450. What chemical reactions cause the basic atoms to form different molecules and, therefore, different polymers?
Covalent bonds are very strong and very directional (meaning that they tend to arrange the atoms at specific angles with respect to one another). Once a molecule has formed, the covalent bonds usually prevent it from rearranging at all but the highest temperatures. Much of the field of organic chemistry is devoted to the problems of controlling the formation of covalent bonds. Very subtle reactions are used to replace one atom with another or with a specific group of atoms. The only real control that the organic chemist has is energetics, dynamics, and statistics. By energetics, I mean that objects tend to follow paths that reduce their potential energies as quickly as possible so that molecules will undergo reactions that reduce the overall potential energies as quickly as possible. If you chose the right chemicals, you can use this energetic control to determine the final molecules. By dynamics, I mean that the reaction pathways are also influenced by issues of motion (inertia, momentum, etc.) so that some energetically favorable reactions may not form because inertia and momentum makes it hard for them to occur. By statistics, I mean that reactions that increase the order of the molecules tend to be rather rare. Nature is always becoming more disordered so that a reaction that brings more order to the universe is unlikely to occur. When you mix chemicals together, they are unlikely to react to form a complete Faberge Egg, complete with a miniature winter scene inside. These different reaction issues can be used together or separately to manipulate atoms into a specific molecule. Usually some of the molecules produced in a synthesis are imperfect and must be separated from the desired molecules. So most organic synthesis projects involve many reaction and purification steps.