Chemical nomenclature

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 (IUPAC).

The IUPAC's rules for naming organic and inorganic compounds are contained in two publications, known as the Blue Book[1][2] and the Red Book,[3] respectively. A third publication, known as the Green Book,[4] describes the recommendations for the use of symbols for physical quantities (in association with the IUPAP), while a fourth, the Gold Book,[5] contains the definitions of a large number of technical terms used in chemistry. Similar compendia exist for biochemistry[6] (the White Book, in association with the IUBMB), analytical chemistry[7] (the Orange Book), macromolecular chemistry[8] (the Purple Book) and clinical chemistry[9] (the Silver Book). These "color books" are supplemented by shorter recommendations for specific circumstances that are published periodically 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. The American Chemical Society's 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 (such as the construction of large indices), it becomes necessary to ensure that each compound has a unique name: This requires the addition of extra rules to the standard IUPAC system (the CAS system is the most commonly used in this context), at the expense of having names that are longer and less familiar to most readers. Another system gaining popularity is the International Chemical Identifier (InChI) – 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 (for example, in differing reactivity of sulfur allotropes, which IUPAC does not distinguish). 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 (such as rapamycin) are human-readable, and so most researchers simply use the informal names.

Differing aims of chemical nomenclature and lexicography

It's 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 (with IUPAC nomenclature as the best example) 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 (SAR).

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 (and so access to SAR understanding). 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 at odds with any accepted chemical nomenclature connecting polyphenol structure and bioactivity).

History

Lavoisier Nomenclature01
First page of Lavoisier's Chymical Nomenclature in English.

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 (and often esoteric) 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 (by Lavoisier) between elements and compounds, in the late eighteenth century.

The French chemist Louis-Bernard Guyton de Morveau published his recommendations[10] 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,[11] and promoted by the latter in a textbook that would survive long after his death at the guillotine in 1794.[12] The project was also espoused by Jöns Jakob Berzelius,[13][14] 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.[15]

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

For type-I ionic binary compounds, the cation (a metal in most cases) is named first, and the anion (usually a nonmetal) is named second. The cation retains its elemental name (e.g., iron or zinc), but the suffix of the nonmetal changes to -ide. For example, the compound LiBr is made of Silvio 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 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 (indicating the charge of the cation) is written in parentheses next to the cation name (this is sometimes referred to as Stock nomenclature). 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 (3+ and 3− balance to 0). 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 (giving a 4− charge), the compound must be balanced with a 4+ charge on the Pb cation (lead is a transition metal, and can form cations with a 4+ or a 2+ charge). 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 (instead of a Roman numeral next to it) has an "-ic" or "-ous" suffix added to it to indicate its oxidation state ("-ous" for lower, "-ic" for higher). For example, the compound FeO contains the Fe2+ cation (which balances out with the O2− anion). Since this oxidation state is lower than the other possibility (Fe3+), this compound is sometimes called ferrous oxide. For the compound, SnO2, the tin ion is Sn4+ (balancing out the 4− charge on the two O2− anions), and because this is a higher oxidation state than the alternative (Sn2+), 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:

The formula Na2SO3 denotes that the cation is sodium, or Na+, and that the anion is the sulfite ion (SO2−
3
). 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 (CrO2−
4
). 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 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 (root name of the element + -ide suffix). Then, prefixes are used to indicate the numbers of each atom present: these prefixes are mono- (one), di- (two), tri- (three), tetra- (four), penta- (five), hexa- (six), hepta- (seven), octa- (eight), nona- (nine), and deca- (ten). The prefix mono- is never used with the first element. Thus, NCl3 is called nitrogen trichloride, P2O5 is called diphosphorus pentoxide (the a of the penta- prefix is dropped before the vowel for easier pronunciation), 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 (groups 13–17) are given -ane base name, e.g. borane (BH3), oxidane ( H2O), phosphane (PH3) (Although the name phosphine is also in common use, it is not recommended by IUPAC). The compound PCl3 would thus be named substitutively as trichlorophosphane (with chlorine "substituting"). However, not all such names (or stems) are derived from the element name. For example, N H3 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

