How do you draw geometric isomers?

1 Answer
May 15, 2016

With difficulty.


Get yourself an organic text, and see how the text represents geometric isomerism. For the typical chiral centre, two bonds lie in the plane of the page, one bond extends into the page, and one bond protrudes from the plain of the page.

Note that you will be expected to reproduce this geometry when you write answers in an exam. So how do you learn to do this? Get a set a molecular models; these may be as simple as balls of plasticene and toothpicks, and see how well you can translate this 3D geometry to the 2D printed page. Of course you can buy sophisticated sets of molecular models.

Here is ONE tip. Suppose you have correctly represented a chiral centre, #CR_1R_2R_3R_4# on the printed page so that its geometry, its handedness, is correctly represented by the diagram. The interchange of position of ANY 2 substituents (#R_1# for #R_3#, #R_1# for #R_4#) gives rise to its optical isomer, its enantiomer. Interchange again, and you get back to the original molecule, i.e. the mirror image of a mirror image is the original.