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

Abstract

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.

Empirical Hydrogen Bonding Donor (HBD) Parameters of Organic Solvents Using Solvatochromic Probes – A Critical Evaluation

“…Similar correlations of solvent‐dependent infrared frequency shifts with respect to the hydroxyl group density of alcohols are reported by Zhang [7] . The linear correlation of E T (30) as a function of N of the surrounding solvent is physically reasoned due to the energy level of the ground state of B30 is mainly influenced by solvents compared to the excited state [1b,c] . It was also shown that the E T (30) parameter of various alcohols, including monohydric and polyhydric alcohols, correlates significantly with D HBD [1c] .…”

“…The linear correlation of E T (30) as a function of N of the surrounding solvent is physically reasoned due to the energy level of the ground state of B30 is mainly influenced by solvents compared to the excited state [1b,c] . It was also shown that the E T (30) parameter of various alcohols, including monohydric and polyhydric alcohols, correlates significantly with D HBD [1c] . Furthermore, both the solvent dependent 129 Xe NMR shift and the rate constant k 1 of S N 1 solvolysis reaction of 2‐chloro‐2‐methylpropane ( tertiary butyl chloride) partially correlate with D HBD [1b] …”

“…The holistic nature of the physicochemical properties of hydrogen‐bond donating (HBD) solvents and their solutions is determined both by the interactions between the solvent molecules and by the molecules of the dissolved substances [1,2] . In the previous studies, the global polarity of alcoholic solvents was considered using the molar concentration N or the hydroxyl group density, the D HBD quantity, of the solvent as a well‐defined physically determined measurand [1c] . D HBD includes N and the sum of OH‐groups of the certain alcohol with the determined impact factor f p (primary) f s (secondary) and f t (tertiary) of the OH‐group position as proposed by Equation $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr D{_{{\rm HBD}}}=N(f{_{{\rm p}}}{\rm n}{_{{\rm p}}}+f{_{{\rm s}}}{\rm n}{_{{\rm s}}}+f{_{{\rm t}}}{\rm n}{_{{\rm t}}})=\Sigma {\rm n}\ {\rm \rho} /{\rm M}=\Sigma {\rm n}/{\rm V}{_{{\rm m}}}\hfill\cr}}$$$ $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr \Sigma {\rm n}=f{_{{\rm p}}}{\rm n}{_{{\rm p}}}+f{_{{\rm s}}}{\rm n}{_{{\rm s}}}+f{_{{\rm t}}}{\rm n}{_{{\rm t}}}\hfill\cr}}$$$ …”

“…with n p ‐numbers of primary OH‐groups, n s ‐numbers of secondary OH‐groups, and n t ‐numbers of tertiary OH‐groups within the molecule [1c] . ρ is the density and M the molar mass of the solvent.…”

“…V m is the molar volume. Basically, the factor f correlates significantly with the physical density of the solvent [1c] …”