Vibrational Spectra and Structure of Four-Membered Ring Molecules. II. Chlorocyclobutane, Chlorocyclobutane-d1, and Chlorocyclobutane-d4

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Abstract
The infrared spectra of chlorocyclobutane, α‐chlorocyclobutane‐d1, and β,β,β′,β′‐chlorocyclobutane‐d4 in both the gaseous and liquid states have been recorded from 4000 to 250 cm−1. The far‐infrared spectrum of β,β,β′,β′‐chlorocyclobutane‐d4 in the vapor state has been recorded down to 33 cm−1. The Raman spectra of the three isotopic species of chlorocyclobutane have also been recorded of the liquid phases and depolarization values measured. The spectra have been interpreted by considering the molecule to have a plane of symmetry and belonging to point group Cs. Assignment of the frequencies of the fundamental vibrations is based on position, isotopic shift, band type, and depolarization values. The ring‐puckering vibration in chlorocyclobutane was observed in the Raman spectrum at 165 cm−1, and found at 159 cm−1 in the far‐infrared spectrum of the vapor. The data shows that the first upper‐state transition of the ring‐puckering vibration is centered at 142 cm−1. For the tetradeuterated molecule the ring‐puckering vibration was found at 144 cm−1 in the far‐infrared spectrum of the vapor. The nature of the potential energy function governing the ring‐puckering vibration is discussed.