Which of the following is not a nucleophile ?

Options

A. BF3
B. NH3
C. OH-
D. CN-

Explanation

To determine which of the following is not a nucleophile, we need to analyze each option based on the definition of a nucleophile. A nucleophile is a species that has a pair of electrons or a negative charge and can donate these electrons to an electrophile.

### Step-by-Step Solution:

1. **Understand the Definition of Nucleophile**:
- A nucleophile is a "nucleus-loving" species, which means it has an excess of electrons (either as lone pairs or negative charges) and can donate these electrons to an electrophile.

2. **Analyze the First Option: BF3 (Boron Trifluoride)**:
- Boron trifluoride (BF3) has a boron atom that is electron-deficient because it has only six electrons in its valence shell. It has an empty p orbital and can accept a pair of electrons.
- Since BF3 can accept electrons but does not have any to donate, it behaves as an electrophile, not a nucleophile.

3. **Analyze the Second Option: NH3 (Ammonia)**:
- Ammonia has a nitrogen atom with one lone pair of electrons. The electronic configuration shows that nitrogen has five valence electrons, and in NH3, it forms three bonds with hydrogen, leaving one lone pair.
- This lone pair allows ammonia to donate electrons, making it a nucleophile.

4. **Analyze the Third Option: OH- (Hydroxide Ion)**:
- The hydroxide ion (OH-) carries a negative charge due to the extra electron. This negative charge means it has an excess of electrons available for donation.
- Therefore, OH- is a nucleophile.

5. **Analyze the Fourth Option: CN- (Cyanide Ion)**:
- The cyanide ion (CN-) also has a negative charge, indicating that it has an extra electron that can be donated.
- Thus, CN- is also a nucleophile.

6. **Conclusion**:
- Among the options analyzed, BF3 is the only species that does not act as a nucleophile. Therefore, the correct answer is **option A: BF3**.