Knowledge Bank

The infrared and Raman spectra of 3-butenenitrile, $CH2=CH-CH2-CN$, have been obtained and the vibrational assignments are reported. The vibrational bands at 499 and $565cm-1$ were used to study the concentrations of the gauche and cis isomers, respectively. The cis isomer is the stable form in the solid phase and there is some indication of more than one solid phase within a few degrees of the freezing point. Intensity ratios of these bands were used to determine an energy difference between the isomers of approximately 500 calories. Infrared intensities and NMR coupling constants in polar and non-polar solvents were used to determine an equilibrium ratio of cis to gauche isomer of about .53 to .47 at ambient temperature. The potential barrier to internal rotation is estimated from the torsional frequency of $105cm-1$. measured in the Raman spectrum, to be 2175 cal. per mole.