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Conformational equilibria and structure of 2,3-butadienal and 2,3-butadienoyl halides
of ~O~a~F striieiare@Y&?dlm), 2T6 (1992) 251-257 Efsevier science Publishers B.V., Amsterdam
Joarraal
251
~o~for~ational equilibria and structure of 2,3butadienal and 2,3-butadienoyl halides
Abstract The confo~ational equilibria and stability of 2,3-butadienal and 2,3-butadienoyi fluoride and chloride were investigated using ab initio calculations with the extended 4-3lG and 6-31G* basis sets. The results indicate that the molecules show s-trans $ s-cis conformational equilibria similar to the corresponding allylic molecules. The conformational stability of these molecules was found to be more dependent on the nature of the substituent and less dependent on the type of z system. The replacement of the allylic group by an allenic group slightly influenced the ~~nformational equilibrium between the two stable conformers of the molecules. For 2,3-butadienal the s-trans conformer was predicted to be predominantly more stable than the s-cis conformer at ambient temperatures. For 2,&butadienoyl halides the energy difference between the two conformers was calculated to be very small with slight thermodynamic stability favouring the s-trans form at room temperature.
INTRODUCTION
The reactivity of allylic and linear polynes in synthetic and polymer chemistry has attracted the attention of chemists for many years, The role of these compounds as models for understanding conjugation and polarization effects has promoted several studies investigating their structure and conformational equilibria [l-d]. Vinyl compounds with a CXO group (X = H, F and Cl) as a substituent are examples of fundamental molecules containing allylic systems. Both theoretical and spectroscopic results have shown this series of molecules to exist as a mixture of s-trans and s-cis conformers at ambient temperatures [5--S]. From a study of the Raman spectrum of gaseous propenal (acrolein) the torsional potential function was determined and the barrier Gorrespcmdence &X H.M. Badawi, Department of Chemistry, King Fahd University of Petroleum and Minerals, Bhahran 31261, Saudi Arabia.
0166-1280/92/$05.00 0 1992 Elsevier Science Publishers
B.V. All rights reserved,
Fig. 1. Molecular structure of 2,3-butadienal {X = IS), and !2,3-butadienoyl halides (X = F and Cl) in tbe s-cis (upper) and the s-trans (lower) conformations.
for s-transes-cis interconversion was determined to be 2236cm-l 171. Furth~~ore, the enthalpy difference AH between the two conformers was determined to be 584cm-1, which was considerably higher than the value of 285~rn-~ obtained from ab initio calculations [9]. More recently, a combined study of ab initio calculations and vibrational spectra of propenoyl (acryloyl) halides has been reported, in which the s-trans form was clearly found to be more stable for the chloride, but the data were inconclusive fur the fluoride [3]. The theoretical calculation results were consistent, with the s-trans form being thermodynamically preferred for propenoyl fluoride and the s-&s form being favoured for propenoyl chloride; this contradicted the experimental data for the chloride [8]. For purposes of comparison, the present ab initio geometrical optimizations of the co~esponding series of molecules containing the allene moiety were undertaken for 2,3-butadienal and 2,3-butadienoyl halides and the results are presented here. AB INITIO CALCULATIONS The GAUSSIAN 90program was used to perform FRAU-MU-~CF restricted Hartree-Fock calculations [IO]. The extended 4-31G and 6-3lG* basis sets were used in order to optimize the structures and to predict the energies and dipole moments of the stable conformations of 2,3-butadienal, and 2,3-butadienoyl fluoride and chloride, The structural parameters of the s-cis (Q = 0’) and the s-trans (0 = BOO) conformers (Fig. 1) of each of these molecules were optimized by mi~~izing the energy with respect to all the parameters. It is important to point out that optimization of the gauche (0 = SO”) conformer led to the cis conformer on its completion. Therefore, the data for the gauche form art3not reported here. The conformational stabilities were determ’ned by comparing the calculated total energies t (Table 1). From these calculations 2,3-butadienal and 2,3-butadienoyl
H.M. BadawilJ.
