J . Phys. Chem. 1989, 93, 6296-6303
6296
number of bands observed in the range of the phonon frequencies5** are internal fundamentals. In particular, the torsional modes are expected in this frequency range, and they have been assigned to these sexcessbands". we believe that these assignments may make it possible to provide a more complete interpretation of the molecular motions giving rise to the lattice modes which may help to better understand the molecular and crystal dynamics of benzil, as well as to elucidate more completely the mechanism of the
observed phase transition of the solid.
Acknowledgment. The authors thank Dr. B. Wyncke from the University of Nancy for the gift of the benzil crystal. The authors also acknowledge Partial financial support of this study by the USA-YWoslav Scientific Exchange Program by Grant YFP680/NSF. Registry No. B e n d , 134-8 1-6.
Spectra and Structure of Small Ring Compounds. 54.+ Infrared and Raman Spectra, Conformational Stability, and Vibrational Assignment of Cyclobutylgermane J. R. Durig,* T. S. Little, T. J. Geyer,i Department of Chemistry, University of South Carolina, Columbia, South Carolina 29208
and M. Dakkouri Abteiling fur Physikalische Chemie. Universitat Ulm, 7900 Ulm, West Germany (Received: October 31, 1988: In Final Form: April 1I , 1989)
The infrared spectra (3500-50 cm-l) of gaseous and solid cyclobutylgermane, c-C4H7GeH3,along with the Raman spectra (3500-20 cm-I) of the gas, liquid with qualitative depolarization values, and solid have been recorded. A comparison of the spectra of the fluid phases with that of the solid shows that two stable conformers exist in the fluid phases at ambient temperature with the equatorial conformer the predominant form in the gas and liquid and the only conformer present in the solid. A series of Q branches obtained from the low-frequency Raman spectrum of the vapor have been assigned to the ring-puckering vibration of both the low-energy equatorial and high-energy axial conformers and fitted to an asymmetric potential function of the form V (cm-I) = (5.46 f 0.10) X 105p (2.63 f 0.07) X 104X3- (2.62 f 0.03) X 104J?. This potential is consistent with the equatorial conformation, being more stable than the axial by 191 cm-I (546 cal/mol), and the equatorial to axial barrier is 432 cm-' (1.24 kcal/mol). From this potential function, ring-puckering angles of 18O and 14' were obtained for the equatorial and axial conformers, respectively. From sum and difference bands on the GeH3 stretching modes, the frequencies for the germy1 torsional modes have been determined from which the barriers of 440 f 2 cm-' (1.26 kcal/mol) and 415 i 10 cm-' (1.19 kcal/mol) have been calculated for the equatorial and axial conformers, respectively. These results are compared to corresponding quantities for some similar molecules.
+
Introduction From studies of microwave'q2 and vibrational3* spectra, it has been determined that the monosubstituted cyclobutyl halides exclusively prefer the equatorial conformation. Although it was originally suggested6 that cyclobutylmethane behaved in a similar manner, relatively recent a b initio7**calculations indicated that the axial conformer may also be stable for this and some other four-membered ring compounds, which has prompted renewed interest in the conformational stability of such molecules. These caIculations7~*predicted a correlation between the electronegativity of the substituent and the conformational stability with the axial form being increasingly favored by substituents with decreasing electronegativities. From electron diffractiong and microwavelo studies, the presence of two conformers of cyclobutylsilane in the gas phase was confirmed. This conclusion was later supported by the determinations of the barrier for ring inversion and conformational energy difference from the ring-puckering transitions and numerous "conformer doublets", respectively, observed in the low-frequency Raman spectrum of the vapor." This study" was followed by a reinvestigation of the conformational stability of cyclobutylmethane'2 where a similar potential was determined from the ring-puckering transitions. For both of these compounds, the equatorial conformation was determined to be the more stable form. 'Part 53: J . Mol. Struct. 1988, 190, 475. 'Taken in part from the thesis of T.J.G., which was submitted to the Department of Chemistry, University of South Carolina, in partial fulfillment of the Ph.D. degree, May 1988.
