Question

Assertion :The two $-C{H}_2$ groups in $C_2{H}_4$ do not rotate freely around the bond connecting them, although the two $-C{H}_3$ groups in $C_2{H}_6$ have almost an unhindered rotation around the C - C bond. Reason: $C_2{H}_4$ has $\pi$ bond and the overlap of the atomic p-orbitals making up this bond would be destroyed if the $-C{H}_2$ groups rotate.

Read the above assertion and reason and choose the correct option regarding it.

• A. Assertion is true, Reason is true and Reason is correct explanation for Assertion
• B. Assertion is true, Reason is true and Reason is NOT the correct explanation for Assertion
• C. Assertion is true, Reason is false
• D. Assertion is false, Reason is true

Answer 1

The correct option is A Assertion is true, Reason is true and Reason is correct explanation for Assertion

Assertion: The two $-C{H}_2$ groups in $C_2{H}_4$ do not rotate freely around the bond connecting them, although the two $-C{H}_3$ groups in $C_2{H}_6$ have almost an unhindered rotation around the $C-C$ bond.
This is the reason why alkenes show cis trans isomerism but alkanes do not show such isomerism.
Reason: $C_2{H}_4$ has $\pi$ bond and the overlap of the atomic p-orbitals making up this bond would be destroyed if the $-C{H}_2$ groups rotate.
To form a pi bond, the p orbitals must have proper orientation which is not possible if the bond is rotated.
Hence, Assertion is true, Reason is true and REason is the correct explanation for Assertion.