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Topic Review
August 15: Gerty Theresa Cori Borned
Gerty Theresa Cori (1896–1957) was a pioneering biochemist, best known for her discovery of the enzymatic processes involved in the breakdown and synthesis of glycogen, which is fundamental to our understanding of cellular energy metabolism. Along with her husband, Carl Cori, Gerty received the Nobel Prize in Physiology or Medicine in 1947, becoming the first woman to be awarded this prestigious honor in the field. Cori's research into biochemical reactions within living cells laid the groundwork for much of modern cellular biochemistry and molecular biology.
  • 329
  • 15 Aug 2025
Topic Review
Conductive Polymers
Within materials science and electronic engineering, conductive polymers denote a class of organic macromolecules that combine a conjugated backbone with the ability to transport electronic charge over technologically useful length scales. In contrast to conventional insulating plastics, these materials can reach conductivities spanning from those of semiconductors to values approaching metallic behavior when appropriately doped, while preserving attributes typical of polymers such as low density, mechanical flexibility and solution processability. The discovery of high conductivity in doped polyacetylene in the late 1970s established the modern field of conducting polymers and demonstrated that organic solids with extended π‑conjugation can exhibit conductivity increases of many orders of magnitude upon oxidation or reduction (“p‑doping” or “n‑doping”). Subsequent work generalized these principles to a broad family of heteroatom‑containing polymers, including polyaniline (PANI), polypyrrole (PPy), polythiophenes and their derivatives, as well as copolymers and blends tailored for specific applications. In contemporary organic electronics and photonics, conductive polymers occupy roles ranging from transparent electrodes and charge‑transport layers to active materials in sensors, electrochemical capacitors, actuators and organic thermoelectric devices. Their tunable electronic structure, compatibility with large‑area solution processing, and amenability to molecular design have made them central components in emerging flexible and wearable electronics.
  • 33
  • 11 Sep 2026
Topic Review
Allene Synthesis
Allenes are cumulenes containing two consecutive carbon–carbon double bonds (C=C=C) whose terminal substituents lie in orthogonal planes. Allene synthesis is the set of transformations that install this 1,2-diene array. One established route is the propargyl Claisen rearrangement, in which a propargylic vinyl ether undergoes a 3,3-sigmatropic reorganization to an allenic carbonyl derivative [1]. Radical processes generate the cumulene by addition–elimination or hydrogen-atom transfer sequences that terminate in an allenic radical or closed-shell allene [2]. Fragmentative constructions create the two double bonds by scission of a C–C bond in a suitably disposed precursor, releasing the allene as the unsaturated fragment [3]. SN2' displacement of a propargylic leaving group by an organometallic nucleophile likewise produces a substituted allene. The defining structural criterion is the cumulative C=C=C unit, which distinguishes allenes from isolated dienes, conjugated 1,3-dienes, and alkynes. Axial chirality arises when the four termini are appropriately substituted, so stereochemical control is an intrinsic feature of many allene-forming bond reorganizations.
  • 26
  • 23 Sep 2026
Topic Review
Gibbs Energy Minimization
Gibbs energy minimization is a thermodynamic computational method that determines the equilibrium composition of a closed multiphase, multicomponent system by finding the set of phase amounts and species mole numbers that minimize the total Gibbs free energy subject to elemental mass-balance constraints at specified temperature and pressure [1]. At fixed temperature and pressure, the second law requires the total Gibbs energy G to reach a global minimum at equilibrium, equivalently requiring equality of the chemical potential of each species among all phases in which it appears [2]. The formulation does not require selection of independent chemical reactions; instead, G is expressed as a function of the unknown mole numbers using ideal or non-ideal mixing models, and the minimum is found by constrained optimization, commonly via Lagrange multipliers or the RAND algorithm [3]. It is distinguished from equilibrium-constant methods, which solve reaction stoichiometry explicitly, by treating equilibrium as an optimization over the distribution of phases and species rather than over reaction extents [4].
  • 19
  • 18 Sep 2026
Topic Review
Diimide Reduction
Transfer of hydrogen from diimide (HN=NH) to a carbon–carbon multiple bond constitutes diimide reduction. The reagent is generated in situ, typically by oxidation of hydrazine or by thermal decomposition of an arylsulfonylhydrazide, and delivers both hydrogen atoms in a concerted, syn fashion to an alkene or alkyne through a six-membered transition state. Carbonyl groups, nitro groups, and most aromatic rings are not reduced under standard conditions, so the process is a chemoselective saturation of C=C and C≡C bonds rather than a general hydride reduction of carbonyls to alcohols. The method applies to solution-phase and solid-supported alkenes [1]. Organocatalytic generation of diimide enables reduction of enamides in water while preserving the same HN=NH delivery step [2]. Selective diimide reduction has been used to saturate a strained alkene in the presence of a peroxide, underscoring discrimination between a C=C bond and other reducible functions [3]. The concept is bounded as stoichiometric or catalytic use of diimide as the hydrogen donor, distinct from catalytic hydrogenation on a metal surface and from dissolving-metal reduction.
