Question

What is an enantiomer (stereo) isomer?

Answer 1

Could you superimpose your right hand on you left hand? (Or on your identical twin's left hand?) The answer is NO.

Explanation:

Just as your left hand is the mirror image of your right hand, an enantiomer is the mirror image of its optical isomer. In carbon chemistry, it turns out that ANY carbon centre that has 4 different substituents, i.e. `CR_1R_2R_3R_4`, can be CHIRAL or HANDED around `C`, and generate a left-handed and right-handed optical isomer; the `C` atom is known as the chiral centre; and the 2 molecules, identical but for their handedness, are STEREOISOMERS, non-superposable mirror images.

I would urge you to make a few simple models (with toothpicks and plasticene) in order to confirm this optical isomerism. You need to practise visualizing the optical isomerism, and you also need practise to represent three-dimensional optical isomers on the printed page. These are not trivial things to do, but you should spend some time and effort in order to understand it. You will not get that understanding by solely reading this spray.

So here's a tip. You have made this model, `CR_1R_2R_3R_4`; carbon is at the centre of tetrahedron. The interchange of ANY 2 substituents, `R_1`, `R_2` etc., results in representation of the enantiomer.

Biology is replete with examples of handedness. All proteins are left-handed; all sugars are right-handed, and our digestive enzymes (themselves handed) would not act on the left-handed isomer. Most drugs that are administered today are handed, and use of the wrong isomer may have severe biological effects.