Exploring Noncovalent Interactions of Thiophene-2-Car¬boxylic Acid in Ethanol Via Vibrational Spectroscopy and DFT Calculations

The spectral bands of pure 2-thiophene carboxylic acid (TCA) and its solution in ethanol (EtOH) are investigated over a wide range using vibrational spectroscopy (Raman and FTIR). In the TCA solution with EtOH, the maxima of the C=O, O–H, C–H stretching, and C–H breathing vibration bands show either a redshift or a blueshift. This indicates that H-bonding, van der Waals interactions, and hyper-conjugation interactions are likely in solutions. MEPS, HOMO and LUMO, AIM, NCI, RDG, ELF, and LOL analyses are performed using a quantum chemical computational approach based on density functional theory (DFT). The MEPS map was used to visually show the charge distribution in the complexes and determine charge-dependent characteristics. Frontier molecular orbitals (FMO) have been utilized to explain chemical reactivity of TCA, its molecular stability, as well as electrical and optical properties. According to AIM, NCI, and RDG analysis, TCA and TCA-EtOH complexes mainly have moderate H-bonding.