O-H stretching force constant in associated methanol species and the cooperativity effect

Abstract

The effect of molecular interaction on the O−H stretching force constant of methanol (MeOH) is reported for its associated species. The various electron donors (D) and acceptors (A) considered include organic molecules such as methanol, dimethylether, acetone, acetonitrile, dimethyl formamide, pyridine, and ions such as F^-, Cl^-, Li⁺, and H⁺. The variation in the O−H stretching force constant of MeO−H...D species on interaction with the electron acceptor such as in the species A...O^|Me−H...D is explained on the basis of the cooperativity effect. (CE). The effect is discussed in terms of the relationship CE=(ΔF/F)×100, where ΔF is the reduction is force constant of the hydrogen-bonded OH stretching mode of the associated methanol species MeOH...D when the lone pair electrons on oxygen of the methanol molecule are involved in hydrogen bonding with A, and F is the hydrogen-bonded O−H stretching force constant of the species when the lone pair electrons are free. The cooperativity effect (CE) is found to increase with increasing electron acceptor and electron donor capacities of A and D. The calculated force constants are compared with the experimental results.