Benzene ring deformation and rotational isomerism in terephthalaldehyde: A study by electron diffraction and molecular orbital calculations

Charles W. Bock, Aldo Domenicano, Philip George, I. Hargittai, Gustavo Portalone, György Schultz

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Abstract

The molecular structure and rotational isomerism of terephthalaldehyde have been investigated by gas-phase electron diffraction at 418 K and by ab initio MO calculations with the 6-31G basis set. The experimental data indicate that the vapor is a nearly 1:1 mixture of the trans and cis conformers. The MO calculations find the trans conformer to be more stable than the cis conformer by only 0.21 kcal mol-1. In the electron diffraction study the trans and cis conformers were assumed to have C2h, and C2v symmetry, respectively, and to contain identical benzene rings and formyl groups. The benzene ring was constrained to D2h symmetry. The following geometrical parameters were obtained for the heavy-atom skeleton: 〈rg(C-C)ring〉 = 1.402 ± 0.003 Å, rg(C-CHO) = 1.487 ± 0.004 Å, rg(C=O) = 1.208 ± 0.003 Å, ∠C-C(CHO)-C = 120.5 ± 0.4°, ∠C-C=O = 123.7 ± 0.4°. The experimental data indicate that the two adjacent C-C-CHO angles differ by 0.7 ± 0.5°; they also suggest that the central C-C bonds of the ring are some 0.01-0.02 Å shorter than the Cipso-Cortho bonds. The effect that the formyl group has on the ring geometry is much less pronounced than with other common substituents. In the MO calculations the two conformers were assumed to be planar. The calculated geometries of the heavy-atom skeletons are consistent with the experimental results. Also, the small "tilt" of the C-CHO bonds out of the Cipso⋯Cipso′ axis and the shortening of the central C-C bonds of the ring with respect to the Cipso-Cortho bonds are well reproduced. In addition, the calculations show that the inherent asymmetry of the substituent causes the ring deformation to be unsymmetrical with respect to the Cipso⋯Cipso′ axis. Comparison with the calculated geometry of benzaldehyde indicates that the distortion of the benzene nucleus in the two conformers may be reproduced by superimposing separate distortions from each formyl group. The minute differences between the calculated geometries and those predicted by the superposition model suggest that the interaction of the formyl group with the benzene ring is less pronounced in terephthalaldehyde than in benzaldehyde. An attractive interaction appears to exist between the carbonyl of the substituent and the nearest aromatic proton.

Original languageEnglish
Pages (from-to)6120-6127
Number of pages8
JournalJournal of Physical Chemistry
Volume91
Issue number24
Publication statusPublished - 1987

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Orbital calculations
Molecular orbitals
Benzene
Electron diffraction
molecular orbitals
electron diffraction
benzene
orbitals
Geometry
rings
Atoms
geometry
musculoskeletal system
Molecular structure
Protons
Gases
Vapors
symmetry
atoms
molecular structure

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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Benzene ring deformation and rotational isomerism in terephthalaldehyde : A study by electron diffraction and molecular orbital calculations. / Bock, Charles W.; Domenicano, Aldo; George, Philip; Hargittai, I.; Portalone, Gustavo; Schultz, György.

In: Journal of Physical Chemistry, Vol. 91, No. 24, 1987, p. 6120-6127.

Research output: Contribution to journalArticle

Bock, Charles W. ; Domenicano, Aldo ; George, Philip ; Hargittai, I. ; Portalone, Gustavo ; Schultz, György. / Benzene ring deformation and rotational isomerism in terephthalaldehyde : A study by electron diffraction and molecular orbital calculations. In: Journal of Physical Chemistry. 1987 ; Vol. 91, No. 24. pp. 6120-6127.
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abstract = "The molecular structure and rotational isomerism of terephthalaldehyde have been investigated by gas-phase electron diffraction at 418 K and by ab initio MO calculations with the 6-31G basis set. The experimental data indicate that the vapor is a nearly 1:1 mixture of the trans and cis conformers. The MO calculations find the trans conformer to be more stable than the cis conformer by only 0.21 kcal mol-1. In the electron diffraction study the trans and cis conformers were assumed to have C2h, and C2v symmetry, respectively, and to contain identical benzene rings and formyl groups. The benzene ring was constrained to D2h symmetry. The following geometrical parameters were obtained for the heavy-atom skeleton: 〈rg(C-C)ring〉 = 1.402 ± 0.003 {\AA}, rg(C-CHO) = 1.487 ± 0.004 {\AA}, rg(C=O) = 1.208 ± 0.003 {\AA}, ∠C-C(CHO)-C = 120.5 ± 0.4°, ∠C-C=O = 123.7 ± 0.4°. The experimental data indicate that the two adjacent C-C-CHO angles differ by 0.7 ± 0.5°; they also suggest that the central C-C bonds of the ring are some 0.01-0.02 {\AA} shorter than the Cipso-Cortho bonds. The effect that the formyl group has on the ring geometry is much less pronounced than with other common substituents. In the MO calculations the two conformers were assumed to be planar. The calculated geometries of the heavy-atom skeletons are consistent with the experimental results. Also, the small {"}tilt{"} of the C-CHO bonds out of the Cipso⋯Cipso′ axis and the shortening of the central C-C bonds of the ring with respect to the Cipso-Cortho bonds are well reproduced. In addition, the calculations show that the inherent asymmetry of the substituent causes the ring deformation to be unsymmetrical with respect to the Cipso⋯Cipso′ axis. Comparison with the calculated geometry of benzaldehyde indicates that the distortion of the benzene nucleus in the two conformers may be reproduced by superimposing separate distortions from each formyl group. The minute differences between the calculated geometries and those predicted by the superposition model suggest that the interaction of the formyl group with the benzene ring is less pronounced in terephthalaldehyde than in benzaldehyde. An attractive interaction appears to exist between the carbonyl of the substituent and the nearest aromatic proton.",
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T1 - Benzene ring deformation and rotational isomerism in terephthalaldehyde

T2 - A study by electron diffraction and molecular orbital calculations

AU - Bock, Charles W.

