ROTATIONAL SPECTROSCOPIC STUDIES OF PARA-NITROBENZOIC ACID, PARA-AMINOBENZOIC ACID, PARA-CHLOROBENZOIC ACID, AND PARA-HYDROXYBENZOIC ACID

Al-Jabiri, Mohamad H.

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Title

ROTATIONAL SPECTROSCOPIC STUDIES OF PARA-NITROBENZOIC ACID, PARA-AMINOBENZOIC ACID, PARA-CHLOROBENZOIC ACID, AND PARA-HYDROXYBENZOIC ACID

Author(s)

Al-Jabiri, Mohamad H.

Contributor(s)

• Jäger, Wolfgang
• Insausti, Aran
• Hazrah, Arsh Singh

Issue Date

2023-06-21

Keyword(s)

Structure determination

Abstract

para-substituted benzoic acids, such as para-nitrobenzoic acid, para-aminobenzoic acid, para-chlorobenzoic acid, and para-hydroxybenzoic acid, play important roles in atmospheric chemistry and are used as precursors for a wide range industrial products. Surprisingly, there are no high-resolution spectroscopic studies of these compounds, and we describe here their rotational spectroscopic investigations combined with electronic structure calculations. The rotational spectra were recorded using a 2 to 6 GHz chirped-pulse Fourier transform microwave spectrometer, which is based on the design by Pate et al.¹ Experimentally, all four substituted benzoic acids were found to exist in the cis-configuration, the global minimum energy configuration, of the carboxylic acid group. In all instances, except para-aminobenzoic acid, the global minimum structure is planar. Nudged elastic band calculations² for the wagging motion of the amino group in para-aminobenzoic acid suggest that it is a barrierless large amplitude motion and indeed, no tunnelling splittings were observed in the spectra. For para-chlorobenzoic acid, the nuclear quadrupole hyperfine structures of the ³⁵Cl and ³⁷Cl isotopologues were measured and analyzed. In the case of para-hydroxybenzoic acid two conformers were experimentally and theoretically identified. We noticed in the theoretical structures of the trans-conformers that the carboxylic acid group is pushed slightly out of plane, depending on the nature of the para-substituent. We were able to correlate the out-of-plane angle with the corresponding Hammett constant³ via the molecular electrostatic potential

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122353

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