This illustration shows one of the enantiomers of alanine. You should build a model of its structure if you can. The carbon atom surrounded by four different groups is the chiral centre.

As well as the hydrogen atom it has an amine group (A), a carboxyl group (C) and a methyl group (M). This lettering is used with these 3-dimensional models of alanine to show the optical isomers.

alanine structure 1 THE MODEL CAN BE ROTATED BY CLICKING AND DRAGGING RIGHT CLICK FOR OPTIONS, e.g. to change to spacefilling. Hold down "shift" and drag to change size. Click on image and drag to rotate.

alanine structure 2 THE MODEL CAN BE ROTATED BY CLICKING AND DRAGGING RIGHT CLICK FOR OPTIONS, e.g. to change to spacefilling. Hold down "shift" and drag to change size. Click on image and drag to rotate.

WHAT TO DO

• Start with the structure 1. Identify the chiral carbon and rotate the model till the C-H bond is pointing into the screen, hydrogen furthest away.
• Organise structure 2 in exactly the same way to allow comparison.
• Allocate a letter A, M, or C, to each of the three groups around the carbon. You may wish to write the positions down.

Answer these questions.

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