)(%)1 (A,)(B,)(

2960 m _L

(b&L)

2994 W I/

2593 w 2624 2678 2742 2791 2883

VW VW VI,VW, b VW

1;:;;

m 2992 W, sh

(Q(&,)

3017 w, sh i

3013 vs

(al)(K)

3024 s 1

3021

@,)(A,)

3035 W I/

6048 s

(a,)(%)

3045 s .L

3056 w, sh

3056 m 1.

3075 vs

I),’ BU’ 1 &A,) (A&B,) 1 (&)(A,) (&N-4,) (14,)(K)\ (A,)(&)( (A,)(&) (B&A,)\ (-4,)(B,)I (A,)(%) (A,)(%)!

v7

2 (Contd.)

3080 w, b 11 n.0. 3148 VW, p.n.m.

(&JB,)J

see Table

s, sh

n.0. 3116 sh 3156 W, sh

n.0.

3180 W

n.0.

3209 VW, sh, b

n.0.

3846 w

no.

3890 W

3925 w, b, p.n.m.

3945 w

1.

azulene molecule does not have C 2v symmetry in this model the deviations from this symmetry are considered to be sufficiently small, so that it still can be used for the discussion of the vibrational crystal spectra. For the free molecule, a model with average bond lengths and angles is used, so that symmetry C,, results. The crystal field is assumed to be small. This assumption is supported by the fact that for only a very few absorption bands does the crystal dichroism appear to be of measurable magnitude. From this fact we conclude that the crystal spectra can be discussed also in terms of the oriented free gas model.

Infrared Table Assignment

spectra

3. Observed

of four isotopic

infrared

species of azulene

bands of azulene-d,-(2,4,5,6,7,8)

(crystal)

~‘yaCuum (cm-l)

c. (-150) n.m. c. (-160) n.m. c. (N&75) vs 320 m, p.n.m.

387 VW, b, p.n.m. 411 m, p.n.m. 478 vs

481 vs, sh :I 591 vs j;

610 s 11 -

n.m. n.m. c. ( -275) vs 318 m 3.92 m 405 w

1.

480 vs II 1

v34

1511

477 vs 480 vs, sh 590 vs GO6 m GdO VW, sh

'48

y40 - V48 ~tcccr v3s

635 m Ii

632 m

y13

651 w, p.n.0.

645 vu’

&I!)IV,p.n.0.

66.3 VW?

681 vs ,;

G79* “8

-

y47

:! x v*5 AICCC, VI4 -

%3

'48

VL Vlfi +~ VP6 y39

+ :'

V46

YlS %5* 97

+

v45

%

+

V45

+

y45

vl!3Y y39 %5

i- Y46

v44

+

v12

-- V48

v46

y34* z'll -- Y46 '3B

+- '48

v39

+

v17

'"15 +

V45

1698 IV jfig4 sh II’ 1 7OG \-IV? i 713 m (1 1 ( 716m ii 722 w )I (735 VW i\ )7.x VW /j I 747 w’, p.n.o. 757 VW? .L 770 m (1 (782 VW, p.n.o. 1789 VW II

2

x

z'3s

VI4

+ 1'

V47

y37

+

Y46

'19

+

'48

y44

L

y17

724* VW n.0. 740* VW 7S3* VW, sh? 7t?5* w 784* VW, sh?

so(i*

2'10 i- P3S VlS

n.0. 711* VW

790” VW

"$&!,"4" 1113

:! x

699* VW, sh?

vs

828* sh 835* vs

"41

Vl:, -t v17 1'2J -t 1'17

n.0. 874 T’W I_?

870 VW

1512

A. VAN TETS and Hs. H. C~~NTHARD Table 3 (Co&L) (sol. cc141

Assignment v4fJ”

%4

+

V46

'32

-

y47

(A,)?

y20

+

"45

(WA,)?

v44

+

v15

(B,)(%)

2

x

I44

(A,)(B,J

2

x

VI5

(A,)(%)

2

'

'38

(A,)(%)

2 x VP1

(BW,)

y35

935 WV? _L

i

(A,)

V46

v37

+

%

(WA,)

037

+

v39

(A,)(%,

V43

+

v39

945 w, b Ij

968 w, b 1.

(A,)(%)

v37

+

v15

(BW,)

%4

+

v39

(WA,)

%3

+

Y46

(B,)(W

?2

+

v47

(B,)(%)?

'35

+

'16

(BlKA,)

992 m, b 11 1020 w 1 1029 “S 1.

v13

+

2145

(B,)(%)

'34

+

'16

'42

+

'21

835

+

%5

(9,)(k) (MB,) (%)(A,) (%)(A,)? (%)(A,) (BW,)? (B,)(A,)

'12

+

'46

(B,)(B,)

%9

+

v44

(B,WU?

V4l

+

VI7

(B,)(%)

y30

-

'48

(A,)?

+

v45

v14

+

v15

'14

-+ '38 -v47

Y36

+

y43

(A21

v41

+

139

(A,)

V34

+

v44

(A,)

'32

+

v48

(AZ)? i

'42

+

'37

Z','"'"'

'40

+

'16

(&U

"13

+

y44

(B,)(A,)

y40

+

y39

(A,)

n.0.

lo.?8 s

7048 vs

1

I

1

1090 w, sh 1

1083 w, sh

1102 vs j_

1099 s

1127 w, b /I

1128 w

1149 m j/

1147 s

1170 w, sh jj

1176 w, sh

1190 s,

1183 w

i 1

p.n.0

1200 vs

(WA,)

Y316

n.0.

1065 w, sh

(w%)

y41

958 w

i

(A,)

v17

v326

n.0.

I

(ad(B,) +

937 VW

1

(W%)

%I6

921 s

(B,)(h)?

+

y9

914w // 922 m \I

s90 8 903 sh 907 w

(A,)(%)?

%1 + %a ‘38 + %S

v33a

1

905 w, p.n.0. (a&%) (A,)(%) (WB,,)

%4

889s

(b,)(h)

i i

%2* v43 + VP5

v"acu"m

(cm-l)

1

%06

I

p23ovw

1198 s I?

n.0.

1241 VW? 1

n.0.

1253 w, b _L

n.0.

1267 VW, p.n.0. 1275 VW ((

12F5 w

1294 w 1

1286 VW, sh

n.0.

Infrared

spectra

of four isotopic Table

Assignment y33 + pC=C) s

V46

-

v47

(%)(B,)?

+

y43

(WA,)?

%9

-

V48

(bd-0

+

v15

v34 + pC=CI 8

V36

VI3

y37

i;J~;)

n.0.

