Ring strain and hydrogen bond acidity

The ability of strained hydrocarbons to act as hydrogen bond donors has been explored with a hybrid HF-DFT ab initio method, B3LYP, and the 6-31G* and 6-311++G** basis sets. The results have been correlated with geometrical parameters (number of three- and four-membered rings, bond angles, and hydrogen bond distances), electronic characteristics of the complexes and isolated monomers (electron density at the bond critical points, atomic charges, and dipolar magnetization), and other properties (gas-phase acidities and atomic volume and energy). The results have been rationalized on the basis of a simple strain model and compared to nonsaturated hydrocarbons with donor C-H groups.