  • 16
  • 23 Sep 2026
Topic Review
Phytotoxins Involved in the Quercus Fungal Diseases
The importance for world life and the economic value of forest his reported as well as the benefit of this precious heritage. The severe diseases induced by the fungal phytotoxins to quercus are in deep described as well as their chemical and biological characterization and potential application essentially in agriculture and medicine. Forests are an indispensable resource for human existence in the different regions of the world. Forests are often concentrated in a few parts and vary in sizes. The most important and extensive green reserve on earth is the Amazon rainforest. Unfortunately, this fundamental resource, like others on other continents, is continually suffering massive losses due to various factors. In addition to abiotic stresses and deforestation to obtain other arable lands, these include microbial diseases, particularly those caused by pathogenic fungi. This review reports essentially the isolation, chemical, and biological properties of phytoxins produced by quercus pathogenic fungi, discussing their role in pathogenesis. For some phytotoxins the enatioselective synthesis, the structure-biological activity relationships, and the potential applications in agriculture and medicine are also discussed. In addition, for the Diplodia species the comparison between their secondary metabolite profile and taxonomy with those of fungal pathogens of other close forest plants was discussed. 
  • 13
  • 06 Jul 2026
Topic Review
Grignard Reaction
Organomagnesium halides (Grignard reagents, RMgX) add to polarized multiple bonds, most classically to aldehydes and ketones, to form a new carbon–carbon bond and, after hydrolysis, an alcohol. The reagent is prepared from an organic halide and magnesium metal; in solution it exists as a Schlenk equilibrium among RMgX, R2Mg, and MgX2, and the addition step is nucleophilic transfer of the organic group to the electrophilic carbon [1]. The same organomagnesium species alkylate or arylate other electrophiles, including epoxides, esters (with double addition), carbon dioxide, and activated carbon–halogen or carbon–fluorine sites on extended π systems such as fluorographene [2]. Sequential Staudinger/aza-Wittig/Grignard sequences use the addition to an in situ imine as the C–C-forming step toward iminosugars [3]. The concept is bounded as the reactivity of the C–Mg bond toward electrophiles. Transition-metal-catalyzed coupling of Grignard reagents (Kumada coupling) is a related but distinct process in which the elementary C–C bond-forming step occurs at the metal, not by direct polar addition of RMgX to a carbonyl [1].
  • 13
  • 23 Sep 2026
Topic Review
Autocatalysis
A reaction is autocatalytic when a product (or a later intermediate) catalyzes its own formation, so that the observed rate increases with conversion until the substrate is depleted. The catalytic species is generated by the same stoichiometric transformation that it accelerates, producing a kinetic signature of a lag phase followed by acceleration. Mechanistically, autocatalysis may involve direct catalysis by the product, a product-assisted pre-equilibrium, or a closed cycle in which an intermediate is regenerated with net formation of product [1]. Nonlinear autocatalysis coupled to recycling can amplify a minute enantiomeric excess to complete chiral purity during crystallization, illustrating the kinetic consequence of a product-dependent rate law [2]. In molecular organic reactions, autocatalysis appears in protodeboronation pH–rate profiles and in related disproportionation manifolds where a product or byproduct participates in the rate-determining step [3]. The concept is a kinetic and mechanistic category, not a named reagent class: any transformation whose rate law contains a positive power of a product concentration is autocatalytic, whether the chemistry is organic, inorganic, or crystallization-based [1].
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  • 23 Sep 2026
Topic Review
Phase Transfer Catalysis
Phase transfer catalysis is the transport of a reactant from one immiscible phase into another, where the desired transformation occurs, by a catalyst that shuttles the reactive ion or molecule across the phase boundary [1][2]. In advanced synthetic organic chemistry the concept is bounded by a biphasic (or interfacial) reaction medium and by a catalyst—commonly a quaternary ammonium or phosphonium salt, a crown ether, or a chiral ion-pairing species—that is not itself the stoichiometric nucleophile. Essential features are ion exchange or complexation that solubilizes an otherwise phase-restricted anion, and return of the catalyst to the source phase so that turnover is achieved. Enantioselective variants use a chiral quaternary ammonium cation to ion-pair with a prochiral enolate, most classically a glycine Schiff-base ester, and thereby differentiate the faces of alkylation [1][3][4]. Chiral anion phase-transfer catalysis inverts the ion-pairing logic: a chiral phosphate or related anion associates with a cationic reagent and delivers it enantioselectively [2]. The concept is distinguished from micellar catalysis, in which rate effects arise from compartmentalization within aggregates rather than from stoichiometric ion transport, and from homogeneous organocatalysis conducted in a single phase.