253
Mol. Struct. (Theochem) 276 (1992) 251-257
TABLE 1 Calculated total and relative energies of 2,3-butadienal and 2,8butadienoyl Molecule
halides
6-31G*
Conformation 4-31G
Total energy Relative energy Total energy Relative energy (kcalmol-‘) (Hartree) (kcal mall’) (Hartree) 2,3-Butadienal
sTrans s-Cis
- 228.25614 - 228.25300
0.00 2.35
- 228.59201 0.00 - 228.58751 2.82
2,3-Butadienoyl s-Trans fluoride s-Cis
- 327.00903 - 327.00845
0.00 0.37
- 327.47019 - 327.46896
0.00 0.71
2,3-Butadienoyl s-Trans chloride s&is
- 686.66994 - 686.66976
0.00 0.12
- 687.50189 - 687.50139
0.00 0.32
halides were predicted to exist in an s-trans z$ s-cis conformational equilibrium, with the s-trans form being the more stable at room temperature. The calculated structural parameters, dipole moments and rotational constants of the two conformers of the three molecules are given in Tables 24. The data were compared with those values obtained from experimental results for the corresponding allylic compounds. DISCUSSION
From the energy optimization of the possible conformers of 2,3-butadienal and 2,3-butadienoyl fluoride and chloride, the s-trans conformation was predicted to be the lowest energy form at room temperature for the three molecules. However, the energy difference between the s-trans and s-cis forms was calculated to decrease in the order aldehyde > fluoride > chloride. For 2,3-butadienal the s-trans form was predicted to be the predominant conformer for the molecule, and for 2,3-butadienoyl halides the thermodynamic stability of the s-cis conformer was predicted to increase relatively, particularly in the case of the chloride. Thus, changing the substituent had a considerable effect on the relative stability of the s-trans and s-cis conformers, whereas replacing the allylic group by the allenic one had a small effect on the conformational equilibrium between the two stable conformers of these types of molecules. The calculated structural parameters at the 4-31G and 6-31G* levels for both stable conformers (Tables 24) are compared with those obtained from microwave and electron diffraction data of the corresponding allylic compounds [5,8]. The C=C bond lengths are predicted r 2,3-butadienal and 2,3-butadienoyl halides to be about 0.04A shorter th % n the reported lengths for the corresponding allylic molecules [ES].This shortening of the C=C bond lengths indicates that the spsp’ carbon-carbon distances are
TABLE 2 Structural parameters, dipole moments and rotational constants of 2,3-butadienal 431G
Parameter
6-31G*
s-Trans
s-C%
s-Tram3
s-Cis
1.302 1.299 1.464 1.212 1.084 1.073 1.073
1.303 1.289 1.467 1.213 1.084 1.073 1.072
1.304 1.293 1.479 1.190 1.093 1.076 1.076
1.304 1.291 1.484 1.189 1.093 1.077 1.075
121.7 123.2 116.1 121.2 121.3 180.0
123.0 125.3 114.7 120.0 121.3 0.0
121.0 123.4 115.2 121.4 121.0 180.0
121.1 125.1 114.3 120.0 120.9 0.0
4.370 0.707 0.000 4.428
2.230 2.639 0.000 3.455
3.883 0.583 0.000 3.926
1.940 2.310 0.000 3.016
Rotationab constant (MNZ) A 37981 B 2408 c 2299
14490 3307 2742
36944 2419 2306
14491 3318 2750
Bond length (A) r(C,=C,) r(C,=W rf%C,I JiC, = G) tic,-%I r(C,-H,) r(C,-R,) = r(C,-W Bond angle (deg) GC&, C&G W&H, C,W% W&J& = W, W&G
I-f,,
Bipote moment (debye) K pb
I& Ft
PropenaP s-Trans
1.345 1.470 1.219 1.108 1.084 1.086 119.8 123.3 115.1 122.8 180.0
“Ref. 5.
