Phenyl- and mesitylglyoxylic acids: catemeric hydrogen bonding in two alpha-keto acids
alpha-Oxobenzeneacetic (phenylglyoxylic) acid, C(8)H(6)O(3), adopts a transoid dicarbonyl conformation in the solid state, with the carboxyl group rotated 44.4 (1) degrees from the nearly planar benzoyl moiety. The heterochiral acid-to-ketone catemers [O.O = 2. 686 (3) and H.O = 1.78 (4) A] have a second, longer, intermolecular O-H.O contact to a carboxyl sp(3) O atom [O.O = 3.274 (2) and H.O = 2.72 (4) A], with each flat ribbon-like chain lying in the bc plane and extending in the c direction. In alpha-oxo-2,4, 6-trimethylbenzeneacetic (mesitylglyoxylic) acid, C(11)H(12)O(3), the ketone is rotated 49.1 (7) degrees from planarity with the aryl ring and the carboxyl group is rotated a further 31.2 (7) degrees from the ketone plane. The solid consists of chiral conformers of a single handedness, aggregating in hydrogen-bonding chains whose units are related by a 3(1) screw axis, producing hydrogen-bonding helices that extend in the c direction. The hydrogen bonding is of the acid-to-acid type [O.O = 2.709 (6) and H.O = 1.87 (5) A] and does not formally involve the ketone; however, the ketone O atom in the acceptor molecule has a close polar contact with the same donor carboxyl group [O.O = 3.005 (6) and H.O = 2.50 (5) A]. This secondary hydrogen bond is probably a major factor in stabilizing the observed cisoid dicarbonyl conformation. Several intermolecular C-H.O close contacts were found for the latter compound.
Chen
CD
Carl A. Olson Memorial Laboratories, Department of Chemistry, Rutgers University, Newark, NJ 07102, USA.
Brunskill
AP
Hall
SS
Lalancette
RA
Thompson
HW