Total number of molecules, in which each covalent bond is comprised of effective back bond.

Question

Total number of molecules, in which each covalent bond is comprised of effective back bond.
$BF_3, N(SiH_3)_3, PF_3, POF_3, B(OH)_3, O(SiH_3)_2, NH(SiH_3)_2, BFH_2, BF_2(NH_2)$

Prashant Kotian · Accepted Answer

Correct answer: 3

**SOLUTION:** BACK BOND FOUND IN EACH COVALENT BOND IN $\RIGHTARROW BF_3, PF_3, POF_3$. Step 1: The strength of the P=O bond in phosphoryl compounds is highly influenced by back-bonding (p-pi d-pi) from Oxygen to Phosphorus. Step 2: Highly electronegative substituents like Fluorine (F) pull electron density away from Phosphorus, increasing its partial positive charge and contracting its d-orbitals. Step 3: This orbital contraction significantly improves the overlap efficiency for p-pi d-pi back-bonding with Oxygen, making the P-O bond exceptionally strong and short in F3PO, corresponding to option (a).

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