Activity 1 Enantiomers

There are four different possible arrangements at a tetrahedral carbon atom: One with four identical groups; one with three identical groups; one with two identical groups and one where all the groups are different. These are shown in the table below as pairs of compounds.  At this stage, do not worry about the nature of the groups, the models have been built using different coloured atoms to represent different groups.

Align the molecules in each pair so as to look like mirror images, in a fashion similar to that in figure 1.6. Having done this, move one molecule of each pair to see if it can be positioned to look exactly like its partner.  Only for the models with four different groups should there be no arrangement in which the models align. They are enantiomers.

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You may find it valuable to complete this exercise using your model kit:
Use your Molymod kit to build the four different possible arrangements at a tetrahedral carbon atom: One with four identical groups; one with three identical groups; one with two identical groups and one where all the groups are different. At this stage, do not worry about the nature of the groups, just use different coloured atoms to represent different groups.

Next, build a mirror image partner of each model. Place your completed model pairs next to each other in a similar fashion to that shown in figure 1.6. Having ensured that the models really are mirror images, try lining them up. Only for the models with four different groups should there be no arrangement in which the models align. They are enantiomers.

Take one of your enantiomers and swap the positions of any two of the groups. Now try lining it up with its partner. By inverting two groups, you have converted one enantiomer into the other - the models should now align.