-

y47

2

x

v35

p33

+

v17

Y18

+

V42

y41

+

y37

'34

-t '42

(A,)

Yll

+

(WA,)

2 x VI9

y39

1397 VW II?\ 1

1422 VW? /I? 1 1440 xv, sh I] 1448 sh? 1.

+

V35

(A,)

1

\

(A,)?!

y11 + y21 N(C=C) V% i%L,v47 V28

WA,)

y32

-t V38

(A,)(B,)

VI2

-t v14

(A,)(%)

2

x

VI3

(A,)(B,)

v31

+

v39

PWB,)

y7

+

v49

(B,HB,)?

v31

+

V16

(%)(A,)

y9

+

y45

(B,)(B,)

+

*'37

'17

+

%5

'8

+

'16

"31

+

V37

y33

+

y34

y31

+

y35

n.0.

n.a.

(A&B,) (A,)(B,) (MB,) (MB,) @W&J (MB,)

1606 m

1

1619 m 1

1619 w

1640 w, b 11

1635 VW

1671 m 1 n.0.

1662 m

1

I

@,)bk)

(A,)(%) (A,)(%) (B,)(&,)

1580 s

1

n.a.

-I- y15

1590 m .L

I

(B,HA,) (%&B,)

1573 VW I/

1563 sh 1566 sh 1574 vs

1558 vs 1

b&B,) (B,)(B,)?

+

ll.0.

n.0.

y41

v9

n.0.

1546 sh 1

(A,)? 1

'8

1419 sh

n.0.

EBu'2?

V48

n35

1399vs

1512 xv, b, p.n.o.

VI9

'42

1402 m 1) j

WA,)

+

+

1385 sh

1456 sh?

+

+

1336 m 1365m

1460 s 1483 vs

v13

y33

1342 w 1 1365 w jj

1457 s J_

V30

'11

1317 x-s

1463 s, sh j[? 2481 m I)?

(B,)(B,)

"g&p vz8 N(C=C) v7

v$?,,=+v13 Vi7

1318 w [(

n.0.

(&Bd (%)(A,) (B,)(B,)? (A,)(%) (A,)(%)? (WA,) (B&4,) (Ad

V6

VlO

(sol. ccl,) ~,,CU”rn (cm-l)

(A,)?

i

N(C=C, V.30

%I

(cm-‘)

(al)(%)

v7

+

v,,,,,,

1308 VW, sh? I/

(A,)

1513

3 (COY&Z.)

(crystal)

y19

%2

species of azulene

1716 VW, sh? 1735 m

1745 VW, p.n.m. I

n.0.

1747 VW, sh? 1779 VW’

n.0.

1795 m

n.0.

1907 w

1514

A. VAN TETS and Hs. H. G~THARD Table 3 (Contd.)

(sol. cc'141 ~,a,""",

Assignment

vg -I-

V36

y33 + VJ y30 + U36

2 x

n.a. n.a.

(CVStal)

(B,)(4) (B,)(4) i (A,)(B,)

%J3

(A,)(-%)

%

+

2138

kWB,J

%9

+

*37

L4,)(W

n.a. n.a. y9

+

%3

v30

+

V34

y32

+

y33

y7

+

y14

%7

+

1'38

1'6 +

2137

y32

+

%3

+

2137

v29

+

y3.5

v3

+

y13

Y2R + Y36 "CC-D, V2B d--D, VZS vcc--D) V6 tJ,C--uI V4 "CC--D, v3 VCC_-D, VZ v3

+

v12

v27

+

Y36

y29

+

y41

y&

n.a. n.a. 2130 +

(a:)(B,u) (A,)(%) (A,)(%) (-4,) i

y32

'8

+

'32

y9

+

y31

n.a. n.a. n.a. n.a.

2 x Yg y9

v7

+

ys

VI

+

%9

(A,)(%)

Wl)(B,A

VI3 +

y30

+

y42

(B,HKJ

i

Y6

+

ta

(B,)(B,,) (.4,)(B,) (MB,)

i

V35

n.0. 2022 vw? p.n.m. n.0.

1990 w 2020 VW, sh? 2034 VW

n.0.

2052 VW

n.0. n.0.

2069 VW 2093 VW, b

no.

2127 w

2150 VW? p.n.m.

2151 w

2171 VW, p.n.m.

2169 m

n.0. 22.39 w, b 11 2252 w j] 2254 s 1 2254 s 1 2254 s 1 i 2261 w 1

2201 m 4239 2262 2224 1 2247 \ 2266’

s, sh s w t sh s sh

2294 s, b 2312 VW, p.n.m. I n.0. n.0. n.0.

2360 VW 2389 VW 2459 w

2505 vm, b, p.n.m.

2507 VW?

11.0.

y4

Y26 +

1952 w

11.0. n.0. n.0. n.0. n.0.

(A,)(&) (WA,,) (B,)(Au)

2 x 11,

(cm-l)

_____

1954 w, p.n.m.

n.0. n.0.

n.8. Vu +

(cm-l)

I

(A,)(%) (MB,) (MB,) I (A,)(%) (~4,)(%) (B&L) (B,)(a4,) 1 (B,)(k) 1 (A,)(k) (A,)(k) i (A,)(%) (WA,) (WA,,) (%)(B,)

Yll

VVaCUUm

2528 2560 2580 2605 2625 2711 2872 2888

vwVW VW VW w VW, b w w

2935 w, b, p.n.m.

n.0.

2960 VW, b

Infrared spectra of four

isot,opic species of azulene

1515

Table 3 (Co&d.)

(sol. ccl,)

Assignment

%6

+ y13

(WA,) (W4)

%?

+ I'30

(Ad(

v3 + v34

Y28 + 2'29 l.*'K--H, 1 "(C--H, 2'14 d x Y9 1'3 + y41 ," x v29 V3 + y40 %I7 + 117 "26 + V6 Vl + 2135 v24 + y35 '24 i- '19 u3 + v27 1'29+ v9 -t VI3 VI +

1'41

1

vvitcuum

(cm-‘)

(crystal) yc.&cIIunl (cm-l) 3035 w, b 11

3036 w 3042 w, b 1

(~4,)(B,)~ (Q(%) (WA,)

3083 s

w2;j (A:)(& (B,)(%) (B,)(d,) I (B,)(A,) (B,)(A,,) (A,)(%) (B,)(K)? (W(A,) (B&4,)

3107 VW?p.n.m.

3109 w, sh

315.5 w, b, p.n.m.

3151 w, b, sh

3786 VW? p.n.m.

3780 VW, b

3927 w, p.n.m.

3935 VW, b

(B,)(RL) I

i = isotopic (?) impuritv For other notations se; Table

1 and 2.

