JEE Main · 2020 · 03 Sep 2020 · Shift 1 · Coordination Compounds

The complex that can shows optical activity is:

(A)cis- $[CrCl_{2} (ox)_{2}]^{3 -}$ (ox = oxalate)✓ Correct
(B)trans- $[Cr (Cl_{2}) (ox)_{2}]^{3 -}$
(C)cis- $[Fe (NH_{3})_{2} (CN)_{4}]^{-}$
(D)trans- $[Fe (NH_{3})_{2} (CN)_{4}]^{-}$

Answer: (A)

Solution

A complex is optically active when it has neither a plane nor a centre of symmetry. In cis-

[CrC l_{2} (ox)_{2}]^{3 -}

the two bidentate oxalate rings and the two cis chlorides wrap into a handed arrangement with no such symmetry element, so it exists as a pair of non-superimposable mirror images and is optically active. The trans chromium isomer and both forms of the iron complexes each possess a plane of symmetry and are inactive.

JEE Main · 2020 · 03 Sep 2020 · Shift 1 · Single correct option

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