References

  1. ^ "1958 (A: Hydrocarbons, and B: Fundamental Heterocyclic Systems), 1965 (C: Characteristic Groups)", Nomenclature of Organic Chemistry (3rd ed.), London: Butterworths, 1971, ISBN 0-408-70144-7.
  2. ^ Rigaudy, J.; Klesney, S. P., eds. (1979). Nomenclature of Organic Chemistry. IUPAC/Pergamon Press. ISBN 0-08022-3699.. Panico R, Powell WH, Richer JC, eds. (1993). A Guide to IUPAC Nomenclature of Organic Compounds. IUPAC/Blackwell Science. ISBN 0-632-03488-2.. IUPAC, Chemical Nomenclature and Structure Representation Division (27 October 2004). Nomenclature of Organic Chemistry (Provisional Recommendations). IUPAC.}}
  3. ^ International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSCIUPAC. ISBN 0-85404-438-8. Electronic version..
  4. ^ International Union of Pure and Applied Chemistry (1993). Quantities, Units and Symbols in Physical Chemistry, 2nd edition, Oxford: Blackwell Science. ISBN 0-632-03583-8. Electronic version..
  5. ^ Compendium of Chemical Terminology, IMPACT Recommendations (2nd Ed.), Oxford:Blackwell Scientific Publications. (1997)
  6. ^ Biochemical Nomenclature and Related Documents, London:Portland Press, 1992.
  7. ^ International Union of Pure and Applied Chemistry (1998). Compendium of Analytical Nomenclature (definitive rules 1997, 3rd. ed.). Oxford: Blackwell Science. ISBN 0-86542-6155. .
  8. ^ Compendium of Macromolecular Nomenclature, Oxford:Blackwell Scientific Publications, 1991.
  9. ^ Compendium of Terminology and Nomenclature of Properties in Clinical Laboratory Sciences, IMPACT Recommendations 1995, Oxford: Blackwell Science, 1995, ISBN 978-0-86542-612-2.
  10. ^ Guyton de Morveau, L. B. (1782), "Mémoire sur les dénominations chimiques, la necessité d'en perfectionner le système et les règles pour y parvenir", Observations sur la physique, 19: 370–382.
  11. ^ Guyton de Morveau, L. B.; Lavoisier, A. L.; Berthollet, C. L.; Fourcroy, A. F. de (1787), Méthode de Nomenclature Chimique, Paris: Cuchet, archived from the original on 2011-07-21.
  12. ^ Lavoisier, A. L. (1801), Traité Élémentaire de Chimie (3e ed.), Paris: Deterville.
  13. ^ Berzelius, J. J. (1811), "Essai sur la nomenclature chimique", Journal de physique, 73: 253–286.
  14. ^ Wisniak, Jaime (2000), "Jöns Jacob Berzelius A Guide to the Perplexed Chemist", Chem. Educator, 5 (6): 343–50, doi:10.1007/s00897000430a.
  15. ^ "Congrès de nomenclature chimique, Genève 1892", Bull. Soc. Chim. Paris, Ser. 3, 7: xiii–xxiv, 1892.

External links

Arene substitution pattern

Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon.

ChEBI

Chemical Entities of Biological Interest, also known as ChEBI, is a database and ontology of molecular entities focused on 'small' chemical compounds, that is part of the Open Biomedical Ontologies effort. The term "molecular entity" refers to any "constitutionally or isotopically distinct atom, molecule, ion, ion pair, radical, radical ion, complex, conformer, etc., identifiable as a separately distinguishable entity". The molecular entities in question are either products of nature or synthetic products which have potential bioactivity. Molecules directly encoded by the genome, such as nucleic acids, proteins and peptides derived from proteins by proteolytic cleavage, are not as a rule included in ChEBI.

ChEBI uses nomenclature, symbolism and terminology endorsed by the International Union of Pure and Applied Chemistry (IUPAC) and Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB).

Chemical formula

A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than are chemical names and structural formulas.

The simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the simple numbers of each type of atom in a molecule, with no information on structure. For example, the empirical formula for glucose is CH2O (twice as many hydrogen atoms as carbon and oxygen), while its molecular formula is C6H12O6 (12 hydrogen atoms, six carbon and oxygen atoms).

Sometimes a chemical formula is complicated by being written as a condensed formula (or condensed molecular formula, occasionally called a "semi-structural formula"), which conveys additional information about the particular ways in which the atoms are chemically bonded together, either in covalent bonds, ionic bonds, or various combinations of these types. This is possible if the relevant bonding is easy to show in one dimension. An example is the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH. However, even a condensed chemical formula is necessarily limited in its ability to show complex bonding relationships between atoms, especially atoms that have bonds to four or more different substituents.

Since a chemical formula must be expressed as a single line of chemical element symbols, it often cannot be as informative as a true structural formula, which is a graphical representation of the spatial relationship between atoms in chemical compounds (see for example the figure for butane structural and chemical formulas, at right). For reasons of structural complexity, there is no condensed chemical formula (or semi-structural formula) that specifies glucose (and there exist many different molecules, for example fructose and mannose, that have the same molecular formula C6H12O6 as glucose). Linear equivalent chemical names exist that can and do specify any complex structural formula (see chemical nomenclature), but such names must use many terms (words), rather than the simple element symbols, numbers, and simple typographical symbols that define a chemical formula.

