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Structure of gaseous tetramethylsuccinic anhydride
of Molecular Structure, 30 (1976) o Eisevier Scientific Publishing Company,
JOLMM~
STRUCTURE
OF GASEOUS
A. ALMENNINGEN, Department (Received
-
Printed in The Netherlands
TETRAMETHYLSUCCINIC
L. FERNHOLT,
of Chemistry.
291-296 Amsterdam
University
S. RUSTAD
ANHYDRIDE
and H. M. SEIP
of Oslo, Oslo 3 (Norway)
19 March 1975)
ABSTRACT Tetramethylsuccinic anhydride has been studied by gas electron diffraction. A nonplanar ring was obtained, with torsional angles @(CSOlCZC3) = 10.6 -c 1.5O, o(OlC2C3C4) = 26.5 + 3.2” and @(C2C3C4C5) = 30.4 f 4.0”. Torsional angles cakulated by the molecular mechanics method were in fairly good agreement with the experimental values. INTRODUCTION
Succinic anhydride has an essentially planar skeleton both in the crystalline [l] and in the gaseous phase [2]. In order to study the effect of substituents we have now also determined the structure of gaseous tetramethylsuccinic anhydride by electron diffraction. It was pointed out by Eberson and Welinder that the structures of these compounds are of importance to understand the energetics of the equilibria diacid * anhydride + H,O which they studied for succinic acid and several methyl substituted derivatives, and found that K increased by a factor of 2.5 X lo4 in going from succinic to tetramethylsuccinic acid [3] . EXPERIMENTAL
The sample of tetramethylsuccinic anhydride was kindly supplied by Prof. L. Eberson, University of Lund, Sweden. Electron-diffraction intensity data were recorded with the Oslo apparatus [4]. Two sets of plates were used; each consists of 6 plates, with nozzle-to-plate distances of 480.67 mm and 200.67 mm, respectively. The nozzle temperature was about 105 “C and the electron wavelength 0.06458 a. The data* were treated in the usual way [ 51, using a modification function s/(ifc I - If,l). The scattering amplitudes *Experimental least-square from BLL.
and theoretical
calculation
intensity
values and the correlation
are available as Supplementary
Publication
matrix from the No. 26014
(5 pages)
292
were calculated as described previously [6] . A composite intensity curve ranging from s = 1.675 A-‘to .s= 41.75 A-’ was computed and used in the structure determination. The s-intervals were 0.125 A-’ for s < 10 A-’ and 0.25 A-’ for higher s-values. STRUCTURE
DETERMINATION
AND RESULTS
The molecule was assumed to have C2 symmetry and local CxV symmetry for the methyl groups. The Bastiansen-Morino shrinkage effect [7] was neglected and all asymmetry constants assumed to be zero [5]. As independent parameters the following were chosen: the six bond distances given in Table 1; LOlC2C3, LOlC2C7, LCCH, four angle parameters to define the positions of the carbon atoms in the methyl groups; one torsional angle [@(C5OlC2C3)] in the ring; and two torsional angles for the methyl groups. The assumption that the ClOC3Cll plane is perpendicular to the C2C3C4 plane used in the first calculations resulted in poor agreement. It turned out to be difficult to refine the torsional angles for the methyl groups. Calculations were carried out for various fixed values of these parameters. The best agreement was obtained for @(C2C3ClOH14) = 155” and Q(C2C3CllH17) = 175”. However, the agreement was nearly the same when both angles were fixed at 180”. Near staggering of the bonds about C3-Cl0 and C3-Cl1 is thus probable, and positions which lead to near eclipsing of bonds are certainly avoided. It is, of course, impossible to determine all the mean amplitudes of vibration [7 J (u) in tetramethylsuccinic anhydride from the electrondiffraction data. Values were therefore computed as described by St@levik et al. [S] . The force field given by DiLauro et al. [9] for succinic anhydride was applied as well as force constants for the methyl groups transferred from other molecules. The computed values for the most important distances are included in Table 1. The results obtained by least-squares refinement are given in Tables 1 and 2. The number of different distances close to 1.50 a makes these parameters uncertain. The results in Tables 1 and 2 were obtained by assuming the exocyclic C-C bond length to be 1.537 A and the mean amplitudes for the C-C and 01-C bonds to be equal. Other refinement schemes gave somewhat different C-C bond lengths, but the other parameters varied OdY slightly. The angle parameters, especially the torsional angles in the ring, are the most interesting results. Eclipsing of the methyl groups is avoided by a twist of about 30” around the C3-C4 bond. Apart from this deviation from ring planarity, the other parameters are close to the values found in succi& anhydride 123, though there is an indication of a slight lengthening Of the
bonds in the ring.
