Infrared and Raman spectra of heterocyclic compounds—III

SpectrochimicaActa, Vol. 27A, pp. 209 to 221. Pergamon Prw8 1871. Printed in Northern Ireland

Infrared and Raman spectra of heterocyclic compounds-III The inkwed studies and normal vibrations of 2,2’-bipyridine J. S. STRUEL* and J. L. WALTER Department of Chemistry and the Radiation Laboratoryt University of Notre Dame, Notre Dame, Indiana 46566 Ah&&--The infrared spectra of 2,2’-bipyridine and 2,2’-bipyridine-ds were obtained from 4000 to 40 cm-l, The absorption bands of these compounds were assigned by a comparison of their spectra to each other se well as to the structurally similar molecules: pyridine, 2- substituted pyridinee and biphenyl. Normal Coordinate Analysis (NCA) were performed on 2,2’-bipyridine and ite deutero analogue aa oomplete twenty body problems with 0, symmetry. A Urey-Bradley Force Field (TJRFF) containing a resonance potential was employed yielding the in-plane and out-of-plane force constants and vibrational descriptionsfor these molecules. 1.

IIVTR~D~~T~~N

2,2’-BIPYRIDINE possesses the a-diimine chromophore which is known to form highly stable metal chelates ; the most thoroughly studied being the iron (II) complex [l]. This stability is attributed to the potential “pi” or back-bonding interaction between metal and ligand producing partial double bond character in the M-N bond. No complete assignment of the infrared spectra of the ligand 2,2’-bipyridine or of its 1: 1 metal chelates appears in the literature. In this paper is presented a complete assignment of the infrared spectra and a normal coordinate analysis of 2,2’-bipyridine and of its deuterated analog. 2,2’-Bipyridine is a weak diimine base consisting of two pyridine rings joined together at the alpha or 2-position on each ring. It can exhibit various geometrical configurations of which the cis and trans coplanar isomers are the extremes. In solution it assumes a slightly transoid configuration with a dipole moment of O-91D indicating an azimuthal angle of approximately 26’. As the mono-hydrochloride, it is slightly cissoid with only minimal N ---H-M interaction while the dihydrochloride reverts back to a slightly transoid configuration [2,3]. In the solid state, the system of interest here, the 2,2’-bipyridine molecule is in the tnm.s coplanar configuration as determined by X-ray analysis [a]. This con@nation displays the simplest spectral geometry since any configurations with an azimuthal angle greater than 0” possess very little or no symmetry allowing all vibrational degrees of freedom to be infrared active. The & coplanar isomer possesses Ceo symmetry disallowing some of the out-of-plane modes only. The C,, tram configuration has a center of symmetry, making the l&man and infrared * This work based on the Ph.D Thesis of J. S. Strukl, Notre Dame, August, 1909. t The Radiation Laboratory is operated by the Univemity of Notre Dame under contract with the Atomic Energy Commission. This is AEC dooument No. COO-38-096. Aclmowledgment is also made for the support by N.I.H. &ants He-0221314 and AM-13162. [l] [2] [3] [4]

J. BAXENDALEand P. &CORQE, !Z’mne. Fcmdizy Soo. &?,66 (1950). K. NAKAMOT~,J. Phye. C%ma.64,142O (1960). J. R. BEA!JXIEarid M. WEBSTEB,J. Phya. Ohm 66, 116 (1962). W. B. PEARSON, Structwe Rep&, Vol. 20, pp. 609-610. N. V. A. Oosthoek’s Uitageves Mij (1956). 209

