Question

Draw the addition products formed when one equivalent of HBr reacts with 2,4-hexadiene. Draw a single product for each, ignoring stereochemical or chiral isomers.

Answer 1

Concepts and reason

The problem is based on the concept of electrophilic substitution reaction of alkene. This is initiate by formation of carbocation, which further rearrange depending upon its stability and the stability of final product.

Fundamentals

The Electrophilic substitution reaction leads with the attack of electrophile on the of alkene forming complex. This complex results in the formation of carbocation. Rearrangement takes place if possible to form stable carbocation. After the formation of stable carbocation attack of the negative part of the reagent position is decided. The tertiary carbocations formed by the attack of an electrophile are most stable and forms the more stable and high yield product.

The order of stability of carbocation is as follows:

Here, and is tertiary, secondary and primary carbocation respectively.

Reactant (2, 4-hexadiene) is a symmetrical alkene on which attack of electrophile take place. Thus, the electrophile can attack on either of the bonds present on the two different carbon atoms. Therefor there are two possible attacks shown as follows:

Substitution of bromide ion, take place on the carbocation. For substitution there are two possibilities that is resulting formation of 1, 2- and 1,4- addition product. This is represented as follows:

Ans:

The two addition products are as follows:

.

Answer 2

Concepts and reason

The problem is based on the concept of electrophilic substitution reaction of alkene. This is initiate by formation of carbocation, which further rearrange depending upon its stability and the stability of final product.

Fundamentals

The Electrophilic substitution reaction leads with the attack of electrophile on the of alkene forming complex. This complex results in the formation of carbocation. Rearrangement takes place if possible to form stable carbocation. After the formation of stable carbocation attack of the negative part of the reagent position is decided. The tertiary carbocations formed by the attack of an electrophile are most stable and forms the more stable and high yield product.

The order of stability of carbocation is as follows:

Here, and is tertiary, secondary and primary carbocation respectively.

Reactant (2, 4-hexadiene) is a symmetrical alkene on which attack of electrophile take place. Thus, the electrophile can attack on either of the bonds present on the two different carbon atoms. Therefor there are two possible attacks shown as follows:

Substitution of bromide ion, take place on the carbocation. For substitution there are two possibilities that is resulting formation of 1, 2- and 1,4- addition product. This is represented as follows:

Ans:

The two addition products are as follows:

.