Organic Chemistry | Encyclopedia MDPI

Summary

Organic chemistry explores the structure, properties, synthesis, and reactions of carbon-containing compounds. This collection covers key topics such as organic reaction mechanisms, functional groups, stereochemistry, synthetic methods, and organometallic chemistry. It also highlights applications of organic chemistry in pharmaceuticals, materials science, biotechnology, and chemical manufacturing, showcasing advances in molecular design, sustainable synthesis, and innovative chemical processes that contribute to scientific research and industrial development.

Expand All

Entries

Topic Review

Solvothermal Synthesis

Solvothermal synthesis denotes chemical transformation in a solvent contained within a closed vessel at a temperature above the solvent’s normal boiling point, so that autogenous or externally imposed pressure maintains a condensed reaction medium. The solvent is an active physicochemical variable: its polarity, proticity, coordinating ability, viscosity, and supercritical or subcritical state influence precursor solubility, hydrolysis, condensation, transport, and nucleation [1]. Temperature, pressure, fill fraction, precursor concentration, and mineralizers jointly define the reaction domain. Hydrothermal synthesis is the aqueous subset; solvothermal synthesis is broader and includes nonaqueous solvents [2]. The concept is not synonymous with ordinary reflux, because the sealed system permits temperatures and pressures inaccessible at the solvent’s atmospheric boiling point, and it is distinct from dry solid-state reaction because molecular transport and chemical speciation occur in a fluid medium. Products may precipitate or crystallize in situ as supersaturation develops.

2
19 Oct 2026

Topic Review

Solid Phase Synthesis

Solid phase synthesis is a method in which the initial substrate is covalently attached through a cleavable linker to an insoluble polymeric or inorganic support, and subsequent transformations are performed on the support-bound intermediate. Reagents are normally supplied in solution and may be used in excess; after each reaction, unconsumed reagents and soluble by-products are removed by filtration and washing rather than by isolating the growing molecule [1]. A complete cycle therefore comprises support loading, reaction, washing, and, when required, temporary protecting-group removal, followed eventually by cleavage from the support. Merrifield peptide synthesis established the defining iterative form of the method, while solid-phase organic synthesis extends the same support-and-linker logic beyond peptides [2]. The concept excludes simple heterogeneous catalysis because the product-forming substrate, not merely a catalyst, is immobilized, and it excludes adsorption without a designed covalent attachment and cleavage strategy.

5
19 Oct 2026

Topic Review

[1,2]-Wittig Rearrangement

The [1,2]-Wittig rearrangement converts an ether bearing a carbanion or organolithium center adjacent to oxygen into an alcohol through migration of one carbon substituent from oxygen to the carbanionic carbon. The α-alkoxy organolithium precursor is commonly generated by deprotonation, tin–lithium exchange, or another metalation method. Carbon–oxygen bond homolysis then gives a radical pair whose recombination forms the new carbon–carbon bond; work-up protonates the resulting alkoxide [1]. The migrating group and the lithium-bearing terminus move across one atom, which accounts for the [1,2] designation. Configurational behavior often includes retention at the migrating carbon and inversion at the organolithium terminus under suitable substrate control [2]. The reaction is distinct from phosphorus-ylide olefination and from the concerted [2,3]-Wittig rearrangement of allylic ethers. Its defining substrate is an ether-derived α-oxy carbanion, and its defining product is a rearranged alcohol with a newly formed C–C bond.

4
19 Oct 2026

Topic Review

Von Pechmann Reaction

The von Pechmann reaction, commonly called the Pechmann condensation, forms a coumarin by acid-catalyzed condensation of a phenol with a β-ketoester or β-keto acid derivative. Acid activation enables transesterification or direct electrophilic acylation of the phenolic oxygen, followed by intramolecular electrophilic aromatic substitution at an ortho position, dehydration, and formation of the fused α-pyrone ring [1]. The β-keto component supplies the carbonyl-containing three-carbon unit, while the phenol supplies the benzene ring and ring oxygen of the coumarin. Substituent placement follows the orientation of the phenolic ring and the constitution of the β-keto reagent [2]. The transformation is distinct from the Perkin and Knoevenagel routes to coumarins because it constructs the heterocycle directly from a phenol and a β-carbonyl carboxylic derivative under acidic conditions. Formation of the fused 2H-chromen-2-one framework is its defining structural outcome.

2
19 Oct 2026

Topic Review

Ullmann Reaction

The Ullmann reaction is a copper-mediated coupling of aryl halides that forms a biaryl carbon–carbon bond. In its classical form, two aryl halide molecules are coupled by copper at elevated temperature, with loss of halide and creation of the bond between their ipso carbons [1]. Modern Ullmann-type chemistry extends the copper-mediated or copper-catalyzed manifold to arylation of nitrogen, oxygen, and sulfur nucleophiles, but these C–heteroatom variants are more precisely designated Ullmann-type amination, etherification, or thioetherification [2]. Proposed mechanisms depend on ligand, substrate, and conditions and can involve copper(I)/copper(III) cycles, single-electron pathways, or surface processes. The defining boundary of the original Ullmann reaction is reductive aryl–aryl coupling, which distinguishes it from nucleophilic aromatic substitution and from palladium-catalyzed cross-couplings. Both coupling partners are aryl fragments, and copper is the characteristic metal mediator.

