Conformers of 1,4-dioxane and their hydrogen bond complexation with methanol

Abstract

FTIR spectral studies has been carried out on the 1,4-dioxane (Dx), methanol (MeOH) and their binary solutions at different molar ratios. Using the experimental results in combination with the quantum chemical calculations, the conformers of Dx and their H – bonded complexes with MeOH have been analyzed. Dx exists in three different conformers, the chair, 2,5 boat and 1,4 boat with the population of 58.8 %, 21.2 % and 20.0 %, respectively, whose distinct methylene and C−O−C stretching bands have been assigned. The O−H and C−O stretching bands of MeOH existing as monomer, dimer, trimer and tetramer in liquid state have been assigned. The hydrogen bonded Dx – MeOH multimer complexes that present in each one of the binary solutions have been identified. The natural bond orbital analysis shows that the lone pair (LP)2 of oxygen involves in stronger delocalization homomolecular O−H⋯O interactions than LP(1) in all the pure MeOH multimers. This trend is retained in MeOH multimer – Dx complexes. In all the classical heteromolecular H – bond interactions also, LP(2) participates in stronger stabilization interaction while mixed trend is observed in the non-classical H – bond interactions. The energy decomposition analysis based on force field (EDA-FF) appears to fail to describe the stability of MeOH multimers as well as the Dx-MeOH hydrogen bonded complexes. But, Shubin Liu’s energy decomposition analysis (EDA-SBL) gives a correct description on the stability.