Impact of Molecular Conformation on Barriers to Internal Methyl Rotation: The Rotational Spectrum of m-Methylbenzaldehyde
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- 作者：Amanda J. Shirar ; David S. Wilcox ; Kelly M. Hotopp ; Giana L. Storck ; Isabelle Kleiner ; Brian C. Dian
- 刊名：Journal of Physical Chemistry A
- 出版年：2010
- 出版时间：November 25, 2010
- 年：2010
- 卷：114
- 期：46
- 页码：12187-12194
- 全文大小：243K
- 年卷期：v.114,no.46(November 25, 2010)
- ISSN：1520-5215
文摘
The ground state spectrum of m-methylbenzaldehyde (m-MBA) was measured with a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer. The methyl rotor on m-MBA introduces an internal rotation barrier, which leads to splitting of the torsional energy level degeneracy into A and E states. Ab initio calculations predict a low torsional barrier for both the O-cis and O-trans conformers, resulting in a large doublet splitting up to several gigahertz in the frequency spectrum. The rotational constants, distortion terms, and V3 values for both species have been determined from the ground state rotational spectrum using the BELGI-Cs fitting program. There are significant differences in the torsional potential for the O-cis and O-trans m-MBA conformers. Molecular orbitals and resonance structures for each conformer are analyzed to understand the difference in torsional barrier height as well as the irregular shape of the O-trans torsional potential.