Question

Vinyl acetylene reacts with one equivalent of \(\mathrm{HCl}\) to produce (1) chloroprene (2) neoprene (3) lewisite (4) mesitylene

Short answer

Option (1) chloroprene.

Step-by-step solution

- Identify the Reactants

Understand that the reactants in this reaction are vinyl acetylene and one equivalent of \(\mathrm{HCl}\). Vinyl acetylene has the formula CH≡C-CH=CH2.

- Recognize the Type of Reaction

This is an addition reaction where \(\mathrm{HCl}\) adds across the multiple bonds of vinyl acetylene.

- Understanding the Reaction Mechanism

Add the \(\mathrm{H}\) atom to one of the carbon atoms of the triple bond, and the \(\mathrm{Cl}\) atom to the other carbon atom, forming 3-chloroprene (CH2=CH-C(Cl)=CH2).

- Identify the Product

The product formed by the addition of HCl to vinyl acetylene is 3-chloroprene. This matches with option (1) chloroprene.

- Confirm the Correct Answer

Review the structure to ensure the correct product has been identified. The structure (CH2=CH-C(Cl)=CH2) confirms that the resulting compound is chloroprene.

Key concepts

Chloroprene Synthesis

In studying the reaction between vinyl acetylene and \(\text{HCl}\), we come across the synthesis of chloroprene. Chloroprene, also known as 2-chloro-1,3-butadiene, is a key monomer used in the production of neoprene, a synthetic rubber known for its chemical stability and flexibility.
To synthesize chloroprene, we need to understand the structure of our starting material - vinyl acetylene. Its formula is CH≡C-CH=CH2. When reacting with \(\text{HCl}\), we are dealing with an addition reaction where \(\text{H}\) and \(\text{Cl}\) atoms add across the multiple bonds present in the molecule. The result of this reaction is the formation of 3-chloroprene (CH2=CH-C(Cl)=CH2).
This straightforward synthesis is essential as chloroprene is a building block for many useful materials. Knowing how to synthesize it from vinyl acetylene lays the foundation for understanding many industrial and chemical processes.

Addition Reaction

An addition reaction, as the name suggests, involves the addition of atoms or groups to a molecule without the loss of any atom. In our case, we're adding \(\text{H}\) and \(\text{Cl}\) from \(\text{HCl}\) to the double and triple bonds of vinyl acetylene.
Let's break it down: Vinyl acetylene has both a triple bond and a double bond. When \(\text{HCl}\) is added, the \(\text{H}\) atom attaches to one carbon of the triple bond, and the \(\text{Cl}\) atom attaches to the other carbon. This action breaks the triple bond and forms a double bond, resulting in 3-chloroprene. The simplified process is:

• Vinyl acetylene: \( CH≡C-CH=CH_2\)
• Addition of \(\text{HCl}\)
• 3-Chloroprene: \( CH_2=CH-C(Cl)=CH_2\)

Understanding addition reactions is crucial in organic chemistry because they are common mechanisms in creating more complex molecules from simpler ones.

Reaction Mechanism

The reaction mechanism in an addition reaction shows us step-by-step how the reactants convert into products. For the addition of \(\text{HCl}\) to vinyl acetylene, the mechanism involves the following steps:
First, the \(\text{HCl}\) molecule dissociates into \(\text{H}\) and \(\text{Cl}\) ions. The \(\text{H}\) ion is positively charged and seeks out the negative electron-rich regions, such as the triple bond in vinyl acetylene. The \(\text{H}\) ion attaches to one of the carbon atoms of the triple bond. In turn, the \(\text{Cl}\) ion, negatively charged, attaches to the other carbon atom, forming a carbocation intermediate.
The chemical structure evolves from a triple bond to a double bond, and the end product is 3-chloroprene. The mechanism can be summarized as:

• Dissociation of \(\text{HCl}\) into \(\text{H}\) and \(\text{Cl}\)
• Electrophilic addition of \(\text{H}\) to the triple bond
• Formation of a carbocation intermediate
• Nucleophilic attack by \(\text{Cl}\) on the carbocation

This process underscores the importance of understanding how electrons move during chemical reactions, providing insight into how complex compounds are synthesized.