Organic chemistry, branch of chemistry in which carbon compounds and their reactions are studied. A wide variety of classes of substances such as drugs, vitamins, plastics, natrual and synthetic fibers, as well as carbohydrates, proteins, and fats consist of organic molecules. Organic chemists determine the structures of organic molecules, study their various reactions, and develop procedures for ther synthesis of organic compounds. Organic chemistry has had a profound effect on life in the twentith century: It has improved natural and artifical materials that have, in turn, improved health, increased comfort, and added to the convenience of nearly every product manufactured today.