4AB › Chemistry PYQ › CSIR-NET › June 2018 › Q48Q48 · CSIR-NET Chemistry, June 2018 Paper: CSIR-NET June 2018 · Subject: Inorganic Chemistry · Chapter: Organometallic Compounds · Topic: Organometallic Compounds – General · Marks: 2 · Difficulty: Hard
The correct increasing order of C-C bond length in the following molecules (A-D) \[ \left[\mathrm{PtCl}_{3}\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)\right]^{-}(\mathrm{A}),\left[\mathrm{Pt}\left(\mathrm{PPh}_{3}\right)_{2}\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)\right](\mathrm{B}),\left[\mathrm{Pt}\left(\mathrm{PPh}_{3}\right)_{2}\left\{\mathrm{C}_{2}\left(\mathrm{CH}_{4}\right)\right\}\right](\mathrm{C}) \]
(a) $(\mathrm{C})<(\mathrm{A})<(\mathrm{B})$
(b) $(\mathrm{A})<(\mathrm{B})<(\mathrm{C})$
(c) (B) $<$ (C) $<$ (A)
(d) (C) $<$ (B) $<$ (A)
Answer Answer: B ✓ checked by 4AB · confidence high
The source book printed D; on checking, B is correct — see the explanation.
Explanation Back-donation lengthens C=C. It is weakest in Zeise's anion (Pt(II), A), stronger in Pt(0)(PPh₃)₂(C₂H₄) (B), and strongest in the tetracyanoethylene complex (C), which has the best π-acceptor alkene. A < B < C (b).
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