Theoretical investigation using DFT Calculations, Vibrational Assignments, Infrared Spectrum and Normal Coordinate Analysis of (2-Chloro-4-fluorophenyl) boronic Acid

The geometry, vibrational frequencies, and thermodynamic parameters of 2-chloro-4-fluorophenylboronic acid (CFPB; C?H?BClFO?) have been computed using the Gaussian 09 software package. Initially, four distinct rotamers were proposed for this compound, arising from the internal rotation of the hydroxyl groups around the C–B bond. A conformational stability analysis for an isolated molecule was performed using the B3LYP functional with the standard 6-311++G(d,p) basis set. Our calculations identified the CT structure where one OH group is cis to both the phenyl Cl and F atoms, and the other OH is trans to the phenyl Cl atom—as the most stable conformation. The energy differences between the CT conformer and the others (2-4) range from 1700 to 2000 cm?¹ (4.88 – 5.72 kcal/mol). This stability is attributed to stabilizing O?...H14 and Cl?....H15 intramolecular hydrogen bonds. A complete vibrational assignment of the observed IR bands is provided, supported by calculated wavenumbers, IR intensities, and a normal coordinate analysis. The computed wavenumbers and IR intensities for the CT form agree well with the experimental data.

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