shorter than the sp’-sp2 distances. For 2,3-but~dienal the calculated C-C bond length is in better agreement with the microwave value for propenal [5]. The reported C-X distances for propenoyl halides are longer than the 6-31G” predicted values for 2,3-butadienoyl halides and only slightly comparable with the optimized 4-31G parameters. Furthermore, the reported C=O bond lengths lie between the average values of the parameters calculated by the two basis sets. The predicted bond angles are in general resonably within the experimental uncertainties of the reported data, but there are some differences to be noted, Ab initio calculations predicted the CCC and CCX angles of the s-cis form to be smaller than those parameters for the s-trans conformer of the halides, and the CC0 bond angle of the s-cis form to be greater than that of the s-trans conformer, consistent with
H.&f. Bada~~l~.
Mol. Struct.
(~~~~~)
276 (1992) 251-257
255
TABLE3 Structural parameters, dipole moments and rotational constants of 2,8butadienoyl Parameter
6-31G*
4-31G
Bond length (rf) G=Q r(C,=Gf tic,-C,) tic, =0) r(G-F) r(w%) rlC,-H,) = r(G-I-W
fluoride
Propenoyl fluoride*
s-Trans
s-Cis
s_Trans
a-Cis
s-Trans
s-Cis
1.302 1.287 1.454 1.188 1.366 1.071 1.072
1.303 1.267 1.456 1.188 1.369 1.070 1.072
1.303 1.290 1.471 1.171 1.321 1.074 1.075
1.304 1.289 1.474 1.170 1.325 1.074 1.075
1.35
1.35
1.49 1.18 1.35 1.085 1.085
1.48 1.18 1.35 1.085 1.085
123.4 127.2 113.2 121.6 121.2 180.0
121.5 130.3 110.2 121.6 121.2 0.0
123.0 126.1 113.0 121.6 120.9 180.0
120.7 128.9 110.3 121.4 120.8 0.0
121.8 127.0 111.3
119.9 128.2 110.1
160.0
0.0
4.840 0.927 0.000 4.927
4.296 2.053 0.000 4.761
4.194 0.400 0.000 4.213
3.288 2.040 0.000 3.869
(MHZ) 9932 2287 1882
10477 2113 1780
10235 2289 1895
10667 2138 1803
Bond angle (deg)
Rotational A B c
~~~~t
“Ref. 8.
the experimental data shown in Tables 3 and 4. However, it is predicted that there is an approximate 2-5'difference between the CCC bond angles of the two conformers, disagreeing with the reported data for the chloride. The calculated dipole moments and rotational constants of the s-trans and s-cis conformations of the three molecules are shown in Tables 2-4. There are slight differences in the calculated dipole moments on going from the 4-3lG to the 6-31G” level, as expected from the difference in the calculation of the charge densities by the different basis sets. There are no reported experimental values for the dipole moments of these molecules in their stable conformations, although the moments found from ab initio calculations are generally larger than those determined exper~entally [ll]. The
256
EM.
3adaw~l~.
Mol. Stract.
(~~~~ern)
276 (1992) 251-257
TABLE 4 Structural parameters, dipole moments and rotational constants of 2,3-butadienoyl chloride Parameter
4-31G
631G*
Propenoyl chloride”
s-Trans
s-Cis
s-Trans
s-Cis
s-Trans
s-Cis
1.302 1.287 1.454 1.184 1.878 1.072 1.072
1.305 1.287 1.467 1.184 1.879 1.068 1.072
1.303 1.290 1.477 1.172 1.773 1.075 1.075
1.305 1.289 1.478 1.170 1.781 1.073 1.075
1.345
1.339
1.476 1.192 1.816 1.084 1.086
1.484 1.192 1.772 1.100 1.100
125.4 126.5 114.8 121.0 121.2 180.0
120.8 130.1 110.7 121.7 121.2 0.0
125.2 123.9 116.2 121.2 120.8 180.0
119.7 127.5 112.3 121.6 120.8 0.0
122.6 122.2 116.3 117.4
123.4 125.2 111.8 121.5
180.0
0.0
5.009 0.311 0.000 5.019
4.427 2.304 0.000 4.990
4.218 0.212 0.000 4.224
3.386 2.136 0.000 4.003
~o~t~o~a~ constant (iWHz) A 4527 3 2139 c 1467
8901 1418 1233
4848 2114 1487
9377
Bond length (A) r(c, = (4) tic, =CJ tiC,--G) tic, = 0) G-W r(‘&-H,) r(G-&,) = 43&,) Bond angIe (deg) W&G W,O C,C,Cl C& Bs C,C, f% = C&, B,, c,c,w Dipok
moment (d&ye)
P’a Pb PC Pt
1456 1271
“Ref. 8.
