2130
Vibrational Spectra of Bicyclo[P.1.O]pentane
Vibrational Spectra and Structure of Bicycle[ 2.1 .O]pentane‘ J. Bragin* and D. Guthals Department of Chemistry, California State University, Los Angeies, Los Angeies, California 90032 (Received January 8, 1975: Revised Manuscript Received July 11, 1975) Publication costs assisted by the Petroleum Research Fund
Vibrational spectra of bicyclo[2.1.O]pentane are presented for the molecule in the gaseous, liquid, and solid states and assignments for all vibrational fundamentals are proposed. The transannular bond results in an unusual potential function for puckering of the five-membered ring. This and other structural features are discussed, qualitatively, in terms of the proposed vibrational assignments.
Introduction Recent interest in transition metal complex promoted rearrangements of strained hydrocarbons2*has promoted an investigation of the mechanism and intermediates in reactions of this type involving bicyclo[2.1.O]pentaneusing lowtemperature vibrational spectroscopy as a probe. Since no vibrational assignments for this molecule were found in the literature the complete spectrum of vibrational fundamentals was obtained and is presented herein along with a proposed assignment.2b Relatively few assignments of the vibrational spectra of highly strained molecules have been reported yet such data has found wide application in elucidating the quantitative relationships between the structure, energy, and reactivities of small acyclic systems.2cAlso, there has been considerable recent interest in spectra-structure relationships for the conformation changing vibrations of small rings3 yet few polycyclic or highly strained molecules have been included in such studies. For these reasons it is felt that the vibrational data and analysis presented here are of sufficiently general interest to warrant publication as a separate paper. Experimental Section Bicyclo[2.1.0]pentane was prepared by the method of Gassman and M a n ~ f i e l d Sample .~ purity was checked by comparing the infrared spectrum of this compound with that reported by Criegee and Rimmelin.5 In addition, since the major impurity of the synthetic reaction is known to be cyclopentene, a careful search was made for spectroscopic evidence of that molecule in the sample. The low-temperature infrared spectrum of solid bicyclo[2.1.O]pentane(Figure 1) shows no sign of absorption in regions in which solid cyclopentene exhibits its most intense vibrational bands.6 Since the two compounds boil within 1’C of each other, the failure to observe any cyclopentene is not due to any purification by fractional sublimation resulting from the deposition and annealing processes accompanying preparation of the solid film a t low temperatures. Furthermore, the Raman spectrum of gaseous bicyclo[2.1.O]pentane (Figure 2) showed no evidence of cyclopentene impurity. Infrared spectra were recorded on a Beckman IR-12 double-beam grating spectrophotometer which was purged with a continuous stream of dry nitrogen gas and calibrated in the usual manner.7 The spectrum of the gaseous molecule a t 90 mm pressure (Figure 3) was obtained in a 10-cm Pyrex cell fitted with CsI windows and viton 0 ring vacu-
um seals. Polycrystalline films of bicyclo[2.1.O]pentane were prepared in a modified Wagner-Hornig cold cells by permitting the vapors to slowly distill onto a CsI substrate in good thermal contact with a dewar of liquid nitrogen at its normal boiling point. The solid samples were repeatedly annealed until no further change in the spectrum was observed. The use of a silicon wedge as a substrate gave spectra identical with those obtained for the sample deposited on CsI and^ there were no differences in the spectra of several different depositions on CsI. The Raman spectrum of liquid bicyclo[2.1.O]pentane (Figure 4), degassed and sealed under vacuum in a Pyrex capillary, was excited with 150 mW (measured at sample) of 488.0-nm radiation from an Ar+ laser and recorded on a Cary Model 82 spectrometer. The sample capillary was illuminated and viewed normal to its long axis and depolarization ratios were obtained by rotating a piece of Polaroid in the scattered beam which subsequently passed through a