AU - Domenicano, Aldo

AU - George, Philip

AU - Hargittai, I.

AU - Portalone, Gustavo

AU - Schultz, György

PY - 1987

Y1 - 1987

N2 - The molecular structure and rotational isomerism of terephthalaldehyde have been investigated by gas-phase electron diffraction at 418 K and by ab initio MO calculations with the 6-31G basis set. The experimental data indicate that the vapor is a nearly 1:1 mixture of the trans and cis conformers. The MO calculations find the trans conformer to be more stable than the cis conformer by only 0.21 kcal mol-1. In the electron diffraction study the trans and cis conformers were assumed to have C2h, and C2v symmetry, respectively, and to contain identical benzene rings and formyl groups. The benzene ring was constrained to D2h symmetry. The following geometrical parameters were obtained for the heavy-atom skeleton: 〈rg(C-C)ring〉 = 1.402 ± 0.003 Å, rg(C-CHO) = 1.487 ± 0.004 Å, rg(C=O) = 1.208 ± 0.003 Å, ∠C-C(CHO)-C = 120.5 ± 0.4°, ∠C-C=O = 123.7 ± 0.4°. The experimental data indicate that the two adjacent C-C-CHO angles differ by 0.7 ± 0.5°; they also suggest that the central C-C bonds of the ring are some 0.01-0.02 Å shorter than the Cipso-Cortho bonds. The effect that the formyl group has on the ring geometry is much less pronounced than with other common substituents. In the MO calculations the two conformers were assumed to be planar. The calculated geometries of the heavy-atom skeletons are consistent with the experimental results. Also, the small "tilt" of the C-CHO bonds out of the Cipso⋯Cipso′ axis and the shortening of the central C-C bonds of the ring with respect to the Cipso-Cortho bonds are well reproduced. In addition, the calculations show that the inherent asymmetry of the substituent causes the ring deformation to be unsymmetrical with respect to the Cipso⋯Cipso′ axis. Comparison with the calculated geometry of benzaldehyde indicates that the distortion of the benzene nucleus in the two conformers may be reproduced by superimposing separate distortions from each formyl group. The minute differences between the calculated geometries and those predicted by the superposition model suggest that the interaction of the formyl group with the benzene ring is less pronounced in terephthalaldehyde than in benzaldehyde. An attractive interaction appears to exist between the carbonyl of the substituent and the nearest aromatic proton.

AB - The molecular structure and rotational isomerism of terephthalaldehyde have been investigated by gas-phase electron diffraction at 418 K and by ab initio MO calculations with the 6-31G basis set. The experimental data indicate that the vapor is a nearly 1:1 mixture of the trans and cis conformers. The MO calculations find the trans conformer to be more stable than the cis conformer by only 0.21 kcal mol-1. In the electron diffraction study the trans and cis conformers were assumed to have C2h, and C2v symmetry, respectively, and to contain identical benzene rings and formyl groups. The benzene ring was constrained to D2h symmetry. The following geometrical parameters were obtained for the heavy-atom skeleton: 〈rg(C-C)ring〉 = 1.402 ± 0.003 Å, rg(C-CHO) = 1.487 ± 0.004 Å, rg(C=O) = 1.208 ± 0.003 Å, ∠C-C(CHO)-C = 120.5 ± 0.4°, ∠C-C=O = 123.7 ± 0.4°. The experimental data indicate that the two adjacent C-C-CHO angles differ by 0.7 ± 0.5°; they also suggest that the central C-C bonds of the ring are some 0.01-0.02 Å shorter than the Cipso-Cortho bonds. The effect that the formyl group has on the ring geometry is much less pronounced than with other common substituents. In the MO calculations the two conformers were assumed to be planar. The calculated geometries of the heavy-atom skeletons are consistent with the experimental results. Also, the small "tilt" of the C-CHO bonds out of the Cipso⋯Cipso′ axis and the shortening of the central C-C bonds of the ring with respect to the Cipso-Cortho bonds are well reproduced. In addition, the calculations show that the inherent asymmetry of the substituent causes the ring deformation to be unsymmetrical with respect to the Cipso⋯Cipso′ axis. Comparison with the calculated geometry of benzaldehyde indicates that the distortion of the benzene nucleus in the two conformers may be reproduced by superimposing separate distortions from each formyl group. The minute differences between the calculated geometries and those predicted by the superposition model suggest that the interaction of the formyl group with the benzene ring is less pronounced in terephthalaldehyde than in benzaldehyde. An attractive interaction appears to exist between the carbonyl of the substituent and the nearest aromatic proton.

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