Description and nomenclature

 

     Classification is not possible without having a full description of the individual compounds. In contrast with inorganic chemistry, in which describing a chemical compound can be achieved by simply enumerating the chemical symbols of the elements present in the compound together with the number of these elements in the molecule, in organic chemistry the relative arrangement of the atoms within a molecule must be added for a full description.

     One way of describing the molecule is by drawing its structural formula. Because of molecular complexity, simplified systems of chemical notation have been developed. The latest version is the line-angle formula, which achieves simplicity without introducing ambiguity. In this system, the endpoints and intersections of each line represent one carbon, and hydrogens can either be notated or assumed to be present by implication. Some disadvantages of chemical notation are that they are not easily described by words and they are not easily printable. These problems have been addressed by describing molecular structures using organic nomenclature .

     Because of the difficulties arising from the very large number and variety of organic compounds, chemists realized early on that the establishment of an internationally accepted system of naming organic compounds was of paramount importance. The Geneva Nomenclature was born in 1892 as a result of a number of international meetings on the subject.

     It was also realized that as the family of organic compounds grew, the system would have to be expanded and modified. This task was ultimately taken on by the International Union on Pure and Applied Chemistry (IUPAC). Recognizing the fact that in the branch of biochemistry the complexity of organic structures increases, the IUPAC organization joined forces with the International Union of Biochemistry and Molecular Biology, IUBMB, to produce a list of joint recommendations on nomenclature.

     Later, as the numbers and complexities of organic molecules grew, new recommendations were made within IUPAC for simplification. The first such recommendation was presented in 1951 when a cyclic benzene structure was named a cyclophane. Later recommendations extended the method to the simplification of other complex cyclic structures, including heterocyclics, and named such structures phanes.

     For ordinary communication, to spare a tedious description, the official IUPAC naming recommendations are not always followed in practice except when it is necessary to give a concise definition to a compound, or when the IUPAC name is simpler (viz. ethanol versus ethyl alcohol). Otherwise the common or trivial name may be used, often derived from the source of the compound.

     In summary, organic substances are classified by their molecular structural arrangement and by what other atoms are present along with the chief (carbon) constituent in their makeup, whilst in a structural formula, hydrogen is implicitly assumed to occupy all free valences of an appropriate carbon atom which remain after accounting for branching, other element(s) and/or multiple bonding.