4-Vinylbenzoic acid and 9-vinylanthracene.

The crystal structures of two styrene analogues, 4-vinylbenzoic acid, C(9)H(8)O(2), (I), and 9-vinylanthracene, C(16)H(12), (II), were determined by X-ray analyses at 108 and 293 K for (I) and at 123 and 293 K for (II). In (I), a pair of molecules around an inversion center form a dimer connected by two carboxyl groups. The anthracene planes of two molecules in (II) are antiparallel to each other around an inversion center. The vinyl group of (I) is almost coplanar with the phenyl ring, whereas the vinyl group of (II) is nearly perpendicular to the anthracene plane. In (I), the bond length of the vinyl group at 293 K is significantly shorter than that at 108 K [1.288 (2) versus 1.3248 (14) A] suggesting a bias of the thermal motion, whereas the bond lengths are not so different between the two temperatures in (II) [1.3266 (15) versus 1.310 (2) A].