210

J. S.

STRUEL and J. L. WALTEB

modes mutually exclusive, thus eliminating approximately half of the vibrational degrees of freedom from infrared activity. The infrared spectral assignment of 2,2’-bipyridine in the trans coplanar con&mation is based, in this study, primarily on a comparison to its deuterated analog to differentiate between the hydrogen and ring modesand secondarily by a comparison to the spectral assignments of pyridine [5-81, a-substituted pyridines in general [9], and biphenyl [lO-121. 2. EXPERIMENTAL 2.1 Absorption measurements The infrared spectra were obtained with Perk&Elmer 221 and 621 infrared spectrophotometera in the 4000-300 wavenumber region and with a RIIC Fourier Spectrophotometer in the 400-40 cm-l region. The KBr disc method [13] and nujol mulls were employed in the former region. Crystalline polyethylene was employed in the latter region. The crystalline polyethylene was prepared according to a method supplied by Prof. Kazuo Nakamoto. Epolene C-10 (Eastman Chemical) polyethylene was dissolved in hot xylene with constant, rapid stirring until a viscous solution was obtained. The solution was cooled and the excess xylene was decanted. The white powdery polyethylene was placed in methanol and heated with constant stirring for one-half hour. This mixture was filtered and the polyethylene squeezed dry with suction and by being pressed between filter paper. It was then broken up and passed through a nylon mesh and dried $7~vacw, for two days. The discs were then made in the same fashion as a KBr disc with 8-10 mg sample per 100 mg crystalline polyethylene. 2.2 Preparation of comp0wd.s 2,2’-Bipyridine obtained from Aldrich Chemicals Co. was recrystallized from a 50% solution of ethanol/water and then from absolute ethanol. Platelike crystals were obtained with a melting point of 696%. 2,2’-Bipyridine was deuterated using the methods employed for biphenyl [14] and pyridine [15]. Approximately O-1g of purified 2,2’-bipyridine, 10 ml of 99.9% pure D,O, and 0.76 g Ca(OD), (Ca0 mixed stoichiometrically with D,O and vacuum dried) were placed in a sealed glass tube and heated at 180°C with shaking for 24 hr. The 2,2’-bipyridine was recovered by being distilled onto a cold finger after the excess Da0 had been pulled off. The process was repeated once more. The partially deuterated 2,2’-bipyridine was then placed in another sealed tube with an equal volume amount of Pt catalyst and a suitable volume of D,O and [6] J. K. W ILXEIJRSTwd H. J. BERSTEIN,Can. J. Chem. 88, 1183 (1967). [S] D. A. LONG and E. L. THOBXAS, Tram. Faraday Sot. 69, 783 (1963). [7] D. A. LONUand W. 0. GEORUE,Spectrochim. Acta 19,1777 (1963). [S] M. A. KO~NER, Ju. 8. KORO~OV and V. I. BERE~N, O#.Sm 10,233 (1961). [Q] A. R. KATIUTZW, Quart. Rev. 18, 313 (1959). [lo] J. E. KATON and N. T. Mc&~IL, J. Mol. Spectry 14,308 (1964). [Ill K. ?!bEBS,S. SANDRONIand G. ZERBI,J. Chem. Bye. 40,3602 (1964). 1121 D. H. WEIIfIPEN, Spectrochim.Acta 7,253 (1966). [13] M. M. STI~~SONand M. J. O’DONNELL,J. Am. Chews.Soo. 74, 1806 (1962). [14] R. A. ASEBY and J. L. GAX~T, Au&-al&a J. Chem. 16,649 (1963). [IS] F. GEISSand S. SANDRONI, Spectrochim.Acta 22, a86 (1966).

Infrared and Raman spectra of heterocyclic compounds-III

211

heated at 180°C for 24 hr. The Pt catalyst was prepared by passing D, gas over platinum oxide in an oven at 200°C until the reddish brown oxide was completely ashy-black in appearance. After 24 hr, the D,O solution was cooled and atered. The precipitate was mixed with EtOD and the catalyst filtered out. The EtOD was then evaporated in wocuo leaving the 2,2’-bipyridine-d,. The process was repeated once more yielding deuterated ligand (no appearance of the C-H stretching bands about 3000 cm-1 under scale expansion and the appearance of new bands, C-D, in the 2260-2300 cm-l region), m.p. 70°C. 3. DISCTJSSION 3.1 Empirical assignment The infrared absorption frequencies obtained for 2,2’-bipyridine and 2,2’bipyridine-ds are listed in Table 1 with their respective assignments and in comparison to pyridine and biphenyl. The actual spectra for these molecules are given inFig. 1. 2,2’-Bipyridine is basically a S-substituted pyridine with pyridine being the substituent group. Consequently, the hydrogen bending vibrations should be similar (four-adjacent) to those of 2-substituted pyridines in general [16]. Being a pyridine compound, the ring stretching and bending vibrations should be similar to the much studied pyridine itself [G-8, 171. A possible exception would be the difference in symmetry and greater number of atoms in such a comparison. Aside from its pyridine character, it possesses certain inter-ring motions similar to those of biphenyl [lO-12,1&J. With the aid of deuteration and the above considerations, the following assignment was arrived at: 3600-1600 cm-l. In this region, four C-H stretching bands are obtained between 3lOO-3000 cm-l commensurate with the center of symmetry negating four of the eight possible stretching bands from infrared activity. Deuteration shifts these bands to the 2300-2250 cm-l region as expected. 1600-1300 cm-l. Benzoid aromatic compounds exhibit four characteristic phenyl nucleus ring stretching modes in this region. For pyridine they are at 1680, 1672, 1482 and 1439 cm-l. 2,2’-Bipyridine has four similar absorptiona at the slightly lower frequencies of 1579, 1553, 1448 and 1410 cm-l reflecting the effect of substitution on the latter three absorptions. Deuteration shifts these bands to 1659, 1629, 1346 and 1300 cm-l indicating minimal hydrogen bending interactions for the former two bands (20 cm- l shift) and significant hydrogen interaction for the latter two (100 cm-l shift). In the case of the 1439 cm-l band in pyridine, some authors have assigned it as shifting to a band at 1228 cm-l in the deutro analogue [17) ; whereas, others [5-81 have assigned it as shifting to a band at 1301 cm-l with the 1228 cm-l band being a combination band. 2,2’-Bipyridine-d, has a similar band at 1240 cm-l which for reasons to be given later is matched with a similar band at 1245 cm-i in 2,2’-bipyridine. 1300-1100 cm-l. A weak absorption occurs at 1270 cm-l in both 2,2’-bipyridine and its deutero analogue. This is either a combination band or the appearance of [IS] A. R. KATRITZXY, Quart. Reu. 18, 353 (1969). [17] Q. ZE~BI, B. CRAWTORD and J. OVEREND,J. Chum.Phy8.88,

