What is stereoisomerism? Draw the geometric isomers of [CoCl₂(en)₂]⁺ and show which of them is optically active.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define.Stereoisomers have the same formula and the same bonds, but a different arrangement of ligands in space.
2 · Draw the trans isomer. Octahedron with Co at the centre, Cl at the top and bottom (180°), and two en rings round the middle. Label it trans.
3 · Draw the cis isomer and its mirror image. Cl on adjacent corners (90°). Draw its mirror image beside it with a dotted mirror line. Label them d and l.
4 · Explain optical activity. The cis form has no plane of symmetry, so it is chiral and optically active. The trans form has a plane of symmetry, so it is inactive.
5 · Close in one line. So [CoCl₂(en)₂]⁺ has three stereoisomers: trans, d-cis and l-cis.
Scoring tip: Always draw the mirror line between the d and l forms, and label every isomer.