293
Fig. 1. The numbering
of the atoms in tetramethylsuccinic
anhydride.
Fig. 2. Experimental (circles) and theoretical (full line) radial distribution functions for tetramethylsuccinic anhydride. An artificial damping constant [ 5 J k = 0.0025 .+I’ was applied. The differences between experimental and theoretical values are also shown. The positions and approximate areas of the peaks corresponding to the most important distances are indicated.
294
TABLE
1
The most important distances (r=” ) and corresponding mean amplitudes of vibration in tetramethylsuccinic anhydride (the standard deviations given in parentheses apply to the last digit given”)
uED(A)b
r(X) c2-01 c2-c3 c3-c4 c3-Cl1 C2-07 C-H 01. .06 06 -07 01. -c3 c3- -07 C2- -06 C3- -06 06. -C8 Ol- -C8 06. - C9 C2- C8 C8- -Cl0 01. SC9 06. -Cl1 c2. C9 06. -Cl0 c2- -CT4 c2* -c5 c2- Cl0 c2* -Cl1 c3- -C8 c3. C9 C8- C9 C8- -Cl1 c9- Cl0
l-396(4) l-524(6) l-567( 15) 1.537 1.192(3) l-118(6) Z-254(4) 4:458( 5) 2.382(i) Q-464(7) 3.399(5) 3.522(9) 3.212(20) 3.142(12) 2.977( 15) 3.125(15) 2.959(30) 3.683(6) 4.035( 20) 3.753(7) 4.901(7) 2.384(6) 2.282(7) 2.542(10) 2.450( 13) Z-593(12) 2.613(10) 2.505(12) 3.945( 20) 3.448(25)
us(A)=
0.108 1 0.092 \ 0.226 , (7)d 0.085 0.077 0.064 0.055 0.078 0.081
0.052 0.050 0.049 0.04s 0.039 0.079 0.057 0.065 0.059 0.059 0.061 0.085 0.152 0.147 0.125 0.139 0.137 0.079 0.213 0.072 0.077 0.064 0.055 0.078 0.081
0.074
0.074
0.073 0.074 0.079 0.114
0.073 0.074 0.079 0.114
0.039 0.079 0.057 0.065 0.060 0.058 0.066 I 0.090 (8)d 0.157 J 0.168 \
=The standard deviations were corrected for the correlation between the intensity data [ 13 ] _ Parameter values with no standard deviations were assumed. bMean amplitudes of vibration obtained or assumed in the electron-diffration investigation =Mean amplitudes computed by using an assumed force field (see text). dThe difference between the u values were assumed.
STRUCTURES
CALCULATED
BY MOLECULAR
MECHANICS
Calculation of conformational energies by molecular mechanics [lo] has given quite good results for several five-membered rings (ref. 11 and references given therein). The angle parameters, both in succinic anhydride and in tetramethylsuccinic anhydride, were therefore computed in this way The results ar&compared with the observed values in Table 2. The
295 TABLE
2
Observed and calculated angle parameters (degrees) in tetramethylsuccinic anhydride and succinic anhydride (II) (the standard deviations apply to the last digit given) a
II
I
i OlC2C3 LC2C3C4 f_CSOlC2 L OlC207 L C2C3XlO L CZC3Xll L C4C3XlO L C4C3Xll L x10c3x11 LCCH d( C501C2C3) o(OlC2C3C4) O(C”C3C4C5) o(C2C3ClOH14) o(C2C3CllH17)
(I)
Obs.
