Hydrogen bonding in pure base media. Correlations between calorimetric and infrared spectroscopic data

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 (ΔHAH/Bsp.int., kJ mol−1), the weight centers of A-H stretching bands (v, cm−1) and their integral absorption coefficients (α, 104 cm mmol−1) had been measured. The relationships between ΔHAH/Bsp.int. and the parameters of the infrared absorption spectra [weight center shifts Δv and the changes in the square roots of α (Δα1/2)] were analyzed. It was found that the dependence of ΔHAH/Bsp.int. on Δα1/2 consists of two nearly parallel straight lines: the first (−ΔHAH/Bsp.int. = 12·0 Δα1/2 + 0·4) corresponds to water and the weak C(SINGLE BOND)H and O(SINGLE BOND)H H-bond donors (chloroethylenes, acetylenes acetonitrile, nitromethane, chloroform, o, o′-di-tert-butylphenol); the second (−ΔHAH/Bsp.int. = 12·1 Δα1/2 −4·2) corresponds to the stronger N(SINGLE BOND)H and O(SINGLE BOND)H H-bond donors (N-methylaniline, pyrrole, alcohols, phenol, carbon acids). Non-linear dependences of ΔHAH/Bsp.int. on Δv were obtained for all C(SINGLE BOND)H, N(SINGLE BOND)H and O(SINGLE BOND)H H-bond donors except water [−ΔHAH/Bsp.int. = 59·9 Δv/(Δv + 674)]. Enthalpies of specific interaction for water obey another dependence [−ΔHsp.int./2 = 28·5 Δv/(Δv + 269)]. The ΔHAH/Bsp.int. values can be estimated by the above correlations with an accuracy of ±3 to ±6 kJ mol−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.