Structure, conformations, vibrations and quantum chemical investigations of 2–(1H–indol–3–yl)–2–oxoacetic acid

Abstract

Detailed structural, electronic and vibrational properties of 2–(1H–indol–3–yl)–2–oxoacetic acid or 3–indoleglyoxylic acid (3IGA) have been analysed with the help of FT–IR, FT–Raman and FT–NMR spectra along with the support of the theoretical investigations by B3LYP method. The conformational investigations on 3IGA showed that s–trans–I conformer with intramolecular hydrogen bonding is the most stable one. The range of total electron density of the molecule 3IGA is found to be +7.383e × 10–2 to – 7.383e × 10–2 and the electrostatic potential of 3AI is in the range +1.167e × 10–2 to –1.167e × 10–2. The energy gap ΔE = (ELUMO–EHOMO) of 3IGA is 4.1008 eV. The n(O20) → π*(C18–O19) is strongly stabilized by 54.01 kcal mol–1. Significant lowering and broadening of the stretching O–H band indicates the presence of intramolecular O–H···O hydrogen bonding. The chemical shift of C2 (138.00 ppm) and C3 (112.57 ppm) is much higher in 3IGA when compared to indole 125.07 and 100.84 ppm, respectively. The atoms C3, C4, C7, C6 and N1 are favourable for the nucleophilic attack while C16, C18, C2, C9, C5 and C8 are favourable for electrophilic attack.