In connecting the crystal spectra wit’h the free molecule spectra, one encounters the difficulty that the site symmetry group (Ci) is not a subgroup of the molecular symmetry group (C,,.). In t,he left side of Table 5 the types and numbers of the normal vibrations of two (uncoupled) C,,-azulene molecules are listed for a oriented free gas model. In the center columns the cryst,al spectrum of a Cz2 or C,2 lattice (z = 2) including the polarizations of the vibrational transitions with respect to t,he crystal axes a and b is given. If use is made of the geometry of the lattice model Fig. 9, and the usual procedure for calculation of the crystal spectrum intensities for the oriented free gas model * the expected qualitative intensities given in column 7 are obtained.? To evaluate the vibrational spectrum of a perfectly disordered lattice with CZh5 space group and z = 2 one might replace the azulene molecule by a hypothetical molecule with symmetry Dzh, obtained by averaging the superposition of an azulene molecule with its inversion (such superpositions are shown in Fig. 9). The cyclodecapentaen model proposed by PLATT [lo] for the correlation of the U.V.spectra of aromatic hydrocarbons could also be used for correlation of vibrational spectra. But t’he model referred to above avoids the difficulties in removing a pair * For the procedure see Refs. [S] and [9]. t The predicted angular dependence of the polarized spcectru calculat,ed by HUNT [2] is not markedly changed by the latest cry&al data of ROBERTSON e.tal. [6]. [S] C. C. PIMENTEI,, A. L. MCCLELLAS, XV. 13. PERSON and 0. SCHNEPP,J. 234 (1955). [S] W. BRUHN and R. MECKE, 2. Elelctrochem. 65, 543 (1961). [lo] J. It. PLATT, J. C&m. Phys. 1’7, 484 (1949).

Chem.

and Rosi Phvs.

23

1516

A. VAN

TETS and Hs. H. G~~NTHARD

Table 4. Observed infrared bands of Azulene-d,

Assignment --

--I_--~ r(ccc’

(crystal) v vacrrum(cm-l)

VP8

(MB,)

4’ccc’

(b,)(B,) (b,NB,) V-4(%) (al)(%) (a&B,) @,)(A,) (al)(%)

I’ICCC’

Y46

4YC’ A,CCc!’

%7

A(CCC1

c. (-140) n.m. c. (150) mm. c. ( -275) vs, p.n.m. 309 m, p.n.m.

1 (b2’(Bu’l $$l,,,

VI8

ACCCC,

VW!

A(CCC’

VI5

v44y I‘

%l A~CCC~ V38

(sol.CC],) ~vacuuul (cm-l)

n.m.

( -272)

n.m. vs

307 w

395 VW, p.n.m.

391 m

411 m, p.n.m.

405 w

468 vs 1

468 s, sh

471 vs 1) 476 vs, sh j\I

470 vs

Y2DY Vl? + VP6

&?(B,)?

"41 - V46

W(B,)

v17 + v47

(B,)(B,)?

(A,)(B,) (A,)? WA,) (B,)(K)? (A,)(B,)

2 x VP6 v35 --y ,&K!CC~ 47 v13 - v47 v45 +v46

impurity? ilccco VW

(b,)(A,) (a2)? @MB,) (ad(B,) (Al)(B,)? (B,)(4)?

1

vu’ v4gy VP""' v41 - v47 %l

+ 1147

v44 + v47 %

+

V46

%7

+

V46

%a

+ v47

v42?'

i? i?

V356 %SY

i?

%7

+ 1145

%6

+ 1146

546 VW

577 w, p.n.0.

572 w

( 594 m I( 62% vs (1

590 sh

612* vs

653 VW, b 11

645 w

675 w /I?

667 w

@,)(B,,))

683 m 11

677 m

(b,)(4) (a,)?

699 s I/

693 m

i

(A,)(%)? (%)(%) (B,)(%) (B,)(A,)?

I

(B,)(K) (B&B,) (A,)

'44 + '46

(A,)(%)

'38 + '46

(‘42)

'21 + '46

v&‘,

'15 f '46 '36 + '47

(A:)?

y34*

W(4)

1

1

707 w Ij 718vw 1 ( 726 w 11 747 vs 1

705* VW? n.0. n.0. 748* vs

1 754 m, p.n.0.

754* sh

771 m /) 780 vs )I

n.0. 775* vs

(%)(B,)?

VI5 + 145

(I,)

v21 + y45

(W4)?

v3s +

(4)

y45

538 w, b jj

630* s

(a,)(%)

+v47

no.

613 vs 1 1 636 m I/

'41+,V45 V13

%4

1 I

527 w, b 1

785 sh /I

787* VW?

Infrared

spectra

of four isotopic Table

Assignment

146

(B,)(4)? @,)(B,)

V33

-

1147

(A,)?

Y16

+

%7

(A,WL)~

y33

-

'48

V39

+

%7

2

x

116

2

x

v39

y20

(A,)? (B,)(&) (A,)(%) (A,)(%)

8&l s II I 809 w

1

-t 2145

(b,HB,)

V40Y v37

$- V46

642)

y35

+

v47

(A,)?

'35

+

'48

(A,)?

'38

+

'17

(B,k%)

y1.5 +

y39

(%MJ

y44

+

%7

(B,)(B,)

VlO

-

'46

(B,)(B,)

I'44 +

'16

(B,)(%)

'14

+

'46

%I

-

'48

vl9

f

v45

815 VW III

(a,)(K) (B,)(B,) (B,)(B,)? (B&L)?

v43

+

v45

v38

+

'15

v44

+

y21

(MB,,) (%)(A,) (B&C)?

y44

+

%5

(B,)(%)

'38

+

'21

(B,)(B,)?

828* sh

836 vs I/

833* vs

1

869 m

881 VW, sh L?

875 VW, sh

888 m 1

800 m

908s

I

%7

(A,)?

'46

(B,)(%)

Y36

+

%7

(B,)(4)

'36

+

'16

(B,WU

'19

+

'16

(A,)?

v32*

(b,)(4)

%lS

(a,HB,)

VI3

+

v45

v37

+

v21

1

(G)(B,) i? i?

(B,)(B,)?

909 m

922 m iI

921 s

950 b, sh 1)

938

9GO s

VW

n.0.

1012 w I

1011 VW, sh?

1028 m 1 so41s 1

1030 sh 1041 s

1051 w I

1058 VW, sh

1063 w 1

1063 VW, sh

1095 m 1

1094 sh

I (WB,) 1

y42

+

'16

(MB,)

'19

+

'38

(B,)(B,)?

'36

+

'21

(B,)(%)?

I42

+

139

642)

'36

+

'44

(A,)

'43

+

'38

(4

i?

903 sh

L912 m 11

962 vs 1_

+

n.0.

867 w, b 11

1002 w, b ((

f

i n.0.

