Question

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

Answer 1

Start by drawing a chain of five carbon atoms.

Explanation:

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.