Conformational pathways of simple six-membered rings

• Autores: Stortz, Carlos Arturo
• Año de publicación: 2010
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Conformational Analysis; Cyclohexane; Density Functional Calculations; Six-Membered Rings; Transition States
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

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/6-31+G*, and B3LYP/6-311+G* levels, whereas the intrinsic reaction coordinates (IRCs) were evaluated at the B3LYP/6-31+G* level. The degree of puckering and energy data was nearly not basis set-dependent (using B3LYP) in most of the cases. However, DFT methods 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.
Fil: Stortz, Carlos Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; Argentina