Double bonds

In contrast to a single (σ) bond where free rotation is generally assumed, rotation about a double bond is not a low energy process. The presence of a double bond may therefore lead to geometrical isomerism as is observed for N₂F₂. Each N atom carries a lone pair as well as forming one N^__F single bond and an N=N double bond. Structures 1.35 and 1.36 show the trans- and cis-isomers† respectively of N₂F₂.