3-Benzoylpropionic acid: structure and hydrogen-bonding pattern

Abstract

(I) Cl0Hl003, Mr = 178.188, monoclinic, e2~/n, a = 12.728 (6), b = 5.200 (3), c = 14.426 (6)/~, /3 = 111-33 (3) °, V(235 K) = 889.4 (8) A 3, Z = 4, Dm(295 K ) = 131 (1), Dx[295 K; V = 8913 (6) A 3] = 1328 g cm -3 A(Mo Ka) = 0-71069 A, # = 1058 cmi, F(000) = 376, T = 235 (1) K, R = 0.058 for 859 unique observed reflections. Compound (I) adopts a conformation in which all non-H atoms except those in the carboxyl group lie essentially within a single plane. Pairs of molecules of opposite conformational chirality form centrosymmetric dimers by mutual hydrogen bonding of carboxyl groups, leaving the ketone carbonyls uninvolved. Infrared and Raman spectral features consistent with the hydrogen-bonding pattern are discussed. Introduction. The factors which produce catemeric hydrogen bonding (carboxyl-to-ketone chains) instead of the far more common carboxyl dimer for crystalline keto carboxylic acids are not understood. They are evidently subtle and thus far no pattern has emerged which allows theoretical prediction of solidstate hydrogen-bonding modes. In our exploration of hydrogen bonding in keto acids (Leiserowitz, 1976; Vanderhoff, Thompson & Lalancette, 1986; Lalancette, Slifer & Thompson, 1989; Lalancette, Vanderhoff & Thompson, 1990, 1991; Lalancette, Thompson & Vanderhoff, 1991), we have examined the title compound (I). This material belongs to the class of ~,or 4-keto acids, the major category of simple keto acid in which yet a third pattern, internal carboxyl-to-ketone hydrogen bonding, has been demonstrated in the solid state (Griffe, Durant & Pieret, 1972; Sheldrick & Trowitzsch, 1983; Abell, Morris & McKee, 1990). The H-bonding behavior of (I) is of particular interest because this compound constitutes a severely stripped-down model for 4-keto acids, in which no cyclic or unsaturated structures interpose between the acid and ketone, leaving only normal tetrahedral angles as serious conforma-