Isotopic fractionation factor of the hydrogen-bonded complex AcO^–⋯(HOAc)_nand kinetic and equilibrium solvent isotope effects on reactions of acetate ion in acetic acid

Abstract

A value of cp 0.58 +_ 0.05 has been obtained for the deuterium fractionation factor of the hydrogenbonded complex AcO-. . . (HOAc), from "H n.m.r. studies of solutions of potassium acetate in AcOH and 97% AcOD-3% AcOH. The result is used to account for the kinetic solvent isotope effect k ~E ~! / k ~~~E 0.66 0.1 0 measured for formation of acetic anhydride from 2,4,6-trinitrophenyl acetate in AcOH and AcOD in the presence of potassium acetate. The equilibrium solvent isotope effect on complex formation between 2,4,6-trinitrophenol and acetate ion in AcOH and 97% AcOD-3% AcOH, KAcOH/KAcOD 0.83 0.1, leads to a value cp ca.

Electrophilic Additions toanti-Sesquinorbornene. Br2in Methanol and the Addition of Acetic Acid

“…The equation expressing the relationship between the rate constant observed in various mixtures with known atom fractions of D and the fractionation factors (φ) for the exchangeable protons responsible for the isotope effect is given in eq 6 where n is the atom fraction of deuterium in the solvent O−L (L = H, D) bonds, and i and j represent the sites undergoing exchange in the transition and reactant sites, respectively. The fractionation factors for the various hydrogens refer to the tightness of their bonding and are significantly less than unity for H's being transferred in the transition state (relating to primary kinetic isotope effects) and also for H's involved in hydrogen bonds where the overall bonding is loose 27a. The latter relate to secondary deuterium isotope effects of solvation and can contribute significantly to the overall DKIE.…”