3-Oxocyclobutanecarboxylic acid: hydrogen bonding in a small-ring γ-keto acid

Abstract

The title ketocarboxylic acid, C5H6O3, is the smallest carboxy­cyclanone to have its crystal structure determined. It adopts a chiral conformation, by rotation of its carboxyl O atoms away from the plane of skeletal symmetry that passes through the carboxyl carbon and both atoms of the ketone carbonyl. The four-membered ring is non-planar, with a shallow fold of 14.3 (1)° along a line connecting the two α-carbons of the ketone group. In the crystal, the molecules are linked by centrosymmetric hydrogen-bond pairing of ordered carboxylic acid groups [O⋯O = 2.6392 (12) Å and O—H⋯O = 175.74 (15)°], yielding two different sets of dimers, related by by a 21 screw axis in c, in the cell. A C—H⋯O interaction is also present.

(±)-2-Oxocyclopentaneacetic acid: catemeric hydrogen bonding in a γ-keto acid

“…An issue of interest is the minimum requirements for catemer formation. However, the very smallest molecules offer several experimental problems (volatility, low crystallinity, little structural variability), so that few C 3 -C 6 keto-acids have been previously reported (Harata et al, 1977;Malak et al, 2006;Efthimiopoulos et al, 2009). We now report the crystal structure of the title C 7 γ-keto acid (I), among the smallest found to aggregate in the solid as a catemer.…”

“…For background to catemers and hydrogen bonds, see: Barcon et al (1998Barcon et al ( , 2002; Coté et al (1996); DeVita Dufort et al (2007); Efthimiopoulos et al (2009); Harata et al (1977); Lalancette & Thompson (2003); Lalancette et al (2006); Malak et al (2006); Newman et al (2002); Steiner (1997); Stork et al (1963).…”