0022-3654/89/2093-6296$01.50/0
It seems reasonable to assume that cyclobutylgermane would also have significant amounts of each conformer present in the fluid phases, and an electron diffraction study,I3 recently completed, supports the presence of two conformers in the gas. The equatorial conformation appeared to be more abundant than in the silane compound, which was cited as possible evidence that the germanium atom may be more electronegative than silicon. As a logical continuation of our studies of cyclobutylmethane and cyclobutylsilane, we have investigated the infrared and Raman spectra of cyclobutylgermane. The results of this investigation are reported herein and compared to the corresponding quantities obtained for related molecules. ( I ) Kim, H.; Gwinn, W. D. J . Chem. Phys. 1966, 44, 865. (2) Rothschild, W . G.; Dailey, B. P. J . Chem. Phys. 1962, 36, 2931. (3) Durig, J. R.; Willis, J. N.; Green, W. H. J . Chem. Phys. 1971, 54, 1547. (4) Blackwell, C. S.; Carreira, L. A.; Durig, J. R.; Karriker, J. M.; Lord, R. C. J . Chem. Phys. 1972, 56, 1706. ( 5 ) Durig, J. R.; Shing, A. C.; Carreira, L. A. J . Mol. Struct. 1973, 17, 423. (6) Durig, J . R.; Carreira, L. A.; Willis, J . N. J . Chem. Phys. 1972, 57, 2755. ( 7 ) Jonvik, T.; Boggs, J. E. J . Mol. Struct. 1981, 85, 293. (8) Jonvik, T.; Boggs, J. E. J . Mol. Struct. 1983, 105, 201. (9) Dakkouri, M.; Oberhammer, H . J . Mol. Struct. 1983, 102, 315. (10) Wurstner-Ruck, A.; Randolf, H. D. J . Mol. Struct. 1983, 97, 327. (1 I ) Durig, J. R.; Geyer, T. J.; Little, T.S.; Dakkouri, M. J . Phys. Chem. 1985, 89, 4307. (12) Durig, J . R.; Geyer, T. J.; Little, T. S.; Kalasinsky, V. F. J . Chem. Phys. 1987, 86, 545. ( 1 3 ) Dakkouri, M. J . Mol. Srruct. 1985, 130, 289.
0 1989 American Chemical Society
Spectra and Structure of Cyclobutylgermane
The Journal of Physical Chemistry, Vol. 93, No. 17, 1989 6297
Experimental Section The sample of cyclobutylgermane was prepared as described earlier.13 The sample was purified on a low-temperature fractionation column, and the pure cyclobutylgermane was stored in an evacuated sample tube in a slush of dry ice and ethanol. Sample handling was carried out under vacuum. The Raman spectra were recorded on a Cary Model 82 spectrophotometer equipped with a S ectra-Physics Model 171 argon ion laser operating on the 5145- line. The spectrum of the gas was obtained with a standard Cary multipass accessory, and the laser power at the sample was 1 W. The sample was maintained in a quartz cell at its vapor pressure. The spectrum of the liquid was obtained from the sample sealed in a glass capillary. The variable-temperature study of the liquid and the spectrum of the solid were obtained from this capillary contained in a Cryodyne Model 20/70 cryopump connected to a Lake Shore Cryotronics, Inc., Model DTC-5OA cryogenic temperature controller. For the spectrum of the solid, the sample was cooled until frozen and then annealed until no further changes in the spectrum were observed. The final spectrum was recorded a t -23 K. The midinfrared spectra of the gas and solid were obtained from 3500 to 400 cm-l on a Digilab Model FTS-14C interferometer equipped with a Ge/KBr beamsplitter and a TGS detector. The gas was contained in a 10-cm cell fitted with CsI windows. The midinfrared spectrum from which the sum and difference bands were measured was obtained from this cell contained in a Bomem Model DA3.002 Fourier transform interferometer equipped with a vacuum bench, a Globar source, a Ge on KBr beamsplitter, and a Cu-doped Ge bolometer cooled with liquid helium. This spectrum was obtained a t 0. I-cm-' resolution and transformed with boxcar truncation. The spectrum of the solid was obtained by condensing the sample onto a CsI plate contained in an evacuated cell equipped with CsI windows, and 300 scans were collected for both the reference and sample interferograms a t 1-cm-I resolution and then transformed with a boxcar truncation function. The sample was annealed until no further changes in the spectrum were observed, and the final spectrum was recorded with the sample cooled with boiling liquid nitrogen. The far-infrared spectrum of the solid was recorded from 500 to 50 cm-l on a Digilab Model FTS-15B spectrophotometer equipped with a 6.25-pm beamsplitter and a TGS detector. The sample was condensed onto a silicon plate contained in an evacuated cell equipped with polyethylene windows. The sample was annealed as described above and subsequently maintained a t the temperature of boiling nitrogen while the interferograms were collected a t 1-cm-' resolution. The far-infrared spectrum of the gas was recorded on both a Bomen Model DA3.002 and a Nicolet Model 200 SXV interferometer. Both instruments are equipped with a vacuum bench and a liquid-helium-cooled Ge bolometer containing a wedged sapphire filter and a polyethylene window. The sample was contained in a 1-m cell a t its vapor pressure, and a 6.25-pm Mylar beamsplitter was used. The spectra obtained on the Bomem were recorded a t a resolution of 0.05 cm-I, 200 scans were collected for the sample and reference interferograms, and various apodization functions were employed, while the spectrum obtained on the Nicolet was obtained after 250 scans a t a resolution of 0.1 cm-I.
