Spectroscopic and molecular mechanics study of the conformational properties of methyl cyanoacetate and ethyl cyanoacetate

Abstract

Infrared spectra of methyl cyanoacetate and ethyl cyanoacetate have been recorded in different solvents of varying polarity in the region 4000-600 cm^-1 along with laser Raman spectra of the liquid samples of these compounds in the region 4000-50 cm^-1. Existence of conformers has been confirmed in both the molecules on the basis of splitting of some of the bands and CNDO/2 and molecular mechanics computations. Normal coordinate analysis of both the molecules has been carried out and the force constants thus obtained have been employed to compute the energies of different conformers by the method of molecular mechanics. The computed conformational energy of methyl cyanoacetate is in close agreement with the experimental values. It has been concluded that for these molecules the <em>cis </em>conformers are most stable. The energy difference between <em>gauche-trans </em>and <em>cis-trans </em>conformers of ethyl cyanoacetate is computed to be 1.0 kcal mol^-1.