How can I draw the molecular formula for an unsaturated alkyl chloride C5H9Cl with optical activity and E, Z – isomerism?

1 Answer
Ernest Z.
Jun 11, 2015

First, draw the possible (E) and (Z) pentene isomers. Then substitute every possible H atom with Cl until you have generated all possible chiral molecules.

Explanation:

Step 1. Draw the isomeric pentenes.

There is only one pentene that can have (E)and (Z) isomers. That is pent-2-ene.

You can have (E)-pent-2-ene

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or (Z)-pent-2-ene.

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Step 2. Identify the prochiral carbon atoms.

A C atom is prochiral if the replacement of one of its groups by a different group would create a new chiral centre.

It must be bonded to exactly three different groups before any change is made.

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In pent-2-ene, C-4 is bonded to a methyl group, a propenyl group, and two hydrogens.

This fits the criterion of being bonded to exactly three different groups, even though one group is represented twice.

C-4 is a prochiral carbon.

If we replace one H atom, we get an (E) isomer. If we replace the other H atom, we get a (Z) isomer.

So there are four possibilities:

(2E,4R)-4-chloropent-2-ene and (2E,4S)-4-chloropent-2-ene

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and (2Z,4R)-4-chloropent-2-ene and (2Z,4S)-4-chloropent-2-ene

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