127 (1963).

212

J. 5. STRUELand J. L. WALTEB

Table 1. Infrared frequencies (cm-l) and empirical assigumentsof 2,2’-bipyridineh, aud d, Pyridine hs

2.2’-bipy&line d,

%

3083 “S 3064 8 3036 va

3086 3078 3061 3064 2293 2286 2270 2264 1630 1642

1680 VE 1672 8 1482 8

B 8 8 VB 8 B

Desoription

d,

w w wsh w

1679 VB 1663 m 1448 s

ring-H stretch 2296 2280 2270 2266 1660 1629

w w w w s B

ring-D stretch I ring &r&ah (C=N and C=C) ring &ret& (C=N and CA!) ring et?. and ring-H bend ring str. and ring-D bend ring str. and ring-H bend ring str. and ring-D bend

1346 8

1340 w 1401 s

1439 8 or 1376 m or

1300 8

1301 s 1228m 13018 1322m

ring str. 1270 VW 1248 m

1218 l3 1217 1148m

1270 v8 1260 ma

overtone or inter-ring str. (not allowed) ring str.

12lOwm 1138 m 1000 w 1083 m

ring-H in-pLana bend

1088 B

I 1043 m

1029 vs

1063 m 1033 In

1006 m 992 v*

962 s

LO39ms 991 In

990 ma 066 m

890 m

ring-D in-plane bend ring str. tmd bend and C-H ring str. and bend and C-D out-of-plane ring-H bend ring breathing ring-D in-plane bend ring-H out-of-plane bend

bend bend

887 m 860 w ring-D in-plane bend

833 m 841 w 823 8 827 ma 801 w

I

763 “8 734 m

862 w 606 B

626 w 682 s

738 m 7lOw 661 w 618 w

308 m Biphenyl 140 120 -

169 m 04m 42w

716 664 630 602 680 361

w w w wm s m

1

ring-D out-of-plane bend ring-D in-plane bend ring-H out-of-plane bend. (4 adj. H) ring-D out-of-plane bend ring-H out-of-plane bend ring torsion ring bend. (in-plane) ring-D out-of-plane bend ring-D out-of-plane bend (4 adj. D) rmg toreion in-plane aaifmors out-of-plane scissors torsion or crystal mode

Infiwed and Reman spectra of heterooycliccompounds--III

Fig. 1. Infrared spectra of 2,2’-Bipyridine and 2,2’-Bipyridine-d, from 4000 to 40 w8vemunbem (all frequencieslisted iu em+). (A) 2,2’-Bipyridine (4000-700 cm-l). (B) 2,2’-Bipyridine-d, (4000-700 am-l). (C) 2,2’-Bipyridine (700-236 cm-l). (D) 2,2’-Bipyridined8 (700-236 an-l). (E) 2,2’-Bipyridine (400-&O cm-l).

