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 does not represent an example of nucleophilic substitution, we will analyze each option step-by-step.

### Step 1: Understand Nucleophilic Substitution
Nucleophilic substitution is a reaction where a nucleophile (an electron-rich species) replaces a leaving group (usually a halide) in a compound. The general form of the reaction is:
\[ \text{R-X} + \text{Nu}^- \rightarrow \text{R-Nu} + \text{X}^- \]
where R is an alkyl group, X is the leaving group, and Nu is the nucleophile.

### Step 2: Analyze Each Reaction
1. **First Reaction: C2H5Br + S → C2H5S + Br**
- Here, the bromine (Br) is replaced by the sulfur (S) from the nucleophile. This is a nucleophilic substitution reaction.

2. **Second Reaction: C2H5Br + Ag + CN- → C2H5CN + AgBr**
- In this case, the bromine (Br) is replaced by the cyanide ion (CN-). This is also a nucleophilic substitution reaction.

3. **Third Reaction: C2H5Br + H2 → C2H6 + HBr**
- In this reaction, hydrogen (H2) is added to C2H5Br, resulting in the formation of ethane (C2H6) and HBr. This does not involve a nucleophile replacing a leaving group; instead, it is a reduction reaction. Therefore, this is **not** a nucleophilic substitution reaction.

4. **Fourth Reaction: C2H5Br + KOH → C2H5OH + KBr**
- Here, the hydroxide ion (OH-) acts as a nucleophile and replaces the bromine (Br) in C2H5Br, forming ethanol (C2H5OH). This is a nucleophilic substitution reaction.

### Conclusion
From the analysis, the third reaction (C2H5Br + H2 → C2H6 + HBr) does not represent an example of nucleophilic substitution. It is a reduction reaction instead.

### Final Answer
The reaction that does not represent an example of nucleophilic substitution is:
**C2H5Br + H2 → C2H6 + HBr.**

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