Vibrational spectra and normal-coordinate treatment of cyclopentadiene and its deuterated derivatives

8pectrochlmior.Acta.Vol.81A,pp.4Llto 461. PenmmonPre~1976. PrintedinNorthernIrehnd

Vibrational spectraand normal-coordinate treatment of

cyclopentadieneand its deuteratedderivatives E. CASTELLUCOI and P. MANZELIJ I&oratorio di SpettroscopiaMoleaolare, University di Firenze, Firenze, Italy B.

FORTUNATO

Istituto Chimico della Facolti di Ingegneria, Universit&di Bologna, Bologna, Italy

and E. GALLINELLA and P. MIRONE* Istituto di Chimica Fisioa, Universiti di Modena, Modena, Italy (Remived 19 February 1974) qbstr&-The infrared spectra in polarized light and the Raman spectra of crystalline cyclopentadiene and hexadeuterocyclopentadieneand of their solid solutions have been obtained. Pentadeuterooyclopentsdiene(1,2,3,4,6) hes been prepared for the ikst time and its i.r. and Ramen speotm have been recorded. On the b&s of these snd previous results, a vibrational assignmentis proposed for cyolopentadieneand three of its deuterated derivatives. This sssignment is supported by a normal coo&in&e analysis besed on a valence force field. INTRODUCTION

preceding papers some of us studied the infrared spectra in the three a,ggrega;tion states and the liquid-phase Raman spectra of cyclopentadiene [l], hexadeuterooyclopentadiene and cyclopentadiene-6-d [2], and proposed a vibrrttional assignment. In this work we report on the i.r. spectra in polarized light snd the Raman spectra of solid cyclopentadiene and hexadeuterocyclopentadiene and of their solid solutions, and on the infrared and Reman spectra of oyclopentadiene-1,2,3,4,6-d,. In order to confirm and complete the vibrational assignment we also present the results of a. normal coordinate treatment.

IN TWO

EXPEWENTAL Cyolopentediene-de was prepared following the method desoribed elsewhere [S]; the deuterium con-t was 99.0 %. Cyclopentadiene and cyclopentadiene-d, were purified by repeated transfers in a vaouum line from a dry ice to a liquid nitrogen bath. Samples suitable for infrared measurementswere prepared either by deposition from the vapour or by crystallizationfrom the liquid. In the lest case the sample was transferredinto a cell with CsI optics and silver spacer 16~ thick, operating in a dry box at about -30°C to prevent dimer formation. The cell wee firmly tied to the cold finger of an usual low temperature vacuum cell for i.r. measurementswith external CsI optics. By repeatedly cooling and heating the sample through the melting point it was generally possible after a few attempts to orient at least a portion of the solid film suitably for measurements in polarized light. Infrered spectra were registered between 4000 end 260 cm-r on a Perkin-Elmer Model 225 spectrometer equipped with an AgBr grid polarizer. * To whom all correspondencemust be addressed. [l) E. Gw,

B. FORTUNATO and P. MWCONE, J. Mol. &e&y 24, 346 (1967). and P. MJRONE,Qozz. 0&n. Iti. 101,643 (1971). [2]B. FORTUYNATO, E.Gm

Atti Soo. Nat. Mat. Modma 100, 216 (1969); J. Lube&i [3] E. G~NJZILA and P. IMIBONE, compotbnd87, 183 (1971). 12

