Isomers

Isomers are defined as one of several organic compounds with the same molecular formula but different structures and therefore different properties. There are 3 Types of isomers - Structural, Geometric, and Enantiomers. The difference in the main architecture of organic molecules can be seen in the isomers. These compounds have the same molecular formula but different structures therefore different properties.

The first type are the structural isomers they are different because the covalent arrangement of their atoms. As the carbon skeletons increase in size. The possible number of isomers increases. There are only two types of butanes but there are 18 variations and 366,319 possible structural isomers. Then the structural isomers may also vary because of the difference in the locations of the double bonds. Structural isomers are different ways of arranging the same atoms. The more carbons, the more possible ways there will be to arrange the atoms. It is an isomer that exists due to different permutations of element positions in a molecule. Position isomers of pentane are possible since there are 3 ways to build a tree of 5 carbon atoms: n-pentane, isopentane, and neopentane. Geometric structural isomers are related to lack of rotatability in cyclic and multiply bonded species. "Cis" isomers have identical species are located on same side of the multiple bond or ring; "trans isomers" have identical species are located on opposite sides of the multiple bond or ring. Alkanes are the simplest class of structural isomers. They contain only tetravalent (making 4 covalent bonds) Carbon atoms and Hydrogen.

The second type are called the geometric isomers. They all have the same covalent partnership yet they have a difference in their spatial arrangement. Geometric isomers occur from the inflexibility of the double bonds, unlike the single bond. They will not allow the atoms to join geometric isomers that can dramatically affect the biological activities of the organic molecules.

Cis and trans isomers are called geometric isomers. They differ in their geometrical orientation around a double bond that can't rotate. The cis isomer has its substituents on the same side of the double bond while the trans isomer has its substituents on opposite sides of the double bond. Geometric isomers are stereoisomers where the two forms are not mirror images of each other. For example, the compounds cis-2-butene and trans-2-butene both have the same formula, C4H10 and the same atoms are connected to each other in each molecule, but the geometry around the double bond is different. However, the two forms are not mirror images of each other.

The third kind is known as Enantiomers. Enantiomers are non-superimposable mirror images of one another. Not being able to superimpose one molecule on top of the other simply means that the two molecules are not equivalent or identical. For a compound to form an enantiomeric pair, it must have chiral molecules. Chiral molecules must not have an internal plane of symmetry, and they must have a stereocenter. They look like ball and stick figures, where the middle carbon is called an asymmetric carbon. This is because it is attached to four different atoms or groups of atoms. Each enantiomer exhibits what is called optical activity. Each isomer of the pair is capable of rotating plane-polarized light. One isomer rotates this light to the right "x" number of degrees, and the other isomer of the pair rotates this light to the left for the same number of degrees. In fact, this is the only difference in the two isomers, their ability to rotate plane-polarized light in opposite directions. All other physical properties are exactly the same. If the enantiomers are crystalline salts like Pasteur's Tartrate salts, then the enantiomers will have a different appearance when observed under magnification and one can pick them out to separate them, but most enantiomeric pairs are not salts and therefore look the same. This makes it extremely difficult to separate the two isomers should they be mixed as often they are.

The enantiomers are extremely important to people in the pharmaceutical industry. This is because two enantiomers of a drug may not be equally effective. If they are not distrusted properly the drug can produce harmful effects. There are several examples of this throughout history. One small example is of a drug that was prescribed to pregnant women. One of the enantiomers acted as a sedative, which it was supposed to, and the other caused birth defects.