The role of hydrogen bonding in the conformational stability of 2-methoxyresorcinol: Insights from theoretical calculations, SERS spectroscopy, and solvent effect

Resorcinol derivatives exhibit unique structural and electronic features. The presence of two hydroxyl groups, along with other substituents, can greatly impact these molecules’ conformational profile and vibrational characteristics. This work investigates molecular and electronic properties of 2-methoxyresorcinol (2-MR) by combining quantum-chemical and spectroscopic techniques. The molecule of 2-MR can exist in the syn, anti, and anti–syn configurations, depending on the orientation of the hydroxyl groups. The syn and anti–syn forms have been verified from DFT, MP2 and MP4 (SDQ) calculations and from infrared/Raman spectroscopy to be stabilized by intramolecular hydrogen bonding that takes place between the hydrogen atoms of the OH groups and the methoxy moiety's oxygen atom. Such an interaction results in 6–7 kcal/mol more stable states than the corresponding anti-configuration, where only steric forces control the molecule stability. The effect of different solvents on the Raman features has also been accessed. Unlike other solutions, aqueous 2-MR facilitated a split in the OH stretching peak, which can be attributed to the pronounced solute–solvent intermolecular forces through the OH groups. Surface-enhanced Raman scattering (SERS) spectroscopic analysis of trace 2-MR utilizing as-synthesized silver nanoparticles shows a remarkable boost in the Raman signal intensities of several vibrational modes. The SERS detection exhibits a wide dynamic range and a detection limit of 1 × 10⁻⁸ M.