Conformational preferences of ethyl propionate molecule: Raman, temperature dependent FTIR spectroscopic study aided by ab initio quantum chemical and Car-Parrinello molecular dynamics simulation studies

Abstract

The conformational preferences of the industrially significant ethyl propionate (EP) molecule have been investigated from the Raman and FTIR spectra, aided by ab initio and Car-Parrinello molecular dynamics (CPMD) simulation studies. The vibrational signatures of various rotameric forms of the EP molecule have been assigned for the first time from the potential energy distributions (PEDs). The critical analyses of the vibrational signatures reveal the coexistences of the Trans-Trans (TT), Trans-Antigauche (TG(-)) [Trans-Gauche (TG(+))], Antigauche-Trans (G(-)T) [Gauche-Trans (G(+)T)], Antigauche-Antigauche (G(-)G(-)) [Gauche-Gauche (G(+)G(+))], and Gauche-Antigauche (G(+)G(-)) [Antigauche-Gauche (G(-)G(+))] forms of the EP molecule at room and at high temperatures. However, at low temperature (ca. 70 °C), the TT and TG(-) forms of the EP molecule is estimated to be preponderant. The Car-Parrinello molecular dynamics simulation studies of the EP molecule estimated at high, room, and low temperatures are also in harmony with our conjecture as suggested from the vibrational analyses. The ab intio molecular dynamics simulations are observed to be a useful tool for the conformational analyses of the molecule.