-
8:
Ring-Puckering Potential Function From a comparison of the spectra obtained for the fluid phases with those of the solid, it is clear that cyclobutylgermane exists as a mixture of two conformers. The lines observed in the Raman spectrum of the vapor a t 437 and 484 cm-' are assigned to the ring-Ge stretch for the equatorial and axial conformers (see Table 11), respectively, and are observed in approximately a 2:l intensity ratio in this spectrum. In the spectrum of the liquid, the intensities are more nearly equal, whereas the high-frequency line disappears in the spectrum of the solid. These two lines are the most isolated and best resolved conformer pair in the spectra, and in order to determine the magnitude of the enthalpy difference between the two conformers, their relative intensities have been measured as a function of temperature in both fluid phases. Spectral data were
520
480 440 400 W AVENUMBER (cm-'1
Figure 1. Raman spectra of liquid cyclobutylgermane at 276 and 160 K and of the solid at 34 K.
Figure 2.
WAVENUMBER ( c d Low-frequency Raman spectrum of gaseous cyclobutyl-
germane. obtained a t seven temperatures ranging from 23 to 86 O C for the vapor, while for the liquid nine different temperatures ranging from 3 to -1 13 "C were used. From both experiments, it can be concluded that the value of the enthalpy difference must be small (i.e., I 1 kcal/mol) because the intensity ratios remained nearly constant as the temperature was changed. Representative spectra of the liquid obtained at variable temperatures are shown in Figure 1. With this information and the low-frequency Raman spectrum of the gas (Figure 2), it is possible to determine the potential function governing the ring-inversion motion. An assignment of the spectrum shown in Figure 2 can be made on the basis of the theoretical intensity expectations for an asymmetric double-minima potential function governing ring inversion.I4 The intensities follow in the order Z(Au = 2) 2 Z(Au = 1) near the top of the barrier and I(Au = 2) >> I(Au = 1) well below the barrier but above the higher of the two minima. Transitions in the lower well, between levels lying below the other minimum, have I(Au = 1) > I(Au = 2). With the resultant assignment and a program developed by Ueda and Shimano~chi,'~ which employs a function of the form V(X) = a x 4 - b p
+ cX3
where X , the ring-puckering coordinate (A), is defined as the distance between the ring bisectors, the potential function can be (14) (15)
Carreira, L. A,; Lord, R. C. J. Chem. Phys. 1969, 51, 2735. Ueda, T.; Shimanouchi, T. J . Chem. Phys. 1967, 47, 4042.
6298 The Journal of Physical Chemistry, Vol. 93, No. 17, 1989
Durig et al.
