Theoretical study on coordination of methanol clusters to 3-methyl-4-pyrimidone

Abstract

Density functional theory (DFT), MP2, and couple cluster ab initio methods were employed to investigate the microsolvation of 3-methyl-4-pyrimidone (3M4P) surrounded by methanol (MeOH) molecules. Structures are analyzed based on hydrogen bonds with a focus on relative energies, interaction energies, hydrogen bond cooperativity, hydrogen bonding geometries, and redshifts in the frequencies of O-H and C=O stretching modes. Our results show that there is no preferential orientation of MeOH attacks on the carbonyle site of 3M4P; both trans and cis 3M4P-MeOH complexes have same chance to be observed. cis 3M4P-MeOH and 3M4P-MeOH complex in which MeOH is located on N lie 0.56 and 3.11 kJ/mol at CCSD(T)/6-31+G(d,p) (0.63 and 1.67 kJ/mol at MP2/6-311++G(d,p)) above trans 3M4P-MeOH. MeOH dimers form more stable 3M4P-(MeOH)(2) complexes compare to 3M4P-(MeOH)(2) complexes in which individual MeOH molecules bind to carbonyl and N. Relative energies of 3M4P-(MeOH)(3) computed using various DFT methods point out the complex formed by linear MeOH trimer along methyl group of 3M4P (cis 3M4P-(MeOH)(3)) as lowest. Carbonyl group is predicted as preferential site for hydrogen bond interaction. Besides O-H center dot center dot center dot O and O-H center dot center dot center dot N hydrogen bonds, 3M4P-(MeOH)(2) and 3M4P-(MeOH)(3) complexes are also stabilized by H-O center dot center dot center dot H-C weak interactions.