Abstract:
The known correlations between calorimetric and IR spectroscopic data on hydrogen bonding were reinvestigated for hydrogen bond donors (AH) dissolved in pure bases (B). Ninety-five AH⋯B systems were considered for which the enthalpies of specific interaction due to hydrogen bonding AH⋯B (ΔHsp.int. AH/B, kJ mol-1), the weight centers of A-H stretching bands (ν, cm-1) and their integral absorption coefficients (a, 104cm mmol-1) had been measured. The relationships between ΔHsp.int. AH/B and the parameters of the infrared absorption spectra [weight center shifts Δν and the changes in the square roots of a (Δα1/2)] were analyzed. It was found that the dependence of Δsp.int. AH/B on Δα1/2 consists of two nearly parallel straight lines: the first (-ΔHsp.int. AH/B = 12.0 Δα1/2 + 0.4) corresponds to water and the weak C - H and O - H H-bond donors (chloroethylenes, acetylenes acetonitrile, nitromethane, chloroform, o.o'-di-tert-butylphenol); the second (-ΔHsp.int. AH/B = 12.1 Δα1/2-4.2) corresponds to the stronger N - H and O - H H-bond donors (N-methylaniline, pyrrole, alcohols, phenol, carbon acids). Non-linear dependences of ΔHsp.int. AH/B on Δν were obtained for all C - H, N - H and O - H H-bond donors except water [ΔHsp.int. AH/B = 59.9 Δν/(Δν+ 674)]. Enthalpies of specific interaction for water obey another dependence [-ΔHsp.int. H2O/B/2 = 28.5 Δν/(Δν + 269)]. The sp.int. AH/B values can be estimated by the above correlations with an accuracy of ±3 to ±6 kJmol-1. These relationships obtained for solutions of H-bond donors in pure bases differ from the well known dependences determined for the AH⋯B hydrogen bonding in carbon tetrachloride medium. © 1996 by John Wiley & Sons, Ltd.
