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Title:The equivalence of the methyl groups in puckered 3,3-dimethyl oxetane
Author(s):Lopez, Juan Carlos
Contributor(s):Blanco, Susana; Macario, Alberto
Subject(s):Spectroscopy of Large Amplitude Motions
Abstract:The spectroscopic study of molecules with large amplitude vibrations have led to reconsider the concept of molecular structure. Sometimes identifying definite bond lengths and angles is not enough to reproduce the experimental data so one must have information on the large amplitude molecular vibration potential energy function and dynamics. 3,3-dimethyloxetane (DMO) has non-planar ring equilibrium configuration and a double minimum potential function for ring-puckering with a barrier of 47 cm$^{-1}$.\footnote{ J. A. Duckett, T. L. Smithson, and H. Wieser, \emph{J. Mol. Spectrosc. } \textbf{1978}, \textit{69} , 159
\emph{J. Mol. Struct. } \textbf{1979}, \textit{56}, 157}$^,$\footnote{ J. C. L\'{o}pez, A. G. Lesarri, R. M. Villamañán and J. L. Alonso, \emph{J. Mol. Spectrosc. } \textbf{1990}, \textit{141}, 231} The observation of endocyclic $^{13}$C and $^{18}$O monosubstituted isotopologues\footnote{ R. S\'{a}nchez, S. Blanco, A. Lesarri, J. C. L\'{o}pez and J. L. Alonso, \emph{Phys. Chem. Chem. Phys. } \textbf{2005}, \textit{7}, 1157} allow to conclude that the ring is puckered. However an interesting feature was observed for the $^{13}$C substitutions at the methyl carbon atoms. While two different axial and equatorial $^{13}$C-methyl groups spectra are predicted from a rigid non-planar ring DMO model, only one species was found. The observed rotational transitions appear at a frequency close to the average of the frequencies predicted for each isotopologue. The observed lines have the same intensity as that found for the $^{13}$C$_\alpha$ isotopomer and double that that found for the $^{13}$C$_\beta$ isotopomer.$^c$ This behaviour evidences that the two methyl groups of DMO are equivalent as could be expected for a planar ring. In this work we show how consideration of the potential function and the path for ring puckering motion to calculate the proper kinetic energy terms allow to reproduce the experimental results. \textit{Ab initio} computations at the CCSD/6-311++G(d,p) level, tested on related systems, have been done for this purpose.
Issue Date:2016-06-22
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper/Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2016-08-22

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