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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.
Alkyl groups that contain one ring have the formula −C n H 2n−1, e.g. cyclopropyl and cyclohexyl. The formula of alkyl radicals are the same as alkyl groups, except the free valence "−" is replaced by the dot "•" and adding "radical" to the name of the alkyl group (e.g. methyl radical •CH 3).
In allyl compounds, where the next carbon is saturated but substituted once, allylic rearrangement and related reactions are observed. Allyl Grignard reagents (organomagnesiums) can attack with the vinyl end first. If next to an electron-withdrawing group, conjugate addition (Michael addition) can occur.
Alkyl group (e.g., methyl group, ethyl group) Alkenyl group (e.g., vinyl group, allyl group) Alkynyl group (propargyl group) Benzyloxycarbonyl group (Cbz) tert-butoxycarbonyl group (Boc) Carboxyl group
R = heteroatom, alkyl, aryl, allyl etc. or other substituents. In organic chemistry , benzyl is the substituent or molecular fragment possessing the structure R−CH 2 −C 6 H 5 . Benzyl features a benzene ring ( C 6 H 6 ) attached to a methylene group ( −CH 2 − ).
These groups are found in many compounds. Propenyl compounds are isomeric with allyl compounds, which have the formula CH 2-CH=CH 2. The three common precursors to lignin are derivatives of propenylbenzene: paracoumaryl alcohol (1), coniferyl alcohol (2) and sinapyl alcohol (3).
1,2-Methyl shifts also occur in vinyl cations, and like 1,2-hydride shifts, they have higher activation barriers compared to their alkyl cation equivalents. In the protonation of alkynes, both 1,2-hydride and 1,2-methyl shifts may take place. The preference depends on the alkyl substituent since it will dictate the resulting allyl cation product.
Often such agostic interactions involve alkyl or aryl groups that are held close to the metal center through an additional σ-bond. [ 2 ] [ 3 ] Short interactions between hydrocarbon substituents and coordinatively unsaturated metal complexes have been noted since the 1960s.