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Interpretation of the vibrational spectra and calculation of the geometries of cycloheptatriene, 7-d-cycloheptatriene and phenyl substituted cycloheptatrienes
Journal of Molecular THEOCHEM Elsevier
Scientific
85 (1981)
Structure,
Publishing
INTERPRETATION P AT PTTT A ‘PTn’hT (\F “L-lU”“UrxIIVL. VL
Company,
Amsterdam
r-li’f-lMli!‘PRTliX UYVI.IYIlUlYIJ
nli’ VL
in The Netherlands
SPECTRA AND fYV~T.fiFf~,~ATRI~,NR vLvYv*A_-
-L*-L’-I*.-,
CYCLO-
and CH. JUNG*
J. SUHNEL
zu Berlin, DDR-108
6 October
Berlin, Bunsenstraae
I
and K. GUSTAV
Sektion Chemie der Friedrich-Schiller-Universitci’t (D.D.R.) (Received
Printed
AND PHENYL SUBSTITUTED
Sektion Chemie der Humboldt-Universiti (D.D.R.) U. KEMPKA,
-
OF THE VIBRATIONAL ‘T’UT? A1IU
7-d-CYCLOHEPTATRIENE HEPTATRIENES
W. PAULICK
235-240
Jena DDR-69
Jena, Philosophenweg
14
1980)
ABSTRACT Equilibrium geometries, vibrational frequencies and normal coordinates have been calculated quantum chemically for the strained ring compound cycloheptatriene and its phenyl substituted derivatives. The calculated geometry of cycloheptatriene agrees with the experimental one. The l-, 2- and 3-phenyl substituted derivatives have a more nearly planar shape for the seven membered ring than cycloheptatriene itself. Comparison with the experimental vibrational frequencies of cycloheptatriene and 7-d-cycloheptatriene results in a satisfactory interpretation of the vibrational spectra. The three carboncarbon stretching frequencies of the cycioheptatriene n-system show Oiiiji IiiiiiOr effWts caused by phenyl substitution. INTRODUCTION
Cycloheptatriene (CHT) and its phenyl substituted isomers have been of interest for the study of structure-property relationships by spectroscopy and photochemistry [ 1, 21. Experimental investigations of the geometry of CHT have used various methods [3--51, the results concerning nonplanarity differing. The Raman and IR spectra have been measured and the vibrations interpreted and classified by depolarization measurements according to an nL.n,,-nrl ninri a3JUl‘lt;U ~‘Lz”G clTrmmn+r.r JJ111111~U_y r I) ci “, . The purpose of the present work is to explain the vibrational characteristics of these strained ring molecules on the basis of nonplanar geometry. Thus, the equilibrium geometry and the normal frequencies and coordinates of CHT, 7-d-CHT and the phenyl substituted isomers were calculated consistently with the QCFF/PI-method [7] and the calculated frequencies compared with the experimental values supported by the corresponding *Author
to whom
correspondence
OlSS-1280/81/0000-0000/$02.75
should
be addressed.
0 1981
Elsevier
Scientific
Publishing
Company
236
relations for ‘I-d-CHT. The influence of phenyl substitution and vibrational frequencies can also be estimated.
on the geometry
CALCULATIONS
The Quantum Chemical Extension of the Consistent Force Field Method to PI-electron ________.__L molecules (G3C which is &scribed in_ detail \_--l_ FF/PT-method1 _ ,__ -__----_-.,, in ref. 8, was used. For the bending potential used were
Parameter Angle ACA
l/2 F 55.0
112 Ko 15.5
of the CH,-group
the values
40 2.45
with units as in ref. 7. The criteria for the termination of the optimization process for the geometry in all cases were the six zero frequencies (the method works within the cartesian representation) which had to be smaller than 10 cm-’ and did not possess components along the internal molecular coordinates greater -----I ^--Y2:-^L_^ than 10-3 n.R “1^__^ lilU A “I-eL.l_-:.. Lllt?ll l,“rlllal C”“LUlllaLt!s. RESULTS
AND
DISCUSSION
Both experimental investigations [ 3-51 and theoretical calculations [9-l l] on the geometry of CHT have been published. These results are collected in Table 1. Bond lengths and bond angles agree within the limits of experimental uncertainty. The deviations of the CCC-angles and the one C-CH,--C angle from 120 and 109.28”, respectively, indicate that the CHT based molecules have strained ring systems. However, the dihedral angles TABLE
1
Comparison of experimental CHT isomers (pm, degrees) Exp.data
and calculated
geometries
CHT [5J
[ll
[61a
[Ill
[91
1-2 2-3 3-4 l-7
134 147 134 150
135.6 144.6 135.6 150.5
134 145 133 151
134.8 146.3 135.6 150.4
133.2 148.1 133.1 150.5
l-2-3 2-3-4 2-l-7 l-7-6
124.5 124.5 124.5 105
127.2 119.8 121.8
124.8 126.1 122.2 112.2
119.8 122.5 125.0 105.3
29.5 50
40.5 36.5
28 49.5
32.1 58.6
=Averaged
substituted
Calculatedvalues
Bondor angle
CY P
of CHT and phenyl
values.
