The Global Polarity of Alcoholic Solvents and Water - Importance of the Collectively Acting Factors Density, Refractive Index and Hydrogen Bonding Forces

Abstract

The D_HBD quantity represents the hydroxyl group density of alcoholic solvents or water. D_HBD is purely physically defined by the product of molar concentration of the solvent (N) and the factor Σn=n×f which reflects the number n and position (f-factor) of the alcoholic OH groups per molecule. Whether the hydroxyl group is either primary, secondary or tertiary is taken into account by f. Σn is clearly linearly correlated with the physical density or the refractive index of the alcohol derivative. Relationships of solvent-dependent UV/Vis absorption energies as E_T (30) values, ¹²⁹ Xe NMR shifts and kinetic data of 2-chloro-2-methylpropane solvolysis with D_HBD are demonstrated. It can be shown that the E_T (30) solvent parameter reflects the global polarity of the hydrogen bond network rather than specific H-bond acidity. Significant correlations of the log k₁ rate constants of the solvolysis reaction of 2-chloro-2-methylpropane with D_HBD show the physical reasoning of the approach.

Keywords: alcohol; density; polyol; refractive index; solvatochromism.