461

462

E. CASTEIJJJ~OI, B. FORTUNATE, E. ~WUNEUA,

P.=andP.Mmom

Raman scattering experiments were performed as described elsewhere [a]. The spectra were excited with the filtered 4880 A line of a CRL Model 52 argon laser and registered with the aid of a Gary 81 Raman spectrometer. Isotopio mixtures were prepared by mixing the vapours in a molar ratio 1: 20 in a vacuum line. Cyclopentadiene-1,2,3,4,5_db was prepared following the procedure already described for cyclopentadiene-5-d [2]: starting from cyclopentadiene-d,, the thallium derivative was first obtained and then hydrolysed. As monodeuterocyclopentadiene, pentadeuterooyolopentadiene proved to be somewhat unstable with respect to isomerimtion, and was handled with the same preoautions [2]. Infrared speotra were obtained on a Beckman IR 12 spectrophotometer. The vapour-phase spectrum was recorded with a 70 mm gas cell, the solid-phase spectrum with a variable temperature RIIC unit, Model VLT-2. Rsmsn spectra were obtained with a Gary 81 spectrophotometer equipped with an Argon Laser source (CRL Model 62) and with a Coderg PO transfer plate as a fore-optics. The spectra were recorded at temperatures between -30 and -7O”C, using 4 mm o.d. sealed tubes in a Coderg Cryociro oell. CRYSTAL

SPECTRA AND ASSIUNMENT OF C&H, AND

CsD,

The vibrstional assignment of C,H, and C,D, has been performed on the basis of the i.r. spectra in polarized light and of the Ramen ape&a of pure and mixed orystals. The mixed crystal i.r. spectra were not useful for the identification of the isolated species bands owing to the overlap by the host speoies bands. Cyclopentadiene crystallizes in the monoolinic system, spaoe group P2,/n, with four molecules in the unit cell located in generctl positions [6]. The selection rules for the crystal predict splitting of the free molecule bands into four components. Two of these are Rrtmsn active and two infrsred aotive, s,ccording to the g and ec symmetry of the unit cell modes, as shown in Table 1. The 21 optioctlly active lattioe modes classify according to the 0, unit sell symmetry as : 6A, + 64

+ 68, + 4B,

A, species bands whioh are i.r. forbidden in the free mole&e a&iv&e in the orystal as a consequence of the lowering of the molecular symmetry in the crystal. A suitable model which permits the intepretation of the speotra in polarized hght is the oriented gas model. For its full application in vibrational assignments one has to know the type of crystal plene developed by the sample parallel to the Table 1. Correlation diagram among molecular, site and factor groups of cyclopentadiene Molecular c 2u

Site

Factor

Cl

0 2h

[4] E. C~TELLUC~I, &XX&O&~. Acta 99A, 1217 (1873). [6] Q. bEBLINC+ and R.E.Maasr.r, AotaCry8t.19,202 (1966).

Vibrational speatrtx and normal-coordinatetreatment

of

463

cyclopentadiene

windows. This is not our ease; nevertheless, this approximation is still useful for symmetry species identification if one looks at the general pattern of the bands. Bands belonging to the same irreducible representation of the moleoulrtr group should display the same pattern in polarized light. On the other hand, the mixed crystal Rs,msn spectra are also very useful for the assignment of fundamentals as they permit to distinguish “true” bsnds from orystrtl splitting components. The Raman speotra of the pure solids themselves are very valuable as they permit the identification of features whioh are absent or very weak in the i.r. spectra. The results of the spectroscopio measurements performed on C&H, and C&D, are reported in Table 2 and in Figs. 1 and 2. The assignments of the b&nds to the Table 2. Fundementcrlmodes of normal and fully deuterated solid cyclopentadiene*

Ramen (SOOK) 1.r. (SOOK) 3103m

l 3102~ 3088m 1 3037 w 307bm { 3074 w 3038 w 2891 m 2876 s { 2876m 1676m { 1672.6 m 1496.6 w ( 1498m

1374s 1 1372 II 1364~~ 1290.6 m ( 1290m 1240.2 m ( 1237.8 m 1106.6 w ( 1106.6 m 1099 w 1091 w ( 1083.7 8 995 m { 994 m 96lm

cry&l

Solid eolution#

$K)

Pal?

Pure arystal

Solid solutiont

As+unent

3101 w

-

2322 w

4

2322 VW

2320

VlW

3088 vs

3088

2327 w

a>@

2327 VB

2327

v1*Al

3076

2286 m

4

2234 w

2283

VI’

2891.6 2874

2292 w 2170 m 2116 m

a>B 4 4

2293 vw 2168 ve { 2114 2119 m w

2293 2162 2114

VlV Bl VSS.B,

-

1620 w

4

-

VI?.

