ChemInform Abstract: The Crystal Structure of 1,1‐Cyclobutanedicarboxylic Acid at 20 K

Abstract

The structure is disordered at room temperature, with atom C3 (Cγ) of the cyclobutane ring occupying sites on each side of the plane of the other three ring atoms. At 20 K, the structure is ordered. The space group is P21/c with Z=4; the unit cell dimensions at 20 K are a=5.983(2) A, b=10.374(4) A, c=10.917(3) A, β=101.19(3)°, V=664.8(4) A3. The average Cα–Cβ bond length, 1.560 A, is longer than the average Cβ–Cγ bond length, 1.548 A, and the internal ring angles are all acute, with that at Cα, the smallest, 88.52°, those at Cβ intermediate, average 89.11°, and that at Cγ, the largest 89.35°. The cyclobutane ring deviates only slightly from mm symmetry, with Cγ displaced from the CαCβ plane by 0.40 A. The average C=O and C–OH bond lengths in the carboxylate groups are 1.223 and 1.323 A, with each acid group hydrogen bonded to another acid group through an inversion center (O⋅⋅⋅O contacts, 2.65 A, on average). Examination of subtle differences in structural parameters suggests that substituent effects on c...