Abstract
The conformational stability, vibrational frequencies, and thermodynamic parameters of 2-fluoro-4-pyridineboronic acid (FPB, C5H5BFNO2) are theoretically predicted using DFT-B3LYP with 6-31G(d), 6-31+G(d), and 6-311++G(d,p) basis sets employing the Gaussian 09 software. According to the internal rotation of two hydroxyl groups around the C-B bond, four conformers are suggested:TC, CT, TT, andCC (C/Trefer to thecis/transpositions of O-10-H(15)and O-9-H(14)groups towards the C-B bond). The results of calculations favor theTCconformer with a 70% relative population compared with low values of 28%, 1.5%, and 0.06% forCT, TT, andCC, respectively. An additional calculation in the solid state (CASTEP) are performed for a molecule per unit cell (C(1)symmetry) for all conformers using the DFT-PBE method. TheTCconformer is also favored by 2.5 kJ/mol, 2.9 kJ/mol and 16.3 kJ/mol for conformersCT, TTandCC, respectively.TCis the most stable conformer owing to O-9 horizontal ellipsis H-15, O-10 horizontal ellipsis H(12)and F-7 horizontal ellipsis H(11)intramolecular hydrogen bonding. Additionally,C-13 NMR chemical shifts are predicted for theTCconformer by means of B3LYP/6-311++G(d,p) calculations utilizing the GIAO approximation and the PCM solvation model. To precisely assign the observed IR bands vis. the estimated vibrational frequencies, a normal coordinate analysis (NCA) is carried using the calculated force constants. The calculated wavenumbers and IR intensities of theTCform are in good similarity with those experimentally observed. With the aid of the potential energy surface scan (2D and 3D), the OH barrier to internal rotations is estimated using the optimized structural parameters from the B3LYP method with the 6-311++G(d,p) basis set. The results are debated herein and compared with similar available molecules.