Methanol hydrogen-bond enthalpy

The correlation between Av(OH) and the methanol affinity scale is more successful since 84% of the variance of the hydrogen-bond enthalpy can be explained by Av(OH). However, Equation 4.32 ... 

ASvapjn is equal to ratio between the molar enthalpy of vaporisation and the boiling temperature, which leads to Eq. (18.10). The molar enthalpy and entropy of vaporisation and the boiling temperature of some simple liquids are presented in Table 18.2 Some liquids deviate sharply from the rule. This is often because these liquids have structure and so a greater amount of disorder is introduced when they evaporate. Examples are water and methanol due to hydrogen bonds between the molecules. (Atkins and De Paula, 2006)... 

B3LYP and MP2 calculations of the enthalpies of hydrogen-bonded complexes of methanol with neutral bases and anions Comparison with experimental data ... 

Controversy has arisen over the years as to the exact interpretation of the infrared spectra in terms of the type of dimer formed. Van Thiel, Becker, and Pimentel (29) have shown that a cyclic dimer occurs in the solid state of methanol at low temperatures. Quantitative infrared (18) and NMR (2) measurements in dilute solutions have enabled the enthalpy of dimer formation to be calculated if certain assumptions are made. The high value of the enthalpy—9.2 kcal. per mole in the case of methanol— again suggests that cyclic dimers are formed since this is a rather high value for a single hydrogen bond. 

Solvation of the anions in these solvents, as reflected in A/ft(ion), appears to be entirely different from the cations. While anionic enthalpies of transfer as a function of radius appear to follow the same general trend in the aprotic solvents TMSO2, DMSO and DMF, they follow a different trend in water and methanol. This has been attributed to the stronger solvation of the smaller anions as a result of hydrogen bonding with the solvent. Choux and Benoit report that in the aprotic solvents,... 

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