Studies on the conformation of α-arylcinnamic acids and their esters: Crystal structures of methyl (E)-2,3-bis(3,4-dimethoxyphenyl)propenoate and methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate

Abstract

The conformations of stereoisomers of α-arylcinnamic acids and their esters are discussed based on crystal structures of the E and Z forms of 2,3-bis(3,4-dimethoxyphenyl)propenoic acid and its methyl ester. In the E forms of the cinnamic acid and the cinnamic acid ester, the plane of the α-aryl substituent is approximately perpendicular to that of the rest of the molecule. In the Z forms the plane of the carboxyl or methoxycarbonyl group is approximately perpendicular to that of the ethylenic group, and both the aromatic group planes are significantly twisted out of the ethylenic group plane. Crystal structures of methyl (E)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P21/n with a = 8.1697(5), b = 11.3882(9), c = 19.7766(9) A, β = 90.058(4)°, V = 1840.0(2) A3, and Z = 4), monoclinic methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P21/n with a = 11.183(2), b = 5.640(2), c = 29.737(7) A, β = 99.19(2)°, V = 1851.4(9) A3, and Z = 4), and orthorhombic methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P212121 with a = 8.849(4), b = 24.288(9), c = 8.734(3) A, V = 1877(1) A3, and Z = 4) are reported.