dipole moment of the s-trans form was calculated to be considerably greater than that of the s-cis conformer, as a result of a charge density variation with the rotation of the carbonyl moiety about the C-C bond. ACKNOWLEDGEMENT
The author gratefully acknowledges the support for this work provided by the King Fahd University of Petroleum and Minerals. REFERENCES 1 J. Kroner, W. Kosbahn and W. Runge, Ber. Bunsenges. Phys. Chem., 81 (1977) 826. 2 W. Runge, W. Kosbahn and J. Kroner, Ber. Bunsenges Phys. Chem., 81 (1977) 841.
H.M. BadawilJ. 3 4 5 6 7 8 9 10
11
Mol. Struct. (Theochem) 276 (1992) 251-257
257
J.R. Durig, Y.S. Li, J.D. Witt, A.P. Zens and P.D. Ellis, Spectrochim. Acta, Part A, 33 (1977) 529. H. Guo and M. Karplus, J. Chem. Phys., 94 (1991) 3679. E.A. Cherniak and C.C. Costian, J. Chem. Phys., 45 (1966) 104. K. Kuchitsu, T. Fukuyama and Y. Morino, J. Mol. Struct., 1 (1968) 463. L.A. Carreira, J. Phys. Chem., 80 (1976) 1149. J.R. Durig, R.J. Berry and P. Groner, J. Chem. Phys., 87 (1987) 6303. P. George, C.W. Bock and M. Trachtman, J. Mol. Struct., 69 (1980) 183. M.J. Frisch, M. Head-Gordon, G.W. Trucks, J.B. Foresman, H.B. Schlegel, K. Raghavachari, M.A. Robb, J.S. Binkley, C. Gonzalez, D.J. Defrees, D.T. Fox, R.A. Whiteside, R. Seeger, C.F. Melius, J. Baker, R.L. Martin, L.R. Kahn, J.J.P. Stewart, S. Topiol and J.A. Pople, GAUSSIAN 90,Gaussian, Inc., Pittsburgh, PA, 1990. H.M. Badawi, J. Mol. Struct. (Theochem), 228 (1991) 159.
Joarraal
251
~o~for~ational equilibria and structure of 2,3butadienal and 2,3-butadienoyl halides
Abstract The confo~ational equilibria and stability of 2,3-butadienal and 2,3-butadienoyi fluoride and chloride were investigated using ab initio calculations with the extended 4-3lG and 6-31G* basis sets. The results indicate that the molecules show s-trans $ s-cis conformational equilibria similar to the corresponding allylic molecules. The conformational stability of these molecules was found to be more dependent on the nature of the substituent and less dependent on the type of z system. The replacement of the allylic group by an allenic group slightly influenced the ~~nformational equilibrium between the two stable conformers of the molecules. For 2,3-butadienal the s-trans conformer was predicted to be predominantly more stable than the s-cis conformer at ambient temperatures. For 2,&butadienoyl halides the energy difference between the two conformers was calculated to be very small with slight thermodynamic stability favouring the s-trans form at room temperature.
