Influence of Temperature on the Rotameric Forms of the Propyl Acetate Molecule: Raman and FTIR Spectroscopic Studies Aided by ab Initio and Car-Parrinello Molecular Dynamics Simulations.

Abstract

The conformational preferences of the industrially and biologically significant propyl acetate (PA) molecule have been investigated by Raman and FTIR spectra, aided by ab initio and Car-Parrinello molecular dynamics (CPMD) simulation studies. The PA molecule can exist in various rotameric forms at room temperature, trans-trans [TT], trans-gauche [(TG(+))/(TG(-))], gauche-trans [(G(+)T)/(G(-)T)], and gauche-gauche [(G(+)G(-))/(G(-)G(+))], depending upon the rotation about the O3-C4 and C4-C5 bonds of the molecule. The vibrational signatures of different rotameric forms of the PA molecule have been assigned for the first time. Raman and temperature-dependent FTIR spectra of the PA molecule envisage the coexistence of the TT, TG(+)/TG(-), G(+)T/G(-)T, and G(+)G(-)/G(-)G(+) forms of the PA molecule at room temperature. However, at low (ca. -95 °C) and high temperatures (ca. 65 °C), the TG(+) form of the PA molecule is estimated to be preponderant. These results are substantiated by the CPMD simulations, together with the estimation of fwhm values of the vibrational signatures of the PA molecule recorded at high-, room-, and low-temperature domains.