Characterization of intramolecular hydrogen bonds and competitive chalcogen–chalcogen interactions on the basis of the topology of the charge density

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Abstract
Density functional calculations, at the B3LYP/6-311 + G(3df,2p) level, have been carried out for the complete series of β-chalcogenvinylaldehydes to investigate whether the topology of the charge density of these systems can provide some useful information on the strength of X–H⋯Y or X⋯H–Y intramolecular hydrogen bonds or on the strength of H–X⋯Y or X⋯Y–H intramolecular chalcogen–chalcogen interactions. We have shown that, in general, there exist good linear correlations between the charge density at the ring critical point and (a) the relative strength of these interactions as measured by appropriate homodesmotic reactions, (b) the X⋯Y chalcogen–chalcogen distance. It must be emphasized, however, that while the latter correlation is systematically fulfilled, the former is only observed when the relative strength of the intramolecular interaction, either a IHB or a chalcogen–chalcogen interaction, varies inversely with the chalcogen–chalcogen distance. Also importantly, the variation of the charge density at the ring critical point correlates both, with the change in the stability of the system and with the change in the chalcogen–chalcogen distance, when the IHB is replaced by the chalcogen–chalcogen interaction, through an internal rotation of the X–H or the Y–H group.