In this paper systematic DFT calculations were carried out to study hydrogen bond cooperativity of linear and cyclic clusters consisting of up to 5 molecules of methanol at B3LYP/6-311＋＋G (d,p) level. A definition has been proposed for cooperative factor for clusters of different size. Calculated cooperative factors are far greater for cyclic clusters than for linear ones. For comparison, LFHB model (the lattice-fluid hydrogen-bonding equation of state model) with or without cooperative effects was used to fit the ¹H NMR chemical shift data of (methanol or ethanol＋inert solvent) mixtures. More satisfactory results were obtained by including the cooperative effects in the thermodynamic model. Comparing the calculated cooperative factors with those used in cooperative LFHB, liquid methanol could be considered to exist mostly as linear clusters.

Key words: hydrogen bond cooperativity, density functional theory (DFT), lattice-fluid hydrogen-bonding (LFHB), hydrogen nuclear magnetic resonance (¹H NMR)