CalcSb
Ohs.
CaIc_b
109.2(4) 100.9(4) 109.6(5) 121-O(4) 112.2(9) 106.3( 12) 114.6(g) 113.9(10) 109.1(S) 112.5(10)
111.6 101.8 107.0 124.1 110.9 108.i 113.3 112.6 109.5 109.6
110.5(4) 103.8(5) 109.9(5) 122-l(4)
112.5 103.2 107.5 123.8 110.5 110.5 110.6 110.6 111-l
10.8(6) 26-5( 13) 30.4( 16)
8.5 20.1 23.5 -174 159
(180) (180)
4.1(20) 10.2(50) 11.4(60)
3.7 9.1 10.1
=X is C or H. bValues computed keeping all bond lengths fixed. The natural angles were taken as 109.5” except around C2 and C5, where 122.5” was used for L 07C201 and L 07C2C3, 115” for ~01C2C3. The force constants were (mdyn A rad-‘): h,,, = 0.67, ~H~_I = = 1.1, all others 1.0. Intrinsic torsional energies were calculated from 0.50, h,, LT(o) = V,/2 (1 + cos mo ). In a planar ring @I= 0 for all the endocyclic bonds. The constants
were as follows. VCl
c3-C4, c3-ClO, C2-C3, C4-C5 Ol-c2,01-C5
C3-Cl1,
The van der Waals’ energy
C4-C8,
c4-C9
was calculated
as described
m
2.65 [14] 1.16 [15] -5.0 [16] by Eliel et al. [lo].
calculation gives, in agreement with the experiment, considerable deviation from ring planarity in tetramethylsuccinic anhydride, though the torsional angles are somewhat smaller than the observed ones. The deviation from planarity found in succinic anhydride cannot be regarded as significant; the barriercorresponding to the planar form was calculated to be only 0.15 kcal mol-‘. The barrier in tetramethylsuccinic anhydride was found to be about 1.0 kcal mol-‘.
3 3 2
REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13
M. Ehrenberg,
Acta Crystallogr., 19 (1965) 698. K Brendhaugen, M. Kolderup Fikke and H. M. Seip, Acta Chem. Stand., 27 (1973) 1101. L. Eberson and H. Welinder, J_ Amer. Chem. Sot., 93 (1971) 5821. 0. Bastiansen, 0. Hassel and E. Risberg, Acta Chem. Stand., 9 (1955) 232. B. Andersen, H. M. Seip, T. G. Strand and R. StQlevik, Acta Chem. Stand., 23 (1969) 3224. H. M. Seip, R. Seip and K. Niedenzu, J. Mol. Struct., 17 (1973) 361. S. J. Cyvin, Molecular Vibrations and Mean-Square Amplitudes, Universitetsforlaget, Oslo and Elsevier, Amsterdam, 1968. R. Stdlevik, H. M. Seip and S. J. Cyvin, Chem. Phys. Lett., 15 (1972) 263. C. DiLauro, S. Califano and G. Adembri, J. Mol. Struct., 2 (1968) 173. E. L. Eliel, N. L. Allinger, S. J. Angyal and G. A. Morrison, Conformational Analysis, Interscience, New York, 1965. Z. Smith, B. Nahlovsky, D. A. Kohl and H. M. Seip, Acta Chem. Stand. A, 29 (1975), in press. K. Kuchitsu and S. J. Cyvin, in S. J. Cyvin (editor), Molecular Structures and Vibrations, Elsevier, Amsterdam, 1972, chap. 12. H. M. Seip and R. St6Ievik, in S. J. Cyvin (Ed.). Molecular Structures and Vibrations,
Elsevier, Amsterdam, 1972, Chap. 11. 14 R J. Abraham and K. Parry, J. Chem. Sot., B, (1970) 539. 15 R. W. Kilb, C. C. Lin and E. B. Wilson, Jr., J. Chem. Phys., 26 (1957) 1695. 16 H Wennerstrtim, S. Fozdn and B. Roos, J. Phys. Chem., 76 (1972) 2430.
