Knowledge Bank

The infrared spectrum is presented from 2 to 25$\mu$ and $-100\circ$ to $-180\circ C$ for 1,2-dicyanoethane in the liquid and solid states. The results clearly show the presence of two rotational isomers of $C2h$ (trans) and $C2$ (gauche) symmetry at temperatures above $-43.7\circ C$. The variation of the intensities of the infrared bands with temperature gives a value of 360 $\pm$ 50 cal. $mole-1$ for the energy difference, A H, between the two forms, with the $C2$ isomer having the lower energy. At temperatures less than $-43.7\circ C$, 1,2-dicyanoethane exists entirely in gauche isomeric form. In the vapor state, it is predicted, that the $C2$, isomer will be the lower energy form, the energy difference between the isomeric forms, estimated from these results, now being 1.0 kcal. $mole-1$. The infrared spectrum, when combined with the known Raman spectrum, permits a tentative vibrational assignment.