  • 12
  • 23 Sep 2026
Topic Review
Oxidative Lignin Modification
Oxidative lignin modification is a chemical and biochemical process that alters the molecular structure of lignin through controlled oxidation reactions, wherein electron transfer from lignin's aromatic subunits generates reactive radical intermediates that subsequently undergo bond cleavage, coupling, or oxyfunctionalization [1]. Lignin, a complex polyphenolic biopolymer composed of methoxylated phenylpropanoid units (guaiacyl, syringyl, and p-hydroxyphenyl) linked by ether and carbon–carbon bonds, possesses two distinct classes of oxidizable sites: phenolic hydroxyl groups, which are readily oxidized at relatively low redox potentials, and non-phenolic moieties, which require higher oxidation potentials or the presence of redox mediators to undergo transformation [2]. The oxidation of phenolic units proceeds via one-electron abstraction to yield phenoxy radicals, which can delocalize across the aromatic ring and participate in radical–radical coupling reactions that form new interunit linkages (C–C, C–O, or C–N bonds), or undergo further two-electron oxidation to quinone or quinone methide intermediates that are susceptible to nucleophilic attack [3]. Non-phenolic units, particularly the abundant β-O-4 aryl ether linkages, can be oxidatively cleaved through mechanisms involving benzylic Cα-oxidation to ketone or carboxyl functionalities, followed by β-ether bond scission, or through direct attack on the aromatic ring mediated by high-potential oxidants [4]. Oxidative lignin modification is effected through diverse catalytic systems, including fungal multicopper oxidases (laccases), class II peroxidases (lignin peroxidase, manganese peroxidase, and versatile peroxidase), ortho-methoxyphenolases, and synthetic chemical oxidants (metal complexes, TEMPO-based systems, electrochemical and photochemical oxidants), each operating through distinct mechanistic pathways and exhibiting different substrate selectivities [5]. The term encompasses both degradative transformations that depolymerize lignin into lower-molecular-weight fragments and constructive transformations that increase molecular weight or introduce new functional groups, and is distinguished from reductive lignin depolymerization by its reliance on oxidizing agents rather than reducing agents, and from lignin biosynthesis by its occurrence under exogenous, non-physiological conditions [1].
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  • 22 Sep 2026
Topic Review
Natural Product Derivatives
Natural product derivatives are chemical compounds that retain a defined structural relationship to a naturally occurring metabolite while differing from the parent compound through chemical, enzymatic, or biosynthetically directed modification. Within natural-product bioactivity and synthesis, this category principally includes semisynthetic derivatives obtained by transformation of an isolated natural product, as well as analogues derived by modifying its biosynthetic pathway or enzymatic processing [1][2]. The parent natural product provides a recognizable molecular scaffold, whereas modifications may affect functional groups, oxidation state, stereochemical features, glycosylation pattern, substituents, or side chains [1][3]. The term is based on origin and structural lineage rather than on a specific metabolite class, biological source, or biological activity. Accordingly, derivatives can arise from alkaloid, terpenoid, polyketide, peptide, or other natural-product frameworks [2][4]. Natural product derivatives are distinguished from unmodified natural products, which are biosynthesized and isolated in their native molecular form, and from wholly synthetic compounds lacking a demonstrable scaffold-level relationship to a natural metabolite [1][3]. A derivative may preserve, remove, replace, or elaborate structural features of its parent compound, provided that its natural-product-derived core or direct biosynthetic relationship remains identifiable [2][4].
  • 11
  • 23 Sep 2026
Topic Review
Cascade Reactions
Cascade reactions are sequences in which the product of one transformation becomes the substrate of the next without being isolated, so several bonds are formed in one operation. The attraction is that unstable intermediates never accumulate and that no purification or solvent change intervenes; the constraint is that every step has to proceed under the same conditions and that the catalysts present must not interfere with one another. A three-component sequence catalysed by a single base is a compact case: the chromene skeleton is assembled in one pot from simple precursors [1]. Sequences in which each step needs a different catalyst can still be run together if the catalysts are mutually compatible, as a one-pot sequence forming dihydroquinolinones shows [2]. Stereocontrol can be carried through a cascade, and a double asymmetric sequence catalysed by two distinct chiral catalysts gives chlorinated oxindoles with two adjacent stereocentres [3]. Combining a photocatalyst with an enzyme extends the concept across catalytic disciplines [4]. Transition-metal-free variants, among them iodide-mediated cyclisations, widen the scope further [5].