213

214

J. S. STREKL rtnd J. L. WALTER

the inter-ring stretch. Biphenyl [lo, 111 and methyl substituted dipyridyls [18] which cause a slight loss of co-planarity exhibit a weak band between 1270-1280 cm-l. Absorptions also appear at 1248, 1210 and 1138cm-1 in 2,2’-bipyridine and at 1260 cm-l in the deutero compound. Pyridine has absorptions at 1218 and 1148 cm-l that shift to 867 887, and 1048 cm-l on deuteration and 2-substituted pyridines display a hydrogen dependent absorption at 1150 cm-l. Hence, the 1210 and 1138 cm-l absorptions are assigned as hydrogen dependent absorptions. They shift to 965 and 850 cm-l on deuteration. The ~1245 cm-l bands in both analogues are matched together as ring modes because: (a) assigning the 1245 cm-l deutero band as being related to the 1448 or 1410 cm-l bands would result in a very strong 1300 cm-l deutro band being unassigned except as a combination band because of the sufficiency of bands in this region, (b) partial deuteration does not affect the intensity or position of this band whereas all the other hydrogen dependent bands are significantly altered, and (c) a frequency is calculated between 1200-1250 cm-l in both species which is resonant parameter dependent (basically a ring stretching mode). 1000-800 cm-r. 2,2’-Bipyridine is similar to pyridine in this region with two inplane hydrogen deformation modes at 1090 and 1083 cm-l which disappear on deuteration (841, 801 cm-l) and two in-plane ring vibrations at 1063 and 991 cm-l. The former shifts 30 cm-l upon deuteration vs. a 23 cm-l shift, for a similar pyridine band. The latter absorption is the characteristic ring breathing motion of aromatic ring compounds. There are two remaining absorptions at 1039 and 890 cm-l that are assigned as out-of-plane hydrogen deformations which appear at 827 and 734 cm-l in the deutero analogue. The latter corresponds to a similar band in pyridine but the former is somewhat higher than a like band in pyridine (990 cm-l). To equate the assignments of pyridine and bipyridine would necessitate labeling the 1039 cm-l absorption as the ring breathing motion or calling the 991 cm-l absorption both ring-breathing and out-of-plane with the relatively intense 1039 cm-l band a combination band. Neither situation is reasonable and so the 1039 cm-l band was assigned as hydrogen out-of-plane. 800-600 cm-l. There are two ring bending motions at 651 and 618 cm-l similar to pyridine. One exception is that they shift to higher frequencies on deuteration. The four adjacent hydrogen atoms result also in the characteristic out-of-plane hydrogen modes at 753, 738 and 710 cm- l. An anomaly with these absorptions is that the 753 cm-l band seems to shift further to a lower frequency than the 738 cm-l band from intensity considerations or else there is an intensity switch on deuteration. Below 600 cm-l. Four absorptions are apparent in this region. One at 397 cm-l (shifting to 351 cm-1 on deuteration) corresponds to a ring torsion mode with substantial hydrogen-bending coupling. The remaining three bands, 169, 94 and 42 cm-l, correspond to inter-ring vibrations between the two pyridine rings. Biphenyl exhibits an inter-ring scissoring mode at 140, and out-of-plane scissoring mode at 120, and a very low frequency torsion mode [ 10-121. These correspond well to the bands observed in 2,2’-bipyridine. The 42 cm-l band may correspond to a crystal mode rather than to the low frequency inter-ring mode. [I81 P. E. FIELDING and R. J. W. LEFEVRE,J. Chn.fi’oc.

1811 (1961).

216

Infrared and Raman spectra of hetwooyolio compounds-III

3.2 Normal coordinate analysis 2,2’-Bipyridine in the crystalline state (the one considered here) is in a coplanar configuration with the nitrogen atoms tram [4, 19, 201. It possesses C, symmetry with twenty-seven infrared active degrees of vibrational freedom: 9AU modes of out-of-plane character and 18 B, modes of in-plane character. The remaining degrees of freedom are Reman active only. The Wilson GF matrix method [21,22] was employed as coded in Fortran IV by SCEACETSCENEIDER et al. [23]. The molecule was treated in its entirety employing all twenty atoms and all possible internal coordinates. The c3, or kinetic energy matrix, was generated from the molecular parameters, internal coordinates and symmetry coordinates shown in Fig. 2 and 3, and Table 2 respectively. Table 2. Symmetry coordinates for 2,2’-bipyridine_Infrared aotive only

S(1) =

8(2) = S(3) = 8(4) = S(6) = 8(6) = &s(7)= S(8) = 5(Q) = S(10) = S(11) = 5(12) = IY(13)= AY(l4)= 8(16) = S(16) = k?(l7)= S(l8) = S(19) = 5(20) = 8(21) = rs(22) = S(23) = r9(24)= 5(26) = S(26) =

