Resonance raman spectroscopic and density functional theory study of benzoin diethyl phosphate

Raman spectra of benzoin diethyl phosphate (BDP) have been obtained in resonance with two different electronic states using excitation at 252.7 and 354.7 nm in acetonitrile solvent. Extensive overtone and combination bands of the carbonyl C=O stretching (1700 cm-1) and carbonyl attached ring C=C stretching (1597 cm-1) vibrations were observed in the 252.7 nm spectrum. Density functional theory (DFT) calculations were made to determine the structure and the vibrational modes and frequencies for the ground state of BDP. Vibrational bands observed in the resonance Raman spectra were assigned using the DFT results, and it was found that modes showing a strong enhancement in the Raman spectra were mainly related to the benzoinyl moiety, especially the acetophenone subgroup. This was corroborated by the DFT calculated molecular orbitals. Our results indicate that 354.7 and 252.7 nm excitation corresponds to electronic transitions from the ground state to the nπ* and ππ* states, respectively. We briefly discuss the implications of these results in understanding the mechanism of the BDP deprotection reaction.