JOLMM~
STRUCTURE
OF GASEOUS
A. ALMENNINGEN, Department (Received
-
Printed in The Netherlands
TETRAMETHYLSUCCINIC
L. FERNHOLT,
of Chemistry.
291-296 Amsterdam
University
S. RUSTAD
ANHYDRIDE
and H. M. SEIP
of Oslo, Oslo 3 (Norway)
19 March 1975)
ABSTRACT Tetramethylsuccinic anhydride has been studied by gas electron diffraction. A nonplanar ring was obtained, with torsional angles @(CSOlCZC3) = 10.6 -c 1.5O, o(OlC2C3C4) = 26.5 + 3.2” and @(C2C3C4C5) = 30.4 f 4.0”. Torsional angles cakulated by the molecular mechanics method were in fairly good agreement with the experimental values. INTRODUCTION
Succinic anhydride has an essentially planar skeleton both in the crystalline [l] and in the gaseous phase [2]. In order to study the effect of substituents we have now also determined the structure of gaseous tetramethylsuccinic anhydride by electron diffraction. It was pointed out by Eberson and Welinder that the structures of these compounds are of importance to understand the energetics of the equilibria diacid * anhydride + H,O which they studied for succinic acid and several methyl substituted derivatives, and found that K increased by a factor of 2.5 X lo4 in going from succinic to tetramethylsuccinic acid [3] . EXPERIMENTAL
The sample of tetramethylsuccinic anhydride was kindly supplied by Prof. L. Eberson, University of Lund, Sweden. Electron-diffraction intensity data were recorded with the Oslo apparatus [4]. Two sets of plates were used; each consists of 6 plates, with nozzle-to-plate distances of 480.67 mm and 200.67 mm, respectively. The nozzle temperature was about 105 “C and the electron wavelength 0.06458 a. The data* were treated in the usual way [ 51, using a modification function s/(ifc I - If,l). The scattering amplitudes *Experimental least-square from BLL.
and theoretical
calculation
intensity
values and the correlation
are available as Supplementary
Publication
matrix from the No. 26014
(5 pages)
292
were calculated as described previously [6] . A composite intensity curve ranging from s = 1.675 A-‘to .s= 41.75 A-’ was computed and used in the structure determination. The s-intervals were 0.125 A-’ for s < 10 A-’ and 0.25 A-’ for higher s-values. STRUCTURE
DETERMINATION
AND RESULTS
The molecule was assumed to have C2 symmetry and local CxV symmetry for the methyl groups. The Bastiansen-Morino shrinkage effect [7] was neglected and all asymmetry constants assumed to be zero [5]. As independent parameters the following were chosen: the six bond distances given in Table 1; LOlC2C3, LOlC2C7, LCCH, four angle parameters to define the positions of the carbon atoms in the methyl groups; one torsional angle [@(C5OlC2C3)] in the ring; and two torsional angles for the methyl groups. The assumption that the ClOC3Cll plane is perpendicular to the C2C3C4 plane used in the first calculations resulted in poor agreement. It turned out to be difficult to refine the torsional angles for the methyl groups. Calculations were carried out for various fixed values of these parameters. The best agreement was obtained for @(C2C3ClOH14) = 155” and Q(C2C3CllH17) = 175”. However, the agreement was nearly the same when both angles were fixed at 180”. Near staggering of the bonds about C3-Cl0 and C3-Cl1 is thus probable, and positions which lead to near eclipsing of bonds are certainly avoided. It is, of course, impossible to determine all the mean amplitudes of vibration [7 J (u) in tetramethylsuccinic anhydride from the electrondiffraction data. Values were therefore computed as described by St@levik et al. [S] . The force field given by DiLauro et al. [9] for succinic anhydride was applied as well as force constants for the methyl groups transferred from other molecules. The computed values for the most important distances are included in Table 1. The results obtained by least-squares refinement are given in Tables 1 and 2. The number of different distances close to 1.50 a makes these parameters uncertain. The results in Tables 1 and 2 were obtained by assuming the exocyclic C-C bond length to be 1.537 A and the mean amplitudes for the C-C and 01-C bonds to be equal. Other refinement schemes gave somewhat different C-C bond lengths, but the other parameters varied OdY slightly. The angle parameters, especially the torsional angles in the ring, are the most interesting results. Eclipsing of the methyl groups is avoided by a twist of about 30” around the C3-C4 bond. Apart from this deviation from ring planarity, the other parameters are close to the values found in succi& anhydride 123, though there is an indication of a slight lengthening Of the
bonds in the ring.
