Question

Which of the following is not a nucleophile?

• A. \(BF_3\)
• B. \(NH_3\)
• C. \(C_2H_5O^{-}\)
• D. All of these

Hint:

Electron-deficient compounds such as \(BF_3\), \(AlCl_3\), and \(FeCl_3\) are Lewis acids and behave as electrophiles rather than nucleophiles.

Answer 1

The Correct Option is A

Concept: A nucleophile is an electron-rich species capable of donating an electron pair to an electron-deficient center. Characteristics of nucleophiles:
• Possess lone pairs of electrons.
• Carry negative charge or high electron density.
• Act as Lewis bases. Species that accept electron pairs are called electrophiles or Lewis acids.

Step 1: Analyze \(NH_3\). Ammonia contains a lone pair on nitrogen. \[ NH_3 \] Therefore, it acts as a nucleophile.

Step 2: Analyze \(C_2H_5O^{-}\). Ethoxide ion carries a negative charge and possesses lone pairs on oxygen. Hence, it is a strong nucleophile.

Step 3: Analyze \(BF_3\). Boron in \(BF_3\) has only six electrons in its valence shell. Therefore, it is electron deficient and readily accepts electron pairs. Hence, \[ BF_3 \] acts as a Lewis acid (electrophile), not a nucleophile. Thus, \[ \boxed{BF_3} \] is not a nucleophile. Therefore, the correct option is \[ \boxed{(A)} \]