INTRODUCTION
The reactivity of allylic and linear polynes in synthetic and polymer chemistry has attracted the attention of chemists for many years, The role of these compounds as models for understanding conjugation and polarization effects has promoted several studies investigating their structure and conformational equilibria [l-d]. Vinyl compounds with a CXO group (X = H, F and Cl) as a substituent are examples of fundamental molecules containing allylic systems. Both theoretical and spectroscopic results have shown this series of molecules to exist as a mixture of s-trans and s-cis conformers at ambient temperatures [5--S]. From a study of the Raman spectrum of gaseous propenal (acrolein) the torsional potential function was determined and the barrier Gorrespcmdence &X H.M. Badawi, Department of Chemistry, King Fahd University of Petroleum and Minerals, Bhahran 31261, Saudi Arabia.
0166-1280/92/$05.00 0 1992 Elsevier Science Publishers
B.V. All rights reserved,
Fig. 1. Molecular structure of 2,3-butadienal {X = IS), and !2,3-butadienoyl halides (X = F and Cl) in tbe s-cis (upper) and the s-trans (lower) conformations.
for s-transes-cis interconversion was determined to be 2236cm-l 171. Furth~~ore, the enthalpy difference AH between the two conformers was determined to be 584cm-1, which was considerably higher than the value of 285~rn-~ obtained from ab initio calculations [9]. More recently, a combined study of ab initio calculations and vibrational spectra of propenoyl (acryloyl) halides has been reported, in which the s-trans form was clearly found to be more stable for the chloride, but the data were inconclusive fur the fluoride [3]. The theoretical calculation results were consistent, with the s-trans form being thermodynamically preferred for propenoyl fluoride and the s-&s form being favoured for propenoyl chloride; this contradicted the experimental data for the chloride [8]. For purposes of comparison, the present ab initio geometrical optimizations of the co~esponding series of molecules containing the allene moiety were undertaken for 2,3-butadienal and 2,3-butadienoyl halides and the results are presented here. AB INITIO CALCULATIONS The GAUSSIAN 90program was used to perform FRAU-MU-~CF restricted Hartree-Fock calculations [IO]. The extended 4-31G and 6-3lG* basis sets were used in order to optimize the structures and to predict the energies and dipole moments of the stable conformations of 2,3-butadienal, and 2,3-butadienoyl fluoride and chloride, The structural parameters of the s-cis (Q = 0’) and the s-trans (0 = BOO) conformers (Fig. 1) of each of these molecules were optimized by mi~~izing the energy with respect to all the parameters. It is important to point out that optimization of the gauche (0 = SO”) conformer led to the cis conformer on its completion. Therefore, the data for the gauche form art3not reported here. The conformational stabilities were determ’ned by comparing the calculated total energies t (Table 1). From these calculations 2,3-butadienal and 2,3-butadienoyl
H.M. BadawilJ.
253
Mol. Struct. (Theochem) 276 (1992) 251-257
TABLE 1 Calculated total and relative energies of 2,3-butadienal and 2,8butadienoyl Molecule
halides
6-31G*
Conformation 4-31G
Total energy Relative energy Total energy Relative energy (kcalmol-‘) (Hartree) (kcal mall’) (Hartree) 2,3-Butadienal
sTrans s-Cis
- 228.25614 - 228.25300
0.00 2.35
- 228.59201 0.00 - 228.58751 2.82
2,3-Butadienoyl s-Trans fluoride s-Cis
- 327.00903 - 327.00845
0.00 0.37
- 327.47019 - 327.46896
0.00 0.71
2,3-Butadienoyl s-Trans chloride s&is
- 686.66994 - 686.66976
0.00 0.12
- 687.50189 - 687.50139
0.00 0.32