Pure Pelf a p a p a p c$ a >p s” a B a

B :>fl p a a /? B a a>@ j3 a a /? a
Remen (80°K)

3074 8 { 3066 8 3040 w 2892 vs 2374 ve 1677 sh ( 1674 w 1499 VB 1437 w 1 1482 w 1386 vu ( 1332 ve 1369 ve 1243 VW ( 1240 VW Ill9 vs ( 1106 VB 1101 w 1092 VB ( 1086 “8 998 B ( 997 ah 967 m ( 961 w

1497

1377.6 1364 1110 1100 1089

1476.6 s ( 1461 B

1620 w

Bl

4

vat4

Bl

~49 A,%

a>B

a>B

“C 1232 B

1231

vsr4

1041.6 B 1231.6 m 1 1229.3 1oOQw

1061 B 1227.6 w

1046 -

VW4 VlW 4

1000 VW

1000

vlor

929 m

942 w ( 937.6 we 847 B

-

vv 4

1240 w

848.6 w

{ 847.6 vw

997

834m { 832 m 820 w

969

762

a B @ :>s

837 VB { 829 v8 821 vs

aB

763~~

-

B,

847

V11*4

832

VSO~ 4

822

VWAl V11*Bl

l Frequencies ere measured in om-’ unite; VW. very week; w, weak; m, medium; 8, strong; va, very strong; eh, shoulder; in the low frequmoy Reman Bpectnr the following lattice vibretione heve beem identified: 40. 66. 68, 81. 66, 107, 117, 136 om-1 for C,H, end 38, 64, 67. 71, 73, 80. 98, 107, 122 cm-1 for C&D,. t The polackstion obaraoter of the C,H, epeotrmn hea been determined setting the polsrizer et the maximum inteneity of the 1372 cm-1 component (a pokizetion) end rotating by 90° (p pole&&ion); the referez~e cornponent for a polarization of C&D, wan the 84806om--1 bend snd the 0 epMsum her been obtained by 90’ rotation of the polarizer. 2 The guest-host molar ratio (C‘HH, in C,D, end eke esmr) of the solid solution ia 1: 20. 0 The doublet of C,D, essigned to v&4,) ia ectnelly due to Fermi reeonenee between v, end Zv,.

Table 2. (cont.)

W,

Cd’, Reman (80°K)

I.?. (SOOK) 940 w 936 m ( 928~6 m 916.6 vs

PUre Pelt

crystal

-

942 w

a
a

Raman(80°K)

Solid solution$

Pal?

764 811 { 808 736

743 VW 810 e { 809.6 B 734.6 s

( 932 928 m 8

a > p

fC-+K)

PUW orystal

918

Solid soWionS

VW m vs m

-

/I

682 vs 1 672 VB 616~

a

363 m { 360 m

714 sh ( 712 s 720.6 w { 71&S m 711 “S 649 VW

898

a

( 893 897 m w 807 w

p

-

ap 802 w

a<@ a>B

{ 718 700 VW 1 681 676 VW w

/I aB { 616 618 w VW 363 w

B

a

618

608.6 s ( 601~4 s 433 w

369

276#6 s

i;

a>B

m m w w w w

436 ( 432 286 { 286

w w w w

736

vo, -4,

708

VII’ %

716

%il* BI

711 -

VlW v11. i1 1

-

VW B,

-

VW A,

-

VW B,

cm-’ Fig. 1. Raman spectrum of solid cyclopentadiene.

