Knowledge Bank

Cyclohexene, three of its deuterated derivatives, silacyclohex-2-end, and 5,6-dihydrothiopyran have been synthesized and the far-infrared and Raman spectra have been recorded. A series of band assigned as the ring-bending $(90-180cm-1)$. ring-twisting $(230-300cm-1)$, and combinations $(80-120cm-1)$ were observed for each molecule. Expressions for calculating the kinetic energy expansions for the bending and twisting vibrations of the six-membered rings were developed Molecular mechanics calculations were used to make initial estimates for the barriers to conformational interconversion. A two dimensional analysis for the ring-bending and ring-twisting modes was carried out and the potential energy surface for each molecule was calculated. The twisted (half-chair) conformation was found to be the lowest in energy in each case with a barrier to planarity of approximately $1000cm-1$