Vibrational Spectra and Structure of Small-Ring Compounds. X. Spectroscopic Evidence for Pseudorotation in Cyclopentane

Abstract

The infrared spectrum of cyclopentane has been examined from 33 to 4000 cm⁻¹. A series of pronounced $Q$ branches with a 5‐cm⁻¹ spacing was observed on top of the CH₂ deformation. The $Q$ branch frequencies could be reproduced by assuming that the cyclopentane ring was undergoing pseudorotation. The spectroscopically derived parameter ${\mathrm{mq}}_0^2$ was found to be (11.0 ± 0.2) × 10⁻⁴⁰ g·cm².