An oxime derived from a ketone. The two carbon substituents and the N–OH orientation determine which group can migrate in a stereospecific Beckmann rearrangement.

Formation of an oxime O-sulfonate increases leaving-group ability at oxygen. Subsequent anti migration can proceed with N–O bond cleavage.

A metal-assisted pathway in which cleavage of a substrate C-H bond transfers H to an electrophilic ligand while new metal-carbon bonding forms. In directed Fischer-carbene insertion, it can precede carbon-carbon reductive elimination.

Organolithium aggregation associates multiple organolithium or related lithium-anion units, often through bridging donor atoms. Strong donor solvents can change aggregate structure without necessarily making only monomers.

An organolithium reagent used as a strong base and carbon nucleophile.

The lithium salt of an N-deprotonated enamine, stabilized by conjugation and often by aggregation.

Working backward from a target to identify bonds, functional-group changes and simpler precursors that correspond to plausible forward reactions. Tracking atoms and stereochemistry tests a proposed disconnection.

A conjugated polymer with hexyl-substituted thiophene repeat units, often used as a model electron-donor semiconductor. Regioregularity and packing influence its optical and transport response.

A soluble fullerene derivative, commonly the C60-based phenyl-C61-butyric acid methyl ester, used as an electron acceptor in organic photovoltaic blends. Different fullerene cage sizes give related derivatives.

Molecular excitations in organic semiconductors often retain strong local character. Weak screening supports Frenkel excitons or intermolecular charge-transfer admixtures, so a photon can create a bound neutral excitation rather than free carriers. Transition dipoles, spin selection rules, molecular packing and Franck-Condon factors set the bright spectral features. Disorder and thermal vibrations broaden them. Electronic overlap can also produce more delocalized excitons; the molecular limit is a useful model, not a definition covering every organic solid.

An electrophile replaces a substituent, commonly hydrogen, on an aromatic system. Initial bond formation can make an arenium ion; loss of a proton then restores aromaticity.

A Stork enamine reaction uses a carbonyl compound's enamine as a carbon nucleophile, then hydrolyses the resulting iminium ion to restore the carbonyl. It enables alkylation or conjugate addition without retaining the amine in the product.

A nucleophilic substitution replaces a leaving group by a nucleophile. In a concerted SN2 reaction, bond formation and departure occur in the same elementary step, commonly with inversion at the attacked stereocenter.

An SN1 reaction instead forms an intermediate before capture, often a carbocation, so rearrangement and a different stereochemical outcome may be possible. Substrate structure, solvent, leaving-group ability, and nucleophile properties influence which pathway is available. The substitution product alone does not uniquely identify the mechanism.

A nucleophilic addition forms a bond by attack of a nucleophile on an electrophilic multiple bond, reducing its bond order. A common case is attack on the carbon of a carbonyl group, with its pi electrons displaced toward oxygen.

Protonation of the resulting oxygen-centered intermediate can give an alcohol. Unlike nucleophilic substitution, the basic addition step does not expel a leaving group from the attacked carbon. Carbonyl polarization and orbital geometry explain both why carbon is attacked and why the incoming bond follows a preferred approach direction.

A Michael addition makes a bond at the beta carbon of a conjugated electrophile through conjugate addition. An enamine can supply a carbon nucleophile; subsequent hydrolysis restores its original carbonyl group.

The aldol reaction forms a carbon-carbon bond when an enol or enolate adds to an aldehyde or ketone. The initial addition product is a beta-hydroxy carbonyl compound, containing the combined carbon frameworks.

For example, acetaldehyde can add to another acetaldehyde molecule to give 3-hydroxybutanal. Subsequent loss of water gives an alpha,beta-unsaturated carbonyl compound, the condensation product. Keeping addition and dehydration distinct explains why an aldol reaction need not itself eliminate water. The reaction is useful for constructing longer carbon skeletons with predictable functional groups.

An elimination reaction removes groups from a substrate while forming a new multiple bond. Removing a hydrogen and a leaving group from neighboring carbons can produce an alkene.

An E2 elimination combines bond cleavage and bond formation in one elementary step; an E1 elimination passes through an intermediate, usually a carbocation. These alternatives predict different rate laws and stereochemical requirements. In a concerted elimination, orbital alignment can make an antiperiplanar conformation decisive, linking product formation to molecular geometry.

A Robinson annulation combines a Michael addition with an intramolecular aldol reaction and dehydration. Tracking the atoms shows which carbonyl survives and which new bond closes the six-membered ring.

The Weitz-Scheffer epoxidation of an electron-poor alkene uses hydroperoxide addition followed by intramolecular closure and O–O bond cleavage. A planar achiral enone in an achiral environment can give a racemic epoxide pair.