Characterization of solute–solvent interaction at the transition state by thermodynamic and quantum-mechanical approaches. Reactions of imidide ions with ethyl iodide in acetonitrile–methanol

Abstract

Single-ion enthalpies of transfer for transition-state anions of imidide ion plus ethyl iodide reactions have been determined in acetonitrile–methanol mixtures and have been partitioned into component enthalpies, Δ_tH_PHYS^AN→MeOH and Δ_tH_SI^AN→MeOH. Statistical analysis led to the empirical correlation incorporating nucleophiles and transition-state anions between specific interaction enthalpies, Δ_tH_SI^AN→MeOH and the number of methanol molecules participating in the specific interaction with the anion. The molecular mechanistic origin of the specific interaction has been rationalized by introducing the concept of ‘effective atomic charge on the oxygen atom’ which has been derived through semi-emipirical MNDO/PM3 molecular orbital calculations.