Question

Draw and name the product for the following reaction between an alkyne and one equivalent of HCl.

Hint/ Explanation:

H and Cl– will add to the carbon atoms of the triple bond. The addition is regioselective.

Draw and name the product for the following reaction between an alkyne and one equivalent of HCl. Hint/ Explanation: H and Cl- will add to the carbon atoms of the triple bond. The addition is regioselective.

Answer 1

Concepts and reason

Electrophilic Addition Reactions of Alkynes:

Alkynes are similar to alkenes in their reactivity towards electrophiles. The electrophile, attacks on pi bond of alkyne to produce a carbocation intermediate. The carbocation intermediate reacts with a newly formed nucleophile, to form the organic product as an alkene.

Markovnikov’s rule:

Markovnikov’s rule states that the electrophile, adds to the carbon with the highest number of hydrogens present on it.

Regioselective reaction:

If one of the regioisomers is formed over the other by the electrophilic addition reaction between an alkyne and one equivalent of , the reaction is regioselective.

Stereochemistry:

In electrophilic addition reactions of alkynes, both syn-addition and anti-addition products are observed based on the nature of reagents used.

Syn-addition: Substituents add to the pi bond on the same sides.

Anti-addition: Substituents add to the pi bond on the opposite sides.

Fundamentals

E/Z Stereochemical Nomenclature:

• Use priority rules of Cahn, Ingold and Prelog.

• If the substituents of high priority are on the same sides, it is named as Z.

• If the substituents of high priority are on the opposite sides, it is named as E.

Nomenclature:

Nomenclature of organic compounds is done with certain rules assigned by IUPAC (International Union of Pure and Applied Chemistry).

Generally, IUPAC name consists of 3 parts as follows:

Mechanism for the reactions of alkynes with:

The Electrophilic Addition Reactions of Alkynes with:

Ans: