Which of the following is not an ambident nucleophile?

Options

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

Answer

To determine which of the following is not an ambident nucleophile, we need to analyze each option based on the definition of ambidentate nucleophiles. An ambidentate nucleophile has two different atoms that can donate electrons, allowing it to act as a nucleophile at two different sites.

### Step-by-Step Solution:

1. **Identify the Options**: The given options are:
- A) CN⁻ (Cyanide ion)
- B) NO₂⁻ (Nitrite ion)
- C) SCN⁻ (Thiocyanate ion)
- D) OH⁻ (Hydroxide ion)

2. **Analyze CN⁻ (Cyanide ion)**:
- The cyanide ion has a structure of C≡N⁻.
- The negative charge is located on carbon, and nitrogen has a lone pair.
- Both carbon and nitrogen can act as nucleophiles, making CN⁻ an ambidentate nucleophile.
- **Conclusion**: CN⁻ is ambidentate.

3. **Analyze NO₂⁻ (Nitrite ion)**:
- The nitrite ion has a structure of O=N⁻-O.
- The negative charge can be on one of the oxygen atoms, and nitrogen has a lone pair.
- Both nitrogen and oxygen can donate electrons, making NO₂⁻ an ambidentate nucleophile.
- **Conclusion**: NO₂⁻ is ambidentate.

4. **Analyze SCN⁻ (Thiocyanate ion)**:
- The thiocyanate ion can be represented as S=C=N⁻.
- The negative charge can be on the carbon atom, and both sulfur and nitrogen can donate electrons.
- This means SCN⁻ has two donor sites, making it an ambidentate nucleophile.
- **Conclusion**: SCN⁻ is ambidentate.

5. **Analyze OH⁻ (Hydroxide ion)**:
- The hydroxide ion has the structure of O⁻-H.
- The negative charge is solely on the oxygen atom, and there is no other atom that can act as a nucleophile.
- Therefore, OH⁻ has only one donor site.
- **Conclusion**: OH⁻ is not an ambidentate nucleophile; it is a monodentate nucleophile.

### Final Answer:
The species that is not an ambident nucleophile is **D) OH⁻ (Hydroxide ion)**.