C-N

(d.)‘P ())v* (#‘l” (#)‘l’ (a)*/* ())v* (&‘I* (#)l/* (#11* 0)“’ ())I/* (1) (#)‘l’ (f)l/* (t)“’ (&“’ (&)V’ ())V’ (#V* (#V’ (#)‘l’ (#l/’ (+)‘I* (&Y’ ())‘/’ (#“’

EL:

zc-c

%H C-H C-H C&H N-G-C &N-C N---C-C

inter-ring

zz?s C-cc N-C-C N-C-H &C-H &C-H C-C-H w. 11) C(3, 18) C(6.16) C(7.14) c(Q, 12)

A, out-of-plene S(27) = S(28) = 5(29) = S(30) = S(31) = 19(32)= S(33) = S(34) = 5(36) = 9(36) = 5(37) =

(#“* (&‘I* (+)‘I* (&)‘l” (?#l* (#la (1) (+)ll* (&‘I* (&‘I* (#‘/”

TI+ Ts+ T,+ T, + T, + TII+ TII

Ts T, T’, Ts TI, TI,

04+

01,

*,+

01,

on+

016

%I+

01,

I

rcdundmcy

GN O-N

tEEi C-C inter-ring

o-c! C-C H(4. 19) H(6, 17) H(8, 16) H(lO, 13)

* See Fig. 3 for e descriptionof terms end internalooordheta mu&cm.

[19] F. [ZO] K. [21] E. [22] E. [23] J.

BERTINAITTI, A. M. LIQTJORI and R. PERISI, tizz. Chim. Itcd. 86,893 (1956). L. MERIT-P, JR., E. D. SCHROEDER, ActaCv@. 9,801 (1966). B. WILSON, J. C%em. phy8.7, 1047 (1939). B. WILSON, J. Chem. phv8.9, 76 (1941). H. SCHACHTSCHNEIDER, Shell Dept. Company Technical Rep., No. 263-62 (1962).

210

J. 8. STRUKLand J. L. WALTER

I-

1.0806

Fig. 2. Mole&

parametem for 2,2’-bipyridine [4, 19, 201.

The F, or potential energy matrix, was a Urey-Bradley force field containing a resonance potential. The potential field took the following form: 27 = 2 Kt + P,,(Q + ig (G

where

8t,

=

(rs

4,

=

k,

-

rl

- 0.1 t,>)(Ar,)*

+ ~&~~~ + 0.1 st~,str))(r,,r,,Aa,,)2

+ is (%(%P,,

+ 0.1 vrt)(Ar~,A~n))

+ is (P&P,,

- 0.14~,r)r,,(Aa~A4)

+ is G,(AG

+ X4A42

+ v (resom=W

~O%)lP~,

~itYc?u

the end atoms of angle ikj rl is bond ik of angle ikj K, is stretching force constant for bond ik H,, is bending force constant for angle ikj F,, is repulsion force constant between atoms 9 TdI is torsion force constant for bond with atoms ij 71+is force constant for lifting atom i out of a molecular plane p = resonance force constant, V(res.) = f Q(Ar,Ar,)p,, &j me

i,j = internal coordinate numbers

Infrared end Ramau spectra of heterocycliocompounds-III

217

Fig. 3. Internal coordinates for the symmetry coordinates of 2,2’-bipyridine. Deeoription of terms found in Table 2. Ri O* Tt A,, At

= bond stretch for internal coordinate representedby (i). = out-of plane wag of the hydrogen atoms i. = torsion about ring bonds (a). B,, ci axe angdaz deformations of angle i. = (2ac - aQ1 - a~s)/(3)v*, Bi = (at - act.1)/(2)1’a,

Cf

=

(af

+

at+1

+

af+z)/W’l*.

where r’s refer only to bonds forming resonance system, a + 1 contribution results from bond interactions sep8r8ted by zero or an even number of bonds and -1 for 8 separation by an odd number of bonds. Since the V(res.) potential includes all possible bond interactions within the resonance system, one can consider 2,2’-bipyridine as one complete reson8nce system or 8s two independent resonance systems. Since the interring carbon-carbon bond length is very close to the single bond value (1.60 vs. 1.52 A), the molecule was considered as two independent resonsnce systems. Consequently, no interring bond interactions 8re included in the resonance potential. The resonance force constant p usually affects only a small number of frequencies and as such is an 8ver8ge value over all possible interactions. The observed vs. calculated frequencies, percentage errors, and 8pproxim8te descriptions for 2,2’-bipyridine and 2,2’-bipyridine-d, are given in T8ble 3. The calculated values were adjusted to fall within 6% of the observed values. This is suitable accur8cy considering the large degree of mixing between ring modes snd hydrogen bending modes in sromatic compounds and in light of trying to predict the degree of shift upon deuteration. The force constants which generctfed these

