4-Vinylbenzoic acid and 9-vinylanthracene

The crystal structures of two styrene analogues, 4-vinylbenzoic acid, C9H8O 2, (I), and 9-vinylanthracene, C16H12, (II), were determined by X-ray analy ses 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 carbo xyl 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 p erpendicular 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) versu s 1.3248 (14) Angstrom] suggesting a bias of the thermal motion, whereas th e bond lengths are not so different between the two temperatures in (II) [1 .3266 (15) versus 1.310 (2) Angstrom].