The nomenclature in Chimie is the whole of the rules, symbols, terms, intended to represent and pronounce the names of the studied bodies.

The key objective of a nomenclature is to lead to names of chemical compounds without ambiguity, namely that the same name should never be used to indicate two different chemical compounds. On the other hand, the same sufficiently complex chemical compound can receive several different names coming from various nomenclatures, or even sometimes coming from the same nomenclature.

The official nomenclature in organic chemistry is the Nomenclature IUPAC (International union of chemistry pure and applied).

General information

The knowledge of a species in organic chemistry revêt two aspects:

1. the structure which is that of the molecule, defined by the relative position in space of the various atoms (static aspect).

2. the reactivity , related to the structure, which gives an account of the behavior with respect to other molecules (dynamic aspect).

History of the attempts at nomenclatures

The need for a nomenclature was made particularly feel at the end of the XIXe century, in front of progress of the chemistry and the increasingly significant number of known molecules. An international commission was formed in 1889, composed mainly of French. She manages to finalize of them rules at the time of the congress of Geneva of 1892, known under the name of nomenclature of Geneva . She does not take however counts the aromatic molecules of them, nor the compounds having several functions.

This first nomenclature is specified and supplemented in 1930 under the name of nomenclature of Liege . That Ci will be amended at the court of various international congresses, outcome with a new version, will be published in 1958 under the name of nomenclature of Paris .

Structure of the molecules

An organic molecule is made up:

• of a carbonaceous skeleton consisted carbonaceous sequences with the various forms (chain, cycle,…).

• of functional groups characteristic of the chemical functions (Acid alcohol, , amine, etc)

For each molecule, it is necessary to establish the structure while being based on experimental facts (chemical evidence and spectroscopic) and to propose a representation by a symbolism which gives an account of the various types of connection between the atoms (double and triple connections, cycle) and also of the space structure.

Formulate compounds

Empirical formula or stoechiometric formula

The empirical formula or stoechiometric formula indicates the number of atoms of each element present in the molecule (analyzes elementary).

Examples

Formulate developed

The developed formula indicates how are connected between them the various atoms; by respecting the valences, one can simplify it by writing the semi-developed formulas.

Examples

Stereochemical formula

The stereochemical formula restores the architecture of the molecule and gives an account of isomerisms, conformations and the configurations.

Names of hydrocarbons

Alkanes

The Alcane S are saturated hydrocarbons (simple connections only), linear (without cycle) of empirical formula.

^† the form hendécane is not recommended. ^‡ the form " éicos-" is obsolete.

Ramified alkanes or alkylalcanes

They are made up:

• of a basic alkane which is that which has the hydrocarbon chain longest;
• of ramifications alkyls (shorter chains hydrocarbon) which can in their turn being ramified.

To name a ramified hydrocarbon, one indicates the side chains by prefixes joined in the name of basic hydrocarbon.

To name a alkylalcane whose formula is given

• to find the chain hydrocarbon longest to regard as basic alkane and to give him a name
• to identify any alkyl group connected on alkane and to give him a name (radical); to place this name prefixes some in front of the name of basic alkane by respecting the alphabetical order.
• to make precede the name by each radical by a figure indicating the position of the ramification on basic alkane; the classification of basic alkane is done from one end to another so that the sum of the indices is weakest possible. The index (there is as much as ramifications) is always placed in front of the name to which it refers.

Example

• 4-éthyl-3-méthylheptane

• In the event of choice of classification of the substituents, one must low give the index to the priority radical alphabetically.

To write the chemical formula of an alkane whose name is given

• to write as many carbons as requires it the name of basic alkane and to number each one of its atoms;
• to make in the same way with the radicals by positioning them on basic alkane according to the numbers of carrying carbon on basic alkane.

Principal ramified radicals

Other radicals

Cycloalcanes

The monocyclic alkanes of empirical formula are named while making precede by the cyclo prefix the name of alkane.

Examples: cyclobutane, cycloheptane, 1,1,3-triméthylcyclopentane.

The alkanes bicyclic take the name of linear alkane of the same many carbons preceded by the prefix bicyclo. After this prefix, one puts between hooks the number of carbon atoms of each of the 3 bridges, one numbers the atoms of the cycle starting from a head of bridge by numbering in first the longest chain leading to the other head of bridge, one continues by numbering the average chain in revenatn towards the first head of bridge then one finishes by shortest.

Examples:

Unsaturated hydrocarbons

Olefinic hydrocarbons

The name of a Alcène is copied on that of alkanes: the suffix - ass is replaced by the suffix - ene and the position of the double connection must be preceded by an index of position low for the first carbon of the connection. The hydrocarbons carrying 2 double connections are called alcadienes.

Examples

CH₃-CH₂CH=CH₂ goal-1-ène

CH₃CH=CHCH₂CH=CHCH₃ hepta-2-5-diene

Groups derived from olefinic hydrocarbons

• the groups alcényles

CH₂=CH- éthényle or vinyl

CH₂=CH-CH₂- M.-2-ényle or allyl

• the groups alkylidenes

CH₃CH= ethylidene

• the alkylenes groups: divalent groups derived from alkanes by elimination of a hydrogen at each end of the chain

- CH₂- methylene

- CH=CH- vinylene

Alkyne compounds

The name of a Alcyne is obtained starting from the name of alkane by replacing the suffix - ass by the suffix - yne. The numbering of carbons is carried out in the same way that for olefinic hydrocarbons.

Examples of olefinic hydrocarbons and alkyne compounds

Aromatic hydrocarbons

Most current are in general derived from the Benzène.

Hydrocarbons indicated by a commonplace name

Examples:

Cases of derived from disubstituted benzene

• in position 1,2 position ortho ( O )

• in position 1,3 position méta ( m )
• in position 1,4 para position ( p )

Examples: O - dichlorobenzene, p - bromotoluene.

The aromatic hydrocarbons form groups Aryle S:

With in the order from left to right: the remainder phenyl, group pH, the remainder benzyl.

Polycyclic hydrocarbons

Examples of most known:

Functional derivatives of hydrocarbons

The organic functions are announced in the composition of the name of a derivative polyfonctionnel of hydrocarbon either by a prefix or by a suffix.

• the principal function is in suffix.
• All the other functions are in prefix according to a definite hierarchy.

Organic functions always announced in prefix

Principal organic functions classified by decreasing set of priorities

See too

• chemical Compound
• Nomenclature of organic chemistry UIPAC

External bonds

• IUPAC : Nomenclature of the organic chemistry
• assistant IUPAC: helps with the nomenclature of the organic French molecules

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