Molecular structure and O-H•••O hydrogen bond in 1-aryl-1,3-diketone malonates

The molecular structure of four 1,3-diketone malonates 1-4 were studied by analysis of geometric parameters obtained from single crystal X-ray diffraction experiments at 293 K, displaying three sections: aromatic ring (4-substituted phenyl or naphthyl rings), H1O1C1C2C3O3 enol-keto (EK) system and a linear chain with dimethyl malonate. In the malonate moiety which is involved in C6, enolizable fragments are not observed. The two firsts moieties (aromatic ring and enolone system) are almost in a planar conformation. These results are well-supported by OFT B3LYP/6-31++G(d,p) calculations and MO analysis. These compounds are in the enol-keto (EK) tautomer. In comparison with a full pi delocalized enolone (lambda(Q) = 0.5), diketones 1-4 have a EK pi-delocalization in the O-H center dot center dot center dot O moiety because of the lambda(Q) values are between 0.283 and 0.321 angstrom and showing values of O center dot center dot center dot O length between 2.488 and 2.567 angstrom, which describe a resonance assisted hydrogen bonding (RAHB) and may be influenced by the additive effect of the CH2CH2CH(COOCH3)(2) chain. (C) 2012 Elsevier B.V. All rights reserved.