Question

Why do alkenes prefer to undergo electrophilic addition reactions while arenes prefer electrophilic substitution reactions? Explain.

Answer 1

Due to the presence of a $\pi$ -electron cloud above and below the plane of alkenes and arenes, these are electron rich molecules and, therefore, provide sites for the attack of electrophiles. Hence, they undergo electrophilic reactions.

Alkenes preference for electrophilic addition reactions:

Alkenes are the rich source of loosely held $\pi$ electrons, due to which they show addition reactions in which the electrophiles add on to the carbon-carbon double bond to form the addition products.



During this alkenes give a more stable product as $s{p}^2$ hybridization changes to $s{p}^3$ hybridization.

Alkenes does not prefer electrophilic substitution reactions due to unstability of intermediate species.

Arenes preference for electrophilic substitution reactions

On the other hand, in arenes during electrophilic addition reaction, aromaticity of the benzene ring is disturbed making them very unstable, while during electrophilic substitution reaction it remains intact.


Thus, alkenes prefer to undergo electrophilic addition reactions while arenes prefers electrophilic substitution reactions.