Question

Predict the major product of acid catalysed dehydration of


$A$: 1-methylcyclohexanol

$B$: butan-1-ol

Answer 1

$A$:
Major product of acid catalysed dehydration of $1-Methylcyclohexanol$

Acid catalysed dehydration of alcohols undergoes elimination reactions and yield alkene as the product. Major product is decided by Saytzeff''s rule.

Formation of protonated alcohol


It involves proton abstraction.
Formation of carbocation


It is the slowest step and thus called as rate determining step. It involves removal of leaving group.

Formation of alkene



Here, elimination of proton occurs in presence of base $\left(H2O\right)$ . Since, there are two types of protons on neighbouring position of carbocation, So, it led to two different alkenes as product.
Here, $1-Methylcyclohexene$ is the major product., as per saytzeff''s rule.
Final answer: $1-Methylcyclohexene$ is the major product.


$B$:

Major product of acid catalysed dehydration of $butan-1-ol$

$Butan-1-ol$ upon acid catalysed dehydration will give $but-2-ene$ as the major product along with but-1-ene as the minor product. Primary carbocation formed can either lose a $H^{+}$ to form $but-1-ene$ or may undergo rearrangement and shift to secondary carbocation, which is more stable. The latter then forms $but-2-ene$ by losing a $H^{+}$ .
This is given by following reactions involved.
Reactions involving rearrangement


Rearrangement of carbocation occurs because Secondary carbocation is more stable than primary carbocation.
$But-2-ene$ is the major product as per saytzeff's rule.
Final answer: $But-2-ene$ is the major product.