2400

2i

2wa

1600

1400

1200

1000

600

600

400

4

VI0 Bl

707.6 w 717 1 716 711 664 1 661 601

VW 807

{ 919 913 vs VW 898 vs { 893 vs 808.6 m i 807.6 sh 802 w 714 8

Assignment

200

cm-’ Fig. 2. Raman spectrum of solid hexadeuterocyclopentadiene. 464

Vibretional spectra and normal9001dinBte treatment of oyclopntt~&~~~

466

proper species of the molecular C,, sym metry group are also given; in doing this acoount was taken of the most firmly established assignments of Refs. [l] and [2], The doublet (1482,1487 om-l) appearing on the low frequency side of the strong Raman line at 1499 cm-1 of C,H, deserves a brief discussion for its interpretation. It should originate from 1V-isotope substituted molecules isolated in the lattice of normal molecules. The ratio between the total intensity of the doublet and the intensity of the main peak agrees with the 5% content of 1% monosubstituted molecules. The frequenoy shift is also characteristic of the isotopio substitution on carbon atoms. The splitting of the doublet should be an orientational splitting which originates from different orientations of the lsC-molecules at the crystal sites. The above results impose some revision of the assignment of Ref. [l] for oyclopentadiene. The only major change regards the lowest A, fundamental, which is now identified with the line at 802 cm-l of the solid. This assignment is confirmed by the photoelectron-spectrosctopioal result of DERRIK et d. [6], who found a totally symmetric vibration of cyclopentadiene at 803 cm-l. This frequency is masked in the liquid and vapour spectra by the stronger B, fundamental ypZat 806 cm-l. The weak Raman line at 1441 cm-l, which was chosen as an Al fundamental in Ref. [l], has now recognized as spurious. The two A, fundamentals yll and yla, which were tentatively placed at 1135 and 928 cm-1 in Ref. [l], are now identified with the lines at 1100 and 941 cm-l of the crystal. For cyclopentadiene-d, four changes are necessary with respect to the assignments of Ref. [2]. The solid-phase lines at 821 and 711 ctm-1 replace as A, fundamentals the frequencies at 1087 and 980 cm-l, which are both explainable as combination tones (2~~~and Y18 + yip respectively). The frequency at 711 cm-l is the lowest A1 fundamental, and here too it is masked by the stronger B, fundamental Y,~ in the liquid and vapour spectra. In the B, species the lines at 1520 and 1230 cm-1 replace as fundamentals the frequencies at 1562 and 1174 cm-l, both of which can be accounted for as combination tones (yls + vB4or yll + ya6 and yl* + y14 respectively). SPECTBAAND ASEXIQNMENT OF PABTIALLYDEUTEUTED CYCLOPENTADIENES The i.r. and Raman spectra of cyclopentadiene-1,2,3,4,5-d, are reported in Table 3 and Figs. 3 and 4. The only symmetry element of this molecule is the plane containing the CHD group; therefore its 27 normal vibrations are shared among the symmetry species of the C, group in the following way:

GA

+ 12A”.

They are all both Raman and infrared active, and those of speoies A’ give rise to polarized Raman lines. The principal moments of inertia were calculated as described in Ref. [2] for cydopentadiene-5-d.

The following values were obtained:

[6] P. J. DEBRICX,L. ~BBINX,

(1971).

0. EDQVIST

IA = 117.48 . lo-‘0;

and E. LINDHOLM, Speotroch~.

Acta

27A, 2525

Table 3. Speotre of Cyclopentadiene-1,2,3,4,6-d, U&IS-pheee Infrered liquid

band

2890 m 2416 vvw 2466 vvw 2434 w

u

COIh3W

2380 sh 2340 m 2304 w 2288 In

2210 ww 2172 w 2137 mw 2072 VW 2066 VW 2036 vvw

u

1730 w 1606 vw 1680 VW

liquid 2889 8 2479 w 2466 VW 2436 VW 2412 w 2367 ah

P

Assignment

0.17

vl.

P P

2v, = 2480 v,+v,=246s 2v, = 2436

P

2334 vs

O-09

2289 ma 2277 eh 2263 eh 2263 sh 2210 VW 2193 sb 2174 ms 2139 s 2076 VW 2063 vw 2034 vvw 2004 vvw

0.70

P O-16 0.16 ::

1380 VW 1370 VW 1360 vw 1337 VW 1290 vw 1272 VW

v,* = 1609 2v,, = 1686 VII +Af,, = 1640

P 0.06 0.06 0.06 0.06

1390 yyw

P

1372 vvw

P

1338 vvw 1296 vw 1276 ah

E.4

1239 w

A?

