organic chemistry

Amino acids are natural organic compounds that make up proteins and can thus be considered the basic molecules of life. There are 20 different common amino acids. They consist mainly of carbon, oxygen, hydrogen, and nitrogen. Each amino acid has a common core structure (consisting of two carbon atoms, two oxygen atoms, a nitrogen atom, and four hydrogen atoms) to which is attached a variable group, known as the R group. In glycine, the R group is a single hydrogen atom; in alanine, the R group consists of a carbon and three hydrogen atoms (methyl group).

The molecule of benzene consists of six carbon atoms arranged in a ring, with six hydrogen atoms attached. The benzene ring structure is found in many naturally occurring organic compounds.

Branch of chemistry that deals with carbon compounds. Organic compounds form the chemical basis of life and are more abundant than inorganic compounds. In a typical organic compound, each carbon atom forms bonds covalently with each of its neighbouring carbon atoms in a chain or ring, and additionally with other atoms, commonly hydrogen, oxygen, nitrogen, or sulphur.

The basis of organic chemistry is the ability of carbon to form long chains of atoms, branching chains, rings, and other complex structures. Compounds containing only carbon and hydrogen are known as hydrocarbons.

Organic chemistry is largely the chemistry of a great variety of homologous series – those in which the molecular formulae, when arranged in ascending order, form an arithmetical progression. The physical properties undergo a gradual change from one member to the next.

The linking carbon atoms that form the backbone of an organic molecule may be built up from beginning to end without branching, or may throw off branches at one or more points. Sometimes the ropes of carbon atoms curl round and form rings (cyclic compounds), usually of five, six, or seven atoms. Open-chain and cyclic compounds may be classified as aliphatic or aromatic depending on the nature of the bonds between their atoms. Compounds containing oxygen, sulphur, or nitrogen within a carbon ring are called heterocyclic compounds.

Many organic compounds (such as proteins and carbohydrates) are made only by living organisms, and it was once believed that organic compounds could not be made by any other means. This was disproved when Friedrich Wöhler synthesized urea, but the name ‘organic’ (that is ‘living’) chemistry has remained in use. Many organic compounds are derived from petroleum, which represents the chemical remains of millions of microscopic marine organisms.

In inorganic chemistry, a specific formula usually represents one substance only, but in organic chemistry, it is exceptional for a molecular formula to represent only one substance. Substances having the same molecular formula are called isomers, and the relationship is known as isomerism.

Hydrocarbons form one of the most prolific of the many organic types; fuel oils are largely made up of hydrocarbons. Typical groups containing only carbon, hydrogen, and oxygen are alcohols, aldehydes, ketones, ethers, esters, and carbohydrates. Among groups containing nitrogen are amides, amines, nitro-compounds, amino acids, proteins, purines, alkaloids, and many others, both natural and artificial. Other organic types contain sulphur, phosphorus, or halogen elements.

The most fundamental of all natural processes are oxidation, reduction, hydrolysis, condensation, polymerization, and molecular rearrangement. In nature, such changes are often brought about through the agency of promoters known as enzymes, which act as catalytic agents in promoting specific reactions. The most fundamental of all natural processes is synthesis, or building up. In living plant and animal organisms, the energy stored in carbohydrate molecules, derived originally from sunlight, is released by slow oxidation and utilized by the organisms. The complex carbohydrates thereby revert to carbon dioxide and water, from which they were built up with absorption of energy. Thus, a carbon food cycle exists in nature. In a corresponding nitrogen food cycle, complex proteins are synthesized in nature from carbon dioxide, water, soil nitrates, and ammonium salts, and these proteins ultimately revert to the elementary raw materials from which they came, with the discharge of their energy of chemical combination.