Vibrational Spectra and Potential Functions of Cyclohexane and Related Oxanes

Abstract

The vibrational spectra of cyclohexane, s‐trioxane, p‐dioxane, m‐dioxane, and tetrahydropyran and a number of their deuterated derivatives are re‐examined. Particular attention is paid to the low‐frequency modes. A number of low‐frequency difference bands and some hot bands are observed and assigned. Complete normal‐coordinate analyses are carried out for all the molecules. It is concluded that the six ring bending modes contain little contribution from other valence coordinates. A potential function for ring bending is then developed using the vibrational frequencies and the available information on molecular geometries. A onefold term in the torsional part of the potential is found to be necessary. The final potential function gives an excellent fit to the frequencies of the lowest‐frequency modes and to the geometries of the molecules considered. This potential function should be useful in conformational analysis.