1240 ma

0.74

1218 VB

Bt

1219 m 1196 ah 1134 vvw 1114 sh 1090 mw

0.37

1132 ab 1114 w

0.46

A 1064 vvw

973 VW 960 w 892 VW 880 vvw 861 vw 836 B 816 a 792 m 17601 739 s 726 m 709 m I6661 497 VB 301 m

vID + vII = 2033

P

1418 VW

1048 w

2vIl + v,, = 2271 vI + vII = 2269 VII+ vx, + vsI = 2268 v, + va = 2213 v, + VI = 2192 2~,~ = 2174 ~4. A’ vIO + v,, = 2076

VI0 +

1684 VW 1649 sh 116341 1626 w 1607 sh 1482 B 1467 va 1460 va 1448 me

1637 VW 1620 vvw 1606 VW 1481 w 1466 mw 1469 sb

1087 mw

A’

At

a A

Bt a At B Bt u a c

1036 VW 999 sh 973 ve 962 m 898 VW 874 vvw

P P 0.06 0.6 P

837 ms 817 m 796 mw 766 sh 740 m 726 m 713 w 648 w 602 vvw 437 vvw 301 w

O-74 0.49 0.73

1 I : solid-phase value& 466

O-68 O-28 O-73 o-7

V18' vl,, +

vl, = 1627 2v,, = 1612 2v,, = 1478 vs. A’ ~d:,,+_‘~~; 1466

2v,, = 1422 v,1+ VI, = 1388 v,, + vz( = 1384

VII) + VI@ = 1341 v,, + I,‘ = 1304 ve + v15 = 1274 c:;,% v,, A’ v,, + v,, = VI5 + v** = “2:“,e+zyo;

%x0*A” VI1 + %4 = y& v14 + %I = VI1 + VI1 = 1041 255, = 1004 vgr A’ %I9 A’ 3v,5 = 903 2v,, = 874 v’o,A’ %a* A” v10* A’ VlW A” VW -$ Vll. VI.'

;:

VlW VW

2:

VW

0.7

1103 1138 1117

VW VW

-$

Vibrational spectra and normal-coordinate treatment of cyolopentadiene

467

1;;~y--;i: 1

32uO

3000

2600

2600 cm-’

2400

I 2000

2200

T

2000

1600

1600

MOO

I200

1000

800

600

400

cm-’

Ea. 3. Infrared epeotrumof liquid oyclopenttadiene-1,2,3,4,6-d, (thickness:22pm). -The asterisk denok isotopio impurity ban&

3ooo

2500

2000

1500

500

cm-’

Fig. 4. Raman speatrum of liquid cyclopentadiene-1,2,3,4,6-ds. T = -60°C; exciting wavelength: 4880 A. The very weak band at -3100 cm-1 is due to isotopic impurities. 126GO. 10-40; I, = 236.41 . 10m4’J g omS, with the axis of least inertia perpendicular to the plane of symmetry, and the axis of intermediate inertia making an angle of lo 29’ with the plane of the ring. Therefore A” vibrations should give rise to A-type band contours in the infrared spectrum of the vapour phase, whereas A’ vibrations should give rise to more or less hybrid I3 + C contours. Twelve out of the 15 A’ vibrations are readily identified on the basis of their depolarization ratios or gas-phase band contours or both of these criteria. Of the remaining three, the frequency at 2289 cm-r is assigned to an A’ olehio CD stretohing (va) by analogy with C,D,, and those at 1240 and 861 cm-1 are identified aa A’ fundamentals (y6 and YJ mainly on the basis of the normal coordinate treatment (see further). Among the 12 A” vibrations, two (yzo and yZ1) are identified on the basis of

