Question

The product formed when vinylacetylene is passed through concentrated hydrochloric acid in the presence of cuprous and ammonium chloride is (1) \(\mathrm{ClCH}_{2} \mathrm{CII}_{2} \mathrm{C} \equiv \mathrm{CII}\) (2) \(\mathrm{CII}_{3} \mathrm{CIICl} \mathrm{C}=\mathrm{CII}\) (3) \(\mathrm{CII}_{2}=\mathrm{CII} \mathrm{CII}=\mathrm{CIICl}\) (4) \(\mathrm{CII}_{2}=\mathrm{CII} \mathrm{CCl}=\mathrm{CH}_{2}\)

Short answer

Option (4) \( \text{CH}_2=\text{CH}-\text{CCl}=\text{CH}_2 \) is the product.

Step-by-step solution

- Understand the Structure of Vinylacetylene

Vinylacetylene is an organic compound with the formula \(\text{CH}_2=\text{CH}-\text{C}eq\text{CH}\). Recognize the structure as it will help in predicting the reaction pathways.

- React with Hydrochloric Acid

When vinylacetylene is passed through concentrated hydrochloric acid, the addition of \( \text{HCl} \) will occur across the triple bond partially facilitated by the presence of cuprous chloride and ammonium chloride. This typically leads to the Markovnikov addition where the chlorine (Cl) atom attaches to the carbon with more hydrogen atoms.

- Predict the Major Product

Considering the Markovnikov addition, attach one hydrogen (H) to one carbon of the triple bond (the second carbon in the structure of vinylacetylene) and one chlorine (Cl) to the other carbon (the third carbon). This results in the structure \( \text{CH}_2=\text{CH}-\text{CCl}=\text{CH}_2 \).

- Verify the Final Structure

Finally, check all possible answers to see which one matches the predicted product. The correct structure we identified is \( \text{CH}_2=\text{CH}-\text{CCl}=\text{CH}_2 \), and corresponds to option 4.

Key concepts

organic chemistry reactions

In organic chemistry, reactions involve the transformation of organic compounds through various chemical processes. These transformations play a crucial role in synthesizing new molecules and creating complex structures from simpler ones. Reactions often involve breaking and forming covalent bonds.
One key aspect of understanding organic chemistry reactions is recognizing functional groups and their reactivities. Functional groups are specific groups of atoms within molecules that have characteristic properties. For instance:

• Alkenes (C=C) undergo addition reactions where atoms or groups are added to the carbon atoms of the double bond.
• Alkynes (C≡C) can also react via addition reactions, involving pi bonds breaking and sigma bonds forming.

Organic reactions can be catalyzed by acids, bases, or transition metals. In our exercise, hydrochloric acid (HCl) aids in the addition reaction involving vinylacetylene.

Markovnikov addition

Markovnikov addition is a principle that helps predict how hydrogen halides (HX), like HCl, add to alkenes or alkynes. According to Markovnikov's rule, when HX adds to a double or triple bond, the hydrogen (H) atom attaches to the carbon atom that already has more hydrogen atoms, and the halogen (X) attaches to the carbon with fewer hydrogen atoms.
This rule arises from the stability of the carbocation intermediate formed during the reaction. A carbocation (positively charged carbon) is more stable when it is surrounded by more alkyl groups (R groups) rather than hydrogen atoms. Alkyl groups are electron-donating and stabilize the positive charge.
Here's a simple example to illustrate Markovnikov addition:

• An alkene like propene (CH3-CH=CH2) reacts with HCl.
• The hydrogen attaches to the carbon with two hydrogen atoms, forming CH3-CH(-H)-CH2(+Cl).
• The chlorine attaches to the carbon with one hydrogen atom, resulting in CH3-CH(Cl)-CH3.

In our exercise, the reaction of vinylacetylene with HCl follows Markovnikov's rule, leading to the final product: CH2=CH-CCl=CH2.

hydrochloric acid reaction

Hydrochloric acid (HCl) is a strong acid commonly used in organic synthesis. It dissociates fully in water to provide hydrogen ions (H+) and chloride ions (Cl-). This dissociation allows HCl to act as a source of protons, making it a strong acid capable of facilitating various reactions.
In the context of addition reactions, HCl adds across double and triple bonds. The mechanism typically involves proton (H+) transfer, generating a carbocation intermediate, followed by nucleophilic attack by the chloride ion (Cl-).
In our exercise, when vinylacetylene is exposed to concentrated hydrochloric acid, a similar process occurs:

• The hydrogen ion (H+) from HCl adds to one carbon of the alkyne.
• This creates a highly reactive carbocation intermediate at the adjacent carbon.
• The chloride ion (Cl-) then attaches to this carbocation, resulting in a new bond.

This process, facilitated by cuprous chloride and ammonium chloride, transforms the alkyne into an alkene with a chlorine substituent, resulting in CH2=CH-CCl=CH2.