The Lewis acid character of boron trihalides follows the order:
p-Block Elements (Class 11) · Class 11 · JEE Main Previous Year Question
The Lewis acid character of boron trihalides follows the order:
- a
- b✓
- c
- d
Strategy: Rank the Lewis acid character of boron trihalides .
Step 1: Lewis Acidity vs Back-Donation Boron in is Lewis acidic (electron-deficient). However, the halide lone pairs can back-donate into Boron's empty orbital, reducing the Lewis acidity.
Back-donation effectiveness follows size-matching: back-donates most (best 2p–2p overlap with B), back-donates least (poor 2p–5p overlap).
Therefore:
- More back-donation → less Lewis acid character
- Less back-donation → more Lewis acid character
Step 2: Lewis Acidity Order ( has the least Lewis acid character despite common misconception, because F back-donates most effectively to fill B's empty orbital.)
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