293
Fig. 1. The numbering
of the atoms in tetramethylsuccinic
anhydride.
Fig. 2. Experimental (circles) and theoretical (full line) radial distribution functions for tetramethylsuccinic anhydride. An artificial damping constant [ 5 J k = 0.0025 .+I’ was applied. The differences between experimental and theoretical values are also shown. The positions and approximate areas of the peaks corresponding to the most important distances are indicated.
294
TABLE
1
The most important distances (r=” ) and corresponding mean amplitudes of vibration in tetramethylsuccinic anhydride (the standard deviations given in parentheses apply to the last digit given”)
uED(A)b
r(X) c2-01 c2-c3 c3-c4 c3-Cl1 C2-07 C-H 01. .06 06 -07 01. -c3 c3- -07 C2- -06 C3- -06 06. -C8 Ol- -C8 06. - C9 C2- C8 C8- -Cl0 01. SC9 06. -Cl1 c2. C9 06. -Cl0 c2- -CT4 c2* -c5 c2- Cl0 c2* -Cl1 c3- -C8 c3. C9 C8- C9 C8- -Cl1 c9- Cl0
l-396(4) l-524(6) l-567( 15) 1.537 1.192(3) l-118(6) Z-254(4) 4:458( 5) 2.382(i) Q-464(7) 3.399(5) 3.522(9) 3.212(20) 3.142(12) 2.977( 15) 3.125(15) 2.959(30) 3.683(6) 4.035( 20) 3.753(7) 4.901(7) 2.384(6) 2.282(7) 2.542(10) 2.450( 13) Z-593(12) 2.613(10) 2.505(12) 3.945( 20) 3.448(25)
us(A)=
0.108 1 0.092 \ 0.226 , (7)d 0.085 0.077 0.064 0.055 0.078 0.081
0.052 0.050 0.049 0.04s 0.039 0.079 0.057 0.065 0.059 0.059 0.061 0.085 0.152 0.147 0.125 0.139 0.137 0.079 0.213 0.072 0.077 0.064 0.055 0.078 0.081
0.074
0.074
0.073 0.074 0.079 0.114
0.073 0.074 0.079 0.114
0.039 0.079 0.057 0.065 0.060 0.058 0.066 I 0.090 (8)d 0.157 J 0.168 \
=The standard deviations were corrected for the correlation between the intensity data [ 13 ] _ Parameter values with no standard deviations were assumed. bMean amplitudes of vibration obtained or assumed in the electron-diffration investigation =Mean amplitudes computed by using an assumed force field (see text). dThe difference between the u values were assumed.
STRUCTURES
CALCULATED
BY MOLECULAR
MECHANICS
Calculation of conformational energies by molecular mechanics [lo] has given quite good results for several five-membered rings (ref. 11 and references given therein). The angle parameters, both in succinic anhydride and in tetramethylsuccinic anhydride, were therefore computed in this way The results ar&compared with the observed values in Table 2. The
295 TABLE
2
Observed and calculated angle parameters (degrees) in tetramethylsuccinic anhydride and succinic anhydride (II) (the standard deviations apply to the last digit given) a
II
I
i OlC2C3 LC2C3C4 f_CSOlC2 L OlC207 L C2C3XlO L CZC3Xll L C4C3XlO L C4C3Xll L x10c3x11 LCCH d( C501C2C3) o(OlC2C3C4) O(C”C3C4C5) o(C2C3ClOH14) o(C2C3CllH17)
(I)
Obs.
