Conventionally, the horizontal bonds of the chiral carbon atom are assumed to be coming out of the page whereas the vertical bonds are assumed to be directed backward behind the page. Other elements can produce chiral centers such as sulfur, in the compounds sulfoxides, sulfoximides, sulfonates and the sulfonium ion. An example of the chiral sulfur atom in the sulfoxide structure is given in figure 9.

Figure 9. The Chiral Sulfoxide Structure

In addition, the element phosphorous also produces enantiomers for example phosphine, phosphone oxide, phosphinates and the phosphonium ion. Examples of chiral phosphorous compounds are shown in figure 10.

Cruformate (also called Ruelene or Montrel)

Figure 10 Chiral Compounds of Phosphorous

Similarly, there are enantiomers of the element nitrogen such as amine oxide and the ammonium ions. An example of the enantiomers of (+) and ( ) Methylallyl-phenylbenzyl ammonium Iodide are shown in figure 11.

All enantiomers have identical boiling points, densities, refractive indices and other physical properties. All enantiomers also have identical chemical properties except towards other enantiomers. It follows, that in a chiral environment, such as a biological system, specific reactions between enantiomers can be anticipated. For example, one enantiomer (e.g. the (+) isomer) might readily react with another enantiomer whereas the ( ) isomer will not react at all. The selectivity of the mold penicillium glaucum would be a typical example of this occurrence. Glucose (+) can be readily fermented and metabolized by penicillium glaucum yet ( )glucose is completely rejected. In a similar way, (+) ephedrine is the active enantiomer of ( ) ephedrine but the ( ) ephedrine is not merely inactive but its presence with the other isomer actually reduces the activity of the (+) isomer.