How do you name and draw stereoisomers for 2-pentene?

Start by drawing a chain of five carbon atoms.

Draw a double bond between carbons 2 and 3.

Note that there are two ways to insert the double bond.

One has the ##"H"## atoms on opposite sides of the double bond; the other has the ##"H"## atoms on the same side of the double bond.

cis-Pent-2-ene has the ##"H"##-atoms on the same side of the double bond.

trans-Pent-2-ene has the ##"H"##-atoms on opposite sides of the double bond.

You can also use the Cahn-Ingold-Prelog system to name the isomers.

On each end of the double bond, the alkyl groups (ethyl and methyl) have higher priority than the ##"H"## atoms.

The first isomer has the higher-priority groups on opposite sides. This is (##E##)-pent-2-ene.

The second isomer has the higher-priority groups on the same side. This is (##Z##)-pent-2-ene.