This work concerns the typical 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 conformational
inversion-topomerization mechanisms. Full geometry optimizations were
performed at B3LYP/6-311++G(d,p) level of theory to explicitly identify
all distinguishable molecular structures, and thus explore potential
energy surfaces (PES) of the complete interconversion routes for two
stereoisomers of 1,3-dimethylcyclohexane and 1,4-dimethylcyclohexane.
Additional quantum calculations were carried out by separately applying
MP2/6-311++G(d,p), G4, and CCSD(T)/6-311++G(d,p) methods to further
refine all PES’ stationary points. With respect to quantum results, the
conformational analysis was conducted to gain insight into the
determination, thermodynamic stabilities, and relative energies of
distinct molecular geometric structures. On base of highly biased
conformational equilibria, the temperature-dependent populations of
stable local minima for four studied dimethylcyclohexanes were obtained
by utilizing Boltzmann distribution within 300-2500 K. Moreover, two
unique interconversion processes for them, including inversion and
topomerization, were fully investigated, and their potential energy
surfaces were illustrated with the rigorous descriptions in two or
three-dimensional schemes for clarify.
Computational Study of Inversion-topomerization Pathways in 1,3-Dimethylcyclohexane and 1,4-Dimethylcyclohexane: Ab Initio Conformational Analysis
