E–Z configuration, or the E–Z convention, is the IUPACpreferred method of describing the absolutestereochemistry of double bonds in organic chemistry. 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 substituents. E and Z notation are only used when a compound doesn't have two identical substituents.
Following the Cahn–Ingold–Prelog priority rules (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, German:[ɛntˈɡeːɡən], 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, German:[tsuˈzamən], the German word for "together").
(E)-But-2-ene
(Z)-But-2-ene
The letters E and Z are conventionally printed in italic type, within parentheses, and separated from the rest of the name with a hyphen. They are always printed as full capitals (not in lowercase or small capitals), 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 is (2E,4E,6Z,8E)-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 stereochemistryedit
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 IUPAC but may still be required by computer software.[1]
notation, redirects, here, epik, high, album, configuration, convention, iupac, preferred, method, describing, absolute, stereochemistry, double, bonds, organic, chemistry, extension, trans, isomer, notation, which, only, describes, relative, stereochemistry, . E redirects here For e see e Epik High album E Z configuration or the E Z convention is the IUPAC preferred method of describing the absolute stereochemistry of double bonds in organic chemistry 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 substituents E and Z notation are only used when a compound doesn t have two identical substituents Following the Cahn Ingold Prelog priority rules 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 German ɛntˈɡeːɡen 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 German tsuˈzamen the German word for together E But 2 ene Z But 2 eneThe letters E and Z are conventionally printed in italic type within parentheses and separated from the rest of the name with a hyphen They are always printed as full capitals not in lowercase or small capitals 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 E 1 Bromo 1 2 dichloroethene Z 1 Bromo 1 2 dichloroetheneAlitretinoinFor 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 is 2E 4E 6Z 8E 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 editThe 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 IUPAC but may still be required by computer software 1 nbsp Alkene stereochemistrySee also editDescriptor chemistry Geometric isomerism Molecular geometryReferences edit Brecher Jonathan 2006 Graphical representation of stereochemical configuration IUPAC Recommendations 2006 PDF Pure and Applied Chemistry 78 10 1897 1970 doi 10 1351 pac200678101897 S2CID 97528124 Panico R Powell W H Richer J C eds 1993 Recommendation 7 1 2 A Guide to IUPAC Nomenclature of Organic Compounds IUPAC Blackwell Science ISBN 0 632 03488 2 Retrieved from https en wikipedia org w index php title E Z notation amp oldid 1212987371, wikipedia, wiki, book, books, library,
