Computational study of inversion-topomerization pathways in 1,3-dimethylcyclohexane and 1,4-dimethylcyclohexane: Ab initio conformational analysis

摘要

This work concerns the special conformational behaviors for di-substituted cyclohexanes that inherently depend on spatial orientations of side chains in flexible cyclic ring. The 1,3-dimethylcyclohexane and 1,4-dimethylcyclohexane in both cis- and trans-configurations were focused here to unravel their inversion-topomerization mechanisms. Full geometry optimizations were separately performed at B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) levels to explicitly identify all distinguishable molecular structures, and thereby the complete interconversion routes were carefully explored. Additional quantum calculations were carried out by G4 and CCSD(T)/6-311++G(d,p) methods to acquire high-level single point energies. With respect to quantum results, conformational analysis was conducted to study determinations, thermodynamic stabilities, and relative energies of distinct conformers. Temperature-dependent populations of local minima for each dimethylcyclohexane were computed by Boltzmann distribution within 300-2500 K. Moreover, their unique inversion and topomerization processes were fully investigated, and potential energy surfaces were illustrated with the rigorous descriptions in two or three-dimensional schemes for clarify.