polarization scrambler before entering the monochrometer. The Raman spectrum of the gaseous molecule at 85 mm pressure was obtained with the same equipment by focussing €0 passes of a 1-W (measured at sample) 514.5-nm Ar+ laser beam at the center of a quartz cell fitted with quartz windows set at Brewster’s angle. The Raman spectrometer was calibrated with atomic emission lines. The spectral data are summarized in Table I. Assignment The microwave substitution structure of bicyclo[2.1.0]pentanegis shown in Figure 5. The molecule exhibits only a plane of symmetry which bisects both the cyclobutyl and cyclopropyl rings, and is normal to the planes of both rings. The angle between the ring planes is 112.67’. Under the C, point symmetry of the molecule, all 33 vibrational modes are both Raman and infrared active. Of these, 18 are symmetric (a’) and 15 are antisymmetric (a”) with respect to the molecular symmetry plane. The a’ modes may give rise to a maximum of 18 polarized Raman lines all of which may have infrared counterparts. The microwave study of bicyclo[2.1.0]pentane9 has shown that the rotation axes of least and greatest moment of inertia (A and C, respectively) lie in the molecular symmetry plane. Therefore, in the spectrum of the gaseous molecule the a’ modes will give rise to bands with sharp single Q branches whereas the a” modes will be distinguished by the absence of a single central Q branch. The calculatedlo PR separations are 23 and 31 cm-’ for ideal A and C type bands, respectively. This is The Journalof Physical Chemistry. Vol. 79, No. 20, 1975
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J. Bragin and D. Guthals
TABLE I: Observed Frequenciesaof Bicyclo[2.1.0]pentane Infrared Vapor
403 P 416 Q vw A 427 R 698 vw 743 P 755 Q m A/C 769 s h
Raman Solid
424 m
Liquid
Vapor
280 vw brd dp
265 vw brd dp
33
418 w p
417 Q m p
18
---
678 vw brd dp
Assignm
18
755 s
755 m brd p ?
755 Q w p
17
774 Q m A/C
767 w
775 w brd p ?
765 P 774 Q w p 781 R
16
783 Q m B 790 Q m B 799 R 870 P 883 Q m A/C 903 P 914 Q m B 918 Q m B 927 Q m B 962 P 968 Q m A/C 974 Q m B 981 Q m B 1012 Q vw A/C 1017 P 1026 Q w B 1033 Q w B 1039 P 1049 Q w B 1056 Q w B 1066 R
777 s 782 s
781 m brd dp
790 w brd dp
32
881 w 885 w
880 w brd dp
883 Q w dp
15
917 m
914 m brd dp
1094 P 1106 Q w A 1117 R
966 m
966 vs p
978 m 1006 w
1009 m p
978 brd sh 1012 Q m
1234 Q w B 1242 Q w B 1264 P 1274 Q m B 1280 Q m A/C 1284 Q m B 1295 R 1320 Q vw B 1329 Q vw B 1332 Q vw A/C 1341 R 1384 Q vw A/C 1434 P 1446 Q m w A
29 13
1047 m
27
1104 s p
1107 Q s
12
1170 s h p
1179 Q w 1191 Q m s 1195 Q ms
18
1188 s p
1265 sh 1270 s
1324
1237? vw brd
25
1275 vw brd dp
1283? vw brd
9 24
1296 vw brd p 1323 vw dp (obsd in L) 1326 m p
1300 Q vw
15
The Journal of Physical Chemistry, Vol. 79, No. 20, 1975
1441 w brd dp
+
33
+
18
+
18
23 1330 Q m 1335 sh
a 14
1435 sh w 1438 m
32
11 26
10 29
1210 w brd 1217 w 1235 w
+
14
28
1188 w 1190 w 1198 w 1207 P 1218 Q w C
30
1028 s
1096 w 1098 w 1101 w 1104 w 1108 w
33
31 925 w brd dp 961 s h 967 Q vs p
924 w
+
1445 w brd
7
2141
Vibrational Spectra of Bicycle[ 2.1 .O]pentane Table I (Continued) Raman
Infrared Vapor
1458 R 1461 Q mw B 1468 Q mw B 1470 Q m A/C 1481 R 1508 sh 1638 p 1648 Q vw 1656 R 1674 Q ? vw B? 1685 Q ? vw B? 1707 p 1715 Q vw A/C 1723 R 1772 sh 1777 p 1793 R 1800 sh 1825 P 1835 Q vw A/C 1846 R 2016 P 2029 Q vw A/C 2040 R 2074 Q vw A/C 2098 Q vw A/C 2215 Q vw A/C 2682 Q vw A/C 2866 P 2874 Q s A/C 2885
Solid
Liquid
----_
vapor
1440 m 1457 w 1466 w
1450 sh 1464 w dp
2862 s p
2861 s
1470 Q w
2875 Q vs
2880 w
22 6 16 15
+
17
16
+
31
14
+
17
13
+
16
14
+
15
9
+
17
10 9 6 6
+ + + +
15 17 16 10
+ 16
5
2 x 22 6 + 22
2898 sh p ? 2907 P 2921 Q s A/C 2932 Q s B 2939 Q s B 2946 Q vs A/C 2966 Q vw B? 2970 P 2982 Q vs A/C 2993 R 3051 Q s B 3058 Q s B 3070 Q s A/C
Assignm
2910 m
2909 s p
2922 Q vs
4
2929 s 2939 s 2961 sh
2926 sh d p ? 2937 s p 2957 sh d p
2936 Q m 2945 Q vs 2965 w b r d
21 3 20
2974 s
2975 s p
2982 Q vs
2
3045 s 3056 s
3051 sh dp 3060 s p
3058 Q vs 3070 Q vs
19 1
a Frequencies in cm- l . vw = very weak, w = weak, mw = medium weak, m = medium, s = strong. vs = very strong, sh = shoulder. brd = broad, p = polarized, dp = depolarized, A = A-type band, B = B-type band, C = C-type band.