Chemical formulas may be used in chemical equations to describe chemical reactions and other chemical transformations, such as the dissolving of ionic compounds into solution. While, as noted, chemical formulas do not have the full power of structural formulas to show chemical relationships between atoms, they are sufficient to keep track of numbers of atoms and numbers of electrical charges in chemical reactions, thus balancing chemical equations so that these equations can be used in chemical problems involving conservation of atoms, and conservation of electric charge.

Chemically inert

In chemistry, the term chemically inert is used to describe a substance that is not chemically reactive. Most Group 8 or 18 elements that appear in the last column of the periodic table (Helium, Neon, Argon, Krypton, Xenon and Radon) are classified as inert (or unreactive). These elements are stable in their naturally occurring form (gaseous form) and they are called inert gases.

Enyne

An enyne is an organic compound consisting of an double bond (alkene) and triple bond (alkyne). Its called a conjugated enyne when the double and triple bonds are conjugated.

The term is a contraction of the terms alkene and alkyne.

The simplist enyne is vinylacetylene.

Functional analog (chemistry)

In chemistry and pharmacology, functional analogs are chemical compounds that have similar physical, chemical, biochemical, or pharmacological properties. Functional analogs are not necessarily structural analogs with a similar chemical structure. An example of pharmacological functional analogs are morphine, heroin and fentanyl, which have the same mechanism of action, but fentanyl is structurally quite different from the other two.

Homology (chemistry)

In chemistry, homology is the appearance of homologues. A homologue (also spelled as homolog) is a compound belonging to a series of compounds differing from each other by a repeating unit, such as a methylene bridge −CH2−, a peptide residue, etc.

A homolog is a special case of an analog. Examples are alkanes and compounds with alkyl side chains of different length (the repeating unit being a methylene group -CH2-).

IUPAC books

The International Union of Pure and Applied Chemistry publishes many books, which contain its complete list of definitions. The definitions are divided into seven "colour books": Gold, Green, Blue, Purple, Orange, White, and Red. There is also an eighth book—the "Silver Book".

IUPAC nomenclature of chemistry

The International Union of Pure and Applied Chemistry (IUPAC) has published four sets of rules to standardize chemical nomenclature.

There are two main areas:

IUPAC nomenclature of inorganic chemistry (Red Book)

IUPAC nomenclature of organic chemistry (Blue Book)

IUPAC nomenclature of inorganic chemistry

In chemical nomenclature, the IUPAC nomenclature of inorganic chemistry is a systematic method of naming inorganic chemical compounds, as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It is published in Nomenclature of Inorganic Chemistry (which is informally called the Red Book). Ideally, every inorganic compound should have a name from which an unambiguous formula can be determined. There is also an IUPAC nomenclature of organic chemistry.

IUPAC nomenclature of organic chemistry

In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It is published in the Nomenclature of Organic Chemistry (informally called the Blue Book). Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be created. There is also an IUPAC nomenclature of inorganic chemistry.

To avoid long and tedious names in normal communication, the official IUPAC naming recommendations are not always followed in practice, except when it is necessary to give an unambiguous and absolute definition to a compound. IUPAC names can sometimes be simpler than older names, as with ethanol, instead of ethyl alcohol. For relatively simple molecules they can be more easily understood than non-systematic names, which must be learnt or looked up. However, the common or trivial name is often substantially shorter and clearer, and so preferred. These non-systematic names are often derived from an original source of the compound. In addition, very long names may be less clear than structural formulae.

International Chemical Identifier

The IUPAC International Chemical Identifier (InChI IN-chee or ING-kee) is a textual identifier for chemical substances, designed to provide a standard way to encode molecular information and to facilitate the search for such information in databases and on the web. Initially developed by IUPAC (International Union of Pure and Applied Chemistry) and NIST (National Institute of Standards and Technology) from 2000 to 2005, the format and algorithms are non-proprietary.

The continuing development of the standard has been supported since 2010 by the not-for-profit InChI Trust, of which IUPAC is a member. The current software version is 1.05 and was released in January 2017.

Prior to 1.04, the software was freely available under the open-source LGPL license,

but it now uses a custom license called IUPAC-InChI Trust License.

International Nomenclature of Cosmetic Ingredients

The International Nomenclature of Cosmetic Ingredients, abbreviated INCI, is a system of names for waxes, oils, pigments, chemicals, and other ingredients of soaps, cosmetics, and the like, based on scientific names and other Latin and English words. INCI names often differ greatly from systematic chemical nomenclature or from more common trivial names.

