Chemistry prefixes

chemical nomenclature describing absolute stereochemistry of double bonds, generalizing cis–trans notation

The prefix thio-, when applied to a chemical, such as an ion, means that an oxygen atom in the compound has been replaced by a sulfur atom. This term is often used in organic chemistry. For example, from the word ether, referring to an oxygen-containing compound having the general chemical structure , where R and R′ are organic functional groups and O is an oxygen atom, comes the word thioether, which refers to an analogous compound with the general structure , where S is a sulfur atom covalently bonded to two organic groups. A chemical reaction involving the replacement of oxygen to sulfur is

In the nomenclature of organic chemistry, a locant is a term to indicate the position of a functional group or substituent within a molecule.

The prefix aza- is used in organic chemistry to form names of organic compounds where a carbon atom is replaced by a nitrogen atom. The related term "deaza-" refers to when a nitrogen is removed and, usually, a carbon atom is put in its place. Sometimes a number between hyphens is inserted before it to state which atom the nitrogen atom replaces. It arose by shortening the word azote, which is an obsolete name for nitrogen in the English language and occurs in current French usage (azote), meaning "nitrogen".

In chemical nomenclature, nor- is a prefix to name a structural analog that can be derived from a parent compound by the removal of one carbon atom along with the accompanying hydrogen atoms. The nor-compound can be derived by removal of a , , or CH group, or of a C atom. The "nor-" prefix also includes the elimination of a methylene bridge in a cyclic parent compound, followed by ring contraction. (The prefix "homo-" which indicates the next higher member in a homologous series, is usually limited to noncyclic carbons). The terms desmethyl- or demethyl- are synonyms of "nor-".