Q.39 - Organic Chemistry

Question

Draw all constitutional isomers formed in each elimination reaction. Label the mechanism as E2 or E1.

a.

b.

c.

d.

e.

f.

Step-by-Step Solution

Answer

The constitutional isomers mentioning their mechanism are shown below:

Definition of constitutional isomer

Constitutional isomers are those kinds of isomers where the molecular formula and structures are the same but with different bonding arrangements.

Identification of the base

Strong and bulky bases favor E2 reactions whereas, weak bases favor E1 reactions. Weak bases like  ${\text{CH}}_3\text{OH}$ and ${\text{H}}_2\text{O}$ favor E1 reactions, whereas strong bases like ${}^{-}\text{OH}$ and  ${}^{-}\text{OCH}_3$ strong, bulky bases ${}^{-}\text{OC(CH}_3{\text{)}}_3$ favor E2 reactions.

Identification of the substrate

The primary halides always favor E2 reactions, whereas the secondary and tertiary halides favor E1 and E2, both depending on the bases used.

Different types of β hydrogens

Different types of $\text{β}$ hydrogens give different types of elimination products.

So, considering all the steps and the types of $\text{β}$ hydrogens present, the possible constitutional isomers, along with their elimination mechanisms, are shown below:

Representation of all the elimination products from a

Representation of all the elimination products from b

Representation of all the elimination products from c

Representation of all the elimination products from d

Representation of all the elimination products from e

Representation of all the elimination products from f