1-Ph-
2-Ph-
3-Ph-
'I-Ph-CHT
134.7 146.9 135.6 148.2
136.3 146.6 135.7 149.3
135.9 148.4 135.6 148.3
134.6 146.8 136.9 148.1
134.9 147.0 135.7 149.1
110.8
126.3 126.9 124.3 113.3
127.1 127.1 120.7 113.1
123.1 127.4 124.7 112.3
126.5 127.7 123.7 111.7
125.9 126.1 123.7 110.2
31.6 48.2
18.7 46.9
20.2 35.4
34.2 49.3
46.7 48.0
54.3 13.8
CHT
23.7 49.7
1101
125
This work
237
characterizing the deviation from planarity (a and /3 in Fig. l), show considerable differences. Whereas microwave and X-ray diffraction investigations for CHT [3] and substituted CHT [5] yielded 1y< 0, electron diffraction [4] resulted in CY > p. The former agrees with this study as well as the other theoretical values. The geometries of the phenyl substituted isomers have not been investirrntpfleither PxnerimPntnllv nr rfsi~lts ___-__-__ indic2tP &at tb_e ___r_________“__J -_ khp~rpt;i&!v J. Oiw _-_ ___-_-l_ B--“-extent of planarity of the CHT-ring can differ markedly depending on the position of the substituent (Table 1). l-Phenyl-CHT is expected to be the most planar form of all phenyl isomers. Also, weakening of the neighbouring double bonds by the phenyl substituent might be expected. No drastic changes were found within the phenyl substituent. The calculated torsional angles around the C-C (phenyl) single bond between the phenyl plane and the adjacent double bond are 27.7, 29.5 and 23.9” for 1-phenyl-, 2-phenyland 3-phenyl-CHT, respectively. For 7-phenyl-CHT the torsional barrier is very flat and no value is given. The energy differences between different isomers were calculated to be smaller than 4 kJ mol-‘. The axial conformaAJ--c f7 -l_----1 KlTTrn :_ A 1-T --1-I _.I___._ Al_.. -^-__^ _L_Ll- ^_..^ C-.A-l ^-^ blUI1Ul ~-lJIlerlyl-~nl IS Lf Kcl IIIUI auuvt: IJIlt: IIIUIX SCuJlt: equaLAJr1iu UIlt?. In all cases the boat conformation is the most stable; vibrational frequency calculations were done assuming this conformation. 7-d-CHT was calculated with deuterium in the axial position although the experimental frequencies were obtained from both isomers [6]. The results of our interpretation of the vibrational spectra are collected in Table 2. According to this, the proposed interpretation [ 1,6] has to be revised somewhat. The vibrational characteristics for the CH2 and CHD groups at 2900 and 2150 cm-‘, respectively, show the following peculiarity. In contrast to the assumption of La Lau [6], a description based on antisymmetric and symmetric coupling of the two CH-H stretching motions is l--il COrECt for LH 1. Oniy in the case Of deuterium substitution is ihiS COUphg removed and the ratio i;c,/&, = 1.35 found by La Lau was also calculated by us. The next characteristic group is that of the three coupled C=C--stretching vibrations, which are relatively isolated from the remaining bending and
Fig. 1. Geometry
and numbering
of carbon
atoms
in cycloheptatriene
(CHT).