halides were predicted to exist in an s-trans z$ s-cis conformational equilibrium, with the s-trans form being the more stable at room temperature. The calculated structural parameters, dipole moments and rotational constants of the two conformers of the three molecules are given in Tables 24. The data were compared with those values obtained from experimental results for the corresponding allylic compounds. DISCUSSION
From the energy optimization of the possible conformers of 2,3-butadienal and 2,3-butadienoyl fluoride and chloride, the s-trans conformation was predicted to be the lowest energy form at room temperature for the three molecules. However, the energy difference between the s-trans and s-cis forms was calculated to decrease in the order aldehyde > fluoride > chloride. For 2,3-butadienal the s-trans form was predicted to be the predominant conformer for the molecule, and for 2,3-butadienoyl halides the thermodynamic stability of the s-cis conformer was predicted to increase relatively, particularly in the case of the chloride. Thus, changing the substituent had a considerable effect on the relative stability of the s-trans and s-cis conformers, whereas replacing the allylic group by the allenic one had a small effect on the conformational equilibrium between the two stable conformers of these types of molecules. The calculated structural parameters at the 4-31G and 6-31G* levels for both stable conformers (Tables 24) are compared with those obtained from microwave and electron diffraction data of the corresponding allylic compounds [5,8]. The C=C bond lengths are predicted r 2,3-butadienal and 2,3-butadienoyl halides to be about 0.04A shorter th % n the reported lengths for the corresponding allylic molecules [ES].This shortening of the C=C bond lengths indicates that the spsp’ carbon-carbon distances are
TABLE 2 Structural parameters, dipole moments and rotational constants of 2,3-butadienal 431G
Parameter
6-31G*
s-Trans
s-C%
s-Tram3
s-Cis
1.302 1.299 1.464 1.212 1.084 1.073 1.073
1.303 1.289 1.467 1.213 1.084 1.073 1.072
1.304 1.293 1.479 1.190 1.093 1.076 1.076
1.304 1.291 1.484 1.189 1.093 1.077 1.075
121.7 123.2 116.1 121.2 121.3 180.0
123.0 125.3 114.7 120.0 121.3 0.0
121.0 123.4 115.2 121.4 121.0 180.0
121.1 125.1 114.3 120.0 120.9 0.0
4.370 0.707 0.000 4.428
2.230 2.639 0.000 3.455
3.883 0.583 0.000 3.926
1.940 2.310 0.000 3.016
Rotationab constant (MNZ) A 37981 B 2408 c 2299
14490 3307 2742
36944 2419 2306
14491 3318 2750
Bond length (A) r(C,=C,) r(C,=W rf%C,I JiC, = G) tic,-%I r(C,-H,) r(C,-R,) = r(C,-W Bond angle (deg) GC&, C&G W&H, C,W% W&J& = W, W&G
I-f,,
Bipote moment (debye) K pb
I& Ft
PropenaP s-Trans
1.345 1.470 1.219 1.108 1.084 1.086 119.8 123.3 115.1 122.8 180.0
“Ref. 5.
shorter than the sp’-sp2 distances. For 2,3-but~dienal the calculated C-C bond length is in better agreement with the microwave value for propenal [5]. The reported C-X distances for propenoyl halides are longer than the 6-31G” predicted values for 2,3-butadienoyl halides and only slightly comparable with the optimized 4-31G parameters. Furthermore, the reported C=O bond lengths lie between the average values of the parameters calculated by the two basis sets. The predicted bond angles are in general resonably within the experimental uncertainties of the reported data, but there are some differences to be noted, Ab initio calculations predicted the CCC and CCX angles of the s-cis form to be smaller than those parameters for the s-trans conformer of the halides, and the CC0 bond angle of the s-cis form to be greater than that of the s-trans conformer, consistent with
H.&f. Bada~~l~.
Mol. Struct.
