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In organic chemistry, syn-and anti-addition are different ways in which substituent molecules can be added to an alkene (R 2 C=CR 2) or alkyne (RC≡CR).The concepts of syn and anti addition are used to characterize the different reactions of organic chemistry by reflecting the stereochemistry of the products in a reaction.
syn/anti peri/clinal. a torsion angle between 0° and ±90° is called syn (s) a torsion angle between ±90° and 180° is called anti (a) a torsion angle between 30° and 150° or between −30° and −150° is called clinal (c) a torsion angle between 0° and ±30° or ±150° and 180° is called periplanar (p)
When talking of diastereomers, syn and anti are used to describe groups on the same or opposite sites in zigzag projection, see Diastereomer#Syn / anti. syn and anti are always written small and italic, locants (if used) are placed in front of the word and separated by hyphens.
When all reagents are achiral, only simple diastereoselectivity (syn versus anti, see above) must be considered. Addition takes place via an S E ' mechanism involving concerted dissociation of tin and C-C bond formation at the γ position.
When the single bond between the two centres is free to rotate, cis/trans descriptors become invalid. Two widely accepted prefixes used to distinguish diastereomers on sp³-hybridised bonds in an open-chain molecule are syn and anti. Masamune proposed the descriptors which work even if the groups are not attached to adjacent carbon atoms.
The following reaction gives a syn:anti ratio of 80:20 using a lithium enolate compared to 97:3 using a dibutylboron enolate. Where the counterion determines stereoinduction strength, the enolate isomer determines its direction. E isomers give anti products and Z give syn: [21] Anti-aldol formation through E-enolate Syn-aldol formation through ...
Pages in category "Stereochemistry" The following 139 pages are in this category, out of 139 total. ... Syn and anti addition; T. Tacticity; Thorpe–Ingold effect ...
Overview of reaction with consideration of stereochemistry. Whether the anti-diastereomer or the syn-diastereomer is built depends largely on reaction conditions, substrates and Lewis acids. The archetypical reaction is that of the silyl enol ether of cyclohexanone, (CH 2) 5 CO, with benzaldehyde, C 6 H 5 CHO.