238 TABLE
2
Comparison of calculated and experimentally vibrations of CHT and ‘I-d-CHT (cm-‘)
determined
frequencies
of the fundamental
‘I-d-Cycloheptatriene
Cycloheptatriene symmetry CC,, and descriptionc
b %XP
3060 -
s
A’ CH st A" CH st A" CH st A' CH st A" CH st A' CH st A' CH-H st(anti)
s
A' CH-H
m
A' A" A' A" A' A' A" A" A' A" A"
%ak
Icalc
&Pa
kp
3085 3084 3083 3082 3080 3080 2915
0.55 0.50 2.41 1.03 1.12 2.16 1.33
3060”
w
2966
2883
1.18
2838
1675 1661 1601 1463 1441 1432 1413 1381
0.18 0.45 0.12 1.48 1.73 2.40 0.41 1.79
1246 1221
0.07 0.01
1235 1192
sh Ins
1204 1175 1125 1039 1031 1026 1021
0.04 0.29 0.05 0.27 0.03 0.04 0.04
1218 1049
m ms
984 984 922 906
0.47 0.04 0.36 0.50
973 876 908 792
3039
3om.b 3o2-/b 3o27b 3015"
1662 1606 1534 (1393 1442 b ., 1434b . (1393) 3 1298
ws “S
s m
ih “S
s s
829 752
0.06 1.73
729 678
0.77 5.07
743 712
577 501 498 398 304 208
0.09 0.23 0.01 0.47 0.00 0.06
428 421 405 355 291 223
st(sym)
CH ben ip CH ben ip + CH, scis CH, scis + CH ben ip CH ben ip CH, wagg CHD scis + CH ben ip CH, twist CH ben ip
vs vs ws
A" ringdef t CH ben oop A' ringdef + CH ben oop
Ins
m w s s
+ CHJCHD
+ CHJCHD
w
3027 3027 3027 3015 CD-H 2869,) CH-D 2125,)
ficalc
st (2964,
3085 3084 3083 3082 3080 3080 2898,
st (2183,
2126,
C=C st out of phased c=C st out of phased C=C st in phased
A' CH ben ip A' CH ben ip A" C=C st f CH ben ip A' CH, rock + CH ben oop A" CH ben oop A' CH ben oop A" CH ben imp A' CH ben OOP t CHD rock A" CH ben oop A" CH ben oop A' ringst + CH ben oop A' CH, rock + ring def A" CH ben oop A'ring def A' ringdef + CHJCHD rock A' ringdef + CH ben oop
. 1020 994 920
b
A" ringdef A' ring def A"rine def A' riigdef A" rinedef A' ringdef
CH ben ip
1675 1661 1601 1462 1440
CHD wagg (1295, 1276),,,
1413 1344 1271
CH ben ip twist
t
t CHD twist
f CHD twist
+ CHD twist + CHD rock
CHD
1228 1204 1175 1127 1032 1030 1026 1010 991 967 914 903 899 814 732
rock 727 654
rock 573 500 495 378 301 198
aRaman results. bIR results. Cst, stretching; ben, bending; oop, out of plane; ip, in plane; def, deformation; rock, rocking; wagg, wagging; twist, twisting; scis, scissoring; “a” and “e” for axial and equatorial positions respectively. dOut of or in phase vibrations of the 3 C=C double bonds.
239 TABLE
3
The C=C stretching (cm-‘)
vibrations
of CHT and the phenyl
substituted
isomers
(intensities)
CHT
7-Ph-
2-Ph-
3-Ph-
l-PhCHT
1675 (0.18) 1661 (0.45) 1601 (0.12)
1675 (0.14) 1654 (0.22) 1600 (0.19)
1683 (0.10) 1665 (0.35) 1607 (0.01)
1683 (0.11) 1666 (0.42) 1616 (0.02)
1674 (0.25) 1661 (0.31) 1604 (0.01)
skeleton vibrations. The interpretation with two out of phase and one in phase stretching motions agrees with that given in refs. 1,6. The intense vibrations at 1434 and 1442 cm-’ containing different contributions of the CH, scissoring vibration can be assigned with some certainty. For 7-d-CHT this vibration is found at 1271 cm-* and is mixed with bending vibrations. For 7-d CHT the vibration corresponding to the CH, twisting vibration at 1235 cm-’ mixes more strongly with CH bending vibrations in the range 1250-900 cm-‘. For both CHT and 7-d-CHT the CH, rocking vibration is strongly mixed with ring deformation vibrations. Therefore the interpretation of the intense transitions at 657 and 712 cm-’ as being exclusively due to rocking or out of plane vibrations is not warranted. In the group of low frequency vibrations (ring deformation [l] ) the two frequencies at 501 and 398 cm-’ are related to vibrations whose elongations correspond to an early stage of the chair-boat conversion. The lowest frequency, at 223 cm-‘, corresponds to the boat inversion vibration. The torsional frequencies occur at 60 cm-’ for l-, 2- and 3-phenyl-CHT and smaller than 30 cm-’ for 7-phenyl-CHT. The C=C stretching frequencies of the phenyl isomers are shown in Table 3. There are only minor frequency changes compared with CHT. Two factors are operative; i.e. changes in ring strain resulting from strengthened conjugation caused by phenyl substitution, and mechanical coupling between C=C stretching of the CHT and the phenyl rings. It is possible that a more pronounced effect would be obtained by donor substitution in the pm-u position of the phenyl, which may cause a more chinoidal structure and consequently a strengthened conjugation with the CHT moiety. REFERENCES 1 2 3 4 5
