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A 1,6-Conjugate addition attacks the delta carbon of an extended conjugated electrophile. The resulting extended enolate can be protonated at different sites; proton transfer or equilibration can favor a product retaining carbonyl–alkene conjugation.

An addition reaction joins reacting molecular entities while reducing bond multiplicity and retaining their atoms in the combined product. For example, adding hydrogen across an alkene's carbon–carbon double chemical bond produces a saturated product. The reverse transformation is an elimination reaction.^[ref]

The net transformation does not uniquely specify the mechanism. Electrophilic, radical and concerted routes can give addition products with different rate laws and stereochemistry. Tracking both the atoms and the changing bond order separates an addition reaction from a replacement or rearrangement.

An alkenyl aluminate has an anionic aluminium-containing unit attached to an alkene carbon. Intramolecular oxygen coordination can close a five-membered ring in directed propargylic alcohol reductions.

An alkenyl group is a monovalent carbon–hydrogen substituent derived from an alkene by removing one hydrogen atom. The attachment can be at a double-bonded carbon or elsewhere in the carbon skeleton. For an acyclic parent with one double bond, the group composition is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2n-1}$.^[ref]

For example, a vinyl group attaches as $\mathrm{R}-\mathrm{CH}=\mathrm{C}{\mathrm{H}}_2$ and contributes ${\mathrm{C}}_2{\mathrm{H}}_3$, whereas an allyl group attaches as $\mathrm{R}-\mathrm{C}{\mathrm{H}}_2-\mathrm{CH}=\mathrm{C}{\mathrm{H}}_2$ and contributes ${\mathrm{C}}_3{\mathrm{H}}_5$. The attachment atom in the first example belongs to the double bond; in the second it is adjacent to the double bond. A prenyl group is another alkenyl group, with five carbon atoms.^[ref]

The missing hydrogen identifies an attachment site in a larger molecule; it does not mean that the completed attached group must contain an unpaired electron. Formulae alone also do not specify connectivity. For $n=3$, the composition ${\mathrm{C}}_3{\mathrm{H}}_5$ does not by itself tell where the attachment or double bond lies. A structural formula supplies information that the atom count omits.

A carbon fragment doubly bonded to a metal in the present organometallic usage. Metal–alkylidene exchange with an alkene underlies olefin metathesis.

Axial stereoisomerism in suitably substituted alkylidenecyclohexanes, where the constrained ring and alkene distinguish two handed arrangements.

The compound $\mathrm{C}{\mathrm{H}}_2=\mathrm{CHC}{\mathrm{H}}_2\mathrm{Br}$. nucleophilic substitution at its bromomethylene carbon introduces an allyl group without consuming the alkene.

Allylic strain is an unfavourable steric interaction involving substituents around the region next to a carbon–carbon double bond. The double bond restricts rotation and makes the relative placement of nearby groups particularly important.

A rotation around an adjacent single bond can reduce crowding while changing which face of the alkene is exposed to a reagent. This provides a route from conformational preference to reaction stereoselectivity. The term should specify the interacting groups and conformation; it is not a universal fixed energy penalty for every allylic fragment.

An addition whose regiochemical outcome is opposite to the conventional Markovnikov orientation. hydroboration followed by oxidation places OH at the less substituted alkene carbon.

Asymmetric dihydroxylation adds two hydroxyl groups across an alkene while favouring one stereochemical product. In the Sharpless approach, a chiral ligand controls an osmium-based catalytic environment, turning an otherwise face-symmetric reaction into an enantioselective transformation.^[ref]

The new oxygen-bearing centres are formed in a correlated addition. Substrate geometry and the ligand's handedness jointly determine which stereoisomer is favoured.

Beta-hydride elimination transfers hydrogen from the beta carbon of a metal-bound alkyl to the metal while forming an alkene. It can release a growing polymer chain and compete with migratory insertion. Its accessibility depends on geometry, available sites and bond energetics.

Addition of bromine and an oxygen nucleophile across an alkene to form a bromoether. Intramolecular attack on a bromonium ion can close a ring; tether length, charge distribution and anti opening determine the resulting connectivity.

A bromonium ion bridges both carbons of an alkene-derived three-membered ring. Bromide opening from the opposite face gives an anti vicinal dibromide and avoids a freely rotating open carbocation.

Reduction using hydrogen and a catalyst. Selectivity depends on the catalyst, pressure, solvent and functional groups: reducing an alkene while retaining a ketone is a distinct requirement from reducing a nitrile while retaining an ester.

A hydrosilylation cycle involving Si–H oxidative addition, alkene insertion into the metal–hydride bond, and C–Si reductive elimination. This defines the conventional version; insertion into a metal–silyl bond describes a modified alternative.

An ester containing the conjugated fragment Ph-CH=CH-C(=O)-O-R. Its trans alkene commonly has a large vicinal proton coupling, while HMBC can connect an alkoxy methylene to the ester carbonyl.

The Cossee-Arlman mechanism propagates a polymer through alkene coordination followed by insertion into a metal–carbon bond. Repetition extends the metal-bound chain. Regioselectivity controls monomer connectivity; it does not by itself specify tacticity.

A cyclic osmate ester contains the newly formed carbon–oxygen bonds of an osmium-mediated alkene dihydroxylation. Both oxygen atoms attach on the same face; hydrolytic cleavage of metal–oxygen bonds releases the diol.

A puckered conformation with an approximately planar alkene end and a nonplanar saturated part. Bulky substituents commonly favor pseudoequatorial positions.

The Dewar-Chatt-Duncanson model describes an alkene–metal bond through donation from the filled alkene $\pi$ orbital to the metal and pi backbonding from the metal into alkene ${\pi }^{\ast }$. Backbonding weakens and lengthens the alkene double bond. A $d^0$ early-metal ion has little conventional $d$-electron backbonding.