834 s I

(A,)

%9

807* VW

822* sh

(W4

'13

s

823 VW I

i- "45

v33*

798*

844 w .L

I

y35

I

(sol. ccl,) ~,W”“rn (cm-l)

1

1 %26

lkacuum(cm-l)

795 w II?\ I

1517

4 (Contd.)

(crystal)

Y417

v2o +

species of azulene

1518

A. VAN TETS and Hs. H. G~TNTHARD Table 4 (Contd.)

(sol. ccl,)

Assignment -_ -___ v33 f V48

.-__

v14

$- v21

(49 (A,)?

v30

-

C-42)9 1

v47

1103~

%OB y29

-

v45

'42

+

VI5

V9 '42

+

'38

(A,)

+

y20

(B,)(%)?

y14

-t v20

y13

+ +

v15 V46 v39

v34

+

y35

+v3s

Y36

+

-t v37

y29

-

'32

-t '47

Y46

%2

+

v45

y41

+

%6

113

+

v15

%4

-t y37

v13

+

*3a

"42

+

'20

VI3

+

v44

-y47

y35

+

y20

'18

+

'20

y14

+

"43

v&=+vlg V%l vNw=C, 9 v41

+

Y38

'42

+

'36

VI3

+

V20

v40

+- v44

v40

+

v15

y40

+

v21

'42

+

'43

'35

+

'36

V18

+

1119

'18

+

'36

v35

-t y19

VI

-

v7

-v48

v47

i?

n.0.

I

1150s

1

1150 VW?

(A,)?

i (B&4,) (WA,) (%)(B,) (AI) (A,)(%) (A,)(B,) (A,) (A,) (At)? 1 (B,)(B,) (B,)(K) (A,)(%) (WA,) (%)(A,) (B,)(A,)? (B&B,) (B&(&J (B,)(B,)? (A,)(B,)? (B,)(B,) (A,)? (WA,) (QB,) (-4,) (A,) (A,):, I (A,)(%) (B,)(B,) (-%)(A,)? (A,)(%) (A,)(%) (A,)(&)? (B,)(B,J? (B,)(B,)? (B,)(W

y37

v43

Y8

i?

%9

+

1115 s 1131 s

1143 w, sh, p.n.o.

&@d (B,)(B,)?

Y36

y12

n.0.

XB”’

-v4a

y35

J

1118 vs 1 1133 s _

(b,K%A

y31*

(cm-‘)

(crystal) vvacuum (cm-‘)

1160 R, sh 11

1158 w

1176 w, b 1

1178 m

1

i

1

1188 VW /)

i

1199 1206 w VWI?1

I i

I

n.0.

1200 w

i 1210 VW?

1210 w, sh ,, j I 1230 VW, p.n.0.

1241 WV.b

1 1255 m 1

1

1257 VW

1259 m /I 1271 VW /I?

1270 s

1284 w, b jl

n.0.

1301 VW II

1300 m

I

;

(WB,) 1

I 1322 VW, b

1

1326 m

v"aCU"m

-_-_

Infrared

spectra

of four isotopic Table

Assignment Vll

+

V45

i? V12

+

VI5

V34

+

V37

2

x

v42

VI3

+

V43

(A,)(&) (MB,) (MB,,) (B,)(B,,)

V35

+

V42

(A,)

'42

+

%I

V33

+

V16

V33 +- V3$ VNIC=W 8 V34

+

V43

V34

+

VlS

V1a + ;! x

V35 Va5

2 V41

x

VI2

+v43

V.5 -

VP7

V41

+

Y36

V41

+

VIS

VlO

+

V4fi

V34

+

V14

V32

+

V17

I’,,,,,,

1344 m, b 1

11.0.

I

+

V15

+

Va

(~,)(%A

V 31

-f I'45

kh)

Vga

+

V,6

(B,W,)

V41

+

VI4

(BaHBu)

V33

+- V21

CB,H&)?

‘r

1410 VW, p.n.0.

1410 w. sh?

1422 w 1;

1420 w. sh?

]

i

1437

M-,

T’S

sh? p.n.o.

1455

W,)(KJl

1460 W, sh? il

(A,)

V13

C-J,)(%)\

'32

+

'38

b%HB,)~

V31

+

VI7

Vll

+

V38

VI1

+

1'4.4

V12

+

V14

V31

+

V39

V40

+

V42

'8

+

'48

Vll

7

V21

(A,)?

"27

-

V48

(A,)?

V38 V36

1J70 w. sh, b 1; 1495 VW? _L

(MB,)

x

+

1

1453 s 1460 m

(B,)(d

2

+

1436 VW?

i

V34

V33

1366 VW, sh?

1390 vs

(W%,)

V31

\ 1354 m

\ 1378 sh

V33 + v44 N(C=C, Vi?9

V4Q + V35 NCC=C, VII vtC=C, VZS

I (

1

1 (WB,)? 1 (4) (B,)(A,)? j

V33

V40 + "14 VNIP=CI ,

V"aCUlm

(cm-l)

(&B:)*

V13

"35

(sol. ccl,)

1344 m

\

E’i BU’ (&w (B,)(K)?

I$$?; (WA:) (WA,)

+

1519

(cm-l) - -

(%)(~4,)? (WA,) (Q(K)

;:l;i$;?

of azulene

4 (Contd.)

(crystal)

(W,)J

species

1469 8 1500 w, b

1513 VW

1520 VW, b J

1519 VW?

1540 w, sh? 1555 Y 1 156’4 sh Ii

n.0. 1563 vs 1571 s

(B,HB,)?

(-4,) (o,)(B,) (b,W,,) (-$)(%)I (-%)(B,)l

i 1

n.o.

1

1581 R, b

1520

A. VAN TETS and Hs. H. G~NTHARD Table

Assignment

4 (Co&d.)

(crystal)

v,,,,,,

(cm-‘) __-

Yll

+

Y36

(B,)(B,) (A,)? (A,)(B,) (A,HB,) (WA,)

'32

+

'19

(B,W,)?

Vll

+

v44

(B,UU

%o

+

VP4

%o

+

y21

y40

+

I'41

'32

+

'36

I

(sol. ccl,) V,,,,“, (cm-l) -

1596 VW, b 1

1596 VW, sh?

1626 w 1

1622 w

1652 VW? 1

r 1640 VW

(J%~%J

";$&,"17 V,7

WkL) (WA,)

v32

+

y14

y30

+

%6

(WA,)

'8

+

'46

(B,)(%)

v33

+

%3

1667 w jl?

