List I
(Species)
List II
(Type of back bonding)
(P) $(CH_{3})_{3} CO^{-}$
(1) $np π - np π$
(Q) Boron trichloride
(2) $np π - (n + 1) p_{π}$
(R) Phosphorous trifloride
(3) No back bonding
(S) Diflorocarbene (singlate)
(4) $np_{π^{-}} (n + 1) d_{π}$

Question

List I (Species)	List II (Type of back bonding)
(P) $(CH_{3})_{3} CO^{-}$	(1) $np π - np π$
(Q) Boron trichloride	(2) $np π - (n + 1) p_{π}$
(R) Phosphorous trifloride	(3) No back bonding
(S) Diflorocarbene (singlate)	(4) $np_{π^{-}} (n + 1) d_{π}$

TestHub · Accepted Answer

(P) (CH₃)₃CO⁻: The central carbon is sp³ hybridized and lacks vacant orbitals, resulting in no back bonding (3).

(Q) Boron trichloride (BCl₃): Back bonding occurs from the lone pair of Cl (3p) to the vacant 2p orbital of B, which is $n p_{π} - (n + 1) p_{π}$ (2) where $n = 2$ .

(R) Phosphorus trifluoride (PF₃): Back bonding involves electron donation from F (2p) to the vacant 3d orbitals of P, matching $n p_{π} - (n + 1) d_{π}$ (4).

(S) Difluorocarbene (:CF₂): Back bonding occurs between the 2p orbitals of F and the vacant 2p orbital of C, representing $n p_{π} - n p_{π}$ (1).

Matching these gives P $\to$ 3, Q $\to$ 2, R $\to$ 4, S $\to$ 1, which is Option (D).

Chemistry - CHEMICAL BONDING Question with Solution | TestHub

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