M. W. S. M. R.
V. Evans and R. C. Lord, J. Am. Chem. Sot., 82 (1960) 1876. Paulick, W. Abraham, Ch. Jung and D. Kreysig, submitted. S. Butcher, J. Chem. Phys., 42 (1965) 1833. Traetteberg, J. Am. Chem. Sot., 86 (1964) 4265. E. Davis and A. Tulinsky, Tetrahedron Lett., 19 (1962) 839.
240 6 C. La Lau and H. De Ruyter, Spectrochim. Acta, 19 (1963) 1559. 7 A. War-she1 and M. Karplus, J. Am. Chem. Sot., 94 (1972) 5612. 8 A. Warshel in G. Segal (Ed.), Modern Theoretical Chemistry, Vol. 7, Plenum Press, New York, 1977. 9 N. L. Allinger and J. T. Sprague, J. Am. Chem. Sot., 95 (1973) 3893. 10 G. Buemi, F. Zuccarello and D. Grasso, J. Mol. Struct., 42 (1977) 195. 11 V. G. Dashevskij, V. A. Naumov and N. M. Saripov, Zh. Strukt. Khim., 13 (1972) 171
Scientific
85 (1981)
Structure,
Publishing
INTERPRETATION P AT PTTT A ‘PTn’hT (\F “L-lU”“UrxIIVL. VL
Company,
Amsterdam
r-li’f-lMli!‘PRTliX UYVI.IYIlUlYIJ
nli’ VL
in The Netherlands
SPECTRA AND fYV~T.fiFf~,~ATRI~,NR vLvYv*A_-
-L*-L’-I*.-,
CYCLO-
and CH. JUNG*
J. SUHNEL
zu Berlin, DDR-108
6 October
Berlin, Bunsenstraae
I
and K. GUSTAV
Sektion Chemie der Friedrich-Schiller-Universitci’t (D.D.R.) (Received
Printed
AND PHENYL SUBSTITUTED
Sektion Chemie der Humboldt-Universiti (D.D.R.) U. KEMPKA,
-
OF THE VIBRATIONAL ‘T’UT? A1IU
7-d-CYCLOHEPTATRIENE HEPTATRIENES
W. PAULICK
235-240
Jena DDR-69
Jena, Philosophenweg
14
1980)
ABSTRACT Equilibrium geometries, vibrational frequencies and normal coordinates have been calculated quantum chemically for the strained ring compound cycloheptatriene and its phenyl substituted derivatives. The calculated geometry of cycloheptatriene agrees with the experimental one. The l-, 2- and 3-phenyl substituted derivatives have a more nearly planar shape for the seven membered ring than cycloheptatriene itself. Comparison with the experimental vibrational frequencies of cycloheptatriene and 7-d-cycloheptatriene results in a satisfactory interpretation of the vibrational spectra. The three carboncarbon stretching frequencies of the cycioheptatriene n-system show Oiiiji IiiiiiOr effWts caused by phenyl substitution. INTRODUCTION
Cycloheptatriene (CHT) and its phenyl substituted isomers have been of interest for the study of structure-property relationships by spectroscopy and photochemistry [ 1, 21. Experimental investigations of the geometry of CHT have used various methods [3--51, the results concerning nonplanarity differing. The Raman and IR spectra have been measured and the vibrations interpreted and classified by depolarization measurements according to an nL.n,,-nrl ninri a3JUl‘lt;U ~‘Lz”G clTrmmn+r.r JJ111111~U_y r I) ci “, . The purpose of the present work is to explain the vibrational characteristics of these strained ring molecules on the basis of nonplanar geometry. Thus, the equilibrium geometry and the normal frequencies and coordinates of CHT, 7-d-CHT and the phenyl substituted isomers were calculated consistently with the QCFF/PI-method [7] and the calculated frequencies compared with the experimental values supported by the corresponding *Author
to whom
correspondence
OlSS-1280/81/0000-0000/$02.75
should
be addressed.
