Hydrogen bonding in strained cyclic vicinal diols: The birth of the hydrogen bond

We have examined a series of cyclic (n, n + 1)-diols in which the hydroxy groups are constrained to be more closely syn-periplanar than in diols with free rotation around the C–C bond, for their ability to form an intramolecular hydrogen bond. Small IR red-shifts, of the order of ∼50–100 cm−1, are not necessarily associated with intramolecular hydrogen bond formation but may be generated by σ ⇒ σ∗ hyperconjugative effects. Moreover, there exists in (n, n + 1)-diols a clear donor–acceptor cutoff distance below which a (3, −1) bond critical point for an intramolecular hydrogen bond is observed, and above which it is not.