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Stereoisomers     

       Stereoisomers are compounds with the same elements, even in the same places, but with different orientations in space. This means that some of the bonds are switched. The wedged molecule on one may be the dashed molecule on the other. The two chemicals are identical in composition, identical in order, but vary in which atoms or groups point in which direction

Examples of Stereoisomers

      It's hard to talk about stereoisomers without mentioning chirality. Chirality is when two atoms are nonsuperimposable. I've always disliked this explanation, and it never really made sense to me. It always seemed easier to simply say asymmetrical, because chiral molecules are aymmetrical. The two stereoisomers are enantiomers and diastereomers. Enantiomers are the mirror image of each other. They are further explained in the "Enantiomers" section, or the first E in STEREO. Diastereomers are chiral stereoisomers that aren't enantiomers

    Understanding chiral carbons is easier than chiral molecules. Chiral carbons, also called chiral centers, or stereogenic centers, are simply carbons with 4 different groups attached. It could be N, O, C, H, like in example one to the left. Or, if there are repeating groups, like the two carbons in number 2, it is then up to what the common atom is attached to. One carbon in number 2 has H, H, H. The other has H, O, H. Since the two are different, the central carbon is still considered chiral.

Sometimes, you are asked to identify stereogenic centers in a Fischer Projection. 

3D Structure vs. Fischer Projection

       Fischer projections are pretty simple, assuming the vertical parts are pushed back, and the horizontal ones are pointing toward the viewer. Assuming that all 6 pieces are different, this molecule would have 2 chiral carbons.