CalcSb
Ohs.
CaIc_b
109.2(4) 100.9(4) 109.6(5) 121-O(4) 112.2(9) 106.3( 12) 114.6(g) 113.9(10) 109.1(S) 112.5(10)
111.6 101.8 107.0 124.1 110.9 108.i 113.3 112.6 109.5 109.6
110.5(4) 103.8(5) 109.9(5) 122-l(4)
112.5 103.2 107.5 123.8 110.5 110.5 110.6 110.6 111-l
10.8(6) 26-5( 13) 30.4( 16)
8.5 20.1 23.5 -174 159
(180) (180)
4.1(20) 10.2(50) 11.4(60)
3.7 9.1 10.1
=X is C or H. bValues computed keeping all bond lengths fixed. The natural angles were taken as 109.5” except around C2 and C5, where 122.5” was used for L 07C201 and L 07C2C3, 115” for ~01C2C3. The force constants were (mdyn A rad-‘): h,,, = 0.67, ~H~_I = = 1.1, all others 1.0. Intrinsic torsional energies were calculated from 0.50, h,, LT(o) = V,/2 (1 + cos mo ). In a planar ring @I= 0 for all the endocyclic bonds. The constants
were as follows. VCl
c3-C4, c3-ClO, C2-C3, C4-C5 Ol-c2,01-C5
C3-Cl1,
The van der Waals’ energy
C4-C8,
c4-C9
was calculated
as described
m
2.65 [14] 1.16 [15] -5.0 [16] by Eliel et al. [lo].
calculation gives, in agreement with the experiment, considerable deviation from ring planarity in tetramethylsuccinic anhydride, though the torsional angles are somewhat smaller than the observed ones. The deviation from planarity found in succinic anhydride cannot be regarded as significant; the barriercorresponding to the planar form was calculated to be only 0.15 kcal mol-‘. The barrier in tetramethylsuccinic anhydride was found to be about 1.0 kcal mol-‘.
3 3 2
REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13
M. Ehrenberg,
Acta Crystallogr., 19 (1965) 698. K Brendhaugen, M. Kolderup Fikke and H. M. Seip, Acta Chem. Stand., 27 (1973) 1101. L. Eberson and H. Welinder, J_ Amer. Chem. Sot., 93 (1971) 5821. 0. Bastiansen, 0. Hassel and E. Risberg, Acta Chem. Stand., 9 (1955) 232. B. Andersen, H. M. Seip, T. G. Strand and R. StQlevik, Acta Chem. Stand., 23 (1969) 3224. H. M. Seip, R. Seip and K. Niedenzu, J. Mol. Struct., 17 (1973) 361. S. J. Cyvin, Molecular Vibrations and Mean-Square Amplitudes, Universitetsforlaget, Oslo and Elsevier, Amsterdam, 1968. R. Stdlevik, H. M. Seip and S. J. Cyvin, Chem. Phys. Lett., 15 (1972) 263. C. DiLauro, S. Califano and G. Adembri, J. Mol. Struct., 2 (1968) 173. E. L. Eliel, N. L. Allinger, S. J. Angyal and G. A. Morrison, Conformational Analysis, Interscience, New York, 1965. Z. Smith, B. Nahlovsky, D. A. Kohl and H. M. Seip, Acta Chem. Stand. A, 29 (1975), in press. K. Kuchitsu and S. J. Cyvin, in S. J. Cyvin (editor), Molecular Structures and Vibrations, Elsevier, Amsterdam, 1972, chap. 12. H. M. Seip and R. St6Ievik, in S. J. Cyvin (Ed.). Molecular Structures and Vibrations,
Elsevier, Amsterdam, 1972, Chap. 11. 14 R J. Abraham and K. Parry, J. Chem. Sot., B, (1970) 539. 15 R. W. Kilb, C. C. Lin and E. B. Wilson, Jr., J. Chem. Phys., 26 (1957) 1695. 16 H Wennerstrtim, S. Fozdn and B. Roos, J. Phys. Chem., 76 (1972) 2430.