in good agreement with the observed separations of 22 and 31 cm-', respectively. The calculatedlo QQ separation for B type bands is 8 cm-l and the observed separations for such bands average 8 cm-l. C-H Stretches. The structure of the representation formed by the eight CH stretches is 5a' 3a". The approximate descriptions of these modes and their assignments are given in Table 11. In view of the expected s character in the bonds and the correlation between this quantity and vibrational frequency the CH stretching frequencies should
+
occur in the order: 1-bridge methylene > bridgehead methine > 2-bridge methylene. The proposed assignments are consistent with this expectation and also with the infrared and Raman band contours of the gaseous molecule and the Raman depolarization data obtained for the compound as a neat liquid (cf. Table I). In addition, the assignments are consistent with those proposed for cyclopropane,' substituted cyclopropanes,12 cyclobutane,13 cy~lobutene,'~ bicyclobutane,15 norbornane,'6 and bicyclo[l.l.l]pentane.17 C H Deformations. The CH2 deformations should give
'
The Journal ol Physical Chemistry, Vol. 79, No. 20, 1975
2142
J. Bragin and D. Guthals
loo~f=-
3000 2800
1500
1000
500
WAVENUMBER CM-’ Figure 1. The infrared spectrum of polycrystalllne blcyclo[2.1 .O]pentane at - 175OC.
Figure 4. The Raman spectrum of liquid bicycio[2.1.0]pentane excited with milliwatts of 488.0-nm Ar+ laser radiation.
i
I
a
WAVENUMBER Chf’
Figure 2. The Raman spectrum of gaseous bicyclo[2.l.O]pentane at 85 mm pressure excited by 1 W of 514.5-nm Ar+ laser radiation.
Flgure 5. The microwave substitution structure of bicyclo[2.1.O]pentane (ref 9).
+
WAVENUMBER CM.’
