Question

The relative Lewis acid strengths of boron trihalides are in the

• A. BBr\(_3\) \(>\) BC\(_3\) \(>\) BF\(_3\)
• B. BC\(_3\) \(>\) BF\(_3\) \(>\) BBr\(_3\)
• C. BF\(_3\) \(>\) BC\(_3\) \(>\) BBr\(_3\)
• D. BF\(_3\) \(>\) BBr\(_3\) \(>\) BC\(_3\)

Hint:

Fluorine is the most electronegative element, so \( \text{BF}_3 \) is the strongest Lewis acid among the boron trihalides.

Answer 1

The Correct Option is C

Step 1: Understanding Lewis Acidity
Lewis acids are compounds that accept electron pairs.
The strength of a Lewis acid depends on the ability of the central atom to accept electrons.
The more electronegative the substituent, the stronger the acid.
Step 2: Explanation of the Trend
\( \text{BF}_3 \) (boron trifluoride) has the highest electronegativity due to the fluorine atoms, which makes it the strongest Lewis acid.
\( \text{BC}_3 \) (boron trichloride) is less electronegative than \( \text{BF}_3 \), making it a weaker acid.

\( \text{BBr}_3 \) (boron tribromide) has the lowest electronegativity among the three and is thus the weakest Lewis acid.

Step 3: Conclusion
Thus, the correct order of Lewis acid strength is \( \text{BF}_3 > \text{BC}_3 > \text{BBr}_3 \).