(B,)(%)?

i? v32

+

v35

(Al)(%)

y31

+

Y36

(A,)(%)

'8

+

'16

Yll

+

v13

'32

+

'34

n.a. n.a.

n.a. n.a. n.a. v9

+

%3

'32

+

'33

ma. n.a. ma. n.a. "CC-D, 'VZB v,c--Dh y5 "(C--D, V4 "CC--D, v25 ",c!--D, Va ",C_-D, VZ

+

Vll

'6

+

'13

2130 +

131

1'7 +

VP9

-t 1’14 vg -t vg

v24

"25

+

'35

(A,)(%) (AI) (A,)(B,)

(A&B,) (A,)(B,)

I 1

(b,)(4) (a,)(%) (MB,) @d(4) (aJ(B,) (al)(%)

1719 m

2252 2236 2252

n.0. n.0.

1755 VW 1780 VW

n.0.

1799 w

n.0. n.0. n.0.

1846 VW? 1864 VW? 1931 VW

n.0.

2004 w

n.0. n.0. n.0. n.0.

2080 2130 2158 2170

sw 1 // 1 x 1

2251 2252

sw 1 (( 1

2285

m 1_

2285 2285

myi” m 1 1

VW? b VW? b VW VW

2233 s 2245 s 2256 s 2262 s, sh

(A,)(B,)

'32 + '30 "(C--D, VZ4 vIC--DI Vl v9

1718 VW?, p.n.m. I

CM4 (a,)(%)

n.a. n.a. n.a. n.a.

(A,)(%) (A,)(%) (A,)(%)

1

(WA,)

1 1

2319 w, sh, b

n.0. n.0. n.0. n.o.

2374 2427 2446 2835 2854

n.0.

(B,)(4) (A,)(%) (A,)(%,)

i 2310 2304 w, 2292 2283 m sh? s

n.0.

2919 w, b, p.n.m. n.0.

w VW VW VW VW

2918 VW, sh? b 2951 m

Infrared

spect,ra of four isotopic Tablo

species of azulene

1521

4 (Co&.) (sol. ccl,)

(crystal) ---~-~-

Assignment _____ _ ~~---.~--~~-

n.0.

n.a.

v25

+

y34

y3

+

y34

(~,)(~u)~ (%)(A,) (A,)(K) (B,)(A,) (A,)(B,) (BJ.4,) i

'24

+

'41

(A,)

y2 +

y41

(B,)(B,)

y40

(A,)

y40

(A,)

vs i-

%?a +

“‘7

v7

"2

+

VI3

v24

+

v13

v25 %6

+ +

v3

+v40

y4

+

2140

'25

+

'12

2

x

v2*

V,,C""rn

(cm-l)

v,,cuum (cm-l)

2969 VW, sh?

3022 VW, b, p.n.m.

3035 m, b

3076 m, p.n.m.

3084 w, b

1

(B,)(%) I

(B,)(B,)

i? n.a.

J n.0.

(WA,) (A,HB,)

1

3107 VW. sh

3151 w, p.n.m

For conventional

notations

see Tables

3156 w I-3.

of hydrogen atoms in going from the cyclopolyolefin model to the azulene molecule. The averaging process in our model is made by replacing the carbon atoms 1 and 5’, 2 and 6’, 3 and 7’, 4 and 9’, 5 and l’, 6 and 2’, 7 and 3’, 8 and lo’, 9 and 4’, 10 and 8’ of the original and the invertfed molecule by a carbon atom in the center of gravity of the pair. Similarly the pairs of hydrogen atoms 1 and 5’, 2 and 6’, 3 and 7’, 4 and 8’, 5 and 9’, 6 and 2’, 7 and 3’, 8 and 4’ are replaced. In this manner a hypothetical molecule with symmetry D,, is obtained as shown below which allows the establishment of simple relations to the azulene molecule as shown in t’he right-hand side of Table 5. H\C __ c.*c,e_Y_c//H I

H--C! , ‘(\

--j--

) I

j

‘:\c-, /;/

H,c-=q==_+y ‘\ ,’ H

‘H

The usual rules for evaluation of numbers and types of normal vibrations cannot be strictly applied to the disordered azulene lattice. However since this lattice appears to be a typical case of low crystal field, the oriented gas model seems to be a reasonable approximation. In discussing the assignment of the infrared spectra of crystals and solutions, use has been made of the dichroio ratios and relative intensities between crystal and solution spectra given in Table 6. These rules proved to be not strictly applicable for the unravelling of the spectra. As an example, in the case of the CHand CD- stretching bands only the polarizations 9

1522

A. VAN TETS and Hs. H. G~~NTHARD Table 5.

82

-

Table 6. Expected behavior of absorption bands Dichroic ratio expected intensit*y /I a

Transition

intensity // b

type

8 undetermined

4 4

114

Bl

3

B,

Intonsity ratio expected crystal solution .._._-._..-__ __.~ _~_..~.~._i_._-. _..__ 0.1 co 1 1

seem to be reliable criteria in connection with the symmetry species of the transitions (see Section 3.3. iii. below). For the four isotopic azulene molecules studied in this work the following product and sum rules [II] given in Table 7 should hold for each species A,, A,, B, and Bz separately. The product rule proved to be essential for the assignment of the low-frequency fundamentals of each symmetry type. On the other hand the sum rule is rather insensitive to the lower-frequency assignments, but was very useful for the assignment of the high frequencies. As a general rule the group vibrations expected in the azulene spectra were located as indicated in Table 8, in which the number and species of the group vibrations are also given. Before discussing the assignments suggested in the next Section (3.3) a few remarks should be added. First of all, the rule that all frequencies should not increase on substitution by a heavier isotope is obeyed by the assignments in general. Fermi resonance might [ll]

E. B. WILSON, York (1955).

J.

C.

DECIUS

and P. C. CROSS, nloleczslar Vibrations.

McGraw-Hill,

New

Infrared

spectra Table

Transition type -41 *a* B, B,” Transition

of four isotopic 7. Product

1523

and sum rules ~ri(d,)l~ri(&,)

~i(ds)/~i(d,,)

bilk&)

talc.

obs.

talc.

obs.

0.5039 0.7169 0.5102 0.7250

0.4963 (0.7357) 0.5015 (0.711)

0.1279 0.5230 0.1341 0.2650

0.1275 (0.5407) 0.1313 (0.265)

Expected:

type

species of azulene

talc .

obs.

