Chapter 18.14, Problem 33CC

Interpretation Introduction

Interpretation:

The structure of the products has to drawn which are obtained when 4-chloro-2-methyltoluene is reacted with sodium amide followed by treatment with ${\text{H}}_3{\text{O}}^{+}$.

Concept Introduction:

• Aromatic compounds undergo another type of reactions namely Aromatic nucleophilic substitution reactions designated as ${\text{S}}_{\text{N}}\text{Ar}$.

• A nucleophile, unlike an electrophile is a species that is electron rich and always attracted towards electron deficient site. A nucleophile is mobile unlike electrophile.

• The criteria for aromatic nucleophilic substitution reaction to occur are –

• The aromatic ring must contain a strong electron withdrawing group

• The aromatic ring must contain a leaving group

• The leaving group must be posited either ortho or para position to the strong electron withdrawing group.

• Let the substituent be ‘X’ that then $\text{C-X}$ bond gets broken and  $\text{C-Nu}$ bond is formed. The substituent ‘X’ is termed as ‘Leaving group’. A good leaving is large in size with high electron affinity that they are capable to grabbing the bond pair electron and leaving form the aromatic C atom. Halogens are known to be excellent leaving group.

• The overall reaction can be represented as follows –

                    

• In case where there is no possibility of ${\text{S}}_{\text{N}}\text{Ar}$ reactions the compounds undergo another type of reaction under different reaction conditions called elimination – addition reaction. A compound with leaving group when treated with a strong base under high or low temperature undergoes elimination – addition reaction where the leaving group is eliminated and a new group is added.

• The term Regioselectivity is referred as preference of a particular group to occupy a specific position in a compound. In case an aromatic ring has one or more than one substituents the position in the aromatic ring occupied by the incoming electrophile depends on various factors.