Molecular structure and OH⋯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 DFT B3LYP/6-31++G(d,p) calculations and MO analysis. These compounds are in the enol–keto (EK) tautomer. In comparison with a full π delocalized enolone (λQ = 0.5), diketones 1–4 have a EK π-delocalization in the OH⋯O moiety because of the λQ values are between 0.283 and 0.321 Å and showing values of O⋯O length between 2.488 and 2.567 Å, which describe a resonance assisted hydrogen bonding (RAHB) and may be influenced by the additive effect of the CH2CH2CH(COOCH3)2 chain.

► X-Ray and DFT shows three moieties for 1,3-diketone malonates: aromatic, enolone and a linear chain.
► Aromatic and enolone system are conjugated resulting in an strong OH⋯O bonding.
► π-Delocalization parameters (Q and λQ) showed more enol–keto delocalization.
► Hydrogen bonding (RAHB) may be affected by the additive effect of CH2CH2CH(COOCH3)2.