Vitamins are organic compounds that are needed in small amounts so that the body can function properly.
An organic compound is called a vitamin when an organism cannot synthesis enough of the compound. Thus the compound needs to be obtained through the diet.
Vitamins can be both water and fat soluble.
Water soluble vitamins- contain functional groups that can hydrogen bond with water. These compounds are not stored in the body.
Fat soluble vitamins - these compounds are non-polar. They can be stored within fatty tissue via dispersion forces with lipids.
Vitamin A diagram By Bully at Croatian Wikipedia - Transferred from hr.wikipedia to Commons by Roberta F. using CommonsHelper., Public Domain, https://commons.wikimedia.org/w/index.php?curid=5289836
Vitamin b12 image By Ymwang42 (talk).Ymwang42 at en.wikipedia [Public domain], from Wikimedia Commons
Vitamin B1-thiamin by By NEUROtiker (Own work) [Public domain], via Wikimedia Commons
Vitamin C structure By en:user:Mykhal / en:user:Cacycle / User:Jrockley (self made, using Image:Dehydroascorbic acid.png) [Public domain], via Wikimedia Commons