Iodine activation of alcohols: A computational study

Abstract

A DFT study aimed at unravelling the origin of catalytic activity of iodine in reaction with alcohols is presented. Computed free energies for generation of the O---I complexes from the separated reactants are around 3 kcal/mol and solvation increases endoergicity by ca. 1 kcal/mol. Calculations suggest that halogen bond formation between I2 and alcohols does not lead to strong activation of the hydroxyl as a leaving group, although solvent has a notable effect in lowering endoergicity for carbocation formation. Model tertiary alcohols exhibited β-proton abstraction following breaking of the C-O bond, while model secondary and primary alcohols experienced an earlier β-proton abstraction, synchronic with the C-O bond cleavage. Consistent with computed natural bond orbital (NBO) charges, benzylic and propargylic alcohols underwent iodide anion quenching at the para position of phenyl and C-3, respectively.