Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, USA.
J Phys Chem A. 2010 Nov 25;114(46):12187-94. doi: 10.1021/jp107679n. Epub 2010 Oct 29.
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 V(3) values for both species have been determined from the ground state rotational spectrum using the BELGI-C(s) 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.
用啁啾脉冲傅里叶变换微波（CP-FTMW）光谱仪测量了间甲基苯甲醛（m-MBA）的基态光谱。m-MBA 上的甲基转子引入了内部旋转势垒，导致扭转能级简并分裂为 A 和 E 态。从头算计算预测 O-顺式和 O-反式构象的扭转势垒都很低，导致在光谱中高达几个千兆赫的双峰分裂。使用 BELGI-C(s)拟合程序，从基态旋转光谱中确定了两种物质的转动常数、变形项和 V(3) 值。O-顺式和 O-反式 m-MBA 构象的扭转势能有显著差异。分析每个构象的分子轨道和共振结构，以了解扭转势垒高度以及 O-反式扭转势能的不规则形状的差异。