0 1981
Elsevier
Scientific
Publishing
Company
236
relations for ‘I-d-CHT. The influence of phenyl substitution and vibrational frequencies can also be estimated.
on the geometry
CALCULATIONS
The Quantum Chemical Extension of the Consistent Force Field Method to PI-electron ________.__L molecules (G3C which is &scribed in_ detail \_--l_ FF/PT-method1 _ ,__ -__----_-.,, in ref. 8, was used. For the bending potential used were
Parameter Angle ACA
l/2 F 55.0
112 Ko 15.5
of the CH,-group
the values
40 2.45
with units as in ref. 7. The criteria for the termination of the optimization process for the geometry in all cases were the six zero frequencies (the method works within the cartesian representation) which had to be smaller than 10 cm-’ and did not possess components along the internal molecular coordinates greater -----I ^--Y2:-^L_^ than 10-3 n.R “1^__^ lilU A “I-eL.l_-:.. Lllt?ll l,“rlllal C”“LUlllaLt!s. RESULTS
AND
DISCUSSION
Both experimental investigations [ 3-51 and theoretical calculations [9-l l] on the geometry of CHT have been published. These results are collected in Table 1. Bond lengths and bond angles agree within the limits of experimental uncertainty. The deviations of the CCC-angles and the one C-CH,--C angle from 120 and 109.28”, respectively, indicate that the CHT based molecules have strained ring systems. However, the dihedral angles TABLE
1
Comparison of experimental CHT isomers (pm, degrees) Exp.data
and calculated
geometries
CHT [5J
[ll
[61a
[Ill
[91
1-2 2-3 3-4 l-7
134 147 134 150
135.6 144.6 135.6 150.5
134 145 133 151
134.8 146.3 135.6 150.4
133.2 148.1 133.1 150.5
l-2-3 2-3-4 2-l-7 l-7-6
124.5 124.5 124.5 105
127.2 119.8 121.8
124.8 126.1 122.2 112.2
119.8 122.5 125.0 105.3
29.5 50
40.5 36.5
28 49.5
32.1 58.6
=Averaged
substituted
Calculatedvalues
Bondor angle
CY P
of CHT and phenyl
values.
1-Ph-
2-Ph-
3-Ph-
'I-Ph-CHT
134.7 146.9 135.6 148.2
136.3 146.6 135.7 149.3
135.9 148.4 135.6 148.3
134.6 146.8 136.9 148.1
134.9 147.0 135.7 149.1
110.8
126.3 126.9 124.3 113.3
127.1 127.1 120.7 113.1
123.1 127.4 124.7 112.3
126.5 127.7 123.7 111.7
125.9 126.1 123.7 110.2
31.6 48.2
18.7 46.9
20.2 35.4
34.2 49.3
46.7 48.0
54.3 13.8
CHT
23.7 49.7
1101
125
This work
237
characterizing the deviation from planarity (a and /3 in Fig. l), show considerable differences. Whereas microwave and X-ray diffraction investigations for CHT [3] and substituted CHT [5] yielded 1y< 0, electron diffraction [4] resulted in CY > p. The former agrees with this study as well as the other theoretical values. The geometries of the phenyl substituted isomers have not been investirrntpfleither PxnerimPntnllv nr rfsi~lts ___-__-__ indic2tP &at tb_e ___r_________“__J -_ khp~rpt;i&!v J. Oiw _-_ ___-_-l_ B--“-extent of planarity of the CHT-ring can differ markedly depending on the position of the substituent (Table 1). l-Phenyl-CHT is expected to be the most planar form of all phenyl isomers. Also, weakening of the neighbouring double bonds by the phenyl substituent might be expected. No drastic changes were found within the phenyl substituent. The calculated torsional angles around the C-C (phenyl) single bond between the phenyl plane and the adjacent double bond are 27.7, 29.5 and 23.9” for 1-phenyl-, 2-phenyland 3-phenyl-CHT, respectively. For 7-phenyl-CHT the torsional barrier is very flat and no value is given. The energy differences between different isomers were calculated to be smaller than 4 kJ mol-‘. The axial conformaAJ--c f7 -l_----1 KlTTrn :_ A 1-T --1-I _.I___._ Al_.. -^-__^ _L_Ll- ^_..