Vibrational spectra, potential functions, and conformations of cycloheptanone

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Abstract
The vibrational spectra of cycloheptanone are presented in detail. Analysis of the spectra shows that cycloheptanone is a nonrigid pseudorotating molecule with a twist‐chair average structure. The pseudorotation energy surface is calculated and indicates that the symmetric twist‐chair conformer and the two adjacent twist chairs are at practically the same energy. The other twist‐chair forms are separated by barriers of different heights. This complicated picture fits the observed pseudorotation spectrum in detail, giving about the correct shape to the observed band below 30 cm−1 and accounting for the curious observed band at about 90 cm−1. The 90 cm−1 band is assigned as a superposition of Δn=7, 9, and 11 transitions. The agreement between calculation and experiment provides support for our dynamical model of pseudorotation in seven‐membered rings.