Figure 3. The infrared spectrum of gaseous bicyclo[2.1 .O]pentane at 90 mm pressure (insert, 18 mm pressure) and 10 cm absorption path. rise to two A/C hybrid bands and one B-type band in the 1400-1500-~m-~ range of the infrared spectrum of gaseous bicyclo[2.1.0]pentane. This prediction is confirmed (cf. Table I) and the assignments are straightforward. The extent of mixing between the a’ CH2 deformations cannot be determined with the present data and we have chosen to describe these two modes as pure 1-bridge and 2-bridge CH2 scissoring motions. The bridgehead deformations should give rise to two symmetric and two antisymmetric modes. Thus vg and ug are described as a’ bridgehead deformations and V23 and v24 as a” bridgehead deformations. Analogous modes have been assigned a t 1228 cm-l in bi~yclo[l.l.l]pentane~~ and in the range 1145-1317-~m-~in norbornane.16 Thus, the assignments (cf. Table 11) proposed here are consistent with those of analdgous modes in other bicyclic molecules as well as with the band contours and Raman depolarization ratios expected for the bridgehead deformations. There are nine CH2 deformations remaining unassigned and these may be described (in order of decreasing frequency) as twists, wags, and rocks. The structure of the representation formed by these modes is twist (a’ 2a”),
+
The Journal of Physical Chemistty, Vol. 79. No.20, 1975
+
wag (a’ 2a”), and rock (2a’ a”). The extent of mixing of the 1- and 2-bridge a” methylene deformations is not known and these modes will not be characterized further. The twisting modes of cyclobutane13have been assigned a t 1225 cm-l in good agreement with the assignment of u10 to the weak C type band observed at 1218 cm-l in the infrared spectrum of gaseous bicyclo[2.1.0]pentane. It should be noted that v10 cannot involve any 1-bridge methylene twisting due to the symmetry of the molecule. The antisymmetric methylene twists, V25 and V26, are assigned to a weak B-type band observed at 1238 cm-l in the infrared spectrum of the gaseous molecule and to a weak band observed at 1198 cm-l in the infrared spectrum of the solid, respectively. There are four polarized bands observed in the Raman spectrum of liquid bicyclo[2.1.0]pentane in the frequency range expected for the a’ methylene wag ( ~ 1 2 ) .The most intense of these correlate well with the ring breathing frequencies in cyclopropanell and cyc10butane.l~Of the remaining two, v12 is described as a cyclobutylmethylene wag although the possibility of extensive mixing with v13 cannot be excluded in the absence of data for the perdeuterated molecule. Reasons for this assignment will be given in the following section. Of the five, as yet unassigned B type infrared bands in the range expected for the a” methylene wags, those at 1030, 978, and 922 cm-l are assigned to the skeletal deformations as described in the following section. The two a” methylene wags (v27 and ~31)are assigned a t 1053 and 917 cm-*, respectively. The methylene rocking modes 017, u32) should give
2143
Vibrational Spectra of Bicyclo[P.I.O] pentane TABLE 11: Vibrational Assignments of Bicyclo[2. l.O]pentane Vibrn no.
Appr ox description of vibrna
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
CP CH, CP CH2 (+) Bh CH Cb CH, (-) Cb CH2 (+) CH, def CH, def Bh CH def Bh CH def Cb CH2 tw Cp ring breathe Cb CH, wag Cb ring def Cb ring breathe Cp ring def CH, rock CH, rock Envelope flap
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
Bh CH Cb CHZ (-) Cb CH, (+) CH, def Bh CH def Bh CH def CH, tw CH, tw CH, wag Cb ring def Cb ring def Cp ring def CH, wag CH, rock Cb ring pucker
(k)
Infrared Vapor a' 3070 2982 2946 2921 2874 1470 1446 1332 1280 1218
1106 1012 968 883 774 755 416
Raman
solid
Liquid
Vapor
3056 2974 2939 2910 2861 1466 1440 1324* 1270 1210 1190 1098 1006 966 885 767 755 424
3060 2975 2937 2909 2862 1564 1441 1326 1275*
3070 2982 2945 2922 2875 1470 1445 1330 1283*
1188 1104 1009 966 880 775 755 418
1195 "1107 1012 967 883 774 755 417
3045 2961 2929 1457 1324* 1265 1235 1198 1047 1028 978 924 917 782
3051 2957 2926 1450 1323 1275*
3058 2965 2936
a" 3 054 2966 2936 1465 1325 1279 1238
1053 1030 978 922 914 787
914 781 280
1283* 1237
978 925 915 790 280
a Cp = cyclopropyl, Cb = cyclobutyl, Bh = bridgehead, (-) = out-of-phase, (+) = in-phase, def = deformation, tw = twist. * = assigned to more than one vibration.
