Solubility applied to Vitamins

Solubility is the extent which a compound dissolves in a solvent. Compounds tend to dissolve in compounds that have similar intermolecular forces. In my undergraduate class we simplify this into the rule of 5. Basically if there are five or less carbons to each polar (oxygen and nitrogen containing) functional roup then it is probably water soluble. If there are 6 or more carbons per polar functional group then the molecule is likely insoluble in water. It will most likely be soluble in hexane or another less polar solvent. There are exceptions for small molecules like acetone, if there are a small number (1 or 2) carbons with a polar functional group then it is probably at least slighltly soluble in water.

One reason why it is okay to load up on vitamin C when you are sick is because it is water soluble. If you intake too much vitamin C you will just end up excreting it, and it will not harm you. The reason for this is because vitamin C is water soluble. Looking at the structure you see a cyclic ester with 4 hydroxy groups. That is 5 carbons to 5 polar functional groups. It is soluble in water.

Another one that is soluble in water is Niacin. The carboxylic acid and the nitrogen are polar functional groups, there are only 6 carbons, so this too is water soluble.

Some examples of water insolube vitamins are vitamin K and vitamin A. These are not so easlily excreted. Ingesting a moderate excess of probably wont hurt you, but in large excess they can build up and cause problems. Story has it that some artic explorers died from eating polar bear liver which contain an unusual amount of vitamin A, which is just one more reason not to eat polar bear livers.

The structures of the non water soluble vitamins have a few polar functional groups, but they have long carbon chains, their carbon to polar functional group ratio greatly exceeds 5:1, therefore they are water insoluble.
We all know the latin root for vita, but apparantly the -amin part comes from amine. Polish chemist Cashimir Funk named them vitamines because he thought that all of these compounds would be amines. The name has since lost the e and Funk's hypthesis has been refuted, but the rest of the letters have remained.