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

The DHBD quantity represents the hydroxyl group density of alcoholic solvents or water. DHBD 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 ET(30) values, 129Xe NMR shifts and kinetic data of 2‐chloro‐2‐methylpropane solvolysis with DHBD are demonstrated. It can be shown that the ET(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 DHBD show the physical reasoning of the approach. The density of the hydroxyl groups and the molar concentration primarily determine the global polarity of the alcohols and water. To identify this effect, the polar dissolved Reichardt dye (ET(30) value), the nonpolar xenon atom (129 Xe chemical shift) and the solvolysis of the weakly dipolar 2‐chloro‐2‐methylpropane (lgk1 of solvolysis) are introduced, discussed and compared as suitable probes.