Structural Characterization and Photochemistry of 2-Chloro-6-Fluorobenzoic Acid Isolated in a Xenon Matrix

Year 2017, Volume: 18 Issue: 2, 315 - 322, 30.06.2017

Nihal Kuş

https://doi.org/10.18038/aubtda.289194

Cited By: 1

Abstract

2-Chloro-6-fluorobenzoic acid (ClFBA) was studied by low temperature solid
state FTIR spectroscopy in a Xe matrix and complemented by DFT(B3LYP)/6-311++G(d,p)
calculations. The ClFBA molecule exists in three different conformers,
according to the theoretical calculations. The second and third conformers (II, III) are higher in energy than the most stable conformer (I) by ca. 17 kJ mol^-1, and bear a trans carboxylic acid moiety, while form I has this group in the cis
conformation. According to the energy data predicted theoretically only the conformer
I was expected to be present in the cryogenic
xenon matrix, a result that was confirmed experimentally. Attempts for in situ generation and detection of forms
II and III by near-IR (2nOH; 6867 cm^-1) excitation of conformer I indicated that in solid xenon, once produced, these conformers
promptly relax by tunneling to the most stable conformer. Laser UV (l = 235 nm) excitation of matrix-isolated ClFBA led to prompt decarboxylation
of the compound, with production of CO₂ and 1-chloro-3-fluorobenzene
(ClFB), whose vibrational signatures could be doubtlessly identified in the
spectra of the photolysed matrix. 

Keywords

2-Chloro-6-fluorobenzoic acid, Matrix isolation spectra, DFT(B3LYP) calculations, FTIR spectroscopy, 1-Chloro-3-fluorobenzene, UV-induced photolysis

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