The conformational behaviour of 1,2-diaryl-1,1,2,2-tetrachloroethanes, ortho,ortho'-disubstituted with CN (1), F (2) and CO2CH3 (3), and of the mesityl derivative (4), has been studied in solution by variable temperature H-1 and C-13 NMR spectroscopy. The internal rotation processes around the exocyclic C-C and central C-C bonds appear to have similar energy barriers and thus behave differently from the compounds without ortho substituents, studied previously, which have a higher barrier for the interconversion of anti/gauche conformers. At low temperature, compounds 1-3 exist as mixtures of gauche and anti conformers with the former prevailing; compound 4 is almost exclusively in the gauche form. The solid state crystal and molecular structure has been determined for compounds 2 and 3. The molecule of compound 2 has point symmetry ($) over bar 1, which defines perfect staggering around the central C-C bond with the aromatic rings anti. The structure is affected by statistical disorder due to two alternate orientations of the phenyl rings. The crystal structure of compound 3 indicates one asymmetrical molecule in a gauche conformation. Statistical disorder involves both the methoxycarbonyl substituents at the phenyl rings; these latter display almost the same orientation with respect to the C(sp(3)) carbons, in both compounds.
The conformational behaviour of 1,2-diaryl-1,1,2,2-tetrachloroethanes, ortho,ortho'-disubstituted with CN (1), F (2) and CO2CH3 (3), and of the mesityl derivative (4), has been studied in solution by variable temperature H-1 and C-13 NMR spectroscopy. The internal rotation processes around the exocyclic C-C and central C-C bonds appear to have similar energy barriers and thus behave differently from the compounds without ortho substituents, studied previously, which have a higher barrier for the interconversion of anti/gauche conformers. At low temperature, compounds 1-3 exist as mixtures of gauche and anti conformers with the former prevailing; compound 4 is almost exclusively in the gauche form. The solid state crystal and molecular structure has been determined for compounds 2 and 3. The molecule of compound 2 has point symmetry ($) over bar 1, which defines perfect staggering around the central C-C bond with the aromatic rings anti. The structure is affected by statistical disorder due to two alternate orientations of the phenyl rings. The crystal structure of compound 3 indicates one asymmetrical molecule in a gauche conformation. Statistical disorder involves both the methoxycarbonyl substituents at the phenyl rings; these latter display almost the same orientation with respect to the C(sp(3)) carbons, in both compounds.
Effect of ortho substituents on the internal rotation processes and conformational preferences of 1,2-diaryl-1,1,2,2-tetrachloroethanes: A 1H and 13C NMR variable temperature and x-ray structural study / Antolini, L.; Folli, U.; Iarossi, D.; Mucci, A.; Sbardellati, S.; Taddei, F.. - In: JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS II. - ISSN 0300-9580. - STAMPA. - 1995:5(1995), pp. 1007-1015. [10.1039/p29950001007]
Effect of ortho substituents on the internal rotation processes and conformational preferences of 1,2-diaryl-1,1,2,2-tetrachloroethanes: A 1H and 13C NMR variable temperature and x-ray structural study
Antolini L.;Mucci A.;Taddei F.
1995
Abstract
The conformational behaviour of 1,2-diaryl-1,1,2,2-tetrachloroethanes, ortho,ortho'-disubstituted with CN (1), F (2) and CO2CH3 (3), and of the mesityl derivative (4), has been studied in solution by variable temperature H-1 and C-13 NMR spectroscopy. The internal rotation processes around the exocyclic C-C and central C-C bonds appear to have similar energy barriers and thus behave differently from the compounds without ortho substituents, studied previously, which have a higher barrier for the interconversion of anti/gauche conformers. At low temperature, compounds 1-3 exist as mixtures of gauche and anti conformers with the former prevailing; compound 4 is almost exclusively in the gauche form. The solid state crystal and molecular structure has been determined for compounds 2 and 3. The molecule of compound 2 has point symmetry ($) over bar 1, which defines perfect staggering around the central C-C bond with the aromatic rings anti. The structure is affected by statistical disorder due to two alternate orientations of the phenyl rings. The crystal structure of compound 3 indicates one asymmetrical molecule in a gauche conformation. Statistical disorder involves both the methoxycarbonyl substituents at the phenyl rings; these latter display almost the same orientation with respect to the C(sp(3)) carbons, in both compounds.
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