Organic chemistry is a branch of chemistry that studies of structure, properties, composition, reactions, and preparation of carbon-containing compounds. It includes not only hydrocarbons but also compounds with any number of other elements, including hydrogen (most compounds contain at least one carbon-hydrogen bond), nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur. This branch of chemistry was initially limited to compounds produced by living organisms but has been broadened to include human-made substances such as plastics. Organic chemistry is essential because it is the study of life and all of the chemical reactions related to life. Several careers apply an understanding of organic chemistry, such as doctors, veterinarians, dentists, pharmacologists, chemical engineers, and chemists. Organic chemistry is essential because it is the study of life and all of the chemical reactions related to life. Several careers apply an understanding of organic chemistry, such as doctors, veterinarians, dentists, pharmacologists, chemical engineers, and chemists.