Question

In which of the following reaction, the major product alkene is formed by $E_{1}cB$ mechanism?

• A.
• B.
  $C{H}_{3}C{H}_{2}C{H}_{2}C{H}_2-Br\underset{\Delta }{\overset{alc.KOH}{\to }}$
• C.
• D.

Answer 1

The correct option is A

$E_{1}cB$ reaction is the process by which a substituted alkane form its corresponding alkene taking hydrogen from the beta carbon.
For $E_{1}cB$ to occur, the substituted alkane must have a poor leaving group. Strong EWG at the $\beta$ carbon and poor leaving group favors the E1cB reaction.
It also must have a hydrogen on one of its beta carbon.
In (c), reactant has fluorine which is a poor leaving group and also a electron withdrawing carbonyl group so it undergo E1cB reaction.
The compound also has beta hydrogens. The conjugate base generated forms the double bond easily.