How do you draw geometric isomers?

Question

Ella Allen · Accepted Answer

With difficulty.

For the typical chiral center, 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. Pick up an organic text and observe how the text represents geometric isomerism. One way to learn how to do this is to get a set of molecular models, which can be as simple as toothpicks and balls of plasticene, 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. Keep in mind that you will be expected to reproduce this geometry when you write answers in an exam. 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.

Easton Jones · Answer

undefined Geometric isomers arise when there is restricted rotation around a double bond or a ring. To draw geometric isomers, you need to represent different spatial arrangements of atoms or groups around the double bond or within the ring. Start by drawing the structural formula of the molecule, then identify the atoms or groups attached to the double bond or within the ring. Finally, represent the different spatial arrangements by positioning these atoms or groups differently relative to each other.