Question

How can I draw 3–methylpent–2–ene, (`CH_3CH = C(CH_3) CH_2CH_3`), and know if it shows E-Z isomerism?

Answer 1

First you expand the condensed structural formula to a bond-line view, and then you check whether there are two different groups on each end of the `"C=C"` bond.

Explanation:

Step 1. Draw the bond-line structure.

Step 2. Check for two different substituents on each end.

In the structure above, the left hand `"C"` atom has an `"H"` and a `"CH"_3` (two different substituents).

The right hand end has a `"CH"_3` and a `"CH"_2"CH"_3` (two different substituents).

The compound shows `E"/"Z` isomerism.

In the above structure, the `"CH"_3` group on the left hand end has priority 1, while the `"CH"_2"CH"_3` group on the right hand end has priority 1.

Since the two high-priority groups are on opposite sides of the double bond, the compound is (`E`)-3-methylpent-2-ene.