Organic chemistry

Acid-promoted union of a carbonyl-derived oxocarbenium ion with a tethered alkene to form a ring. Cation trapping and the preferred cyclization conformation determine the final substitution and stereochemistry.

An energetic penalty from bond angles, torsions or nonbonded contacts forced away from favourable values by ring closure.

Construction of organic compounds through controlled transformations of simpler precursors.

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.

Assigning the origin and destination of atoms through a synthetic route. carbon counts and the positions of surviving carbonyls expose chain-length and ring-connectivity errors.

A mechanistic correlation by which different reactant stereoisomers lead to different product stereoisomers.

An atom at which exchange of two substituents produces a stereoisomer. A tetrahedral carbon with four distinct substituents is a familiar example.

A carbon bearing both a hydroxyl group and an amino substituent, commonly formed by amine addition to a carbonyl. Cyclic hemiaminals can equilibrate with open-chain carbonyl compounds.

A species with a neutral divalent carbon bearing two nonbonding electrons. Singlet and triplet states differ in their bonding and reaction pathways.

An alkylidene complex with substantial nucleophilic/dianionic carbene character, commonly involving an early high-oxidation-state metal and strongly donating ancillary ligands.

A metal carbene with substantial electrophilic character at carbon, commonly stabilized by a heteroatom substituent and attached to a low-oxidation-state metal carrying pi-acceptor ligands.

A carbene centre in a nitrogen-containing heterocycle, often used as a strong sigma-donor ligand. Steric substitution on nitrogen controls access to a coordinated metal.

A species that transfers carbene-like bonding reactivity without requiring an isolated free carbene. Its reaction depends on its metal or other associated group as well as its substituents.

A metal-associated carbene-like reactive centre. Loss of nitrogen from a diazo precursor can generate a centre capable of alkene cyclopropanation; the catalyst and substituents influence its selectivity.

An alkene with two oxygen substituents on one alkene carbon. Allylic ketene acetals rearrange to unsaturated esters.

A ketene conjugated with a nonaromatic quinoid ring. Elimination from suitable para-hydroxybenzoate anions can form a transient exocyclic ketene that is trapped by water.

Interaction of a filled sigma bond with a neighboring empty or partially occupied orbital. Orbital alignment controls its stabilizing influence and secondary isotope effects.

Elimination through a conjugate base formed before leaving-group departure. The measured kinetic order depends on whether deprotonation equilibrates and which step limits the rate.

Intramolecular electrophilic aromatic substitution that closes a carbon ring. Tether geometry and arene substitution control the accessible site and stereochemistry.

A five-atom pericyclic rearrangement that shifts a sigma bond across adjacent two- and three-atom fragments. Allylic ammonium ylides transfer the terminal allyl carbon to the ylide carbon.

A neutral species with adjacent formally positive and negative centres. Ammonium ylides can undergo stereospecific [2,3]-sigmatropic rearrangements.

A charge-separated species with a nucleophilic carbon adjacent to positively charged sulfur. Conjugate addition followed by displacement of a sulfur leaving group can produce carbocycles or heterocycles.

A ylide with adjacent phosphorus-positive and carbon-negative descriptions, often represented by a phosphorane form. Its carbon can be coupled to a carbonyl carbon in Wittig olefination.

Conjugate addition of a nitrogen nucleophile to an electron-poor alkene. Intramolecular addition can close a nitrogen-containing ring.

Olefination of a carbonyl compound by a stabilized phosphonate carbanion, with phosphate elimination. Many common conditions favor an E alkene.

Carbene addition to an aromatic bond gives a cyclopropane-containing intermediate that can open to a seven-membered cycloheptatriene.

A carbonyl compound with two imidazolyl leaving groups. It activates carboxylic acids as acyl imidazoles, releasing carbon dioxide and imidazole.

A concerted six-electron [3,3]-sigmatropic rearrangement of an allyl vinyl ether into an unsaturated carbonyl compound. Suprafacial bond reorganization correlates stereochemistry across the allyl fragment.

An allylic ester is converted to a silyl ketene acetal, which undergoes a [3,3]-sigmatropic rearrangement to an unsaturated carboxylic-acid derivative.

An allylic alcohol reacts with an orthoester under weak-acid catalysis to give a ketene acetal, which rearranges to an unsaturated ester.

Oxidative conversion of a furfuryl alcohol into a six-membered oxygen heterocycle, often a hydroxypyranone. Oxidation, furan opening and intramolecular lactol formation explain the ring expansion.

A cluster of lithium atoms and carbon-containing ligands in an organolithium solution. Aggregation and exchange depend on solvent, concentration and additional salts.

Catalytic redistribution of carbon–carbon double-bond partners. Intramolecular and intermolecular reactions can compete, producing rings, chains and small alkene coproducts.

A four-membered ring containing one metal and three carbon atoms. Its formation and alternate fragmentation exchange alkylidene groups during olefin metathesis.

Step-growth polymerization in which terminal diene groups undergo intermolecular olefin metathesis. Removing a volatile alkene coproduct can drive conversion.

Intramolecular olefin metathesis connecting two alkene sites into a ring. Terminal-alkene substrates can release ethene; concentration and preorganization influence competition with chain growth.

A compound containing a carbon–nitrogen double bond. Reversible condensation of an aldehyde with a primary amine gives an imine and water under suitable conditions.

An imine whose imine carbon bears two carbon substituents. Hydrolysis passes through a carbinolamine and gives a ketone.

Cleavage of a silicon–oxygen protecting group to reveal an alcohol. Fluoride can drive the transformation through strong silicon–fluorine bond formation.

A cyclic acetal protecting group made from an alcohol and dihydropyran. It protects the original alcohol oxygen and can be removed under suitable acidic hydrolysis conditions.

A tert-butoxycarbonyl group used to protect an amine as a carbamate. Acid-promoted cleavage releases carbon dioxide and restores the amine.

A functional group that can later be converted into a carbonyl at a mapped carbon. A secondary nitro group is a useful example when it also enables carbon–carbon bond formation before unmasking.

Use of ester protecting groups that can be selectively removed under different conditions. A methyl/tert-butyl pair can permit kinetic base hydrolysis at one end and acid-promoted alkyl cleavage at the other.