Question

For the reaction of one equivalent of HCl with butadiene, characterize the four structures below as to whether each might be a product of the reaction, and if so, the type of product. (For each structure, select all terms that apply.)

Answer 1

Concepts and reason

Alkenes contain unsaturated double bonds which undergo addition reactions.

In addition reactions, the weaker pi bond converts into two new stronger sigma bonds.

Addition reactions are regioselective, based on the reagent used.

Fundamentals

Alkenes are more reactive than alkanes, hence they usually undergo addition reactions in which the pi bond is broken and two new groups are added across the double bond to give a saturated compound.

An addition reaction goes via a two-step process:

1.The electrophile attacks the double bond forming a carbocation intermediate.

2.In the second step, the counter ion attacks the carbocation intermediate and forms a saturated product.

The addition of an electrophile to a double bond is regioselective, provided the two atoms that add to the double bond are different.

The general mechanism is shown below.

An addition reaction can follow one of two rules when the two atoms that add to the double bond are different:

1.Markovnikov’s Rule: The electrophile adds to the less hindered carbon atom and the nucleophile adds to the more hindered carbon atom of the double bond.

2.Antimarkovnikov’s Rule: The electrophile adds to the more hindered carbon atom and the nucleophile adds to the less hindered carbon atom of the double bond.

Markovnikov’s addition gives a stable carbocation intermediate over Antimarkovnikov’s addition. Hence, Markovnikov’s addition gives a more stable and major product and Antimarkovnikov’s addition gives a less stable and minor product.

Rearrangement of the carbocation intermediate may take place in case a stable carbocation formation is possible on rearrangement.

A thermodynamically-controlled product is the more stable product.

A kinetically-controlled product is the faster formed product.

(1)

Yes, the given structure is the product of the reaction.

The type of the reaction is 1,4-addition.

(2)

No, the given structure is not the product of the reaction.

(3)

No, the given structure is not the product of the reaction.

(4)

Yes, the given structure is the product of the reaction.

The type of the reaction is 1,2-addition.

It is a kinetically-controlled product.

Ans: Part 1

Answer 2