TABLE I: Observed and Calculated" Frequencies (em-') for the RingPuckerine Vibration in Cvclobutvleermane
transition equatorial 1-0 3-1 5-3
re1 intens obs calc
obs
calc
obs - calc
127.3
0.7 1 .5 -2.9
IO 1.0
1.0 0.8
0.6
0.3
8-5
128 117 94 139
0.8
0.2
0.2
axial 4-2 6-4 9-6
107 84 154
106.9 83.2 155.2
0.1 0.8
0.3 0.2
0.4 0.2
-1.2
0.1
0.1
115.5
96.9 138.2
'Calculated with a potential of the form V(X) = (5.46 f 0.10) X 105X'+ (2.63 f 0.07) X 104X3- (2.62 f 0.03) X IO4? with a reduced mass of 214 amu. The barrier height was found to be 432 cm-' (1.24 kcal/mol), and the AH is 191 cm-I (546 cal/mol).
'tt-w*iI
3000
*
Vibrational Assignment The 39 normal modes of vibration for both the equatorial and
axial conformers of cyclobutylgermane span the irreducible rep-
1500
, ~
~
~
~
500
Wavenumber (cm-1) Figure 4. Infrared spectrum of gaseous (A) and annealed solid (B) cyclobut ylgermane.
Figure 3. Potential function governing the ring-puckering vibration of cyclobutylgermane. V(X) = (5.46 f 0.10) X IOs* + (2.63 f 0.07) X 104X3- (2.62 f 0.03) X 104X, with a reduced mass of 214 amu.
determined. One such assignment is given in Table I, and the shape of the corresponding potential function is shown in Figure 3. This potential function, giving a barrier of 432 cm-l (1.24 kcal/mol), is consistent with the two Q branches observed a t 128 and 117 cm-', being in the equatorial well, and the third Q branch a t 107 cm-l, being assigned to the fundamental transition of the axial conformer. Although other assignments were considered, this potential has the advantage of accounting for the weak lines a t 137 and 154 cm-I as well as the weaker Q branches a t 94 and 84 cm-l (see Figure 2). The AH of 191 cm-' (546 cal/mol) is similar to the value of 188 cm-' (538 cal/mol) calculated for cyclobutylsilane" and is consistent with the aforementioned study of the spectra a t variable temperatures. This value is also only slightly less than the value of 251 f 8 cm-I (717 f 24 cal/mol) reported for the energy difference by the electron diffraction study.I3 From this potential function (Figure 3), it is possible to obtain the ring-puckering coordinate for each conformer and thus calculate the puckering angles. Although the uncertainty in the puckering angles determined a t the minima are directly related to the uncertainty in the reduced mass (we have used the reduced mass determined for bromocy~lobutane,~ 214 amu) as well as the nature of the molecular motions involved, this potential function yields puckering angles at 18' and 14' for the equatorial and axial conformers, respectively. Although these values are lower than those from the electron diffraction study,1325.3 3.1' (equatorial) and 20.4 f 3.6' (axial), in consideration of the reported uncertainties and our uncertainty in the reduced mass, they agree quite favorably. The values of the barriers to ring inversion, energy differences and puckering angles determined for cyclobutylmethane, cyclobutylsilane, and cyclobutylgermane are compared in Table 111.
2000
I 1 1000
I
I
3000
2500
2000 1500 1000 Wavenumber (cm-1)
I
500
Figure 5. Raman spectrum of gaseous (A) liquid (B), and solid (C)
cyclobutylgermane. resentations of 23A' and 16A". The A' modes will exhibit A-, C- or A/C-hybrid-type contours in the infrared spectrum of the vapor with polarized Raman lines whereas the A" vibrations are expected to exhibit B-type infrared contours and depolarized Raman lines. The midinfrared and Raman spectra are shown in Figures 4 and 5, respectively. The present vibrational assignment of the fundamentals associated with the ring of cyclobutylgermane (Table 11) is in excellent agreement with those previously reported for cyclobutylsilane" and cyclobuty1methane.l6 The vibrational assignments associated with the GeH3 group are in agreement with the corresponding modes for other GeH3 substituted compound~."-'~ The assignments of the C-H stretching region and the three CH2 deformations are straightforward; however, the region where the twisting and wagging motions occur ( - 1200 cm-') is complicated in the spectra of the fluid phases by the presence of six fundamentals arising from two conformers. In the Raman spectrum of the solid, three lines persist that correspond to the three Q branches observed in the gas but there are only two A' CH2 bending modes expected in this region; therefore, the a - C H in-plane bend is also assigned here (1264 cm-I). The assignment of the A' @-CH2 rocking mode is controversial. For cyclobutylgermane, the A' @-CH2rock is assigned to a polarized Raman (16) Kalasinsky, V. F.; Harris, W.C.; Holtzclaw, P. W.;Durig, J. R.; Geyer, T. J.; Little, T. S . J . Raman Spectrosc. 1987, 18, 581. (17) DuAg, J. R.; Lopata, A. D.; Groner, P. J. Chem. Phys. 1977,66, 1888. (18) Durig, J. R.; Turner, J. B. Spectrochim. Acta 1971, 27A, 1623. (19) Mackenzie, M. W. Spectrochim. Acta 1982, 38A, 1083.
