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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)
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.
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 disposition of the formed stereocenters is deemed syn or anti, depending if they are on the same or opposite sides of the main chain: Syn and anti products from an aldol (addition) reaction. The principal factor determining an aldol reaction's stereoselectivity is the enolizing metal counterion.
Klyne notation views the placement of the substituent on the front atom as being in regions of space called anti/syn and clinal/periplanar relative to a reference group on the rear atom. A plus (+) or minus (−) sign is placed at the front to indicate the sign of the dihedral angle.
See: E-Z notation Violet leaf aldehyde, systematic name (E,Z)-nona-2,6-dienal, is a compound having one (E)- and one (Z)-configured double bond. The descriptors (E) (from German entgegen, 'opposite') and (Z) (from German zusammen, 'together') are used to provide a distinct description of the substitution pattern for alkenes, cumulenes or other double bond systems such as oximes.
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The Peterson olefination (also called the Peterson reaction) is the chemical reaction of α-silyl carbanions (1 in diagram below) with ketones (or aldehydes) to form a β-hydroxysilane (2) which eliminates to form alkenes (3).