Electronic properties of two adjacent intramolecular hydrogen bonds and their effects to the molecular charge distribution: Experimental synchrotron microcrystal and DFT computational study

The experimental crystal structure and corresponding theoretical electron density determination of 2-hydroxy-4,4-dimethyl-6-oxo-cyclohex-1-ene carboxy amide is reported with special focus on two adjacent intramolecular hydrogen bonds (O-H center dot center dot center dot O and N-H center dot center dot center dot O). The possible tautomeric forms are studied and their theoretical populations in the gas phase were determined. Additionally, theoretical models which refer to the title compound were optimized and investigated in terms of the combined analysis of ED-topology, energy densities, electron localizability indicator (ELI), delocalization index and source function (SF). This analysis confirmed the O-H center dot center dot center dot O interactions to be resonance assisted and of medium strength, while the N-H center dot center dot center dot O interactions are rather weak. Moreover, in all cases the hydrogen bond strength and amount of resonance in the six-membered rings is related to the type of interaction (OH center dot center dot center dot O and/or N-H center dot center dot center dot O) and to the molecular symmetry. (C) 2012 Elsevier B. V. All rights reserved.