Spectra and Structure of Cyclobutylgermane
300
200
WAVENUMBER (cm.’)
Figure 7. Infrared spectrum of gaseous cyclobutylgermane in the region
of the GeH3stretches, showing sum and difference bands from the GeH3 torsion.
100
WAVENUMBER (cm-’)
Figure 6. Far-infrared spectrum of gaseous (A) and annealed solid (B) cyclobut ylgermane.
line a t 847 cm-I in the spectrum of the liquid. The choice of the assignment for this fundamental is heavily influenced by the substituent, as is evident by the wide range of proposed assignments for this mode.3s31,16,2b24A possible alternative is to assign the A’ P-CH2 rocking mode to the 899-cm-I line and then assign the 847-cm-’ Q branch as a combination band of the symmetric GeH, rock (588 cm-I) with the ring-GeH, in-plane bend (268 cm-I). The GeH, deformations are assigned to infrared bands of strong intensity occurring between 800 and 900 cm-l on the basis of the corresponding assignments for ethy1germane.I’ The present assignment leaves unexplained the Q branch a t 899 cm-l in the Raman spectrum of the gas, which is polarized in the liquid and persists a t 900 cm-’ in the spectrum of the solid. To assign this line to the GeH, A’ antisymmetric deformation would be inconsistent with the infrared data as would an assignment of the A’ ring deformation to this frequency, as this would be too low in frequency when compared to the corresponding mode for cyclobutylsilane” (1065 cm-I). Alternatively, this line could be an overtone or combination band in Fermi resonance. The A’-bending motion of the GeH, group against the ring could be assigned on the basis of the Raman spectrum of the gas, where this motion gives rise to a Q branch of moderate intensity (268 cm-I). The A” motion is observed as a B-type band (b-axis perpendicular to the symmetry plane) at 186 cm-I in the far infrared spectrum of the gas (Figure 6). The B-type band occurring at 312 cm-’ cannot be assigned to the GeH, torsion, as will be discussed in the following section, since sum and difference bands indicate this fundamental lies much lower in frequency (-100 cm-I). Furthermore, this frequency is too high to be due to the A” GeH, bending against the ring because this would be much higher than the corresponding motion in the silane-substituted ring” (190 cm-I), and thus it has been assigned in Table I1 as a combination. The only remaining band observed in the far-infrared spectrum of the gas is the broad envelope centered a t 135 cm-I, and on the basis of the corresponding Raman spectrum, this feature clearly arises from the ring-puckering fundamental.
-
Cermyl Torsion In Table IV, the observed sum and difference bands (Figure 7) of the GeH, antisymmetric stretching (A’’) motion with the germyl torsion (A”) are listed. The reference fundamentals were taken to be 2072 cm-I for the equatorial conformer and 2074 cm-’ for the axial form. These were chosen because the average of the 1 0 transitions on the sum and difference side gave these
-
(20) Banhegyi, G.; Fogarasi, G.; Pulay, P. J . Mol. Struct. 1982, 89, 1. (21) Aleksanyan, V. T.; Antipov, B. G. J . Mol. Struct. 1982, 89, 15. ( 2 2 ) Lord, R.C.; Nakagawa, I. J . Chem. Phys. 1963, 39, 2951. (23) Annamali, A,; Keiderling, T. A. J . Mol. Spcctrosc. 1985, 109, 46. (24) Annamali, A,; Keiderling, T. A.; Chickos, J . S. J . Am. Chem. SOC. 1985, 107, 2285.
