A combined experimental and theoretical investigation of 2-Thienylboronic acid: Conformational search, molecular structure, NBO, NLO and FT-IR, FT-Raman, NMR and UV spectral analysis

• Monomeric conformations of 2-Thienylboronic acid were investigated.
• The compound was characterized by FT-IR, FT-Raman, NMR and UV spectroscopy.
• The vibrational frequencies, chemical shifts and electronic absorption wavelengths were calculated by DFT method.

The solid state Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectra of 2-Thienylboronic acid (2TBA), were recorded in the range of 4000–400 cm−1 and 4000–100 cm−1, respectively. DFT/B3LYP theory was used for the optimization of the ground state geometry and simulation of the infrared and Raman spectra of the title molecule. To determine lowest-energy molecular conformation of the studied molecule, the selected torsion angles were varied in steps of 10° and complete 3D molecular energy profile was calculated. Among the four possible conformers (Trans–Trans, Cis–Cis, Trans–Cis and Cis–Trans), the most stable conformer of 2TBA is the Trans–Cis form. The vibrational wavenumbers and their assignments were carried out theoretically using the Gaussian09 set of quantum chemistry codes and the normal modes were calculated using MOLVIB program. Experimental FT-IR and FT-Raman spectra of the title compound were compared with the spectral data obtained by DFT/B3LYP method. Dipole moment, polarizability, first static hyperpolarizability and molecular electrostatic potential surface (MEPs) map have been calculated to get a better perception of the properties of the title molecule. Natural bond orbital (NBO) analysis was performed to study the stability of the molecule arising from charge delocalization. UV–Vis spectrum of the title molecule was also recorded (500–200 nm) in methanol and electronic properties such as frontier orbitals and energy gap were calculated by TD-DFT approach. The 1H nuclear magnetic resonance (NMR) chemical shifts of the studied molecule were recorded in DMSO-d6 and calculated by Gauge-Including Atomic Orbital (GIAO) method.

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