^ C-.A-l ^-^ blUI1Ul ~-lJIlerlyl-~nl IS Lf Kcl IIIUI auuvt: IJIlt: IIIUIX SCuJlt: equaLAJr1iu UIlt?. In all cases the boat conformation is the most stable; vibrational frequency calculations were done assuming this conformation. 7-d-CHT was calculated with deuterium in the axial position although the experimental frequencies were obtained from both isomers [6]. The results of our interpretation of the vibrational spectra are collected in Table 2. According to this, the proposed interpretation [ 1,6] has to be revised somewhat. The vibrational characteristics for the CH2 and CHD groups at 2900 and 2150 cm-‘, respectively, show the following peculiarity. In contrast to the assumption of La Lau [6], a description based on antisymmetric and symmetric coupling of the two CH-H stretching motions is l--il COrECt for LH 1. Oniy in the case Of deuterium substitution is ihiS COUphg removed and the ratio i;c,/&, = 1.35 found by La Lau was also calculated by us. The next characteristic group is that of the three coupled C=C--stretching vibrations, which are relatively isolated from the remaining bending and
Fig. 1. Geometry
and numbering
of carbon
atoms
in cycloheptatriene
(CHT).
238 TABLE
2
Comparison of calculated and experimentally vibrations of CHT and ‘I-d-CHT (cm-‘)
determined
frequencies
of the fundamental
‘I-d-Cycloheptatriene
Cycloheptatriene symmetry CC,, and descriptionc
b %XP
3060 -
s
A’ CH st A" CH st A" CH st A' CH st A" CH st A' CH st A' CH-H st(anti)
s
A' CH-H
m
A' A" A' A" A' A' A" A" A' A" A"
%ak
Icalc
&Pa
kp
3085 3084 3083 3082 3080 3080 2915
0.55 0.50 2.41 1.03 1.12 2.16 1.33
3060”
w
2966
2883
1.18
2838
1675 1661 1601 1463 1441 1432 1413 1381
0.18 0.45 0.12 1.48 1.73 2.40 0.41 1.79
1246 1221
0.07 0.01
1235 1192
sh Ins
1204 1175 1125 1039 1031 1026 1021
0.04 0.29 0.05 0.27 0.03 0.04 0.04
1218 1049
m ms
984 984 922 906
0.47 0.04 0.36 0.50
973 876 908 792
3039
3om.b 3o2-/b 3o27b 3015"
1662 1606 1534 (1393 1442 b ., 1434b . (1393) 3 1298
ws “S
s m
ih “S
s s
829 752
0.06 1.73
729 678
0.77 5.07
743 712
577 501 498 398 304 208
0.09 0.23 0.01 0.47 0.00 0.06
428 421 405 355 291 223
st(sym)
CH ben ip CH ben ip + CH, scis CH, scis + CH ben ip CH ben ip CH, wagg CHD scis + CH ben ip CH, twist CH ben ip
vs vs ws
A" ringdef t CH ben oop A' ringdef + CH ben oop
Ins
m w s s
+ CHJCHD
+ CHJCHD
w
3027 3027 3027 3015 CD-H 2869,) CH-D 2125,)
ficalc
st (2964,
3085 3084 3083 3082 3080 3080 2898,
st (2183,
2126,
C=C st out of phased c=C st out of phased C=C st in phased
A' CH ben ip A' CH ben ip A" C=C st f CH ben ip A' CH, rock + CH ben oop A" CH ben oop A' CH ben oop A" CH ben imp A' CH ben OOP t CHD rock A" CH ben oop A" CH ben oop A' ringst + CH ben oop A' CH, rock + ring def A" CH ben oop A'ring def A' ringdef + CHJCHD rock A' ringdef + CH ben oop
. 1020 994 920
b
A" ringdef A' ring def A"rine def A' riigdef A" rinedef A' ringdef
CH ben ip
1675 1661 1601 1462 1440
CHD wagg (1295, 1276),,,
1413 1344 1271
CH ben ip twist
t
t CHD twist
f CHD twist
+ CHD twist + CHD rock
CHD
1228 1204 1175 1127 1032 1030 1026 1010 991 967 914 903 899 814 732
rock 727 654
rock 573 500 495 378 301 198
aRaman results. bIR results. Cst, stretching; ben, bending; oop, out of plane; ip, in plane; def, deformation; rock, rocking; wagg, wagging; twist, twisting; scis, scissoring; “a” and “e” for axial and equatorial positions respectively. dOut of or in phase vibrations of the 3 C=C double bonds.
