Hydrogen bonding and stereoelectronic effects in the conformational isomerism of trans-2-bromocyclohexanol

The infrared spectra of trans-2-bromocyclohexanol (BC), obtained from non-polar solution and for the neat liquid, have been used to understand the effect of hydrogen bond on the conformational isomerism of this model compound. Intramolecular hydrogen bonding OH⋯Br operates in the diequatorial conformation at low concentrations, leading to its larger population, whilst intermolecular hydrogen bonding is also observed at a more concentrated solution. For the neat liquid, self-association due to intermolecular hydrogen bond is an important effect in BC, and governs the slight preference of the diaxial conformation in this case, as confirmed by theoretical calculations of dimers (monomers of BC self-associated through hydrogen bonding). DFT calculations have also demonstrated the hyperconjugative nature (LPBr → σOH∗) of the intramolecular hydrogen bond in BC.