  • 11
  • 23 Sep 2026
Topic Review
Organosulfur Synthesis
Organosulfur synthesis comprises bond-forming and functional-group interconversion methods that produce organic compounds containing carbon–sulfur bonds or transform one organosulfur class into another. The concept is bounded by sulfur attached to an organic framework and excludes purely inorganic sulfur chemistry. Its defining reactivity follows sulfur across several oxidation states, including thiols, sulfides, disulfides, sulfoxides, sulfones, sulfonium salts, sulfur ylides, sulfinates, and sulfonates. Nucleophilic substitution by sulfur anions, electrophilic sulfur transfer, radical addition, and metal-catalyzed C–S coupling are principal bond-forming modes. Reactions at sulfur(IV) can change both oxidation state and connectivity through sulfoxide activation, sulfonium formation, ylide chemistry, and sulfinate conversion [1]. Sulfur-transfer reagents provide complementary routes in which a defined sulfur unit is delivered to an organic substrate [2]. The field is distinguished from organoselenium and organophosphorus synthesis by sulfur's characteristic oxidation-state ladder, nucleophilicity, and leaving-group behavior.
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  • 23 Sep 2026
Topic Review
Ring Closing Metathesis
Ring-closing metathesis (RCM) is an intramolecular olefin metathesis in which two alkene units of the same molecule exchange alkylidene fragments at a metal–carbene catalyst to produce a cyclic alkene and a volatile olefin, typically ethylene [1]. In advanced synthetic organic chemistry the concept is bounded by the intramolecular pairing of the two alkenes and by the metathesis elementary steps of (2+2) cycloaddition and cycloreversion. Essential features are a diene (or enyne) substrate whose tether length sets the ring size, a well-defined ruthenium, molybdenum, or tungsten alkylidene catalyst, and an equilibrium that is driven toward the cycle by removal of the small-olefin byproduct [2]. RCM constructs five- to medium-sized rings and macrocycles, including oxygen- and nitrogen-containing heterocycles, when the tether geometry permits productive approach of the two olefins [1][3]. The transformation is distinguished from ring-opening metathesis by the direction of the equilibrium (cycle-forming versus cycle-opening) and from intermolecular cross-metathesis by the unimolecular connection of the two reacting alkenes. Conceptual limits exclude metal-catalyzed cyclizations that proceed by oxidative cyclization or radical addition rather than by alkylidene exchange.
  • 11
  • 24 Sep 2026
Topic Review
Azo Coupling Reaction
Electrophilic attack of an arenediazonium ion on an electron-rich aromatic or heteroaromatic carbon constitutes the azo coupling reaction and creates the N=N (azo) linkage of an aryl–N=N–aryl (or heteroaryl) product. The diazonium electrophile is generated from a primary aromatic amine; the nucleophilic partner is typically a phenol, aniline, pyrrole, or indole. Chemoselective rapid azo-coupling can be restricted to a 5-hydroxyindole or 5-hydroxytryptophan nucleus, showing that the electrophile–nucleophile pairing remains the same when the reaction is used as a conjugation method [1]. In aqueous polymer chemistry, azo coupling between a diazonium-functional chain and an activated aromatic partner induces macromolecular connection through the newly formed azo bond [2]. Regioselective C3-azo coupling of arenediazonium compounds with tryptamines illustrates attack at the most nucleophilic heterocyclic carbon [3]. The transformation is an electrophilic aromatic substitution, not a transition-metal cross-coupling: no oxidative addition of a C–X bond is required, and the N=N unit originates entirely from the diazonium reagent.
  • 10
  • 23 Sep 2026
Topic Review
Aldol Reaction
A central carbon–carbon bond-forming transformation in organic synthesis, the aldol reaction joins two carbonyl partners by nucleophilic addition of an enol or enolate to an aldehyde or ketone, producing a β-hydroxy carbonyl (an aldol) whose subsequent dehydration affords an α,β-unsaturated carbonyl. Direct catalytic asymmetric aldol reactions generate the nucleophilic donor in situ and use a chiral catalyst to control the facial selectivity of carbonyl addition [1]. When the two carbonyls differ, the process is a cross-aldol reaction; enantioselective cross-aldol addition of aldehydes establishes a stereogenic center at the newly formed C–C bond [2]. Vinylogous variants extend the same bonding pattern to conjugated enolates, but the defining elementary step remains carbonyl addition rather than conjugate addition to an alkene. Catalytic asymmetric implementations employ metal complexes or organocatalysts. The concept is thereby bounded as a carbonyl–carbonyl coupling, distinct from related enolate alkylations that do not create the aldol oxidation pattern.
