Which can not act as an ambident nucleophile ?

Options

A. `CN^(-)`
B. `NO_(2)^(-)`
C. `SCN^(-)`
D. `OH^(-)`

Answer

To determine which species cannot act as an ambident nucleophile, we need to understand the concept of ambident nucleophiles and analyze the given options.

### Step-by-Step Solution:

1. **Definition of Nucleophile**:
- A nucleophile is an electron-rich species that donates electrons to form a chemical bond.

2. **Definition of Ambident Nucleophile**:
- An ambident nucleophile is a type of nucleophile that can attack from two or more different atoms within the same molecule. This means it has multiple sites from which it can donate electrons.

3. **Analyzing the Given Options**:
- We need to evaluate the structures of the provided options to see if they can act as ambident nucleophiles.

4. **Option 1: CN⁻ (Cyanide Ion)**:
- Structure: C≡N⁻
- The carbon atom can act as a nucleophile due to its negative charge, and the nitrogen atom can also participate due to its lone pair. Therefore, CN⁻ is an ambident nucleophile.

5. **Option 2: NO₂⁻ (Nitrite Ion)**:
- Structure: O=N⁻O
- The nitrogen atom can act as a nucleophile due to its lone pair, and the negatively charged oxygen can also participate in nucleophilic attack. Thus, NO₂⁻ is also an ambident nucleophile.

6. **Option 3: SCN⁻ (Thiocyanate Ion)**:
- Structure: S=C=N⁻
- The sulfur atom has lone pairs and can act as a nucleophile, while the nitrogen atom can also participate due to its lone pair and negative charge. Hence, SCN⁻ is an ambident nucleophile.

7. **Option 4: OH⁻ (Hydroxide Ion)**:
- Structure: O⁻H
- The hydroxide ion has a negative charge on the oxygen atom. The only site for nucleophilic attack is the oxygen atom, as hydrogen does not have a lone pair or negative charge. Therefore, OH⁻ cannot act as an ambident nucleophile.

8. **Conclusion**:
- Among the given options, OH⁻ is the only species that cannot act as an ambident nucleophile. Thus, the answer is **Option 4: OH⁻**.