ATROPISOMERISM IN 2-(2,2-DICYANO-1-METHYLETHENYL)BENZOIC ACID AND 2,2-DICYANO-1-METHYLETHENYL)THIOPHENE-2-CARBOXYLIC ACID STUDIED BY SOLID-STATE C-13 NMR-SPECTROSCOPY AND X-RAY CRYSTALLOGRAPHY

The title compounds have been studied in solution by FTIR, UV, H-1 and C-13 NMR spectroscopy, which indicate atropisomerism where the two en antiomers exist as a centrosymmetric dimer. In solid-state C NMR two s ets of resonance signals are observed indicating diastereoisomerism in the dimer due to rotational restriction. Crystal structures for both acids and the methyl ester of the benzoic acid analogue (1b) have been determined. Compound 1a crystallizes in the orthorhombic space group P2(1)2(1)2(1) with cell dimensions a=8.945(2), b=10.644(2) and c=22.45 8(5) Angstrom, Z=8, R-value 5.2%, 2159 reflections; 2 and 1b both crys tallize in monoclinic space groups with cell dimensions a=11.058(2), b =14.628(3), c=12.713(2) Angstrom and beta=97.98(1)degrees, space group P2(1)/n, Z=8, R-value 3.8%, 5599 reflections; a=14.076(4), b=6.153(1) , c=14.437(2) Angstrom and beta=110.92(2)degrees, space group P2(1)/c, Z=4, R-value 4.8%, 2504 reflections, respectively.