The Journal of Physical Chemistry, Vol. 93, No. 17, 1989 6299
frequencies. Furthermore, these frequencies match the assignment for the A” GeH, antisymmetric stretch given in Table 11, which is degenerate or very nearly so with the A’ motion. This gives a frequency of 102 cm-’ for the 1 0 transition in the equatorial conformer and 98 cm-l for the corresponding transition of the axial form. With these fundamental frequencies, the periodic 3-fold barrier to internal rotation for the GeH, moiety can be calculated. The observed transitions were fit to a potential function of the following form:25
-
The results are summarized in Table IV, and the proposed assignment gives the best fit between the observed (determined from the sum and difference bands) and calculated frequencies. These calculations yield a 3-fold barrier of 440 f 2 cm-l (1.26 kcal/mol) and 4 15 f 10 cm-’ (1.19 kcal/mol) for the equatorial and axial conformers, respectively. One other alternative was to assign the strongest Q branch a t 2166 cm-l as arising from the sum band of the 1 0 transition for the equatorial conformer. This assignment gives both a fundamental frequency (94 cm-I) and a 3-fold barrier (378 cm-I) that seemed unreasonably low by comparison of the barrier for the germyl torsion in ethylgermane” (492 cm-I). These results should be contrasted with the barriers for the silyl torsions in the cyclobutylsilane” study, where the value for the axial conformer was 108 cm-l higher than that for the equatorial conformer. This can be explained, in part, by the slightly longer bond length in cyclobutylgermane between the ring and the substituent, which relieves the “interaction” between the GeH, moiety and the methylene hydrogens of the ring in the axial configuration. Furthermore, the ring is not puckered as much in cyclobutylgermane as in cyclobutylsilane,l’ which allows the substituent to be even further from the y C H 2 hydrogens in cyclobut ylgermane.
-
Discussion Cyclobutylgermane is the third in a series of monosubstituted four-membered ring compounds studied in our laboratory. Now that the methyl, silyl, and germyl derivatives of cyclobutane have all been studied, it is interesting to note comparisons. In Table V, some of the fundamental frequencies of these three compounds are listed. It is interesting to note the trends with substitution, particularly in the ring modes. The first A’ ring deformation, as well as the ring-breathing mode, moves higher in frequency as the group IVA substituent becomes heavier. The other A’ ring deformation and the ring-puckering mode decrease in frequency as the substituent becomes heavier. The same effect was observed in cyclobutylmethaneL2upon deuteriation of the methyl group. The A” ring fundamentals do not reflect a clear trend. It is also worth mentioning that in the halogen series a downward trend in frequency with increasingly heavier mass was observed for all (25) Wurrey, C. J.; Durig, J . R.; Carreira, L. A. In Vibrational Spectra and Structure; Durig, J. R., Ed.; Elsevier: Amsterdam, 1976; Vol. 5, Chapter 4.
6300
Durig et al.
The Journal of Physical Chemistry, Vol. 93, No. 17, 1989
TABLE 11: Observed" Infrared and Raman Frequencies ( c d ) for Cyclobutylgermane
gas 2985 R 2980 Q,C 2974 R 2968 min, B 2959 P
2927
IR rei intens