239 TABLE
3
The C=C stretching (cm-‘)
vibrations
of CHT and the phenyl
substituted
isomers
(intensities)
CHT
7-Ph-
2-Ph-
3-Ph-
l-PhCHT
1675 (0.18) 1661 (0.45) 1601 (0.12)
1675 (0.14) 1654 (0.22) 1600 (0.19)
1683 (0.10) 1665 (0.35) 1607 (0.01)
1683 (0.11) 1666 (0.42) 1616 (0.02)
1674 (0.25) 1661 (0.31) 1604 (0.01)
skeleton vibrations. The interpretation with two out of phase and one in phase stretching motions agrees with that given in refs. 1,6. The intense vibrations at 1434 and 1442 cm-’ containing different contributions of the CH, scissoring vibration can be assigned with some certainty. For 7-d-CHT this vibration is found at 1271 cm-* and is mixed with bending vibrations. For 7-d CHT the vibration corresponding to the CH, twisting vibration at 1235 cm-’ mixes more strongly with CH bending vibrations in the range 1250-900 cm-‘. For both CHT and 7-d-CHT the CH, rocking vibration is strongly mixed with ring deformation vibrations. Therefore the interpretation of the intense transitions at 657 and 712 cm-’ as being exclusively due to rocking or out of plane vibrations is not warranted. In the group of low frequency vibrations (ring deformation [l] ) the two frequencies at 501 and 398 cm-’ are related to vibrations whose elongations correspond to an early stage of the chair-boat conversion. The lowest frequency, at 223 cm-‘, corresponds to the boat inversion vibration. The torsional frequencies occur at 60 cm-’ for l-, 2- and 3-phenyl-CHT and smaller than 30 cm-’ for 7-phenyl-CHT. The C=C stretching frequencies of the phenyl isomers are shown in Table 3. There are only minor frequency changes compared with CHT. Two factors are operative; i.e. changes in ring strain resulting from strengthened conjugation caused by phenyl substitution, and mechanical coupling between C=C stretching of the CHT and the phenyl rings. It is possible that a more pronounced effect would be obtained by donor substitution in the pm-u position of the phenyl, which may cause a more chinoidal structure and consequently a strengthened conjugation with the CHT moiety. REFERENCES 1 2 3 4 5
M. W. S. M. R.
V. Evans and R. C. Lord, J. Am. Chem. Sot., 82 (1960) 1876. Paulick, W. Abraham, Ch. Jung and D. Kreysig, submitted. S. Butcher, J. Chem. Phys., 42 (1965) 1833. Traetteberg, J. Am. Chem. Sot., 86 (1964) 4265. E. Davis and A. Tulinsky, Tetrahedron Lett., 19 (1962) 839.
240 6 C. La Lau and H. De Ruyter, Spectrochim. Acta, 19 (1963) 1559. 7 A. War-she1 and M. Karplus, J. Am. Chem. Sot., 94 (1972) 5612. 8 A. Warshel in G. Segal (Ed.), Modern Theoretical Chemistry, Vol. 7, Plenum Press, New York, 1977. 9 N. L. Allinger and J. T. Sprague, J. Am. Chem. Sot., 95 (1973) 3893. 10 G. Buemi, F. Zuccarello and D. Grasso, J. Mol. Struct., 42 (1977) 195. 11 V. G. Dashevskij, V. A. Naumov and N. M. Saripov, Zh. Strukt. Khim., 13 (1972) 171