How would you define enantiomers?

1 Answer
Dec 18, 2015

Enantiomers are chiral molecules that (i) are mirror images of each other, and (ii) cannot be superimposed upon each other.


Have you got a pair of gloves handy? Can the left glove be placed over the right glove (i.e. occupy the same space)? Of course they cannot do so, unless you turn one of the gloves inside out. Alternatively, have you ever put your right hoof into your left shoe? Was it comfortable?

But why can't they do so? They are precisely the same structurally and chemically; nevertheless their handed geometry forbids their superposition.

What occurs in the macro world with gloves and shoes, also occurs in the micro world with molecules. It turns out that a carbon atom (or any so-called chiral centre) that has 4 different substituents, i.e. #CR_1R_2R_3R_4#, has 2 optical antipodes such that one form is the mirror image of the other, and the isomers cannot be superimposed.

Biochemistry is replete with examples of handedness. The best example is the sugar you sprinkle on your cornflakes. All this sugar derives from a natural source, and it has a particular chirality or handedness.

Remember that in the opening spray, I gave 2 conditions for enantiomers. BOTH must be fulfilled.