Q.64 - Organic Chemistry

Question

Although there are nine stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane, one stereoisomer reacts 7000 times more slowly than any of the others in an E2 elimination. Draw the structure of this isomer and explain why this is so.

Step-by-Step Solution

Answer

Structure of isomer

In this isomer, all the chloride groups are present in an equatorial position. To undergo an elimination reaction, the  $\text{β}$ hydrogens and the leaving group must be in an anti-periplanar orientation which is not observed for this product.

Anti-periplanar orientation

The  $\mathbf{\text{β}}$ hydrogens and the leaving group must be in an anti-periplanar orientation to undergo an elimination reaction. These are the basic criteria in an E2 reaction.

Observation of the stereoisomer

The position of the  $\text{β}$ hydrogens and the leaving group are not in an anti-periplanar orientation to undergo an elimination reaction. In this isomer, all the chloride groups are present in an equatorial position, so the elimination reaction is the slowest in this case.

 

By keeping all the valid explanations, it is observed that this isomer undergoes 7000 times slower elimination reaction compared to other isomers.

Representation of the isomer