CRYSTAL AND MOLECULAR-STRUCTURES OF A LOW-MELTING POLYMORPH OF ALLOCINNAMIC ACID

Crystals of a polymorph of allocinnamic acid having a melting point of 58 -degrees-C are monoclinic, space group P2(1)/c with a=6.2508(8), b =15.524(2), c=8.5067(5) angstrom, beta= 109.295(7)-degrees, and Z=4. T he structure was solved by direct methods and refined to a final R val ue of 0.042 for 1321 reflections [I>3sigma(I)]. The molecules form cen trosymmetric dimers with two O-H...O bonds of carboxylic acid groups [ O...O distance, 2.666(1) angstrom, O...H-O angle, 160.79-degrees]. The plane formed by the olefin group is twisted with respect to the pheny l ring at an angle of 37.8(2)-degrees. The high-resolution solid-state C-13 NMR spectra were also measured and may be useful for distinguish ing polymorphs of allocinnamic acid.