N···C═O n → π* Interaction: Gas-Phase Electronic and Vibrational Spectroscopy Combined with Quantum Chemistry Calculations

Abstract

Herein, we have used gas-phase electronic and vibrational spectroscopic techniques for the first time to study the Nphenyl) acetate (NMe 2 -Ph-EA). We have measured the electronic spectra of NMe 2 -Ph-EA in the mass channels of its two distinct fragments of m/z = 15 and 192 using a resonant two-photon ionization technique as there was extensive photofragmentation of NMe 2 -Ph-EA. Identical electronic spectra obtained in the mass channels of both fragments confirm the dissociation of NMe 2 -Ph-EA in the ionic state, and hence, the electronic spectrum of the fragment represents that of NMe 2 -Ph-EA only. UV−UV holeburning spectroscopy proved the presence of a single conformer of NMe 2 -Ph-EA in the experiment. Detailed quantum chemistry calculations reveal the existence of a N•••C�O n → π* interaction in all six low-energy conformers of NMe 2 -Ph-EA. A comparison of the IR spectrum of NMe 2 -Ph-EA acquired from the gas-phase experiment with those obtained from theoretical calculations indicates that the experimentally observed conformer has a N•••C�O n → π* interaction. The present finding might be further valuable in drug design and their recognition based on the N•••C�O n → π* interaction.