Theoretical Study of the Microhydration of 1-Chloro and 2-Chloro Ethanol as a Clue for Their Relative Propensity Toward Dehalogenation

This work reports a computational analysis of hydrogen bonded clusters of mono-, di-, tri- and tetra hydrates of the chlorohydrins CH₃CHClOH (1ClEtOH) and CH₂ClCH₂OH (2ClEtOH). The goal of the study is to assess the role of the water solvent into the facilitation of the initial step for dehalogenation of these compounds, a process of interest in several contexts. Molecular orbital methods (MP2), density functional methods (B3LYP, M06 and wB97X-D) and composite model chemistries (CBS-QB3, G4) were employed to investigate the structure, electronic distribution and hydrogen-bonded structure of 7 monohydrates, 6 dihydrates, 5 trihydrates and 5 tetrahydrates of both species. Standard reaction enthalpy and standard Gibbs free reaction energy were computed for all aggregates with respect to n independent water molecules and with respect to the dimer, trimer and tetramer of water, respectively, in order to evaluate stability and hydrogen bonding network. The influence of the water chains on the length and vibrational frequencies, especially of the C-Cl and O-H bonds, was evaluated.