DRASTIC INFLUENCE OF BORON ATOM ON THE ACIDITY OF ALCOHOL IN BOTH GAS PHASE AND SOLUTION PHASE, A DFT STUDY.

In this study, the drastic influence of the boron atom on the acidity of alcohol has been con-sidered. The calculated ΔH_acid (320.9--338.1 kcal/mol) and pK_a range of boron containing alcohol (--0.1--9.4) indicate that the boronation of alcohol leads to considerable enhancement of its acidity. For instance, we have obtained the ΔH_acid values 338.1, 335.2 kcal/mol and the pK_a values 4.12, 2.81 for BH₂CH₂OH, BF₂CH₂OH alcohols, respectively, which are much smaller than that of CH₃OH (with ΔH_acid = 374.9kcal/mol and pK_a = 15). The increase in the acidity of boronated alcohol can be related to the stabilization of alkoxy ion due to overlap of unoc-cupied orbital of boron atom with the electron pairs of negative oxygen. All gas phase computations were performed at MP2/6-311++G(d,p)//(B3LYP/6-31+G(d)) level. The primary results indicate that the presence of boron atom in an alcohol might make it as acidic as nitric acid. The geometry optimization of studied structures was performed with DFT computation and optimized structures were used to carry out natural bond orbital (NBO) analysis. NBO analysis revealed that the increase in the acidity of boron-containing alcohols is due to the charge transfer from the negative oxygen (in deprotonated structure) to the empty orbital of --BH₂ and --BF₂. Quantum theory of atoms in molecules (QTAIM) was also applied to determine the nature of bonds formed in the deprotonated structure. [ABSTRACT FROM AUTHOR]