0.06869 0.06794 0.3745 (0.3723) 0.06442 0.06647 0.1918 (0.199)

uds + uds = ud, + ud6, G = Ciui2

ud,

___ _ ~._____

+ ud, obs. (cmp2) .__~_______~______----~-.-~

A, AZ* B, %*

99769735 (3654701) 74822285 (6352812)

ad,

+ ud, obs. (cmp2)

----

~_ ~__

100041260 (3620677) 75342285 (6371076)

* The fundamentals .:tcc’ (a2) and r~~cc) (a2) have not been observed, but seem to undergo no significant isotopic shift. The fundamentals rk~““’ (ba) and v:!“’ (5,) have not been observed, but are calculated. Table

8. Expected

frequency

range for assignment

of fundamentals

Expected Group vibration __ r(C-H) Y(C-D) N(C=C) d(CCH) S(CCD) N(C-C) NCH) y(CCD) A(CCC) r(ccc)

Symmetry, (al) ___5,4,1,0 0,1,4,5 4 3,2,1,0 0,1,2,3 1 L!.

species and number * (%) -

3,2,1,0 0,1,2,3 3

(6,)

(52)

3,2,1,0 0,1,2,3 4 5,4,1,0 0,1,4,5

--

-~4

5,4,1,0 0,1,4,5 -4

-__

-

* The number of group vibrations for each symmetry the following order: d,, d,, d,, and d,

frequency range (cm-l)

3100-3000 2300-2250 1700-1250 1300-1000 llOO- 700 900- 750 IOOO- 700 850- 450 700- 400 600 type is given in

give rise to slight deviations from this rule. All such violations appearing in our assignments seem to be satisfactorily explained by this argument. Secondly, in the case of the d, molecule unpolarized low temperature spectra have been taken. No phase transition was found spectroscopically between the melting point (99°C) and -160°C. The spectrum changed rather continuously and only slightly with

1524

A.VANTETS ~~~Hs.H.G&THARD

temperature. Difference bands and well separated hot transitions of polycrystallinic solids therefore do not seem to contribute noticeably to the absorption at room temperature. Furthermore, by studying the spectra by the KBr-technique a valuable support .of the A, assignments was found. Although it was not possible to obtain there azulene spectra perfectly free from dispersion phenomena, the bands of symmetry type A, show in contrast to bands of other symmetry types the expected increase of intensity in comparison with the polarized spectra taken with light incident on the ab face. 3.3 Assignment In Tables l-4 assignments of the bands observed in the infrared spectra of crystals and solutions are given for each isotopic species. For the A, and B, fundamentals the assignment is considered to be complete and rather reliable, with a few exceptions discussed in other sections below. Furthermore assignments are also given for the B, fundamentals, with the exception of two fundamentals lying below 275 cm-l. For the &-molecule, two farinfrared bands observed by MILLER and FATELEY are assigned as the lowest B, fundamentals, whereas for the other isotopic molecules, values predicted from the product rule are included for the two corresponding modes. In Tables 1-4 assignments are suggested for all three, light atom nonplanar bending fundamentals and for the highest of the three nonplanar ring bending modes of species A,. The two far-infrared A, fundamentals are not observed for all isotopic species thus far. It should be pointed out that the assignment given for the A, fundamentals is tentative. All the assignments proposed in Tables l-4 show remarkably few difference bands in spite of the existence of at least 2 (probably 4) vibrational levels below 200 cm-‘. Furthermore, no hot transitions were included in the interpretation of the infrared spectra; considering the limited resolving power used for measurement of the spectra (Figs. 1-8) we felt that such detailed interpretation would have no meaning. Some further comments are of importance with regard to the assignments of the Y(CH) and Y(CD) fundamentals. The single crystal spectra of d, and d, do not show the complicated band envelope expected for the Y(CD) fundamentals of d, and d, respectively (cf. Fig. 3) from the corresponding (CH) absorption band contours. The solution absorption bands however exhibit the expected behaviour. Five absorption bands of d, and four of d, were found with pronounced polarization above 3000 cm-i. These bands were assigned as A, v(CH) fundamentals and used later for the identification of the u crystal axis. A number of criteria were used in the assignment of the three B,-type v(CH) fundamentals in d, and the two similar B, fundamentals in d, polarized perpendicular to the a axis. (i) From the spectra of d, and d, it might be concluded that the a, and b, light atom stretching fundamentals originating from an equivalent set show very nearly the same frequency. (ii) The Y(CH) fundamentals of type A, and B, ascribed to position 1,3 must show up in the d, and d, spectra around 3080 cm-l and should not occur in the d,

Infrared

spectra

of four isotopic

species of azulene

1525

and d, spectra. On the other hand, the latter should show corresponding bands around the high-frequency edge of the v(CD) absorbing region. (iii) Empirically the intensities of the A, type v(CH) bands of d, and d, were found to be remarkably higher than that of all transitions polarized perpendicular to the a axis, This feature is in contradiction to the expectations indicated in Table 6 and appears to be unique for the light atom stretching vibrations in the spectra of all the isotopic molecules studied. No simple explanation was found so far for this rather surprising phenomenon, although it is probably connected with the relatively strong coupling of the Y(CH)- and Y(CD)- vibrations by the crystal field and the effects of high anharmonicity of these modes. (iv) In the v(CD) re g ion the expected number of B, fundamentals polarized perpendicular to the a axis were observed for d, and d,, two and three respectively. (v) After the B, modes have been assigned in the d, and d, molecules, the corresponding bands originating from the (4,8) or (5,7) positions in the d, and d, The assignment spectra can be identified wit,h the aid of the isotope relationships. of the A, fundamentals of d, and d, encounters the difficulty, that only two distinct bands with polarization parallel to a are observed in the crystal spectra, which are split in a complicated band system in solution. Therefore, the assignment of these modes is based mainly on comparison with the solution spectra.* There remain a number of ambiguities in the assignments of the light atom stretching modes of the solution spectra. It is of some interest to note the possibility of establishing a correspondence between the observed v(CH) fundamentals of the d, isotope and the position, from which they originate. However, this aspect will be discussed elsewhere [12], but we would like to point out that the azulene spectra offer, to our knowledge, an almost unique opportunity to study the existence of a correlation between CH stret,ching frequencies and charge order in detail. The aromatic ring stretching vibrations of all four isotopic molecules may be discussed from a common point of view. According to general belief these modes should occur between 1700 and 1250 cm-l. At the lower edge of this frequency region interaction with the planar 6(CH) modes is to be expected. This seems indeed to be the case, as may be recognized from Tables l-4. The lowest A, and B, modes of the former type shift from 1397 and 1454 cm-l respectively in the d, spectrum to 1271 and 1259 cm-l respectively in the d, spectrum. From the isotope ratio of these band pairs (1.099 and 1.155 respectively) a noticeable interaction between the lowest ring stretching and highest 6(CH) modes can be inferred. Two out-of-plane ring bending vibrations of symmetry type B, have been found for all four isotopic modifications around 300 cm-l. The d, bands at 180 and 170 cm-l found by MILLER and FATELEY are probably the other two I’(CCC)modes of this symmetry. Corresponding bands for the d,, d, and d, isotopic molecules have been roughly calculated by use of the product rule (Table 7). The planar as well as the nonplanar bending modes show in our assignment * Tho assignment of BAUDER arguments given here. [Ia]

and GWTHARD

[3] has to

be revised

A. VAN TETS and Hs. H. GiiiYTHARD, Helv. Chim. Acta 46, 429 (1963).

in accord

with

the

1526

A. VAN TETS andHs.H.

G~THARD

strong interaction within each symmetric species. We, therefore, have made no attempt to relate these bands to certain atomic positions in the molecule, as seems to be possible for the light atom stretching fundamentals. These light atom bending fundamentals also appear to have strong interaction with some of the lower lyingN(C-C), A(CCC) or l’(CCC) ring vibration fundamentals of the same symmetry type. Among the latter, the bands assigned as $Jccc) (al) $jccc) (a,), ~$4~~~)(b,), a$Jccc) (6,), $$ccc) (b,) and v$jccc) (b2) show marked isotopic shift, which clearly indicates them to be fundamentals originating from strong mixing between the ring modes with light atom vibrations. v16 and vSg for instance show isotopic shifts as follows:

'16 39

1.010 1.057

1.178 1.175

1.178 1.175

On the other hand, some of the bands assigned to light atom bending vibrations show irregular isotopic shifts ranging between d, and d, from 1.07 to 1.40. From this behavior of the isotopic shifts, the conclusion may be drawn that the group vibration concept does not give an adequate qualitative description of most of the planar and nonplanar light or heavy atom bending fundamentals respectively. * It should be noted that infrared absorption by the A, type N(C-C) group vibration, which is perpendicular to the dipole moment M,, is made possible only by the interaction resulting from the redundancies connecting the N(C-C) coordinate with the N(C=C) and A(CCC) co-ordinates of both rings in the A, class. Its isotopic shift of about 150 cm-l going from cl, to d, may be satisfactorily explained by interaction with the light atom bending modes of the same symmetry A, which are more crowded around 1000 cm-l with increasing deuteration. In examining the assignments in Tables l-4 one will recognize a number of violations governing the polarization properties of the crystal absorption bands, given in Table 6. Beginning with the assignment of the A, fundamental modes it was noticed generally that the dichroic ratio derived from the lattice model (Fig. 9) is observed experimentally only for a very few absorption bands, but is most often much lower than the model value 8. High dichroic ratios were found for instance for the v(CH) (al) and Y(CD) (al) modes and furthermore for v$‘-‘) (al) of d, and cl,. These highly polarized bands show that the low polarization of Al-bands, generally observed throughout the spectra, is not solely due to imperfect experimental technique. Alternatively, no simple explanation of this behavior was * In most of the assignments reported for naphthalene the same situation appears to exist, cf. Ref. [13]. This feature of the naphthalcne vibration spectrum is also borne out by t,he results of normal co-ordinate analysis published by FREEMAN and Ross [ 141 and SCULLY and WHIFFEN [15]. We hope to report the results of a normal co-ordinate analysis azulene in the near future. [13] H. LUTHER and H. J. DRE~VITZ, 2. Elektroch~em. 66, 546 (1962). [14] D. E. FREEMAN and I. G. Ross, Spectrochim. Acta 16, 1393 (1960). [15] D. B. SCULLY and D. H. WHIFFEN, Spectrochim. Acta 16, 1409 (1960).

1527

Infrared spectra of four isotopic species of azulene

found, but it probably originates from deviations from the oriented free gas mode produced by the crystal field. In a number of cases bands were assigned as A, vibrations in spite of their dichroic ratio being lower than 1. #c=c) (ai) of the d,-crystal may be mentioned as a first example. The nonpolarized crystal spectrum Fig. 1 and the solution spectrum Fig. 7 show it to be nearly coincident with $JcZc) (b,). HCNT and Ross* observed a simple band contour for this absorption, but concluded from polarization measurements the existence of two coincident fundamentals. In examining their curves we were lead to a polarization ratio for us below 1; but from the behavior of the intensity of the low-frequency component of the 1450 cm-’ band in the crystal and solution spectra the A, symmetry seems to be firmly established. No such cases seem to occur in the d, spectra, however several similar violations exist in our assignments for the d, and the d, spectra. The absorption bands ~,(a~), vg(ul) and vlz(al) for d, and v7(al), vg(al) and vi4(ul) for d, clearly show the expected intensity behavior going from crystal to solution spectra, but their dichroic ratio is below 1. On the other hand, the fundamentals vg(al) and vli(ul) in the d, solution spectra, which were assigned to the absorption bands at 1563 and 663 cm-l respectively do not follow the expected intensity behavior. In the former case, the measurements of the absorption in solutions in the latter, by strong atmospheric were disturbed by strong solvent absorption; absorption so that these violations may be apparent only. B,-type transitions should have approximately the same intensity in solution and crystal spectra and should exhibit b polarization in the latter. All bands assigned to B, transitions follow roughly the expected intensity pattern, with the exception of the light atom stretching fundamentals (as was discussed above in criteria iii). The polarization dichroic ratio according to the oriented free gas model should approximate l/4; however, a few fundamental bands assigned as B, show dichroic ratios exceeding 1. These violations are found for the following crystal absorption bands: 722 cm-l

(Q)

for d,.

1007 cm-l

(v& for d,.

1200 cm-l

(vZ1), 1102 cm-l

(vaa) and 1029 cm-l

1455 cm-l

(vZo), 1118 cm-l

(vQ1), 1028 cm-l

(vaa) for d,.

(uSa)and 962 cm-l

(Y& for d,.

Most bands of the B, type seem to have dichroic ratios between 1 and l/4. The model value is approached by a very few bands only [see, for example, v3,(bl) and vz8(b1) in the d, spectrum or vs5(b,) and vs8(b1) of d,]. For B, modes the dichroic ratio should approximate 3 (see Table 6). However the bands assigned as B, fundamentals show smaller dichroic ratios, mostly near unity for all isotopic modifications; although the expected intensity behavior is rather strictly followed. The B, assignment contains a relative large number of violations of the polarization rule, increasing with deuteration. This increase of the number of violations of the * See Fig. 4 of Ref. [2]. Full use of their measurements in the region 2000-670 cm-l was made in this work. Our own measurements with polarized radiation for the d, isotope were limited to the 31OOG2950 and 670-425 cm-l regions.

1528

A.

VAN

and Hs. H.

TETS

EWTHARD

polarization rules with increasing deuteration is quite generally exhibited by all three symmetry types A,, B, and B,. Also the number of combination tones between 1800 and 600 cm-l seems to increase with deuteration. No simple explanation could be found for the above phenomena but it is felt that the internal consistency of the assignments for the four isotopic modification justifies violations of the polarization rules. * Finally we would like to mention some discrepancies in the azulene-d, spectra reported by HUNT and Ross, MILLER and FATELEY and this work. The most relevant discrepancies in these spectra are collected below. The two bands observed by HUNT and Ross near 1578 and 1450 cm-l are definitely double bands, if measured with sufficient resolving power. The discrepancy in the spectra near 1210 cm-l is more difficult to understand, since the high-frequency component of this band sometimes shows up in the nonpolarized crystal spectra, and hence the origin of this band is obscure.