rise to an infrared band with a B-type contour and two with A, C, or A/C hybrid contours. The Raman counterparts of the latter two may be polarized. Since there are only two A-type infrared bands in the frequency range of the methylene rocks and these have polarized Raman counterparts, they may be assigned to V I 6 and V 1 7 with confidence. Similarly, the B-type infrared band centered a t 787 cm-l with a depolarized Raman counterpart may be assigned to v32. Skeletal Modes. The structure of the representation formed by the skeletal vibrations of bicyclo[2.1.O]pentane is 5a' +4af'. The five totally symmetric skeletal motions may be described as ring breathing (two modes), ring deformation (two modes), and envelope flap (bending around the transannular bond). Breathing modes always give rise to the most intense Raman lines and these motions in cyclopropanell and cyclobutane13 have been assigned a t 1188 and 1004 cm-l, re-
spectively. Similarly, the three- and four-membered ring breathes (u11 and u14) are assigned to the bands at 1195 and 967 cm-', respectively, in the Raman spectrum of gaseous bicyclo [2.1 .O]pentane. There has been some controversy as to the deformation frequencies of the cyclopropyl ring.'l Recent analyses of ~ cm-l) these vibrationsllepf indicate that u11 _ _ of C R H (868 has a much larger skeletal component than Ylo(1028 cm-l). In the present assignment the description of ~ 1 and 5 V30 as the symmetric and antisymmetric components of the analog of u11 in the three-membered ring in bicyclo[2.1.O]pentane is consistent with the cyclopropane analyses. One symmetric and two antisymmetric skeletal modes expected above 800 cm-l remain unassigned. These may all be described as cyclobutyl deformations. Two of the three may be considered as arising from a degenerate mode, in an analogous cyclobutyl ring of higher symmetry, which is split in bicyclo[2.1.0]pentane. Thus a pair of closely spaced fundamentals is expected. One of these gives rise to a Btype band in the infrared spectrum of the gaseous molecule and a depolarized Raman counterpart whereas the other exhibits an AjC type band contour and a polarized Raman counterpart. These criteria best fit the assignment of U13 and V 2 8 to the modes under consideration. Although it is possible to assign 1106 cm-l to the a' mode in question, such an assignment presents several difficulties. In the first place this assignment would result in an average cyclobutyl stretching frequency of 1020 cm-' for bicyclo[2.1.0]pentane compared with 975 cm-l for c y ~ l o b u t a n e whereas , ~ ~ ~ the present assignment gives a value of 997 cm-l for this quantity. Some increase in electron density of the cyclobutyl ring in bicyclo[Z.l.O]pentane over that in cyclobutane is consistent with the average bond lengths of these two cyclobutyl rings,9 however, this effect is a small one. Moreover, the alternative assignment would require overlap of the frequency ranges of the cyclobutyl wags and skeletal motions whereas in cyclobutane the methylene wags appear to be firmly assigned a t appreciably higher frequencies than the skeletal modes.13a The third cyclobutyl ring deformation presently under consideration is of a" symmetry and may be assigned to U29 (978 cm-l) by analogy with the 999-cm-lassignment for the B:! ring mode in cyclobutane.13* Only two vibrational modes of bicyclo[2.1.0]pentane are expected to be below 500 cm-' and only the a' envelope flap (~18)may be assigned to a polarized Raman line. Of the two frequencies observed below 500 cm-l, in the vibrational spectrum of bicyclo[2.1.O]pentane, only the Raman counterpart at 417 cm-l is polarized and, therefore, it must be assigned to VIS. The last mode to be assigned is ~ 3 and 3 this must be described as the puckering of the four-membered ring. The only band observed below 500 cm-l in the vibrational spectrum of bicyclo[2.1.0]pentane which may be assigned to an a" fundamental is the depolarized band at 280 cm-l in the Raman spectrum of the liquid molecule. Therefore, this frequency is assigned to u33. As will be discussed in detail below, the analogous mode in cyclobutane has been reported a t 199 cm-l.13 Discussion In the infrared spectrum of polycrystalline bicyclo[2.1.0]pentane the splitting of u7, ull, VI:!,U 1 5 , and u32 is thought to be due to coupling of the motions of at least two symmetry related molecules in the unit cell. Since the multiplet spacing does not appear to be approximately proporThe Journal of Physical Chemistry, Vol. 79, No.20, 1975
2144
