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A site adjacent to the unsaturated carbon atom is called the allylic position or allylic site. A group attached at this site is sometimes described as allylic. Thus, CH 2 =CHCH 2 OH "has an allylic hydroxyl group". Allylic C−H bonds are about 15% weaker than the C−H bonds in ordinary sp 3 carbon centers and are thus more reactive.
An allylic rearrangement or allylic shift is an organic chemical reaction in which reaction at a center vicinal to a double bond causes the double bond to shift to an adjacent pair of atoms: It is encountered in both nucleophilic and electrophilic substitution , although it is usually suppressed relative to non-allylic substitution.
Allylic strain in an olefin. Allylic strain (also known as A 1,3 strain, 1,3-allylic strain, or A-strain) in organic chemistry is a type of strain energy resulting from the interaction between a substituent on one end of an olefin (a synonym for an alkene) with an allylic substituent on the other end. [1]
The Tsuji–Trost reaction (also called the Trost allylic alkylation or allylic alkylation) is a palladium-catalysed substitution reaction involving a substrate that contains a leaving group in an allylic position. The palladium catalyst first coordinates with the allyl group and then undergoes oxidative addition, forming the π-allyl
The Kharasch–Sosnovsky reaction is a method that involves using a copper or cobalt salt as a catalyst to oxidize olefins at the allylic position, subsequently condensing a peroxy ester (e.g. tert-Butyl peroxybenzoate) or a peroxide resulting in the formation of allylic benzoates or alcohols via radical oxidation. [1]
The product is a substituted alkene with the double bond shifted to the allylic position. [1] Figure 1 - the ene reaction. This transformation is a group transfer pericyclic reaction, [2] and therefore, usually requires highly activated substrates and/or high temperatures. [3]
In the initiation phase, a pro-oxidant hydroxyl radical (OH•) abstracts the hydrogen at the allylic position (–CH 2 –CH=CH 2) or methine bridge (=CH−) [clarification needed] on the stable lipid substrate, typically a polyunsaturated fatty acid (PUFA), to form the lipid radical (L•) and water (H 2 O).
Due to the rearrangement of the double bond, terminal olefins tend to give primary allylic alcohols: Cyclic alkenes prefer to undergo allylic oxidation within the ring, rather than the allylic position at the sidechain. In bridged ring systems, Bredt’s rule is followed and bridgehead positions are not oxidized: