Which of the following reactions of C2H5Br does not represent an example of nucleophilic substitution?

Options

A. `C_(2)H_(5)"Br" + C_(2) H_(5) "Sna" rarr C_(2)H_(5)-S-C_(2)H_(5) + `NaBr
B. `C_(2)H_(5)"Br" + "AgCN" rarr C_(2) H_(5)NC + ` AgBr
C. `C_(2) H_(5)"Br+ 2H" rarr C_(2)H_(6) + ` HBr
D. `C_(2) H_(5) "Br + KOH " rarr C_(2) H_(5) OH` + KBr

Answer

To determine which reaction of C2H5Br (ethyl bromide) does not represent an example of nucleophilic substitution, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Nucleophilic Substitution**:
- Nucleophilic substitution reactions involve a nucleophile attacking an electrophilic carbon atom, resulting in the replacement of a leaving group (in this case, bromine) with the nucleophile.

2. **Analyzing the First Reaction**:
- **Reaction**: C2H5Br + S⁻ → C2H5S + Br⁻
- In this reaction, the nucleophile (S⁻) attacks the carbon atom of C2H5Br, displacing the bromine atom. This is a classic example of nucleophilic substitution (SN2 mechanism).
- **Conclusion**: This reaction represents nucleophilic substitution.

3. **Analyzing the Second Reaction**:
- **Reaction**: C2H5Br + AgCN → C2H5NC + AgBr
- Here, AgCN acts as a source of the nucleophile (CN⁻). The CN⁻ ion attacks the carbon atom of C2H5Br, leading to the formation of ethyl isocyanide (C2H5NC) and the release of AgBr. This is also a nucleophilic substitution reaction.
- **Conclusion**: This reaction represents nucleophilic substitution.

4. **Analyzing the Third Reaction**:
- **Reaction**: C2H5Br + H → C2H6 + HBr
- In this case, ethyl bromide reacts with nascent hydrogen (or free radical hydrogen) to form ethane (C2H6) and HBr. This reaction does not involve a nucleophile attacking the carbon atom of C2H5Br; instead, it involves a radical mechanism where the bromine atom is eliminated, and hydrogen is added.
- **Conclusion**: This reaction does NOT represent nucleophilic substitution.

5. **Analyzing the Fourth Reaction**:
- **Reaction**: C2H5Br + KOH → C2H5OH + KBr
- In this reaction, the hydroxide ion (OH⁻) from KOH acts as a nucleophile, attacking the carbon atom of C2H5Br and displacing the bromine atom. This is another example of nucleophilic substitution.
- **Conclusion**: This reaction represents nucleophilic substitution.

### Final Answer:
The reaction that does not represent an example of nucleophilic substitution is **C2H5Br + H → C2H6 + HBr**.

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