Chapter 7, Problem 29P

What is the major product obtained from the reaction of each of the following compounds with excess HCl?

1. a. CH₃CH₂C≡CH
2. b. CH₃CH₂C≡CCH₂CH₃
3. c. CH₃CH₂C≡CCH₂CH₂CH₃

Interpretation Introduction

Interpretation:

The major product obtained from the reaction of given compound with excess of $\text{HCl}$ should be determined.

Concept Introduction:

Addition of halides to alkynes: Halogens like chlorine and bromine adds to the alkyne compounds.  The general form of the reaction is given below.

If excess halides are present, a second addition reaction also occurs.

Answer to Problem 29P

The major product obtained from the reaction of given compound with excess of $\text{HCl}$ is given below:

Explanation of Solution

Hydrogen halides undergo addition reaction with alkynes.  Alkyne is a nucleophile and it reacts with the electrophile to give a $\text{π}$-complex.  In the next step, the halide ion adds to the $\text{π}$-complex and the product will be a halo-substituted alkene.  If excess reagent is present, another addition also occurs.

In this reaction of butyne with $\text{HCl}$, a $\text{π}$ complex is formed and then chloride ion adds to the $\text{π}$ complex and chlorine substituted product is formed.  Here the reagent is excess $\text{HCl}$, therefore a second addition occurs and the final product is obtained.

Interpretation Introduction

Interpretation:

The major product obtained from the reaction of given compound with excess of $\text{HCl}$ should be determined.

Concept Introduction:

Addition of halides to alkynes: Halogens like chlorine and bromine adds to the alkyne compounds.  The general form of the reaction is given below.

If excess halides are present, a second addition reaction also occurs.

Answer to Problem 29P

The major product obtained from the reaction of given compound with excess of $\text{HCl}$ is given below:

Explanation of Solution

Hydrogen halides undergo addition reaction with alkynes.  Alkyne is a nucleophile and it reacts with the electrophile to give a $\text{π}\text{complex}$.  In the next step, the halide ion adds to the $\text{π}\text{complex}$ and the product will be a halo-substituted alkene.  If excess reagent is present, another addition also occurs.

In this reaction of hex-3-yne with $\text{HCl}$, a $\text{π}\text{complex}$ is formed and then chloride ion adds to the $\text{π}\text{complex}$ and chlorine substituted product is formed.  Here the reagent is excess $\text{HCl}$, therefore a second addition occurs and the final product is obtained.

Interpretation Introduction

Interpretation:

The major product obtained from the reaction of given compound with excess of $\text{HCl}$ should be determined.

Concept Introduction:

Addition of halides to alkynes: Halogens like chlorine and bromine adds to the alkyne compounds.  The general form of the reaction is given below.

If excess halides are present, a second addition reaction also occurs.

Answer to Problem 29P

The major product obtained from the reaction of given compound with excess of $\text{HCl}$ is given below:

Explanation of Solution

Hydrogen halides undergo addition reaction with alkynes.  Alkyne is a nucleophile and it reacts with the electrophile to give a $\text{π}\text{complex}$.  In the next step, the halide ion adds to the $\text{π}\text{complex}$ and the product will be a halo-substituted alkene.  If excess reagent is present, another addition also occurs.

In this reaction of hept-3-yne with $\text{HCl}$, a $\text{π}\text{complex}$ is formed and then chloride ion adds to the $\text{π}\text{complex}$ and chlorine substituted product is formed.  Here the reagent is excess $\text{HCl}$, therefore a second addition occurs and the final product is obtained.