14N Nuclear Quadrupole Coupling and Methyl Internal Rotation in N-tert-Butylacetamide As Observed by Microwave Spectroscopy

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• 作者：Raphaela Kannengießer ; Wolfgang Stahl ; Ha Vinh Lam Nguyen ; Isabelle Kleiner
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：June 16, 2016
• 年：2016
• 卷：120
• 期：23
• 页码：3992-3997
• 全文大小：285K
• 年卷期：0
• ISSN：1520-5215

文摘

The rotational spectrum of N-tert-butylacetamide, CH₃(C═O)(NH)C(CH₃)₃, was measured in the frequency range from 2 to 26.5 GHz using a molecular beam Fourier transform microwave spectrometer. Only one conformer with trans configuration and C_s symmetry was observed. Torsional splittings up to 4.3 GHz occurred in the spectrum due to the internal rotation of the acetyl methyl group CH₃(C═O) with a barrier height of approximately 65 cm^–1. Hyperfine structures arise from the quadrupole coupling of the ¹⁴N nucleus appeared for all rotation–torsional transitions. The data set was reproduced with the programs XIAM and BELGI-C₁-hyperfine, an extended version of the BELGI-C₁ code that includes the effect of the ¹⁴N quadrupole coupling, to root-mean-square deviations of 16.9 and 3.0 kHz, respectively. Quantum chemical calculations were performed to complement the experimental results. The BELGI-C₁-hyperfine code was also used to refit the recently published microwave data of N-ethylacetamide to measurement accuracy.