SO.

M and F (cm~l)

H and R (cm-l)

This work (cm-l) 1581

(1)

(s)

(2)

(8)

(3)

n.m.

1450

n.m.

(s) ( 1212 1206 n.0.

(s)

( 1448

(s)

1208

(s)

1115?

n.m.

I:; (7) (8)

(sol) n.0. (sol) 782 n.0. (sol) 730 (8) 664

(9)

(s)

(10) (11) (12)

(s) 1588 1454

(s)

(4)

n.m.

1578

n.m. n.m. nm. n.m.

557

(s) 562

473 460

n.0. n.0. n.0.

n.0.

(sol) 1117 n.0. (s) 744 n.0. n.0. 558 (s) (8)

L566 531 n.0. n.0.

In the case of the weak solution band near 1117 cm-l, the existence of this band seems to be beyond doubt, but its existence in the crystal spect’rum is very uncertain. Nevertheless, this band is interpreted as an A, fundamental in our assignment for the following reasons. There are eight 6(CH) bending vibrations to be Seven of these bands Tqere easily located, expected between 1300 and 1000 cm-l. * The same kind of violations of polarization rules seem to occur occasionally in the infrared crystal spectra of other compounds with weak int,ermolecular int,eractions. For naphthalene SW, for instance, I'IMENTEL et al. [8].

Infrared

spect,ra of four isot,opic specks

of azulene

1529

i.e.vlo(dt

Y&J, ~(6~), a and Gus. In the d,, d, and d, v&J, Gil, spectra a surprisingly high number of strong bands are observed, which in a large part must be combination tones. The 1117 cm-l band of d, seems to be the only reasonable choice for the third d(CH)-A, fundamental, since it shows the expected intensity behavior and relates naturally to the assignments of the &modes of the heavy compounds. No simple explanation has been found for the discrepancies in the 800-600 cm-l region. With respect to the crystal absorption near 560 cm-l we found a complex band envelope if measured on a double-pass instrument, both with polarized and nonpolarized radiation. The weak crystal band near 530 cm-l was found in all the d, spectra investigated in this work, but it was not reported by the ot’her workers. The crystal absorptions 473 and 460 cm-l reported by HUKT and Ross were not found by MILLER and FATELEY nor in this work, although the spectra were carefully checked for their existence. These bands were assigned by the’former investigators as fundamental B, and B, ring deformation modes. Further differencies exist between t’he assignments of HUNT and Ross and this work. One of these is the very wea,k band nea,r 1270 cm-l, which they assigned as an A, fundamental. Their assignment is based on polarization measurements a,nd the intensity of fluorescence spectra, although it violates the expected intensity behavior. In our assignments we have found more than one way to explain this band as an binary combination tone of symmetry B, (see Table 1). Another discrepancy is the band near 820 cm-l, which is assigned as the highest A- A, fundamental by HUNT and ROSS, since it was found to be polarized //a and of higher intensity in the gas spectrum than in that of the crystal. However, we found it to have very low intensity in the crystal powder spectra. Furthermore it also can be explained in at least one ot,her way as a combination tone. We therefore preferred to assign this complex band as y16 + vd5(B2), A further interesting difference is the 790 cm-l absorption, assigned as I/(CH) (6,) by HUNT and Ross. This band, which has strong intensity in the crystal spectrum, seems to have no counterpart in our solubion spectra. Therefore it was preferred to explain it as an A, fundamental. Furthermore we wish to mention the differences occurring in the assignments of the ring bending modes. The B, type modes were selected by HUNT and Ross at 707, 664, 473 and 180 cm-l, whereas in the assignment given in Table 1 they were located near 333, 319, 180 and 170 cm-l. However the existence of the 664 cm-l and the 473 cm-l bands are doubtful, and the bands in the 700 cm-l region show very Most frequently nonplanar ring bendpronounced isotopic shifts on deuteration. ing modes are expected below 600 cm- ‘.* It seems difficult to place two more bands in the 700 cm-l region, which is already densely occupied by t’he nonplanar light atom vibrations. Furthermore the sum rule offers an efficient restriction on t)he choice of the B, fundamentals, since among the nine fundamentals of this symmetry species only vibrations with frequencies below 1000 cm-l are to be expected. * LUTHER et ul. [13] on the other hand, consider non-planar ring bending modes napht,halone vibrational spectrum to have frequencies 8,s high as 778 cm-l for r6(B3,), seems t,o be very high in comparison with the ot.her f~mdmncnkd modes of this t,ype.

in the which

1530

A. VAN TETS and Hs. H. G~NTHARD

It should be mentioned, that a number of coincidences in both the crystal and solution spectra of fundamentals of different symmetry type occur in the assignments (Tables l-4), especially for the low-lying ring bending modes of the heavy molecules. The more important coincidences are as follows: (1586

cm-l)

for d,:

[411

cm-r (s)] for d,:

[411

cm-l

~~(a~) and Gus ail

(s) for cl,: ail

and Gus and Ye&)

All the other coincidences (with the exception of A, fundamentals) are clearly recognized in either the crystal or solution spectra. The 1586 cm-l band of d, is assumed to represent a coincidence of v7 and vs8, since the analogous bands in the cl,, d, and d, nearly coincide, and both v, and vs8 may be influenced by Fermi resonance with vll(ul) + vi6(al) and v3s(b,) + vi7(ul) respectively. That the 411 cm-l band in d, and d, is a coincidence of v16 and vQs was concluded from the product rule and the isotopic shifts of these two fundamentals in going from d, via d, to the heavier isotopes. The interpretation of combination tones based on the assignments in Tables l-4 encounters no noticeable difficulties. The very rich spectra can be explained mostly by binary combinations and overtones, in a very few cases only ternary tones are included. In many cases the effects of Fermi resonance on the frequency of fundaTo avoid getting into detailed mentals and combinations can clearly be recognized. discussions only the strong band in the solution spectra of d, and d, near 1800 cm-l will be considered. This surprisingly strong band disappears in the d, and d8 spectra. If it can be explained in a common manner for all the light isotopic modifications only the ternary combination Gus + vas(b,) + vs1(a2) can account for it. However, there exist several individual binary combinations which coincide with the ternary tone for each of the light molecules. Fermi resonance is probably responsible for the high intensity. Acknowledgements-We gratefully acknowledge the grant of a stipend by Koninklyke Olie/Shell to one of us (il v T). Furthermore we thank by Hoffmann-LaRoche and Cie, Bale, and the Swiss National Foundation (Projects Nr. 1284 and Nr. 1948) for financial support.