On the Existence of Conformers of Cyclobutyl Monohalides. III. Assignments of the Fundamentals of Bromocyclobutane and Chlorocyclobutane

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Abstract
The infrared spectra of the liquid and the vapor and the Raman spectra of the liquid of bromocyclobutane and chlorocyclobutane are reported. The 30 fundamentals of each halide are assigned and an approximate picture of the motions of those atoms, which are mainly involved in the fundamental modes, is given. There is one‐to‐one correlation between the fundamentals of bromocyclobutane with the fundamentals of chlorocyclobutane. This signifies that the amount of interaction between different modes is generally of the same order of magnitude in both halides, in contrast to the corresponding cyclopropyl halides. There is little symmetry correlation between the fundamentals of the cyclobutyl halides and cyclobutane; the out‐of‐plane ring‐bending (ring‐puckering) mode is an exception. In the Appendix, computer calculations of A‐ and C‐type band envelopes are presented and compared with observations; the computations include vibration—rotation interaction.