Question

Give the structures of both 1,2 and 1,4 adducts resulting from reaction of 1 equivalent of HCl with 1,3-pentadiene.

Short answer

Electrophilic addition reaction in which thefirst step there is the electrophile attack and in second step attack of the nucleophile on the double bond of the alkene.

An aromatic compound does not give this reaction (electrophilic addition reaction) due to its high stability; they do not break its pie bond.

Step-by-step solution

Electrophilic addition reaction

Electrophilic addition reaction in which thefirst step there is the electrophile attack and in second step attack of the nucleophile on the double bond of the alkene.

An aromatic compound does not give this reaction (electrophilic addition reaction) due to its high stability; they do not break its pie bond.

Structure of 1,2 and 1,4 adduct 

Electrophilic addition of HCl to a conjugated diene 1,3 Penta diene involves the formation of allylic carbocation intermediates (3 different types of carbocation intermediate). Thus, the first step is to protonate the two ends of the diene and draw the resonance forms of the two allylic carbocations that result. Each resonance form reacts with chlorine , generating three possible products.

• 4-chloro-2-pentene formed from 1,2 addition and 1,4 addition
• 3-chloro-1-pentene formed from 1,2 addition
• 1-chloro-pentene formed from 1,4 addition