Conformers of Cyclic Methanol Cluster (CH₃OH)₄

Abstract

We investigate optimized structures of a cyclic methanol cluster (CH₃OH)₄ by starting different-sized planar symmetric structures, where all the H atoms of the OH groups direct to the next O atom, and all the COH parts are in-plane. At the HF/STO-3G level, initial O-O distances at 2.7 Å and more lead to the most stable structure, whereas those less than 2.7 Å result in two other stable conformers. The border distance indicates the efficient range of hydrogen bonding forces of the OH groups. HF/6-31G (d) results in a planar structure with negative frequencies, whereas B3LYP/6-31G (d) gives a conformer whose methyl groups face the same direction. These structures result from the balance between the stabilization due to the orbital broadening of unshared electron pairs of O and the repulsive force of the methyl groups, reflecting the tendency for transformation among the conformers. To calculate force constants with the calcall option is effective in obtaining the most stable structure regardless of the initial O-O distance.