218

J. 8. STRUKLand J. L. WALTER

Table 3. Caloulatedfrequenoiesand % errors of B, vibrations for 2,2’-bipyridinek, cm-l (v) and 2,2’-bipyridine-d, cm-l (v’) ohs.

oalc.

v(3) v(3)’ v(4) v(4)’ v(5) v(b)’ v(6) v(6)’ v(7)

3086 2295 3078 2280 3061 2270 3054 2255 1579 1559 1553 1529 1448

3082 2275 3077 2265 3075 2262 3074 2255 1579 1561 1537 1520 1454

4 26 1 lb -14 8 -20 0 0 -2 16 9 -6

0.13 0.80 0.03 0.06 -0.46 0.35 -0.65 0.00 0.00 -0.13 1.03 0.58 -0.41

v(7)’

1346

1368

-23

- 1.71

v(8) v(8)’ v(9) v(9)’ v(l0) v(10)’ v(ll) v(l1)’ v(l2) v(12)’ v(l3) v(13)’ vu41 v(14)’ v(lb) v(l5)’ v(l6) v(M)’ v(l7) v(17)’ ~(18) ~(18)’ v(l9) v(19)’ v(20)

1410 1300 1248 1245 1210 965 1138 850 1090 841

1402 1296 1252 1231 1219 950 1145 821 1100 805 1069 795 1043 1042 1013 994 667 650 633 617 168.4

41) v(l)’ v(2)

VW’

vizlj v(21)’ v(22) v(22)’ ~(23) ~(23)’ ~(24) ~(24)’ v(25) v(25)’ v(26) v(26)’ ~(27) ~(27)’

801 1063 1033 991 990 651 664 618 630 169 n.r. 1039 827 890 734 753 580 738 602 710 690 398 351 n.0.t ILO.

94 n.r. t 42 n.r.

1029 817 889 712 762 554 730 640 700 680 397 342 308 264 93.2 42

(0 -

c)*

8 4 -4 14 -9 lb -7 29 -10 36 14 6 20 -9 -22 -4 -16 14 -15 13 .6 10 10 1 22 -9 26 -8 -38 10 10 1 9

0%error*

0.57 0.30 -0.32 1.12 -0.74 1.55 -0.61 3.40 -0.92 4.30 1.29 0.75 1.87 -0.87 -2.21 -0.40 -2.45 2.10 - 2.40 2.06 0.35 0.96 1.20 0.11 2.80 -1.19 4.31 -1.19 -6.31 1.40 1.44 0.25 2.30

Desaription C-H GD C-H GD C-H C-D C-H C-D > >

C-N,

C-C

str.

C-C,

C-N

str.

CN, NCH, CN. NCD, C-C C-C >

str. str. str. str. str. str. str. str.

C-N,

pl hr., HCC def. C-C str.. DCC def. str., CCH def. str., CCD def. C-C

str.

CCH def., pl str. CCD def., C-C str. NCH. CCH def. NCD, CCD def. CCH def. CCD def. CCH def. CCD def. C1 str. C-C str. ring breathing ring breathing

1NCC, CCC def. CCN, NCN, CCC def. > inter-ring NCC def. H wagging D wagging H D H D H D

wegsing =gginp wagging wagging wagging wagging

C-C,

C-N

torsion

)C-C,

C-N

tornion

>

0.8

0.85

inter-ring out-of-plane bend

0

0.00

inter-ring torsion

219

Infrared and Raman speotra of heterooycliocompounds-III Table 4. In-plane force oon&mt~~for 2,2’-bipyridine Z,2d’-13ipyridine

Pyridine*

Tsrpe (mdyn/A) stret.&ing CLN C-C C-C inter-ring C-H BMXGlg

6.10 4.69 3.60 4.70

6.30 4.71 4.64

zE C--C-C UN C-c-c UH

0.23 0.30 0.24 0.60 0.46 0.19 0.20

0.26 0.34 0.26

0.21 0.22

0.43 0.62

0.72 0.80 1.00 0.90 0.80 0.40 0.43

0.42

0.36

0.72 0.80 0.80

inter-ring inter-ring

N&H RepUlkIiE

**-N

~.-.*.*$; . ..c c * - * (C) - * * c ; g,’ .*.Nh*_ring ::: . * * C inter-ring He..(C)...C H*..(C)...N Re8onsxlae

P

* Baaedupon e o&ml&ion done in our laboratory

~PprOximeting

the remlta of

CBAW~OBDand Owcsawr, [24].

