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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.
In organic chemistry, the ene reaction (also known as the Alder-ene reaction by its discoverer Kurt Alder in 1943) is a chemical reaction between an alkene with an allylic hydrogen (the ene) and a compound containing a multiple bond (the enophile), in order to form a new σ-bond with migration of the ene double bond and 1,5 hydrogen shift.
However, as shown in B a hydrogen bond can form that is energetically favorable and cancels the disfavorable allylic strain. Thus, B is the most stable conformation. With certain polar substituents, hydrogen bonding can occur in the allylic system between the substituents. Rather than the strain that would normally occur in the close group ...
Each carbon atom of the double bond uses its three sp 2 hybrid orbitals to form sigma bonds to three atoms (the other carbon atom and two hydrogen atoms). The unhybridized 2p atomic orbitals, which lie perpendicular to the plane created by the axes of the three sp 2 hybrid orbitals, combine to form the pi bond.
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.
The allyl ligand is commonly in organometallic chemistry.Usually, allyl ligands bind to metals via all three carbon atoms, the η 3-binding mode.The η 3-allyl group is classified as an LX-type ligand in the Green LXZ ligand classification scheme, serving as a 3e – donor using neutral electron counting and 4e – donor using ionic electron counting.
The selective activation and functionalization of alkane C–H bonds was reported using a tungsten complex outfitted with pentamethylcyclopentadienyl, nitrosyl, allyl and neopentyl ligands, Cp*W(NO)(η 3-allyl)(CH 2 CMe 3). [11] C–H activation of pentane, as seen in Ledgzdins et al., J. Am. Chem. Soc. 2007; 129, 5372–3.
Early work showed that allylic alcohols give facial selectivity when using meta-chloroperoxybenzoic acid (m-CPBA) as an oxidant. This selectivity was reversed when the allylic alcohol was acetylated. This finding leads to the conclusion that hydrogen bonding played a key role in selectivity and the following model was proposed. [1]