Question

Draw all the optical isomers of ${[Co{(en)_3}]^{3 + }}$

Answer 1

Hint: The different arrangement of the atoms of a molecule in space is termed as isomers. The term isomer is inspired from the Greek language in which it means as iso as same ane mers as parts. The credit for the discovery and the development of isomerism goes to J. Von Liebig of Germany in $1823$ .

Complete answer:
Isomers are classified into structural isomers and stereoisomers.
Structural isomers are further classified into ionisation isomerism, solvent or hydrate isomerism, linkage isomerism, coordination isomerism, coordination position isomerism, and polymerisation isomerism.
Stereo isomers are further classified into geometrical isomers which are further classified into cis, trans, facial and meridonial isomers, and the optical isomers.
The optical isomers are of three types as (i) $[M\,{(AA)_3}\,]$ type with example as ${[Co{(en)_3}]^{3 + }}$ . (ii) $[M\,{(AA)_2}{B_2}\,]$ or $[M\,{(AA)_2}BC\,]$ type with example as $[CoC{l_2}{(en)_2}]$ . and (iii) $[M\,(AA){B_2}{C_2}\,]$ type with example as $[Co(en){(N{H_3})_2}C{l_2}]$ .
The most important criteria for a molecule to be optically active is the prosperity of the chirality. But chirality does not only mean different atoms attached to the central atom. For a molecule to be chiral, there should be absence of all the elements of symmetry.

Note:
 The elements of symmetry are (i) Axis of symmetry, (ii) Plane of symmetry, (iii) Improper axis of symmetry, (iv) Inversion. Iff any of the symmetric elements is present, then that molecule is considered to be achiral and does not possess optical activity. The ${[Co{(en)_3}]^{3 + }}$ has all the same ligands but lacks all the elements of symmetry thus regarded as optically active.