Table 6. Out-of-plane force oonsta~A~for 2,2’-bipyridine and comparative force oon8tants B

I

0.606

0.62 0.66

0.289

0.36

BI

Description

0.40 0.62

(

0.28 to 0.33

0.008

-0.03

-0.03

GPY

Torsion C-C inter-ring GC CLN out-of-plene wag H(4) H(6) H(3) H(l0) Out-of-plane wag: Orrho intaraotion H:H O&m tomion interaotion

0.00

0.00

0.00

0.113 0.069

0.029 (

fO.20

fO.12

to fO.19

to fO.16

IR etanda for inter-ring torsional bond. end bemimidasole by COBD~ [26]. I: imidamle. BI: bemimidasole. B: bemene.

0.370 0.320 0.340 0.330 0.060 0.100

C-C:CN

0.00

0.231 0.420 0.400

0.090 0.100 0.090 0.116

C--C(IR)*:CN C-N:C-N CLC(IR):CC ( (rc:C-C &Z&atorsion interaotion

0.100

cc:C-c cc(IR):c-c

C-N:C-C(IR) C-N:C-C o&w out-of-planewag:tQmion H(a):C-N H(4):CC H(6):C-C H(8):CC H(lO):C--C

0.060 0.060 0.060 0.100 -0.100 -0.080 -0.060 -0.100

Comparative force oonetanta were taken from e thesis on imitiole

[24] B. CRAWEORD, J. O-ND and G. ZERBI, J. Chtm. Phg8.28,127 [26] M. M. HORDES, Ph.D. Thesis, University of Notre Dame (1966).

(1963).

220

J. S. STRVKLand J. L. WAZ.TEB

values are given in Tables 4 and 6 with comparative force constants. The force constant set is the tame for both isotope species since the only change between the compounds is one of maas For the out-of-plane or A, vibrations, the large number of force constants vs. the small number of frequencies is not alarming (twenty-two force constants and eight observable frequencies). Only seven of the force constants (diagonal torsional and out-of-plane elements of the potential energy matrix) play a major role in the calculations. The remaining force constanta are off-diagonal interaction terms. These force constants exhibit only a smaJ1 percentage contribution to the frequencies, their values are small, their descriptions are essentially identical, and their function Table 6. Potential energy distributions (symmetry coordinates and force constank for the calculated frequenciesof the in-plane and out-of-plane modea of 2,2’-bipyridine No.

ml-’

PED:

Symmetry

coordinates

3082 3077 3075 3074 1579 1537 1454

+O.l8iY(7) -0.44&s(7) +0.2%(7) -0.17&7) +0.1&9(l) -0.295(l) -O.l7bs(l)

-0.395(S) -0.53&10) +0.8W(t?) +0.80#(9) -0.385(2) +0.20,9(a) -0.12&4)

8

1402

9

1252

10

1219

-0.39s(20) -O.O9B(8) +0.2W(l) +0.2&S(S) -O.l8b9(8)

-0.275(19) -O.l!L!?(S) +0.10,9(2) -0.OQ69(3) -0.24~9(2) +0.22&3) -0.31#(4) -0.1&S(8) -O.l&S(lQ) -O.lW(21) +0.473(18) +o.zw(el)

11

1145

+o.l&s(l9)

-0.23&20)

12

1100

-0.126(4) +0.18q2q +0.1&s(5)

$0.135(8)

-0.1&9(20)

13 I4 15

1089 1043 1013

18

887

17

845

18 19 20 21

183.4 1029 339 782

22

730

23

701

24

397

25

308

+0.2&S(Q)

-0.215(10)

+O.laS(Q) +0.235(10) -0.21&(S) -OAW(4) -0.235(18)

+0.31&(8) +0.22&21)

PED:

fome constanta

O.I)OK(CH) O.BOK(CH) O.QOK(CHj O.QOK(CH) 0.4OK(CN); 0.27K(CC) 0.23K(CN); 48K(CC) O.l8K(CN); O.l?K(CC); O.Z?H(CCH); O.lSF(HCC) O.lQR(CC); 0.38H(CCH); 0.23F(HCC) 0.27R(CN); 0.42K(CC); 0_3QH(HCC); O.l3F(HCC): -0.213~ O.lQK(cN); O.ZSH(HCC); 0.13H(HCN); O.ZOF(HCC); O.lBF(NCH) O.lSK(CN); 0.83K(CC); O.lSH(HCC); 0.32H(HCN) O.llK(CC); O.IIH(HCN); O.IOH(HCC);

