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

Highlights: ► Molecular structure of two adjacent hydrogen bonds (O–H⋯O, N–H⋯O) was demonstrated. ► The electron localizability indicator (ELI) and delocalization index (DI) were employed. ► The analysis of the source function (SF) was applied. ► The resonance effect is more pronounced for O–H⋯O than for N–H⋯O interactions. -- Abstract: 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⋯O and N–H⋯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⋯O interactions to be resonance assisted and of medium strength, while the N–H⋯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 (O–H⋯O and/or N–H⋯O) and to the molecular symmetry.