IB =

E. Cas~uccr,

458

B. FORTUNATO, E.

GB,

P. Um

and P. mrra:

the gee-phase band contour, four (Ye,,, Yap,ySgand yBB)are suggested by values of the depolarization ratio very close to 0.76, three (Q, yl, and Ye,) by analogies with the spectrum of C6D8, being nearly coincident with the bands at 2324, 2294 and 434 cm-1 of this molecule, and finally two (y18 and a+& are identified on the basis of the normal coordinate treatment. yS5 remains unassigned. In this way the experimental frequency at 1240 cm-l has been used twice: once as y&4’) and once a,s yIB(B”). This siturttion resembles closely that encountered for C&D,: here a polarized Raman line is observed at 1235 cm-l* in Table 4. Valence force oonstants for cyclopentadiene 1 K,=R,

5.150

I8

2

Kt

19 Fw

3

KR

6

K;

6

H, =H,

4.671 8.013 4.701 4.373 I.013

20 21 22 23

lW32 0.391 0.341 0.672 0.666 0.304

24 F?:, 26 Fed’ = Fat,’ = Fdb’ 26 Fat,’ = F+’ = F,; = Fb,,’ 27 Fdod = F,,” = F,,” = Faox = F,,’ 28 FDtie”= F/ 29 F,+* = Fup = F,’

0.444 0.230 0.666

30 31 32

0.092 -0.536

33

4

7 8 9 10 11

K

HP H, Hb=Hy H, = Hv H,

12 Hr, 13 Hr, 14 Hra = R,, 15 15 17

Hrl Ftt FBRV

0.228 0.634 0.886 0.510 0,820 0.233 0.067 -0.301 0.122 0*068 -0.027 0.025 -0.061 0.009

FR, = FRI FRa’ = FEa’ = FT,’ = F$ F - FRY = Frv = FL0 F;: : F& = Fr; = F,+ Fr,

%,‘I-, Fr,rn F&, = F&,

= Fld’

= F; I = F;_,, nR = F; rg = “1 I = F& F;;+, m m’

= “2,

nR 0.079 -0.089

K, stretching force constant (mdyne . ,Lf-l); H, bending or torsion force constant (mdyne F, interaction parameter (stretch-stretch: mdyne *A-1; stretch-bend: mdyne * rad-l; bend-bend: mdyne - A - rad-2); F, one common C atom (apex); F’, two common C atoms (different apex atoms); F”, two common C atoma (same apex atom); F’, common C and H atoms; F’q three common C atoms; Fv, no common C atom.

* A * rad-2);

Fig. 6. Internal coordinate nomenclature. (r: out-of-plane bending; 7; torsion.) * In Ref. 2 a value of O-77ie reported for pn; we have remeasured the depolarization ratio of thie line with laser excitation, obtaining ps = 0.62.

3091 3075 2888 1500 1378 1365 1106 094 915 802

1 2 3 4 5 6 7 8 9 10

I

342

350

27

187E,,

+

17F&

-

106F;en,B

1, Solid-phase vnluas (all other values we t&ken from liquid-phase spectra).

43H&+

23H* + 67Hy, 102Hr,

276

707 494

897 668

891 664

27F;slz

25 26

-

807

17Hr, + 24Hr,

26Fa6’

61~~ +

+ 3OH, -

2324 2294 1522 112311 1000 835 765 714

434

948

45;arB

925

24

-

2177

17F&a

26FB4 - 16Fs ’ 5OH6 + 15FB4= - 2eFBe‘ 19H4 + 2OH6 + 48He + 25FB6’ 5lH6 + 15FBe’

102H,, -

102K,

28

08K,

+

+ + + +

IOlHr,,

4OH,,

17511 545

847

2333 2289 2130 1466 1235 1047 934 823 734 710

obs.

B, 2903

2900

15 I6 17 18 19 20 21 22

706

515

61F’;mrB

28FBe’ 22Hg + 15H, 27H, + 34He + 22F,4 - 28F& 59H6 4aR, 28K, + 24R4 - 17Fn4 - 26FB.’ + 5OFd 15H, + 34Hp - 26F,6’ + 16Fa,d’

22Fz4 -

Cyclopentiene

117Hrm + 15H,# -

09K,, 97Kt 84& + 3%H,, + 16K, + 36H4 + 34K, + 17K, + 24K, +

9%

P.E.D.

