The conformational pathways of simple six-membered rings

CARLOS A. STORTZ

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY

JOHN WILEY & SONS LTD

Lugar: Hoboken, NJ; Año: 2010 vol. 23 p. 1173 - 1186

0894-3230

The conformational equilibria of cyclohexane (as well as its fluoro-, chloro-, methyl-, hydroxy-, and t-butyl derivatives), cyclohexanone, piperidine, tetrahydropyran (and its 2-hydroxy derivative) were studied by ab initio and DFT procedures. The transition states were calculated at HF/6-31G, B3LYP/6-31RG*, and B3LYP/6-311RG** levels, whereas the intrinsic reaction coordinates (IRCs) were evaluated at the B3LYP/6-31RG* level. The degree of puckering and energy data was nearly not basis set-dependent (using B3LYP) in most of the cases. However, DFTmethods gave better agreement with experimental data than HF methods, as expected from electron correlation inclusion. Fluorocyclohexane and 2-hydroxytetrahydropyran showed the largest basis set-energy dependence. It was found that the conversion from chair to skew is direct in some cases, whereas in others it goes through the pseudorotational (skew/boat) pathway. The case of t-butylcyclohexane, with a skew form as stable as one of the chairs, is especially interesting. In this compound, as well as in cyclohexanone and 2-hydroxytetrahydropyran, large deviations from the known pseudorotation/inversion scheme are observedt-butyl derivatives), cyclohexanone, piperidine, tetrahydropyran (and its 2-hydroxy derivative) were studied by ab initio and DFT procedures. The transition states were calculated at HF/6-31G, B3LYP/6-31RG*, and B3LYP/6-311RG** levels, whereas the intrinsic reaction coordinates (IRCs) were evaluated at the B3LYP/6-31RG* level. The degree of puckering and energy data was nearly not basis set-dependent (using B3LYP) in most of the cases. However, DFTmethods gave better agreement with experimental data than HF methods, as expected from electron correlation inclusion. Fluorocyclohexane and 2-hydroxytetrahydropyran showed the largest basis set-energy dependence. It was found that the conversion from chair to skew is direct in some cases, whereas in others it goes through the pseudorotational (skew/boat) pathway. The case of t-butylcyclohexane, with a skew form as stable as one of the chairs, is especially interesting. In this compound, as well as in cyclohexanone and 2-hydroxytetrahydropyran, large deviations from the known pseudorotation/inversion scheme are observed