''E''–''Z'' configuration, or the ''E''–''Z'' convention, is the

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preferred method of describing the

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stereochemistry Stereochemistry, a subdiscipline of chemistry, studies the spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which are defined ...

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 matter, organic materials, i.e., matter in its various forms that contain ...

. 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 In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...

s. E and Z notation are only used when a compound doesn't have two identical substituents. Following the

Cahn–Ingold–Prelog priority rules In organic chemistry, the Cahn–Ingold–Prelog (CIP) sequence rules (also the CIP priority convention; named after Robert Sidney Cahn, Christopher Kelk Ingold, and Vladimir Prelog) are a standard process to completely and unequivocally nam ...

(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

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, within

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, and separated from the rest of the name with a

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. They are always printed as full capitals (not in

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), 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. Alitretinoin2DACS

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

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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''.

Undefined ene stereochemistry

The prefix E''/''Z''-' can be used to indicate uncertainty in the E or Z isomers for an ene bond. For graphical representations, wavy single bonds are the standard way to represent unknown or unspecified stereochemistry or a mixture of isomers (as with tetrahedral stereocenters). A crossed double-bond has been used sometimes; it is no longer considered an acceptable style for general use by

but may still be required by computer software. E-Z notation in alkenes

References

* {{Navbox stereochemistry Chemistry prefixes Stereochemistry

Undefined ene stereochemistry

See also

References