CRYSTAL AND MOLECULAR-STRUCTURES OF ALLOCINNAMIC ACID

Crystals of allocinnamic acid having a melting point of 68-degrees-C a re monoclinic: space group P2(1)/n with a=10.157(4), b=9.798(2), c=15. 770(4) angstrom, beta=91.35(3)-degrees, and Z=8. The structure was sol ved by direct method and refined to a final R value of 0.059 for 3832 reflections [ I>3sigma(I)]. There are two independent molecules (A, B) in the asymmetric unit. The two molecules are hydrogen bonded through carboxylic acid groups [O1A ... O2B 2.643(5) A, O2A ... O1B 2.629(5) angstrom]. Geometric differences between the two molecules are found i n the torsion angle around the C(phenyl)-C(olefin) bond and the olefin ic C=C bond length. In the high-resolution solid-state C-13 NMR spectr a resonances for the C2, C3, and C4 carbons are observed as doublet fe atures in accordance with the conformational variations observed in X- ray crystallography.