TOPOCHEMICAL STUDIES .13. STRUCTURES OF 3-BROMOCINNAMIC ACID AND 3-CHLOROCINNAMIC ACID

3-Bromocinnamic acid (1), C9H7BrO2, M(r) = 227.06, monoclinic, C2/c, a = 19.191 (6), b = 3.9879 (3), c = 24.798 (7) angstrom, beta = 113.05 (2)-degrees, V = 1746.3 (8) angstrom 3, Z = 8, D(m) = 1.72, D(x) = 1.728 Mg m-3, mu = 6.11 mm-1, F(000) = 896, final R = 0.070 for 1232 non-zero reflections. 3-Chlorocinnamic acid (2), C9H7ClO2, M(r) = 182.60, triclinic, P1BAR, a = 8.618 (4), b = 13.627 (5), c = 3.909 (1) angstrom, alpha = 106.77 (3), beta = 96.26 (3), gamma = 75.71 (3)-degrees, V = 425.9 (3) angstrom 3, Z = 2, D(m) = 1.38, D(x) = 1.424 Mg m-3, mu = 3.65 mm-1, F(000) = 188, final R = 0.060 for 1309 non-zero reflections. T = 295 K, Cu K-alpha, lambda = 1.54178 angstrom. The structures were determined with photoreactive crystals of (1) and (2). The C = C bond in (1) takes a cis conformation with respect to the 2 position of the phenyl ring, while that in (2) takes a trans conformation. The C = C double bonds of the nearest neighbours in (1) are related by a b translation and those in (2) are related by a c translation.