. If you look at the drugs on the market over 60% are optically active. In 1980, at least 398 drugs that were marketed as racemic mixtures. We now want to review some of the nomenclature that you never thought you would see again since organic chemistry.
             Remember when you talk about stereochemistry you are talking about a carbon atom which has 4 different ligands. In this case when you have four different ligands this is asymmetric and often referred to as a chiral carbon. This results in 2 mirror images that can not be superimposed. On pg.152 what is shown is an example of L(+) alanine and D(-) alanine and no matter how many times you try to twist and turn that molecule you can never superimpose the left hand side on top of the right hand side. You cannot superimpose optically active isomers, you recall from organic chemistry that when you have this type of situation that such a compound will rotate plane polarized light and one isomer will rotate in one direction and the other isomer in the other. A compound that rotates it to the right is dextrorotatory and that is signified using the term d or (+). A substance that turns it to the left is levoratatory and is signified as L or (-). You also remember when you have a pair of nonsuperimposable images like this there are different words used to describe them. Sometimes they are called optical isomers, optical antipodes, most commonly in the drug literature they are referred to as enantiomers. What is extremely important to recognize is that enantiomers are chemically identical., they have the same melting point, kp, same solubility, same lipophilicity. From a chemical point of view they are identical the only difference is there geometric configuration, that is the only place they are not identical. The other thing you will recognize is that the rotation of plane polarized light does not indicate the configuration. The absolute configuration is generally determined by X-ray crystal...