Preferred IUPAC name

In chemical nomenclature, a preferred IUPAC name (PIN) is a unique name, assigned to a chemical substance and preferred among the possible names generated by IUPAC nomenclature. The "preferred IUPAC nomenclature" provides a set of rules for choosing between multiple possibilities in situations where it is important to decide on a unique name. It is intended for use in legal and regulatory situations.Preferred IUPAC names are applicable only for organic compounds, to which the IUPAC has the definition as compounds which contain at least single carbon atom but no alkali, alkaline earth or transition metals and can be named by the nomenclature of organic compounds. (see below). Rules for the remaining organic and inorganic compounds are still under development.

The concept of PINs is defined in the introductory chapter (freely accessible) and chapter 5 of the "Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013", which replace two former publications: the "Nomenclature of Organic Chemistry", 1979 (the Blue Book) and "A Guide to IUPAC Nomenclature of Organic Compounds, Recommendations 1993". The full draft version of the PIN recommendations ("Preferred names in the nomenclature of organic compounds", Draft of 7 October 2004) is also available.

Saturated and unsaturated compounds

In organic chemistry, a saturated compound is a chemical compound that has single bonds between carbon atoms.

Structural analog

A structural analog, also known as a chemical analog or simply an analog, is a compound having a structure similar to that of another compound, but differing from it in respect to a certain component.It can differ in one or more atoms, functional groups, or substructures, which are replaced with other atoms, groups, or substructures. A structural analog can be imagined to be formed, at least theoretically, from the other compound. Structural analogs are often isoelectronic.

Despite a high chemical similarity, structural analogs are not necessarily functional analogs and can have very different physical, chemical, biochemical, or pharmacological properties.In drug discovery either a large series of structural analogs of an initial lead compound are created and tested as part of a structure–activity relationship study or a database is screened for structural analogs of a lead compound.Chemical analogues of illegal drugs are developed and sold in order to circumvent laws. Such substances are often called designer drugs. Because of this, the United States passed the Federal Analogue Act in 1986. This bill banned the production of any chemical analogue of a Schedule I or Schedule II substance that has substantially similar pharmacological effects, with the intent of human consumption.

Systematic element name

A systematic element name is the temporary name assigned to a newly synthesized or not yet synthesized chemical element. A systematic symbol is also derived from this name. In chemistry, a transuranic element receives a permanent name and symbol only after its synthesis has been confirmed. In some cases, such as the Transfermium Wars, controversies over the formal name and symbol have been protracted and highly political. In order to discuss such elements without ambiguity, the International Union of Pure and Applied Chemistry (IUPAC) uses a set of rules to assign a temporary systematic name and symbol to each such element. This approach to naming originated in the successful development of regular rules for the naming of organic compounds.

Trivial name

In chemistry, a trivial name is a nonsystematic name for a chemical substance. That is, the name is not recognized according to the rules of any formal system of chemical nomenclature such as IUPAC inorganic or IUPAC organic nomenclature. A trivial name is not a formal name and is usually a common name.

Generally, trivial names are not useful in describing the essential properties of the thing being named. Properties such as the molecular structure of a chemical compound are not indicated. And, in some cases, trivial names can be ambiguous or will carry different meanings in different industries or in different geographic regions. (For example, a trivial name such as white metal can mean various things.) On the other hand, systematic names can be so convoluted and difficult to parse that their trivial names are preferred. As a result, a limited number of trivial chemical names are retained names, an accepted part of the nomenclature.

Trivial names often arise in the common language; they may come from historic usages in, for example, alchemy. Many trivial names pre-date the institution of formal naming conventions. Names can be based on a property of the chemical, including appearance (color, taste or smell), consistency, and crystal structure; a place where it was found or where the discoverer comes from; the name of a scientist; a mythological figure; an astronomical body; the shape of the molecule; and even fictional figures. All elements that have been isolated have trivial names.

Vicinal (chemistry)

In chemistry the descriptor vicinal (from Latin vicinus = neighbor), abbreviated vic, describes any two functional groups bonded to two adjacent carbon atoms (i.e., in a 1,2-relationship). For example, the molecule 2,3-dibromobutane carries two vicinal bromine atoms and 1,3-dibromobutane does not. Mostly, the use of the term vicinal is restricted to two identical functional groups.

Likewise in a gem-dibromide the prefix gem, an abbreviation of geminal, signals that both bromine atoms are bonded to the same atom (i.e., in a 1,1-relationship). For example, 1,1-dibromobutane is geminal. While comparatively less common, the term hominal has been suggested as a descriptor for groups in a 1,3-relationship.

Like other such descriptors as syn, anti, exo or endo, the description vicinal helps explain how different parts of a molecule are related to each other either structurally or spatially. The vicinal adjective is sometimes restricted to those molecules with two identical functional groups. The term can also be extended to substituents on aromatic rings.

Periodic table forms
Sets of elements
Elements
History
See also

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