tional to the absolute intensity of the bands, the intermolecular forces are not primarily dipolar. Harris et al.ls have discussed five-membered ring puckering potentials in terms of mixed series in even powers of the two puckering coordinates (applicable to molecules having CzU symmetry in the planar state). Due to the contribution of angle strain, the anharmonic terms in such series may be significant.lg Such a situation has a number of consequences for the vibrational spectrum. In the first place, significant anharmonicity of the bending and twisting modes (VIS and u33, respectively) will shift the frequency of hot bands of these vibrations relative to their respective fundamentals. If the upper states of these low-energy motions are appreciably populated, a band progression may be observed assuming the components are sharp enough to be distinguished. A second consequence of significant anharmonicity in the puckering modes is that higher order cross terms can be large enough to couple V I S and ~ 3 3 . ~ 0 J ~ In the present work, a very broad featureless band, approximately centered a t 265 cm-l, was observed in the Raman spectrum of gaseous bicyqlo[2.1.0]pentane with a weak depolarized counterpart appearing at 280 cm-l in the Raman spectrum of the liquid. This frequency has been assigned to the a” twisting fundamental ( u 3 3 ) , whereas the bending fundamental (VIS) has been assigned to the very weak A-type band observed a t 416 cm-l in the infrared spectrum of the gas with Raman counterparts a t 418 cm-l (liquid, w, p) and 417 cm-l (gas, m, p). A search for overtones and for additional features on the fundamental infrared and Raman bands of the gaseous molecule was limited by the amount of maierial available and a tendency toward increasingly rapid decomposition at higher laser powers. The failure to observe sharp features on the 265-cm-’ Raman band in gaseous bicyclo[2.1.0]pentane and the absence of any appreciable sample scattering in the 100-200cm-l region favor assignment of this feature to the fundamental twisting transition. The single sharp feature observed at 416 f 1 cm-’ in both the infrared and Raman spectrum of the gaseous molecule, and the absence of a feature near 200 cm-1, favors assigning this frequency to a highly harmonic fundamental. Thus the two-dimensional puckering potential well for bicyclo[2.1.0]pentane has a deep, double minimum contour along the bending coordinate which closely approximates a parabola in the region of the equilibrium structure. The contour along the twisting coordinate must be a single minimum but its curvature cannot be further characterized without assignments for upper state twisting transitions. Direct comparisons of the puckering frequencies of bicyclo[2.1.0]pentane with those reported for other five-membered rings22 will not be valid if the comparison molecule exhibits some degree of pseudorotation (i.e., the puckering normal modes are not pure bending or pure twisting). However, the five-membered ring in bicyclo[2.1.O]pentane is unique in that its bending frequency is higher than its twisting frequency. This may be attributed to the high barrier to inversion at the bridgehead carbon (estimated to be 30 kcal/mo1)23 which results in a bending potential function with a high curvature near the equilibrium value of that coordinate. The twisting frequency of the five-membered ring in bicyclo[2.1.O]pentaneis higher than those reported for methylene~yclopentane2~ and c y ~ l o p e n t a n o n e .Al~~ though this may merely reflect a higher degree of quartic angular strain resulting from a twisting deformation of the The Journal of Physical Chemistry, Vol. 79, No. 20, 1975
J. Bragin and D. Guthals
equilibrium structure, it probably includes a significant contribution from steric repulsion of the 1-bridge and 2bridge methylene groups. Harmonp has pointed out that the average length of the skeletal bonds in three-, four-, and five-membered rings in a number of different molecules is quite similar, suggesting that a fixed amount of electron density is available for C-C bonding in such structures and that it will be distributed around the ring in a manner which minimizes the molecular energy. The close correspondence between the present assignments for the breathing modes of the three- and four-membered rings in bicyclo[2.1.0]pentane and the analogous modes in cyclopropane and cyclobutane seems consistent with this idea. Acknowledgment. The authors are indebted to Professor Paul G . Gassman, Department of Chemistry, University of Minnesota, for the sample of bicyclo[2.1.0]pentane. Acknowlqigment is made to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, for the support of this research.
