Mohamad H. Al-Jabiri , Arsh S. Hazrah , Aran Insausti , Yunjie Xu , Wolfgang Jӓger
{"title":"Rotational spectroscopic studies of para-nitrobenzoic acid, para-aminobenzoic acid, para-chlorobenzoic acid, and para-hydroxybenzoic acid","authors":"Mohamad H. Al-Jabiri , Arsh S. Hazrah , Aran Insausti , Yunjie Xu , Wolfgang Jӓger","doi":"10.1016/j.jms.2023.111790","DOIUrl":null,"url":null,"abstract":"<div><p>The rotational spectra of four substituted benzoic acids, i.e., <em>para</em>-aminobenzoic acid, <em>para</em>-nitrobenzoic acid, <em>para</em>-chlorobenzoic acid, and <em>para</em>-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 <em>cis</em>-arrangement. In the case of <em>para</em>-hydroxybenzoic acid, spectra of two conformers were observed which differ in the orientation of the <em>para</em>-OH group. Quantum chemical calculations at the B3LYP-D3BJ/def2-TZVP and B2PLYP-D3BJ/cc-pCVTZ levels show that the <em>trans</em>-conformers are about 23 kJ mol<sup>−1</sup> higher in energy than the global minimum <em>cis</em>-conformers. In general, the calculated rotational constants are in good agreement with the experimental derived ones. Agreement between calculated and experimental <sup>14</sup>N and <sup>35/37</sup>Cl nuclear quadrupole coupling constants is somewhat worse and necessitated the use of the B2PLYP functional in the case of <em>para</em>-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 <em>trans</em>-conformers.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":null,"pages":null},"PeriodicalIF":1.4000,"publicationDate":"2023-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"1","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Molecular Spectroscopy","FirstCategoryId":"101","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0022285223000553","RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"PHYSICS, ATOMIC, MOLECULAR & CHEMICAL","Score":null,"Total":0}
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.
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.