O.l8F(CCC)

28 27

is.:

93.3 44

+0.1&!?(3) +0.2&9(19) -0.293(3) -0.278(4) -O.lOs(l) -0.085(11) -0.105(13) +O.OW(l4) +o.l4Lq18) +0.275(11) -0.125(13) -0.18Ls(18) +0.23B(12) -0.206’(13) -0.Mq18) +899(17) +o.lOAs(2s) -0.7Ls(34) +0.6Ss(38) i_O.?as(37) -0.42&(38) -0.13q30) -0.13q31) +o.a4s(3s) -0.535(36) +0.219(30) -0.2&9(31) +0.235(23) -0.1&5(29) +O.laS(30) -0.54aS~31) -0.SWi28j +0.275(30) -O.SW(ZS) -0.54&32) +0.308(27) +0.178(31) -0.87&9(33) +0.30&32) -0.215(23) -O.l&S(27)

refers to inter-ring

interactions.

-O.lL9(21) +o.oQl9(12) -0.18s(15)

0.3lK(CC); 0.28H(HCC): 0.29F(HCC) 0.4OK(CC); O.l3F(HCC); O.lSF(CCC) O.l3K(CN); O.l3K(CC); O.lSH(HCC); O.lBF(HCC); O.lOF(CCN)

+0.315(14)

O.lQH(CCN);

+0.235(15)

+0.3W(30)

O.lSH(CNC); O.l4H(CCC); O.ZBF(CCC); O.l2F(CNC) 0.4361(CCC)i.r.; 0.23E(CCN)~.r.; O.IIF(CCN)j.,. 0.72x(4) 1.8SH(3) 0.74R(lO); O.SST(CC); 0.42H(8); -0.292?(10)T(CC) 0.84.H(8); O.S3H(8); -0.5211:H; 0.44H(lO); 0.4ST(CC); -0.33H(8)T(CC) 0.772’(CC); 0.35T(CN); -0.32T,(CC)T,(CC); O.$lT,(CC)T,(CN) O.BlT(CC); O.??!Z’(CN); -0.23Z’,(CC)Z’,(CC); -0.2ST,(CN)Z’,(CC) l.B’IT(CC); -38T,(CC)T,(CC)

+0.185(31)

O.QST(CC)~.,.; -O.l2!Z’,(CN)Z’,(CN) O.SZT(CC); 0.35T(CN); O.lCT,(CC)T,(CC)

+o.zLY(ze) +0.44+9(37) +O.lsS(32) -O.lM(27) +0.275(27)

O.l3H(CCC);

0.2lF(CCC)

Infrared end Raman speotra of heteroayoliocompounde-III

221

is one of retiemerit rather than initial calculation. The actual descriptions of the modes in terms of symmetry coordinates and force constants for 2,2’-bipyridine are given in Table 6. The resonance dependent frequency is somewhat different in character from that observed in pyridine by CRAW-RQ~D and OVEREND[24]. The latter’s mode showed a significant degree of hydrogen character. In 2,2’-bipyridine, there is only a 21 cm-l calculated shift between deutero and non-deutero species. The description is also that which one might expect for a resonance dependent mode in that its description is one of alternating bond extensions and bond contractions. Such a description is similar to stating that bipyridine has alternating single and double bond character. The resonance force constant is somewhat lower than for pyridine in line with its 2-substituted character and its lesser basicity vs. pyridine. A mode was calculated at 308 cm-l which was not observed. No band at all appeared in the region 400-170 cm-1 which could be assigned to this calculated frequency. The remaining calculated frequencies all shift in accordance with that observed in the actual spectra. The force constants for the in-plane modes are highly similar to those for pyridine. Because of the 2-substitution, some of the ring stretching force constants are slightly lower. This also is in line with the slightly lower resonance force constant (a supposed measure of aromaticity). The out-of-plane force constants fall in the appropriate ranges in comparison to those of benzene, imidazole and benzimidazole which contain the more constricted five membered ring or else possess greater aromatic or double character. The negative force constants result from computer convention and do not have any special chemical meaning. Certain out-of-plane interactions can occur in phase (in the same direction) or out of phase (in opposite directions). The former are given a positive sign and the latter a negative sign.