`Ph-C-=CH overset(Hg^(+),H^(+)//H_(2)O)to A`
Aditon of `H_(2)O` in the reaction is an example of

Options

A. Electrophlic addition
B. Nucleophillic addition
C. Free radical addition
D. Electrophillic additon

Answer

To solve the question regarding the reaction of phenylacetylene (Ph-C≡CH) in the presence of Hg^2+, H^+, and H2O, we will break down the process step by step.

### Step-by-Step Solution:

1. **Identify the Reactants:**
The reactant is phenylacetylene, which has the structure Ph-C≡CH. Here, "Ph" represents a phenyl group (C6H5), and C≡CH indicates a terminal alkyne.

2. **Reaction Conditions:**
The reaction is carried out in the presence of mercuric ion (Hg^2+) and protons (H^+), along with water (H2O). The presence of Hg^2+ is crucial as it facilitates the addition of water across the triple bond.

3. **Protonation of the Alkyne:**
The first step involves the protonation of the alkyne. The H^+ ion attacks the terminal carbon of the alkyne (C≡CH), forming a carbocation. This can lead to two possible carbocations:
- Ph-C^+(H)-CH2
- Ph-CH^+(C)-CH

However, the more stable carbocation is the one where the positive charge is on the carbon adjacent to the phenyl group due to resonance stabilization.

4. **Nucleophilic Attack by Water:**
Water (H2O) acts as a nucleophile. The hydroxide ion (OH^-) from water will attack the carbocation formed in the previous step. This results in the formation of an enol:
- Ph-C(OH)=CH2

5. **Tautomerization:**
The enol formed is not the final product. It undergoes tautomerization, where the hydrogen atom from the hydroxyl group shifts to the adjacent carbon, and the double bond shifts to form a carbonyl group (C=O). This results in the formation of a ketone:
- Ph-C(=O)-CH3 (acetophenone)

6. **Conclusion:**
The addition of water in this reaction is an example of **nucleophilic addition**. The water molecule acts as a nucleophile, attacking the electrophilic carbocation intermediate.

### Final Answer:
The addition of water in the reaction of Ph-C≡CH in the presence of Hg^2+ and H^+ is an example of **nucleophilic addition**.

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