A chemical nomenclature is a set of rules to generate systematic names for
chemical compounds. The nomenclature used most frequently worldwide is the
one created and developed by the International Union of Pure and Applied
Chemistry. The IUPAC's rules for naming organic and
inorganic compounds are contained in two publications, known as the Blue Book and
the Red Book, respectively. A third publication, known as the Green Book,
describes the recommendations for the use of symbols for physical quantities,
while a fourth, the Gold Book, contains the definitions of a large number of
technical terms used in chemistry. Similar compendia exist for
biochemistry, analytical chemistry, macromolecular chemistry and clinical
chemistry. These "color books" are supplemented by shorter recommendations
for specific circumstances that are published from time to time in the
journal Pure and Applied Chemistry. Aims of chemical nomenclature
The primary function of chemical nomenclature is to ensure that a spoken
or written chemical name leaves no ambiguity concerning which chemical
compound the name refers to: each chemical name should refer to a single
substance. A less important aim is to ensure that each substance has a single
name, although a limited number of alternative names is acceptable in some
cases. Preferably, the name also conveys some
information about the structure or chemistry of a compound. CAS numbers
form an extreme example of names that do not perform this function: each CAS
number refers to a single compound but none contain information about the
structure. The form of nomenclature used depends on
the audience to which it is addressed. As such, no single correct form exists,
but rather there are different forms that are more or less appropriate in
different circumstances. A common name will often suffice to
identify a chemical compound in a particular set of circumstances. To be
more generally applicable, the name should indicate at least the chemical
formula. To be more specific still, the three-dimensional arrangement of the
atoms may need to be specified. In a few specific circumstances, it
becomes necessary to ensure that each compound has a unique name: This
requires the addition of extra rules to the standard IUPAC system, at the
expense of having names that are longer and less familiar to most readers.
Another system gaining popularity is the International Chemical Identifier— which
reflects a substance's structure and composition, making it more general than
a CAS number. The IUPAC system is often criticized for
the above failures when they become relevant. While IUPAC has a
human-readable advantage over CAS numbering, it would be difficult to
claim that the IUPAC names for some larger, relevant molecules are
human-readable, and so most researchers simply use the informal names.
Differing aims of chemical nomenclature and lexicography
It is generally understood that the aims of lexicography versus chemical
nomenclature vary and are to an extent at odds. Dictionaries of words, whether
in traditional print or on the web, collect and report the meanings of words
as their uses appear and change over time. For web dictionaries with limited
or no formal editorial process, definitions—in this case, definitions of
chemical names and terms—can change rapidly without concern for the formal
or historical meanings. Chemical nomenclature on the other hand is
necessarily more restrictive: It aims to standardize communication and practice
so that, when a chemical term is used it has a fixed meaning relating to chemical
structure, thereby giving insights into chemical properties and derived
molecular functions. These differing aims can have profound effects on valid
understanding in chemistry, especially with regard to chemical classes that
have achieved mass attention. Examples of the impact of these can be seen in
considering the examples of: resveratrol, a single compound clearly
defined by this common name, but that can be confused, popularly, with its
cis-isomer, omega-3 fatty acids, a reasonably
well-defined chemical structure class that is nevertheless broad as a result
of its formal definition, and polyphenols, a fairly broad structural
class with a formal definition, but where mistranslations and general misuse
of the term relative to the formal definition has led to serious usage
errors, and so ambiguity in the relationship between structure and
activity. The rapid pace at which meanings can
change on the web, in particular for chemical compounds with perceived health
benefits, rightly or wrongly ascribed, complicates the matter of maintaining a
sound nomenclature. A further discussion with specific examples appears in the
article on polyphenols, where differing definitions are in use, and there are
various, further web definitions and common uses of the word odds with any
accepted chemical nomenclature connecting polyphenol structure and
bioactivity). History
The nomenclature of alchemy is rich in description, but does not effectively
meet the aims outlined above. Opinions differ about whether this was deliberate
on the part of the early practitioners of alchemy or whether it was a
consequence of the particular theoretical framework in which they
worked. While both explanations are probably
valid to some extent, it is remarkable that the first "modern" system of
chemical nomenclature appeared at the same time as the distinction between
elements and compounds, in the late eighteenth century.
The French chemist Louis-Bernard Guyton de Morveau published his recommendations
in 1782, hoping that his "constant method of denomination" would "help the
intelligence and relieve the memory". The system was refined in collaboration
with Berthollet, de Fourcroy and Lavoisier, and promoted by the latter in
a textbook that would survive long after his death at the guillotine in 1794. The
project was also espoused by Jöns Jakob Berzelius, who adapted the ideas for the
German-speaking world. The recommendations of Guyton covered
only what would be today known as inorganic compounds. With the massive
expansion of organic chemistry in the mid-nineteenth century and the greater
understanding of the structure of organic compounds, the need for a less
ad hoc system of nomenclature was felt just as the theoretical tools became
available to make this possible. An international conference was convened in
Geneva in 1892 by the national chemical societies, from which the first widely
accepted proposals for standardization arose.
A commission was set up in 1913 by the Council of the International Association
of Chemical Societies, but its work was interrupted by World War I. After the
war, the task passed to the newly formed International Union of Pure and Applied
Chemistry, which first appointed commissions for organic, inorganic, and
biochemical nomenclature in 1921 and continues to do so to this day.
