Foundations

E1 elimination proceeds through ionization followed by loss of a proton from a carbocation intermediate.

In carbocation-mediated addition of HX to an alkene, protonation creates an intermediate that a nucleophile subsequently captures.

In the elementary Hückel description, a planar cyclic continuously conjugated π system with 4n+2 π electrons has a closed-shell aromatic pattern.

In a typical electrophilic aromatic substitution, the aromatic π system bonds to an electrophile, forming a nonaromatic σ intermediate.

A nucleophile adds to the electrophilic carbonyl carbon while the π electron pair moves toward oxygen, forming a tetrahedral intermediate.

For a carboxylic acid derivative, nucleophilic addition can form a tetrahedral intermediate whose collapse expels a leaving group and restores the carbonyl.

Removal of an α proton from a suitable carbonyl compound forms an enolate whose charge is distributed between oxygen and carbon by conjugation.

In a simple aldol pathway, an enolate or enol donor adds to another carbonyl acceptor to create a carbon–carbon bond.

A radical chain has initiation steps that generate radicals, propagation steps that transform reactants while regenerating a radical carrier, and termination steps that consume carriers.

Kinetic control favours products formed more rapidly before equilibration; thermodynamic control reflects an accessible equilibrium product distribution.

In a typical thermal Diels–Alder reaction, a conjugated diene and a dienophile form two σ bonds and a new π bond through a concerted cyclic pathway.

An analytical result concerns the sampled material; inference to a larger population requires a defensible sampling plan.

A detection limit specifies a decision about distinguishability from an appropriate blank or background, with a stated statistical model.

Gravimetry infers analyte amount from a measured mass or mass change and a known chemical or physical relation.

Retention factor measures time spent beyond an unretained marker relative to its transit time.

Molecular infrared absorption probes transitions between vibrational states.

Nuclear magnetic resonance distinguishes magnetically responsive nuclei in different electronic environments.

Coupled nuclear spins can split resonances into multiplets.

A mass spectrometer ionizes material, separates ions by mass-to-charge ratio and detects their abundance.

A molecular symmetry operation leaves the specified nuclear arrangement indistinguishable from its original arrangement.

In an octahedral crystal-field model, d orbitals separate into a lower t2g set and an upper eg set.

Electronic excitation between metal-centred or ligand-involving states can absorb visible light and contribute to complex colour.

Valence occupation and electronic stabilization organize main-group chemistry: alkali metals commonly form +1 ions and alkaline-earth metals +2 ions, while p-block elements support varied covalent structures and oxidation states.

In a common mononuclear two-electron oxidative addition, a substrate bond is replaced by two metal–ligand bonds and the metal's formal oxidation state increases by two.

Migratory insertion combines ligands within a metal coordination sphere, such as an alkyl and CO forming an acyl group.

A conjugated carbonyl has an electrophilic β carbon as well as a carbonyl carbon.

An ester enolate attacks another suitable ester carbonyl.

Hydride-transfer reduction of an aldehyde or ketone forms an alkoxide that can be protonated to an alcohol.

An organomagnesium reagent can transfer its carbon group to an aldehyde or ketone carbonyl, forming an alkoxide and a new carbon–carbon bond.

Oxidation of a primary alcohol can give an aldehyde or continue to a carboxylic acid, while a secondary alcohol can give a ketone.