How many of the following carbanions are stabilised by d-orbital resonance (p-d π overlap) ?
(i) (ii) (iii) (iv)
(v) (vi) (vii)

Question

How many of the following carbanions are stabilised by d-orbital resonance (p-d π overlap) ? (i) (ii) (iii) (iv) (v) (vi) (vii)

TestHub · Accepted Answer

The carbanion lone pair can overlap with a vacant 3d orbital of a second-row atom such as S or P.

(i) $- SC H_{3}$ : sulphur has vacant d orbitals: yes. (ii) $- OC H_{3}$ : oxygen has no d orbitals: no. (iii) $- N^{+} (C H_{3})_{3}$ : nitrogen has no d orbitals (only an electrostatic effect): no. (iv) $- P^{+} (C H_{3})_{3}$ : phosphorus has d orbitals (a phosphonium ylide): yes. (v) Benzyl: stabilised by ordinary p-π resonance with the ring: no. (vi) $- S O_{2} C H_{3}$ : sulphur d orbitals: yes. (vii) $- C \equiv N$ : p-π resonance, not d orbitals: no.

Total = 3.

Answer: 3.

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