Types of nomenclature = Organic chemistry =
Substitutive name Functional class name, also known as a
radicofunctional name Conjunctive name
Additive name Subtractive name
Multiplicative name Fusion name
Hantzsch–Widman name Replacement name
= Inorganic chemistry = Compositional nomenclature
= Type-I ionic binary compounds = For type-I ionic binary compounds, the
cation is named first, and the anion is named second. The cation retains its
elemental name, but the suffix of the nonmetal changes to -ide. For example,
the compound LiBr is made of Li+ cations and Br− anions; thus, it's called
lithium bromide. The compound BaO, which is composed of Ba2+ cations and O2−
anions, is referred to as barium oxide. The oxidation state of each element is
unambiguous. When these ions combine into a type-I binary compound, their
equal-but-opposite charges are neutralized, so the compound's net
charge is zero. = Type-II ionic binary compounds =
Type-II ionic binary compounds are those in which the cation does not have just
one oxidation state. This is common among transition metals. To name these
compounds, one must determine the charge of the cation and then write out the
name as would be done with Type I Ionic Compounds, except that a Roman numeral
is written in parentheses next to the cation name. For example, take the
compound FeCl3. The cation, iron, can occur as Fe2+ and Fe3+. In order for the
compound to have a net charge of zero, the cation must be Fe3+ so that the
three Cl− anions can be balanced out. Thus, this compound is called iron(III)
chloride. Another example could be the compound PbS2. Because the S2− anion has
a subscript of 2 in the formula, the compound must be balanced with a 4+
charge on the Pb cation. Thus, the compound is made of one Pb4+ cation to
every two S2− anions, the compound is balanced, and its name is written as
lead(IV) sulfide. An older system – relying on Latin names for the elements
– is also sometimes used to name Type II Ionic Binary Compounds. In this system,
the metal has an "-ic" or "-ous" suffix added to it to indicate its oxidation
state. For example, the compound FeO contains the Fe2+ cation. Since this
oxidation state is lower than the other possibility, this compound is sometimes
called ferrous oxide. For the compound, SnO2, the tin ion is Sn4+, and because
this is a higher oxidation state than the alternative, this compound is called
stannic oxide. Some ionic compounds contain polyatomic
ions, which are charged entities containing two or more covalently bonded
types of atoms. It is important to know the names of common polyatomic ions;
these include: ammonium
nitrite nitrate
sulfite sulfate
hydrogen sulfate hydroxide
cyanide phosphate
hydrogen phosphate dihydrogen phosphate
carbonate hydrogen carbonate
hypochlorite chlorite
chlorate perchlorate
acetate, permanganate dichromate
chromate peroxide
The formula Na2SO3 denotes that the cation is sodium, or Na+, and that the
anion is the sulfite ion. Therefore, this compound is named sodium sulfite.
If the given formula is Ca(OH)2, it can be seen that OH− is the hydroxide ion.
Since the charge on the calcium ion is 2+, it makes sense there must be two OH−
ions to balance the charge. Therefore, the name of the compound is calcium
hydroxide. If one is asked to write the formula for copper(I) chromate, the
Roman numeral indicates that copper ion is Cu+ and one can identify that the
compound contains the chromate ion. Two of the 1+ copper ions are needed to
balance the charge of one 2− chromate ion, so the formula is Cu2CrO4.
= Type-III binary compounds = Type-III binary compounds are covalently
bonded. Covalent bonding occurs between nonmetal elements. Covalently-bonded
compounds are also known as molecules. In the compound, the first element is
named first and with its full elemental name. The second element is named as if
it were an anion. Then, prefixes are used to indicate the numbers of each
atom present: these prefixes are mono-, di-, tri-, tetra-, penta-, hexa-,
hepta-, octa-, nona-, and deca-. The prefix mono- is never used with the
first element. Thus, NCl3 is called nitrogen trichloride, P2O5 is called
diphosphorus pentoxide, and BF3 is called boron trifluoride.
Carbon dioxide is written CO2; sulfur tetrafluoride is written SF4. A few
compounds, however, have common names that prevail. H2O, for example, is
usually called water rather than dihydrogen monoxide, and NH3 is
preferentially called ammonia rather than hydrogen nitride.
Substitutive nomenclature This naming method generally follows
established IUPAC organic nomenclature. Hydrides of the main group elements are
given -ane base name, e.g. borane, oxidane, phosphane. The compound PCl3
would thus be named substitutively as trichlorophosphane. However, not all
such names are derived from the element name. For example, NH3 is called
"azane". Additive nomenclature
This naming method has been developed principally for coordination compounds
although it can be more widely applied. An example of its application is
[CoCl(NH3)5]Cl2 pentaamminechloridocobalt(III) chloride.
Ligands, too, have a special naming convention. Whereas chloride becomes the
prefix chloro- in substitutive naming, in a ligand it becomes chlorido-.
See also IUPAC nomenclature of inorganic
chemistry 2005 IUPAC nomenclature of organic chemistry
Preferred IUPAC name IUPAC numerical multiplier
IUPAC nomenclature for organic transformations
International Chemical Identifier List of chemical compounds with unusual
names References
External links