Rotational spectroscopic studies of para-nitrobenzoic acid, para-aminobenzoic acid, para-chlorobenzoic acid, and para-hydroxybenzoic acid

IF 1.4 4区 物理与天体物理 Q4 PHYSICS, ATOMIC, MOLECULAR & CHEMICAL
Mohamad H. Al-Jabiri , Arsh S. Hazrah , Aran Insausti , Yunjie Xu , Wolfgang Jӓger
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引用次数: 1

Abstract

The rotational spectra of four substituted benzoic acids, i.e., para-aminobenzoic acid, para-nitrobenzoic acid, para-chlorobenzoic acid, and para-hydroxybenzoic acid were recorded with a chirp-pulse Fourier transform microwave spectrometer and analysed in terms of rotational constants and, where applicable, nuclear quadrupole coupling constants and tunnelling motions. In all instances, the experimentally identified conformer contains a carboxylic acid group in the cis-arrangement. In the case of para-hydroxybenzoic acid, spectra of two conformers were observed which differ in the orientation of the para-OH group. Quantum chemical calculations at the B3LYP-D3BJ/def2-TZVP and B2PLYP-D3BJ/cc-pCVTZ levels show that the trans-conformers are about 23 kJ mol−1 higher in energy than the global minimum cis-conformers. In general, the calculated rotational constants are in good agreement with the experimental derived ones. Agreement between calculated and experimental 14N and 35/37Cl nuclear quadrupole coupling constants is somewhat worse and necessitated the use of the B2PLYP functional in the case of para-nitrobenzoic acid to reduce the discrepancy. Conversion barriers between possible conformers were calculated to explain the absence of tunnelling splittings and/or higher energy conformers in the experimental spectra. An analysis of the electron density distribution was used to rationalize the calculated out-of-plane excursions of the carboxylic acid group in the trans-conformers.

Abstract Image

对硝基苯甲酸、对氨基苯甲酸、对氯苯甲酸和对羟基苯甲酸的旋转光谱研究
用啁啾脉冲傅立叶变换微波光谱仪记录了对氨基苯甲酸、对硝基苯甲酸、对氯苯甲酸和对羟基苯甲酸四种取代苯甲酸的旋转光谱,并根据旋转常数和核四极耦合常数和隧穿运动进行了分析。在所有情况下,实验鉴定的构象含有顺式排列的羧酸基团。在对羟基苯甲酸的情况下,观察到两种构象的光谱,它们在对羟基的取向上不同。在B3LYP-D3BJ/def2-TZVP和B2PLYP-D3BJ/cc-pCVTZ能级上的量子化学计算表明,反式构象的能量比全局最小顺式构象高约23 kJ mol−1。总的来说,计算的旋转常数与实验推导的旋转常数符合得很好。14N和35/37Cl核四极耦合常数的计算值与实验值之间的一致性较差,需要在对硝基苯甲酸的情况下使用B2PLYP功能来减小差异。计算了可能构象之间的转换势垒,以解释实验光谱中隧道分裂和/或高能量构象的缺失。通过对电子密度分布的分析,对反式构象中羧酸基的面外偏移进行了合理化计算。
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来源期刊
CiteScore
2.70
自引率
21.40%
发文量
94
审稿时长
29 days
期刊介绍: The Journal of Molecular Spectroscopy presents experimental and theoretical articles on all subjects relevant to molecular spectroscopy and its modern applications. An international medium for the publication of some of the most significant research in the field, the Journal of Molecular Spectroscopy is an invaluable resource for astrophysicists, chemists, physicists, engineers, and others involved in molecular spectroscopy research and practice.
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