What are some examples of enantiomers?

1 Answer
Oct 29, 2015

Your left hand and your right hand are good examples of enantiomers. I'll think of some chemical examples in a minute.


Suppose you had an identical twin (for all I know you might have one!). When you two shake hands, can your right hand shake his/her left hand? The answer is no, even though your hands should be identical.* I raise this example, because left and right hands are enantiomers; they are "handed" or enantiomeric. Some molecules can exhibit the same sort of isomerism; where one stereoisomer cannot be superimposed on its mirror image. In simple terms, any carbon that has 4 distinct substituents, i.e. #CR_1R_2R_3R_4#, can exist as a pair of non-superimposable mirror images. That particular carbon is the steroegenic or chiral centre.

Lactic acid, #H_3C-C(OH)(H)(CO_2H)#, fits the above description. I can't recall which is the naturally occurring isomer. The amino acid alanine, #H_3C-C(NH_3^+)(H)CO_2^-#, glyceraldehyde, #HOCH_2CH(OH)C(=O)H#, are all examples of molecules that can exist as two optical isomers, depending on disposition of substituents around the chiral carbon (can you identify this centre?). Biology features a great deal of handedness: proteins and sugars all have a particular such handedness or chirality.

PS *I am told that the hands of identical twins would not be identical; identical twins do not have the same sets of fingerprints. I used the hypothetical twins for illustration.