Question

N-methylpiperidine, when reacted with excess methyl iodide and then moist silver oxide, produces an alkene on heating (Hofmann elimination). Name the alkene formed.

• A. Penta-1,4-diene
• B. 1,3-Butadiene
• C. Penta-1,3-diene
• D. Ethene

Hint:

A cyclic amine needs two rounds of exhaustive methylation and Hofmann elimination to open the ring and remove nitrogen completely.

Answer 1

The Correct Option is A

Alternative approach: count carbons. N-methylpiperidine's ring has five carbon atoms; none are destroyed, so the final hydrocarbon must have five carbons, ruling out 1,3-butadiene (four) and ethene (two). Two rounds of Hofmann elimination are needed; each pushes its new double bond toward the end nearest where nitrogen last was attached. This gives double bonds at 1-2 and 4-5, i.e. penta-1,4-diene.

\[\boxed{\text{Penta-1,4-diene}}\]