RELATIVE NUCLEOPHILICITY - THE ROLE OF SOLVATION AND THERMODYNAMICS

The relative reactivity of a series of nucleophiles that includes alkenes, sulfides, sulfoxides, amines, and phosphines toward peroxyformic acid has been examined at an ab initio level of theory MP4SDTQ/MP2/6-31G*. Solvation effects and the exo- versus endothermicity of oxygen transfer from a peroxy acid (:NUC + HCO3H --> O-NUC + HCO2H) has a much greater influence upon the relative nucleophilicity than polarizability. The intrinsic reactivity of dimethyl sulfide was found to be nearly identical to that of dimethyl sulfoxide. The classical gas phase barrier for oxidation of trimethylamine to trimethylamine oxide was also only slightly higher (0.4 kcal/mol) than that for oxygen atom transfer to trimethylphosphine. When the transition states were examined by self-consistent reaction field (SCRF) methods the predicted barriers were found to be in good agreement with experiment. Protic solvents are shown to play a major role in determining the relative reactivity of this series of nucleophiles.