Inter- and intramolecular O–H···pi hydrogen bonding in the methanol–ethene complex and syn-7-norbornenol, probed by IR, 1H NMR and quantum chemistry

The geometries and energies of syn-7-norbornenol (1) have been investigated with theoretical and experimental methods, while its epimer anti-7-norbornenol (2) has been investigated by theoretical methods only. It was found that 1 is intramolecularly hydrogen bonded and exists almost exclusively in its hydrogen bonded form, the Anti conformer. Compound 2, for which intramolecular hydrogen bonding is impossible, was found to exist as the Gauche conformer. A theoretical investigation of the model complex between methanol and ethene showed that the interaction energy is -3.1±0.1 kcal mol-1 (estimated Hartree–Fock basis set limit plus correlation contribution, not including vibrational zero point energy). Electron correlation is essential in the evaluation of the interaction energy and also for the geometry of the complex. It was found that the potential energy surface around the minimum energy structure is flat, with an almost freely rotating methanol part.