Abstract:

Methyl 3-nitrosalicylate (3-MNS) and methyl 5-nitrosalicylate (5-MNS) were synthesized by a nitration reaction between methyl salicylate (MS) and iron (III) nitrate under reflux. 3-MNS and 5-MNS were characterized by infrared spectra (IR), proton nuclear magnetic resonance spectra (1H-NMR), electronic absorption spectra (UV-Vis), and photoluminescence (PL). The structures of 3-MNS and 5-MNS were fully optimized at the B3LYP/6-31G** level. The optimized results and nature bond orbital (NBO) analysis results were used to illustrate the red-shift of the O—H and C=O stretching vibrations in the IR, the lower field shift of the phenol hydroxyl proton chemical shift in 1H-NMR, and the bathochromic shift in the UV-Vis spectra of 3-MNS. Potential energy surfaces for the intramolecular proton transfer of ground (GSIPT) and excited (ESIPT) states of MS and 3-MNS were obtained and the Stokes-shift values for MS and 3-MNS were computed to be 8.4 ×103 and 8.9×103 cm -1 using CIS/6-31G**, respectively. All these results demonstrate that differences in intramolecular hydrogen bonding in MS, 3-MNS, and 5-MNS give rise to large differences in their spectral properties.

Key words: Intramolecular hydrogen bond, Nitration, Methyl salicylate, B3LYP/6-31G**