(~~~~~)
276 (1992) 251-257
255
TABLE3 Structural parameters, dipole moments and rotational constants of 2,8butadienoyl Parameter
6-31G*
4-31G
Bond length (rf) G=Q r(C,=Gf tic,-C,) tic, =0) r(G-F) r(w%) rlC,-H,) = r(G-I-W
fluoride
Propenoyl fluoride*
s-Trans
s-Cis
s_Trans
a-Cis
s-Trans
s-Cis
1.302 1.287 1.454 1.188 1.366 1.071 1.072
1.303 1.267 1.456 1.188 1.369 1.070 1.072
1.303 1.290 1.471 1.171 1.321 1.074 1.075
1.304 1.289 1.474 1.170 1.325 1.074 1.075
1.35
1.35
1.49 1.18 1.35 1.085 1.085
1.48 1.18 1.35 1.085 1.085
123.4 127.2 113.2 121.6 121.2 180.0
121.5 130.3 110.2 121.6 121.2 0.0
123.0 126.1 113.0 121.6 120.9 180.0
120.7 128.9 110.3 121.4 120.8 0.0
121.8 127.0 111.3
119.9 128.2 110.1
160.0
0.0
4.840 0.927 0.000 4.927
4.296 2.053 0.000 4.761
4.194 0.400 0.000 4.213
3.288 2.040 0.000 3.869
(MHZ) 9932 2287 1882
10477 2113 1780
10235 2289 1895
10667 2138 1803
Bond angle (deg)
Rotational A B c
~~~~t
“Ref. 8.
the experimental data shown in Tables 3 and 4. However, it is predicted that there is an approximate 2-5'difference between the CCC bond angles of the two conformers, disagreeing with the reported data for the chloride. The calculated dipole moments and rotational constants of the s-trans and s-cis conformations of the three molecules are shown in Tables 2-4. There are slight differences in the calculated dipole moments on going from the 4-3lG to the 6-31G” level, as expected from the difference in the calculation of the charge densities by the different basis sets. There are no reported experimental values for the dipole moments of these molecules in their stable conformations, although the moments found from ab initio calculations are generally larger than those determined exper~entally [ll]. The
256
EM.
3adaw~l~.
Mol. Stract.
(~~~~ern)
276 (1992) 251-257
TABLE 4 Structural parameters, dipole moments and rotational constants of 2,3-butadienoyl chloride Parameter
4-31G
631G*
Propenoyl chloride”
s-Trans
s-Cis
s-Trans
s-Cis
s-Trans
s-Cis
1.302 1.287 1.454 1.184 1.878 1.072 1.072
1.305 1.287 1.467 1.184 1.879 1.068 1.072
1.303 1.290 1.477 1.172 1.773 1.075 1.075
1.305 1.289 1.478 1.170 1.781 1.073 1.075
1.345
1.339
1.476 1.192 1.816 1.084 1.086
1.484 1.192 1.772 1.100 1.100
125.4 126.5 114.8 121.0 121.2 180.0
120.8 130.1 110.7 121.7 121.2 0.0
125.2 123.9 116.2 121.2 120.8 180.0
119.7 127.5 112.3 121.6 120.8 0.0
122.6 122.2 116.3 117.4
123.4 125.2 111.8 121.5
180.0
0.0
5.009 0.311 0.000 5.019
4.427 2.304 0.000 4.990
4.218 0.212 0.000 4.224
3.386 2.136 0.000 4.003
~o~t~o~a~ constant (iWHz) A 4527 3 2139 c 1467
8901 1418 1233
4848 2114 1487
9377
Bond length (A) r(c, = (4) tic, =CJ tiC,--G) tic, = 0) G-W r(‘&-H,) r(G-&,) = 43&,) Bond angIe (deg) W&G W,O C,C,Cl C& Bs C,C, f% = C&, B,, c,c,w Dipok
moment (d&ye)
P’a Pb PC Pt
1456 1271
“Ref. 8.
dipole moment of the s-trans form was calculated to be considerably greater than that of the s-cis conformer, as a result of a charge density variation with the rotation of the carbonyl moiety about the C-C bond. ACKNOWLEDGEMENT
The author gratefully acknowledges the support for this work provided by the King Fahd University of Petroleum and Minerals. REFERENCES 1 J. Kroner, W. Kosbahn and W. Runge, Ber. Bunsenges. Phys. Chem., 81 (1977) 826. 2 W. Runge, W. Kosbahn and J. Kroner, Ber. Bunsenges Phys. Chem., 81 (1977) 841.
H.M. BadawilJ. 3 4 5 6 7 8 9 10
11
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