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''E''–''Z'' configuration, or the ''E''–''Z'' convention, is the 
For organic molecules with multiple double bonds, it is sometimes necessary to indicate the alkene location for each ''E'' or ''Z'' symbol. For example, the chemical name of
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
preferred method of describing the absolute Absolute may refer to:
Companies
* Absolute Entertainment, a video game publisher
* Absolute Radio, (formerly Virgin Radio), independent national radio station in the UK
* Absolute Software Corporation, specializes in security and data risk manag ...
stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereo ...
of double bond
In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...
s in organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...
. It is an extension of ''cis''–''trans'' isomer notation (which only describes ''relative stereochemistry'') that can be used to describe double bonds having two, three or four substituent
A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and '' functional group'', as well as '' ...
s.
Following the Cahn–Ingold–Prelog priority rules
In organic chemistry, the Cahn–Ingold–Prelog (CIP) sequence rules (also the CIP priority convention; named for R.S. Cahn, C.K. Ingold, and Vladimir Prelog) are a standard process to completely and unequivocally name a stereoisomer of a ...
(CIP rules), each substituent on a double bond is assigned a priority, then positions of the higher of the two substituents on each carbon are compared to each other. If the two groups of higher priority are on opposite sides of the double bond (''trans'' to each other), the bond is assigned the configuration ''E'' (from ''entgegen'', , the German word for "opposite"). If the two groups of higher priority are on the same side of the double bond (''cis'' to each other), the bond is assigned the configuration ''Z'' (from ''zusammen'', , the German word for "together").
The letters ''E'' and ''Z'' are conventionally printed in italic type
In typography, italic type is a cursive font based on a stylised form of calligraphic handwriting. Owing to the influence from calligraphy, italics normally slant slightly to the right. Italics are a way to emphasise key points in a printed tex ...
, within parentheses
A bracket is either of two tall fore- or back-facing punctuation marks commonly used to isolate a segment of text or data from its surroundings. Typically deployed in symmetric pairs, an individual bracket may be identified as a 'left' or 'r ...
, and separated from the rest of the name with a hyphen
The hyphen is a punctuation mark used to join words and to separate syllables of a single word. The use of hyphens is called hyphenation. ''Son-in-law'' is an example of a hyphenated word. The hyphen is sometimes confused with dashes ( figur ...
. They are always printed as full capitals (not in lowercase
Letter case is the distinction between the letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowercase (or more formally ''minuscule'') in the written representation of certain languages. The writing ...
or small capitals
In typography, small caps (short for "small capitals") are characters typeset with glyphs that resemble uppercase letters (capitals) but reduced in height and weight close to the surrounding lowercase letters or text figures. This is technicall ...
), but do not constitute the first letter of the name for English capitalization rules (as in the example above).
Another example: The CIP rules assign a higher priority to bromine than to chlorine, and a higher priority to chlorine than to hydrogen, hence the following (possibly counterintuitive) nomenclature.
For organic molecules with multiple double bonds, it is sometimes necessary to indicate the alkene location for each ''E'' or ''Z'' symbol. For example, the chemical name of alitretinoin
Alitretinoin, or 9-cis-retinoic acid, is a form of vitamin A. It is also used in medicine as an antineoplastic (anti-cancer) agent developed by Ligand Pharmaceuticals. It is a first generation retinoid. Ligand gained Food and Drug Administratio ...
is (2''E'',4''E'',6''Z'',8''E'')-3,7-dimethyl-9-(2,6,6-trimethyl-1-cyclohexenyl)nona-2,4,6,8-tetraenoic acid, indicating that the alkenes starting at positions 2, 4, and 8 are ''E'' while the one starting at position 6 is ''Z''.
See also
*Descriptor (chemistry)
A descriptor is in chemical nomenclature a prefix placed before the systematic substance name, which describes the configuration or the stereochemistry of the molecule. Some listed descriptors are only of historical interest and should not be us ...
* Geometric isomerism
Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
* Molecular geometry
Molecular geometry is the three-dimensional space, three-dimensional arrangement of the atoms that constitute a molecule. It includes the general shape of the molecule as well as bond lengths, bond angles, torsional angles and any other geometric ...
References
* {{DEFAULTSORT:E-Z notation Chemistry prefixes Stereochemistry