References and Notes (1) Abstracted from the thesis of D. Guthals submitted in partial fulfillment of the requirements for the degree of Master of Science (Chemistry), California State University, Los Angeles, 1975. (2) (a) P. G. Gassman, T. J. Atkins, and J. T. Lamb, J. Am. Chem. Soc., 94, 7757 (1972); (b) Reference 26 appeared in Chemical Abstracts after the present manuscrlpt was submitted for review. (c) J. E. Williams, P. J. Stang, and P. v. R. Schleyer, Ann Rev. Phys. Chem., 19, 531 (1968). (3) See, for example, ref 22. (4) P. G. Gassman and K. T. Mansfield. Org. Syn., 49, 1 (1969). (5) R. Criegee and A. Rimmelin, Chem. Ber., 90,414 (1957). (6) A. Le Roy and J. C. Thouvenot, C. R. Acad. Sci., Paris, Ser. 6, 265, 545 (1967). (7) (a) IUPAC, “Tables of Wavenumbers for the Calibration of Infrared Spectrometers”, Butterworths, Washington, D.C., 1961; (b) R. T. Hall and J. M. Dowling, J. Chem. fhys., 47, 2454 (1967); 52, I 1 6 1 (1970). (8) E. L. Wagner and D. F. Hornig. J. Chem. fhys.. 18, 296 (1950). (9) R. D. Suenram and M. D. Harmony, J. Chem. fhys., 56,3837 (1972). (10) 1. Haller, Research Paper No. RC-1152, iBM Watson Research Center, 1964. (11) (a) J. L. Duncan and D. C. McKean, J. Mol. Spectrosc., 27, 117 (1968); (b) J. B. Bates, J. Chem. fhys., 58, 4236 (1973); (c) Hs. H. Gunthard, R. C. Lord, and T. K. McCubein, Jr., ibid., 25, 768 (1956); (d) A. W. Baker and R. C. Lord, ibid.. 23, 1636 (1955); (e) J. L. Duncan and 0. R. Burns, J. Mol. Spectrosc., 30, 253 (1969); (f) T. Hirokawa, M. Hayashi, and H. Murata, J. Sci. Hiroshima Univ., Ser. A, fhys. Chem., 37, 271 (1973). (12) (a) R. W. Mitchell and J. A. Merritt, Spectrochim. Acta, fat? A, 27, 1609 (1971); (b) R. W. Mltchell and J. Nakovich. Jr., ibid., 29, 1153 (1973); (c) R. C. Lord and C. J. Wurrey, /bid., 30, 915 (1974); (d) L. H. Daly and S. E. Wiberley. J. Mol. Spectrosc.,2, 177 (1958); (e) T. Hirokawa, M. Hayashi, and H. Murata, J. Sci. Hiroshima Univ., Ser. A, fhys. Chem., 37, 301 (1973). (13) (a) F. A. Miller, R. J. Capwell, R. C. Lord, and D. G. Rea, Spectrochim. Acta. Part A, 28, 603 (1972); (b) R. C. Lord and 1. Nakagawa. J. Chem. fhys., 39, 2951 (1963). (14) R. C. Lord and D. G. Rea, J. Am. Chem. SOC.,79,2401 (1957). ( 1 5 ) 1. Haller and R. Srlnivason, J. Chem. Phys., 41, 2745 (1964). (16) i. W. Levin and W. C. Harris, Spectrochim. Acta, fat? A, 29, 1815 (1973). (17) K. B. Wibera. D. Sturmer. T. P. Lewis, and I. W. Levin, SDecfrochlm. Acta, fat? A; 31, 59 (1975). D. 0. Harris, G. 0 . Engerholm. L. A. Toiman. A. C. Luntz, R. A. Keller, H. Kim, and W. D. Gwinn, J. Chem. fhys., 50,2438 (1969). R. P. Bell, froc. R. Soc., Ser. A, 183, 328 (1945). T. lkeda and R. C. Lord, J. Chem. Pbys., 58,4450 (1972). L. A. Carreira, I. M. Mills, and W. B. Person, J. Chem. Phys., 56, 1444 (1972). (a) J. Laane. “Vlbrational Spectra and Structure”, Vol. 1, J. R. Durlg. Ed., Marcel Dekker, New York. N.Y.. 1972, p 25; (b) C. S. Blackwell and R. C. Lord, bid., p 1. (23) J. P. Chesick, J. Am. Chem. SOC.,84, 3250 (1962). (24) (a) T. B. Malloy. Jr., F. Fisher, J. Laane, and R. M. Hedges. J. Mol. Spectrosc., 40, 239 (1971); (b) J. R. Durig, Y. s. Li. and L. A. Carreira. J. Chem. fhys., 57, 1896 (1972). (25) (a) J. R. Durlg, G. L. Coulter, and D. W. Wertz, J. Mol. Spectrosc., 27. 285 (1968); (b) H. Kim and W. D. Gwinn, J. Chem. fhys., 51, 1815 (1969). (26) V. T. Aleksanyan, Izv. Akad, Nauk. SSSR, Ser. Khim., 1999 (1974).