2
19 Oct 2026

Topic Review

Transalkylation

Transalkylation is the transfer of an alkyl group from one organic molecule to another, producing a new pair or distribution of alkylated and dealkylated products without changing the total number of alkyl groups in the reacting system. In aromatic chemistry, an alkylbenzene acts as the alkyl donor and another aromatic ring as the acceptor, commonly on a Brønsted-acidic zeolite through carbocationic or surface-bound alkyl intermediates [1]. The process interconverts mono-, di-, and trialkylbenzenes, and product distributions reflect alkyl-transfer equilibria, aromatic substitution selectivity, pore topology, and acid-site accessibility [2]. It differs from simple alkylation, which introduces an alkyl group from a distinct alkylating reagent, and from dealkylation, in which the removed group is not transferred to an organic acceptor. Disproportionation is the special case in which two molecules of the same alkylated compound exchange groups to yield less- and more-substituted products.

3
19 Oct 2026

Topic Review

Thio-Claisen Rearrangement

The thio-Claisen rearrangement is the sulfur analogue of the Claisen rearrangement: a thermal or promoted [3,3]-sigmatropic reorganization of an allyl vinyl sulfide or a related allyl sulfur substrate. In the classical form, the six-atom cyclic transition structure reorganizes the allyl–sulfur and vinyl π bonds to create a new carbon–carbon σ bond and a homoallylic thiocarbonyl product [1]. Allyl aryl sulfides can undergo a related thio-Claisen process that transfers the allyl group to an ortho carbon of the aromatic ring and initially forms a dearomatized sulfur-containing intermediate, which then rearomatizes to an ortho-allyl thiophenol derivative [2]. The reaction is distinguished from the oxy-Claisen rearrangement by sulfur at the heteroatom position and from ionic allylic substitution by its concerted pericyclic bond topology. Substrate geometry and chair- or boat-like transition-state conformation govern regio- and stereochemical transfer.

3
19 Oct 2026

Topic Review

Suzuki Coupling

Suzuki coupling, more precisely the Suzuki–Miyaura cross-coupling, is a palladium- or nickel-catalyzed reaction that joins an organoboron compound with an organic electrophile to form a carbon–carbon bond. Typical partners are aryl, vinyl, or alkyl boronic acids, boronate esters, or organotrifluoroborates and aryl or vinyl halides or pseudohalides. The catalytic sequence comprises oxidative addition of the electrophile to a low-valent metal, base-assisted activation and transmetalation of the carbon group from boron, and reductive elimination of the coupled product [1]. The base converts the organoboron reagent or metal-bound ligand sphere into a form competent for transfer, but it is not itself the coupling catalyst. The defining distinction from Stille coupling is use of organoboron rather than organotin reagents, and from Heck coupling is transfer of a discrete carbon group rather than migratory insertion of an alkene. The reaction accommodates stereodefined alkenyl partners and commonly preserves their alkene geometry [2].

4
19 Oct 2026

Topic Review

Stille Coupling

Stille coupling is a palladium-catalyzed cross-coupling between an organostannane and an organic electrophile, usually an aryl, vinyl, allyl, or acyl halide or pseudohalide, that forms a new carbon–carbon bond. The catalytic cycle comprises oxidative addition of the electrophile to Pd(0), transmetalation that transfers the organic group from tin to palladium, and reductive elimination of the coupled product while regenerating Pd(0) [1]. The carbon group bound to tin is transferred with retention of its basic carbon skeleton, whereas the other substituents on tin generally remain in an organotin byproduct. Ligands, additives, electrophile identity, and the relative transfer aptitude of groups on tin control rate and chemoselectivity. The defining organometallic partner is an organotin reagent; organosilicon compounds instead participate in Hiyama coupling, and organoboron compounds in Suzuki–Miyaura coupling. Stille's account of palladium-catalyzed coupling of organotin reagents with organic electrophiles establishes this specific reaction boundary [2].

3
19 Oct 2026

Topic Review

Spirocyclization

Spirocyclization is a ring-forming transformation that creates a spiro compound, a polycyclic structure in which two rings share exactly one atom and no bond. The shared spiro atom is usually tetrahedral carbon but may be a heteroatom; formation of one or both bonds to that center establishes the orthogonal or near-orthogonal ring arrangement characteristic of spiro connectivity. Intramolecular nucleophilic addition, radical addition, cycloaddition, dearomatization, and transition-metal-mediated bond formation can all produce this topology. Dearomative spirocyclization forms a spiro center while converting an aromatic or heteroaromatic π system into a nonaromatic ring, as demonstrated in electrochemical processes [1] and ynamide cyclizations [2]. The term specifies product topology rather than a single mechanism. It differs from fused-ring cyclization, where two rings share two adjacent atoms and their connecting bond, and from bridged-ring formation, where rings share two nonadjacent bridgehead atoms connected by multiple paths.

4
19 Oct 2026

Other Entry Collections