99K” 80KB 30Kr 28K, 28H4 46H, 5OK,

3105 3043 1580 1292 1289 1090 959 805

14

933

1097

3088 3080 2890 1504 1388 1364 1113 1001 913 820

4

CelO.

‘31 3086 8081 1587 1340 1284 1093 968 808

700

15161

13

19411

12

11 ~1100~

ohs.

V

cyclop&adiene-a,

41I1, +

99Hr, 35Hsa

SZK,, 95K, 77K~ 61% 2lH4 2lH, 3OH4 27K,

lOOK,

543 430 4 2312 2294 1537 1229 1004 831 745 705 B, 2166

+

123H,,

29Hy,

285

+

16H, + 75Hr,,, lOSHy,

897 487

+

-

+

-

-

_ .- -

43F&B

61F;&

81F;fnTa

+ 26H,,

15FzIE

16Hr,

49F;m,B

+ 26H,, 18HTB -

2lFB6’ l8H6 - %SFa, 3OH, + 15F& 18H6 16H, - 22FB6’ 15F:,’

+

+ 46Hrm

+ + + + +

6OH, + 25Hr,,

2lF~4 16H, 42H6 28H4 49He 54H,

74Hr,

79Hr,

19Hr,

797

+ + + + $ +

5261, +

756

82K~g + 2OFp.$ - 27FB6’ 25K, + 25K, + 38H9 + 34Fa4 - 29FBor’ - 33Fze’ 23K, + 46H,, 36K, + 28K, 2lH4 + 23H6 28H4 + 47H9 + lSFx4 - 29F& 2OK, + 19K, f 25H4 + 3lHe - 24F~,# - 19FBaa’ + 48Fze’

9%

gwa

g=m

PAD.

835

2314 2289 2119 1471 1229 1051 931 822 736 705

4

CdC.

Table 6. Vibrational assignment and caloulated frequencies for cyclopentadiene and hexadeuterocyclopentadiene

_

927

817 783 I698I

16061

23

24 26 26

27

613

4QH,a +

-

103F;_

26Fm’ + 48Fd

10IHr,, -

16H,, -

17F&

6lF;_

-

23F~6’

46F&

16Fsor’ - 26Fm’ lbFa+ 21H6 + 4lH, + 28FB6’ ZlH,

113Hr, +

-

22K, + SQH, + 27H, 26R, + 46Ha + 17Hr, 17H, + SlHr,

26FB.+ 62Hg + 2OH4 + 46Hg +

830 760 693

80K~ + 2QK, + 26R, + 26Hb + 62E,

98K,, QQK,,

936

3086 3081 1687 1339 1218 1093 1026

AN

“F:‘,rB

3103 3040 1677 1291 1216 1090 1022

131H,, +

16 17 18 19 20 21 22

+

42Hr,

317

314

16

16F~# -

23FnrB

Qar,

-

666

14

36H; + 6QH; 36Ka + 44c 17Hy, + 82Hr,

661

848 793

11 12 13

917

cyolopentiene-dl

34Kp+ 22F~# - 28F~zQ’ 18H+ + 66Hg+ 30FB.+ - 16&,’ - 36F~e’ 68H”+ 26Ha

97K,

98K* QQKm lOOK.

P.E.D.

16K, + 3OK, + 23H4 16K, + 16Hp + 37H, l8Hb + 348,

913

10

3088 3080 2897 2143 1608 1368 1233 1112 996

A’

O&10.

913 846 776

3089 3076 2889 2167 1498 1374 1226 1164 993

obs.