sh
w
2981
m
2970
sh, p
2969
S
y-CH, antisym str
2967
s
2954
s,
p
2964
S
j3-CH2 antisym str
2961
sh
2952
sh
2944
sh
2956 2935 2932
S S
j3-CH2 antisym str j3-CH2 sym str
2935 2927 2919 2905 2885 2879
s
2915 2906
S
2884
W
2855 2851
sh
p
sh
2059 1466
vs, p w, dp
2064 2060 2050 1460
W
GeH3 antisym str GeH, sym str y-CH2 deformn
1444
w,
dp
1438
m
j3-CH2 deformn
1433
sh
j3-CH2 deformn
1262
W
a-CH in-plane bend
1243 1232 1228 1220 1216 1192 1178 1129
vw
y-CH2 wag
rei
solid
intens
S
S
gas 3019
Raman re1 intens liquid and depol 3006 w, p
2965
S
2954 2933
m S
2915 2905
S
2879
m
sh
re1 intens
2911
s s w vw,
s, p
sh
2879 Q
m
2873 2077 R 2074 Q 2072 Q 2068 Q 1473
sh
2854
S
2872
m
vs vs vs
2054
vs
vs vs
sh, vw
1462
W
1457 Q 1451 Q 1445 P
vw
1435
vw
2074 2070 1475 1466 1459 1453 1443
w, sh
13821
vw
1370 1269 1264
vw
1365
vw,
sh m
1261
w,
1236 1233
sh m
1262 Q 1257 R 1251 min 1246 P 1231 Q 1201 Q
W
W
1263
W
W
1246 1235 1229
W
sh, vw vw
1071 Q 1067 Q
vw
1036 Q
W
999 Q
W
W
1187 1176
vw vw
1081 1062
W
1048
sh
1003 997
m m
924 883 Q 876
834 R 828 Q 824 P 783 R 779 min, B 774 P 680 R 675 Q,C 670 P 598 588 Q 566 min, B 484 440
S S
vs
W
879 874 87 1 842
m
m S
sh sh
836
S
820
sh
770
m
689
W
sh m
590 556 443
w
2859
s,
S S
ut
assignmt approx description
S
y-CH2 sym str a-CH str 2"9 2y27
m vw
p
1230 1222
m, p sh,dp
1193 1180 1146
w,
vw,dp
p
vw,
p
w
1065
w, p
1036 1005 999 940
w
1032
w, p
sh s vw, bd
sh m
S
S
vs
j3-CH sym str
p
1072
904 899 885 878
~
sh
999 936 917
s,
p m,dp
899
m, p
vw,dp
sh W W
j3-CH2 wag &CH2 wag
sh W
vw
j3-CH twist y-CH2 twist
W
@-CHItwist ring deformn
1063
m
1002 997 939 921
W
W
m
combination? GeH3 antisym deformn GeH3 antisym deformn
S
m W
ring breathing ring deformn a-CH bend
w
878
m,dp
900 877 873
m
847
m, p
843
m
j3-CH2 rock
824
m
828
m
GeH, sym deformn
815
m
ring deformn
769
vw
j3-CH2 rock
689
W
ring deformn
sh
853 846
sh
831
m
780
ww,
db, dp
m
708 692
w m
708 692
w,p
sh, p
668
w
665
w, p
601
m
601
m, p
598
W
566 484 437
bd, w m m
563 486 441
bd, w, dp m, p m, p
562
m
y-CH2 rock GeH, rock GeH3 rock
447
m
ring-Ge str
S
W W
sh, vw sh, w sh
W
W
m
1200 1183
re1 intens
m
m vw
solid
The Journal of Physical Chemistry, Vol, 93, No. 17, 1989 6301
Spectra and Structure of Cyclobutylgermane TABLE I1 (Continued)
IR re1 intens
solid
re1 intens
318 R 312 min, B 307 P
vw
322
W
262
m, bd
254
W
gas
192 R 186 min, B 181 P -135
vw
212
gas 426
re1 intens sh
314
w
274 268 260 254 248 236
sh
Raman re1 intens liquid and depol
w w
317
w, p
264
bd, m, p
solid
w, bd
up
assignmt approx description
"38
265
w
vZ2
+ "23
ring-GeH3 bend
Yl2/
sh sh sh
W
154 139 128 117 107 84
re1 intens
212
vw
v3*
ring-GeH, bend
157
vw
"23
ring puckering
130 116 95 86 18 67 56 51 39 31
vw
vjg
GeH, torsion laser
vw vw vw vw vw vw
w ww ww
lattice modes
w w w w w
w
"Abbreviations used: s, strong; m, medium; w, weak; v, very; bd, broad; sh, shoulder; p, polarized; min, minimum; dp, depolarized; R, Q,and P, refers to the assignments made for the axial conformer. vibrational-rotational branches; A, B, and C, the band contours. TABLE 111: Comparison of Energy Differences, Barrier Heights, and Puckering Angles for Cyclobutylmethane, Cyclobutylsilane, and Cyclobutylgermane
molecule methylcyclobutane cyclobutylsilane
cyclobutylgermane
energy diff" 295 f 75 247 142 147 i 50 191 35 67 i 33
