Geometric Isomerism
Stereoisomerism arising from restricted rotation about a double bond or within a ring.
Formula / equation
cis / trans or E / Z
Unit
Dimensionless
In depth
It requires each doubly bonded carbon to carry two different groups. The cis isomer, with the priority groups on the same side, is usually more polar and lower melting than the trans isomer, which packs more efficiently into a crystal lattice.
Examples in the real world
Cis-but-2-ene boiling at 4 °C against trans at 1 °C; cis unsaturated fats being liquid where trans fats are solid.