1 2 3 4 6 6 7 8 9

Y

36H,,, + 73Hr,

loo%, 431

18H7, -I- 38Hr, -

437

QQHr,,, +

24H4 + 36H.g + 29H, 29K, + 2OH6 + 34H,

747 726 648 766 648

+

16Hr,

796

794

21Fa4 - 21F& 3lH, - 23F~~’ - 16F~s’ 66H. 26H; + 41He + 16Fz6’ 28H4 + 18H6 1637 1240 1087 961 836

QZK, 96K, 77KB + 67K, + 22Ha + IS?; + SlH, +

2312 2294 1637 1243 1097 960 831 2340

28Hr, + 126H,, + 16Fzrp

+ 2OHy,

21FBFe.’+ 24Fa’

80FgmrB

302

301

17F:s,z -

108HHr, -

488

600

A*

6QHr,,,

“OF;_

26E+ + 61H6 + 16F.94 - 3OF& 24a+ + 24Ho - 18F~+ + 39F&

743 710 701

740 726 711

+ + + +

2sa, 16HQ + 36Hn -

97K, 82K~ 3lH,, 28Kr 26K,

9%

812

21F89 - 27Fa’ 17H6 + 16E, 28H,, + 22Hg + 22F.5+ 46K,

cyolopmtiene-a,

816

lOOK, 92K,,

P.E.D.

2897 2313 2289 2143 1473 1246 1218 966 862

A’

ado.

2332 2289 2138 1466 1240 1219 973 861

ObB.

Table 6. Vibrational assignment and oalculated frequenciw for partially deutemted oyelopentadien~

Vibrational spectraand normal-coordinate

treatmentof cyclopentadiene

461

the liquid, whereas the infrared spectrum of the solid shows a doublet at 12314i122@8 cm-1 whose polarization pattern is the same normally encountered for B1 vibrations (Table 2). In the light of the preceding results, some revision is necessary for the assignments of Ref. [2] for cyclopentadiene-5-d. In particular, the band at 793 cm-l, previously assigned to an 8” fundamental, appears now to be the counterpart of the lowest Al fundamental of C&H, at 802 cm-l, and therefore it is to be identified with an A’ fundamental, in better agreement with its hybrid gas-phase contour. The place of this band as A” fundamental is now taken by the weak depolarized Raman line at 817 cm-l, previously assigned to a combination tone. Also the i.r. line of solid C,H,D at 783 cm-l and the i.r. shoulder of liquid C,H,D at 1215 cm-l, previously unassigned, could be taken into consideration as A” fundamentals; this is contimed by the normal coordinate treatment. NORMALCOORDINATETREATMENT For the construction of the G-matrix the molecular geometry obtained by electron diffraction was used [7]. An initial set of force constants, transferred from cyclohexene [S] and l,3cyclohexadiene [9], gave a rather poor fit to the experimental frequencies; a considerable improvement was however obtained by changing some of the interaction constants as suggested by the Jacobian matrix. This modified set of force constants was used in the least-square reiinement using the program of SCEUUHTSCEINEZDER [lo]. For the refinement the experimental frequencies of cyclopentadiene and of its -dl, -d, amd -d,, derivatives were used. The refined force constants are listed in Table 4. Fig. 6 shows the internal coordinates. A comparison of the experimental and calculated frequencies is shown in Tables 5 and 6 together with an approximate potential energy distribution (for simplicity the contributions smaller than 16 per cent are omitted). A&twwledge~&-Some Raman measurements were csrriedout in the Centro di Spettroscopia Raman, Istituto Chimioo G. Ciamician, Universiti di Bologna; the authors thank Dr. G. P. BAILGDI for assistance. This work was supported by the financial aid of the ConsiglioNazionallede& Ricerche.

[7] V. SCHOIKAXER and L. PAVLIN~,J. Am. Ch. Sot. 61,1769 (1939). [a] N. NETO, C. DI LATJRO,E. CASTELLUCCI and S.CALIFMO,Specsrochim. Acta a 1763 (1967). [9] C. DI LAW-IL+N. NETO and S. CAIJWANO, J. hfol. Stvuct. 8, 219 (1969). [IO] J. H. SCEACHTSCHNEIDER, Tech. rep. N.231-64, Shell Development Company, Emeryville, California (1966).