Question

The tendency of carbon to loose electrons even at the expense of gaining positive chargeIdentify intermediate forms in following substitution reaction:

• A. Cyclohexa-1,3-dien-4-yne
• B. Cyclohexa-1,4-dien-5-yne
• C. Cyclohexa-1,3-dien-5-yne
• D. Cyclohexa-1,5-dien-4-yne

Answer 1

The Correct Option is C

In the given substitution reaction, we need to identify the intermediate form involved in the reaction mechanism. The reaction presents an image where chlorine is substituted by an amine group. This type of reaction often involves intermediates such as benzyne, which facilitate nucleophilic aromatic substitution. 

The reaction shown involves the elimination of HCl leading to the formation of an intermediate. This intermediate is a diradical species known as a benzyne. Benzyne formation occurs when a bond forms between two ortho carbons, producing a triple bond.

To determine the correct intermediate, we look for the presence of both a dienyl and triply-bonded carbon structure. The correct identification among the options should match the structure formed after the chloride leaves and before the amine adds to the benzyne:

1. Option Analysis:
2. \(\text{Option 1: Cyclohexa-1,3-dien-4-yne}\) - Incorrect, wrong position of the alkyne.
3. \(\text{Option 2: Cyclohexa-1,4-dien-5-yne}\) - Incorrect, improper conjugation of double bonds.
4. \(\text{Option 3: Cyclohexa-1,3-dien-5-yne}\) - Correct, consistent with the elimination and formation of benzyne.
5. \(\text{Option 4: Cyclohexa-1,5-dien-4-yne}\) - Incorrect, does not match the benzyne structure.

The correct form is Cyclohexa-1,3-dien-5-yne, characterized by two double bonds and one triple bond at the 5th position, showing typical benzyne structure.