Large amplitude torsions in nitrotoluene isomers studied by rotational spectroscopy and quantum chemistry calculations.,ChemPhysChem

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Large amplitude torsions in nitrotoluene isomers studied by rotational spectroscopy and quantum chemistry calculations.
ChemPhysChem ( IF 2.3 ) Pub Date : 2020-08-28 , DOI: 10.1002/cphc.202000591
Anthony Roucou _{1,

2} , Manuel Goubet ₃ , Isabelle Kleiner ₄ , Sabath Bteich ₁ , Arnaud Cuisset ₁

Affiliation

Rotational spectra of ortho‐nitrotoluene (2‐NT) and para‐nitrotoluene (4‐NT) have been recorded at low and room temperatures using a supersonic jet Fourier Transform microwave (MW) spectrometer and a millimeter‐wave frequency multiplier chain, respectively. Supported by quantum chemistry calculations, the spectral analysis of pure rotation lines in the vibrational ground state has allowed to characterise the rotational energy, the hyperfine structure due to the ¹⁴N nucleus and the internal rotation splittings arising from the methyl group. For 2‐NT, an anisotropic internal rotation of coupled −CH₃ and −NO₂ torsional motions was identified by quantum chemistry calculations and discussed from the results of the MW analysis. The study of the internal rotation splittings in the spectra of three NT isomers allowed to characterise the internal rotation potentials of the methyl group and to compare them with other mono‐substituted toluene derivatives in order to study the isomeric influence on the internal rotation barrier.

中文翻译：

通过旋转光谱法和量子化学计算研究了硝基甲苯异构体的大振幅扭转。

分别在低温和室温下使用超音速喷射傅立叶变换微波（MW）光谱仪和毫米波倍频链记录了邻硝基甲苯（2-NT）和对硝基甲苯（4-NT）的旋转光谱。在量子化学计算的支持下，振动基态的纯旋转线的光谱分析可以表征旋转能，由¹⁴ N核形成的超精细结构以及由甲基引起的内部旋转分裂。对于2-NT，耦合的-CH ₃和-NO ₂的各向异性内旋转扭转运动是通过量子化学计算确定的，并从MW分析的结果中进行了讨论。对三种NT异构体光谱的内部旋转分裂的研究可以表征甲基的内部旋转电位，并将其与其他单取代的甲苯衍生物进行比较，以研究异构体对内部旋转壁垒的影响。

更新日期：2020-08-28

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