  • 9
  • 23 Sep 2026
Topic Review
Aza-Diels-Alder Reaction
Replacement of a carbon atom of the classical Diels–Alder pair by nitrogen defines the aza-Diels–Alder reaction, a [4+2] cycloaddition that constructs a six-membered nitrogen heterocycle. Either the diene (1-azadiene) or the dienophile (imine) may carry the nitrogen. Inverse-electron-demand variants pair an electron-deficient azadiene with an electron-rich dienophile and are frequently catalyzed by chiral Brønsted acids [1]. Organocatalytic regio- and stereoselective inverse-electron-demand aza-Diels–Alder reactions of α,β-unsaturated aldehydes with N-tosyl-1-aza-1,3-butadienes proceed through a chiral enamine or related covalent intermediate [2]. Three-component asymmetric implementations generate ring-fused tetrahydroquinolines by assembling the azadiene or dienophile in situ [3]. The bonding event is a concerted or highly asynchronous cycloaddition that forms two new σ bonds and a six-membered ring, distinguishing the process from stepwise Mannich–Michael sequences that reach the same connectivity without a cycloaddition transition state. Normal-electron-demand aza-Diels–Alder reactions invert the electronic roles but share the same [4+2] topology.
  • 9
  • 23 Sep 2026
Topic Review
Ene Reaction
A pericyclic process in which an alkene bearing an allylic hydrogen (the ene) reacts with an electron-deficient multiple bond (the enophile) to form a new σ bond and to transpose the double bond defines the ene reaction. In the concerted limit a six-electron cyclic transition state transfers the allylic hydrogen to the enophile while the new C–C (or C–X) bond forms. The nitroso ene reaction is a regioselective and stereoselective allylic nitrogen functionalization in which a nitroso compound is the enophile [1]. When both the ene and the enophile are tethered in one molecule, the intramolecular variant (including the Conia-ene reaction of an enol or enol equivalent with an alkyne) produces a carbocycle [2]. Gold(I)-catalyzed Conia-ene reactions proceed by metal activation of the alkyne [2]. Enantioselective variants impose facial control while retaining the same C–C-forming cyclization topology [3]. The concept is distinct from the Diels–Alder reaction (a [4+2] cycloaddition without hydrogen transfer) and from stepwise allylic substitutions that do not follow the pericyclic ene topology [1].
  • 9
  • 23 Sep 2026
Topic Review
Hafner Synthesis
The Hafner synthesis, often called the Ziegler–Hafner azulene synthesis, constructs an azulene framework by reacting a cyclopentadienyl anion with a seven-carbon electrophilic chain derived from a pyridinium or pyrylium salt. Nucleophilic substitution or addition first joins the five-carbon cyclopentadienyl unit to the activated C7 fragment; subsequent electrocyclic ring closure and elimination establish the fused five- and seven-membered rings of azulene. Hafner's original synthesis used glutacondialdehyde-derived electrophiles and furnished azulene without a separate dehydrogenation step [1]. Modern accounts distinguish pyridinium-derived Zincke iminium routes and related pyrylium variants while retaining the same cyclopentadienyl-plus-C7 construction [2]. The term is constitutionally and mechanistically specific: it is not a general palladium cross-coupling, nor does it include unrelated annulations that produce azulenes from different carbon frameworks.
  • 9
  • 23 Sep 2026
Topic Review
Homogeneous Catalysis
Homogeneous catalysis occurs when the catalyst and reactants are present in the same macroscopic phase, most commonly as molecularly dispersed species in a liquid solution. The catalyst may be a neutral molecule, coordination complex, ion, or ion pair, but it undergoes a sequence of elementary steps that regenerates the catalytically active species. For metal complexes, these steps can include ligand association or dissociation, oxidative addition, migratory insertion, and reductive elimination; homogeneous organocatalysis instead proceeds through covalent or noncovalent activation by an organic catalyst. The defining criterion is phase and molecular dispersion, not catalyst composition: both metal and metal-free catalysts can be homogeneous. Molecular catalysts that transform carboxylic acids illustrate the breadth of substrates addressed by homogeneous cycles [1]. The concept is distinguished from heterogeneous catalysis, where the catalyst forms a separate phase and reaction occurs at an interface, although immobilized or biphasic systems can combine features of both classes [2].
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  • 23 Sep 2026
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