A study of the intramolecular hydrogen bond in acylphloroglucinols

Acylphloroglucinols are a broad class of compounds derivative from 1,3,5-trihydroxybenzene, widely spread in nature and exhibiting a variety of biological activities, what makes them interesting for potential pharmacological utilisations. They are characterised by the presence of a COR group, whose oxygen atom can form an intramolecular hydrogen bond with either of the two neighbouring OH groups. The characteristics of this H-bond have been investigated on a number of actual and model structures with different R chains, and they appear to be less dependent on the size and structure of R, and more on the features of the phloroglucinol moiety, with rather regular patterns. The removal of the H-bond causes a relevant geometry change minimising the O lone pair repulsion, and the energy increase associated with the H-bond removal follows regular patterns. MP2 and B3LYP/DFT calculations (with 6-31G∗∗ and 6-31+G∗∗ basis sets) yield similar trends.