Rotational isomers of methyl trans-cinnamate: A Raman study

The Raman and infrared spectra of methyl trans-cinnamate were measured as a function of temperature in the liquid and solid phases. The temperature dependence of the band intensities established the presence of two conformers in the liquid phase (the s-cis and s-trans forms, with CC CO dihedral angles equal to 0° and 180°, respectively; ΔH_{(s-trans)-(s-cis)} = 3.43 ± 0.84 kJ mol⁻¹) and led to the conclusion that the thermodynamically most stable s-cis form is the only form present in the solid.