REVISED VIBRATIONAL ASSIGNMENT FOR CYCLOBUTENE
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Date
1989
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Ohio State University
Abstract
Lord and $Rea^{1}$ and Aleksanyan and $Garkusha^{2}$ observed the infrared and Raman spectra of cyclobutene and proposed assignments of its vibrational fundamentals. Baggott, Clase and $Mills^{3}$ contributed a higher resolution, FT-infrared study and reevaluated the assignments. For this molecule of $C_{2v}$ symmetry with 24 fundamentals, they left $v_{20}$ (in-plane ring bend) unassigned and gave provisional assignments for three of the five $a_{2}$ modes based on indirect evidence. Our assignments of the out-of-plane modes for 1-chlorocyclobutene and 1-fluorocyclobutene raised doubts about some of the assignments for the $a_{2}$ modes of cyclobutene and about the previous characterizations of some of the $a_{2}$ and $b_{2}$ modes of this molecule. We have examined the Raman spectrum of liquid cyclobutene at - $100^{\circ} C$. We contirm $v_{10}(a_{2})$ at $1142 cm^{-1}$ and propose $V_{11}(a_{2}$ at $1011 cm^{-1}, v_{12}(a_{2}) 816 cm^{-1}$, and $v_{20}(b_{2}$) at $888 cm^{-1}$. We concur with Baggott, Clase, and Mills on all of the other fundamentals. $v_{12}(a_{2}$) and $v_{24}(b_{2}$) are more appropriately characterized as out-of-plane modes of vinylic CH bonds than as CH2 modes, in accord with the normal coordinate calculations of Sverdlov and $Krainov.^{4}$
Description
$^{1}$R. C. Lord and D. G. Rea. J. Am. Chem. Soc. 79, 2401 (1957). $^{2}$V. T. Aleksanyan and O. G. Garkusha, Izv. Akad. Nauk SSSR Ser. Khim. 2227 (1976). $^{3}$J. E. Baggott, H. J. Clase and I. M. Mills, Spectrochim. Acta 42A 319 (1986). $(b_{1} \leftrightarrow b_{2})$ $^{4}$L. M. Sverdlov and E. P. Krainov. Opt. Spectrosc. (Engl. Transl.) 6. 94 (1962).
Author Institution: Department of Chemistry., Oberlin College.
Author Institution: Department of Chemistry., Oberlin College.