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.

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Topic Review
Smiles Rearrangement
The Smiles rearrangement is an intramolecular nucleophilic aromatic substitution in which a tethered nucleophile attacks an activated aromatic ipso carbon, displacing the atom or group that connects the aryl ring to the tether and thereby transferring the aryl group to the nucleophile. Classical substrates contain an electron-deficient arene bearing substituents that stabilize the anionic σ-complex formed during addition [1]. The nucleophile may be nitrogen, oxygen, sulfur, or carbon, and cleavage of the original aryl–heteroatom bond completes the connectivity change. Because attack and leaving-group departure occur within one molecule, effective proximity can permit reactions that would be unfavorable intermolecularly. The Truce–Smiles rearrangement is a carbon-nucleophile variant and includes radical forms, but it retains the defining intramolecular aryl migration [2]. The reaction is not simple double-bond migration and is distinguished from the Newman–Kwart rearrangement by its tethered SNAr architecture rather than direct O-to-S transfer of an aryl group within a thiocarbamate.
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Topic Review
Sabatier Reaction
The Sabatier reaction is the catalytic methanation of carbon dioxide with hydrogen according to CO2 + 4 H2 → CH4 + 2 H2O. It is an exothermic heterogeneous catalytic transformation in which carbon dioxide is adsorbed and successively hydrogenated on a metal surface, commonly nickel, ruthenium, rhodium, or cobalt [1]. Depending on the catalyst, support, and surface state, mechanistic descriptions invoke either formation and further hydrogenation of adsorbed carbon monoxide or hydrogenation through formate and other oxygenated surface intermediates. The defining product is methane, and complete removal of both oxygen atoms as water requires four hydrogen equivalents. Carbon monoxide methanation is closely related but has the different net equation CO + 3 H2 → CH4 + H2O. The Sabatier reaction is also distinct from the reverse water–gas shift reaction, which stops at CO rather than proceeding to methane. Nickel-catalyst composition and metal–support interactions govern the elementary adsorption and hydrogenation sequence [2].
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Topic Review
Ring Opening Reaction
A ring opening reaction cleaves at least one bond of a cyclic substrate so that the atoms formerly connected through the broken bond become termini of an acyclic chain or part of a less-cyclic framework. Cleavage is commonly coupled to formation of new bonds when a nucleophile, electrophile, radical, or metal species captures one or both termini. Strained three- and four-membered rings are especially susceptible because bond cleavage relieves angle and torsional strain; regioselectivity and stereochemistry depend on substrate polarization and whether opening follows SN2-like, cationic, radical, or concerted behavior [1]. Ring contraction may accompany opening when a new, smaller ring forms during cleavage, as in rearrangements of 2-halocyclobutanols [2]. The category includes stoichiometric opening of epoxides, aziridines, cyclopropanes, and related rings, but excludes mere conformational changes that leave connectivity intact. Ring-opening polymerization is a distinct iterative subset in which repeated opening of cyclic monomers propagates a macromolecular chain.
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Topic Review
Reductive Amination
Reductive amination converts an aldehyde or ketone into an amine by condensation with ammonia or a primary or secondary amine followed by reduction of the resulting imine or iminium species. Carbonyl addition first forms a carbinolamine, which loses water to establish the C=N intermediate; delivery of hydride or catalytic hydrogenation then creates the C–N-bearing saturated carbon [1]. Ammonia gives a primary amine, a primary amine gives a secondary amine, and a secondary amine gives a tertiary amine. In direct reductive amination, condensation and reduction occur in one vessel and the reducing system preferentially reduces the imine or iminium ion in the presence of the starting carbonyl. Catalytic variants may use H2 or hydrogen-transfer reagents, while chemoselective hydride reagents operate stoichiometrically. The reaction is distinguished from reductive alkylation of nitro compounds and from simple imine formation because reduction is required to replace the carbonyl oxygen formally with a saturated amino substituent [2].
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Topic Review
Pschorr Arylation
Pschorr arylation is an intramolecular radical substitution in which an arenediazonium group generates an aryl radical that attacks a second aromatic ring, forming a new aryl–aryl carbon bond. The diazonium precursor is commonly obtained by diazotization of an ortho-amino biaryl or related tethered aniline. Single-electron reduction releases nitrogen gas and produces the aryl radical; cyclization onto the neighboring arene, followed by oxidation and deprotonation, restores aromaticity and gives a fused or bridged biaryl framework [1]. Copper salts can facilitate diazonium reduction and improve cyclization, although the key bond-forming intermediate remains radical rather than an organopalladium species [2]. The defining features are an arenediazonium radical source, loss of N2, and intramolecular C–C arylation. Pschorr arylation is therefore distinct from palladium-catalyzed cross-coupling of aryl halides and from the Gomberg–Bachmann reaction, which typically couples an aryl radical intermolecularly with a separate arene.
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Topic Review
Payne Rearrangement
The Payne rearrangement is a base-catalyzed, reversible migration of an epoxide within a vicinal hydroxy epoxide. Deprotonation of the alcohol gives an alkoxide, which attacks an adjacent epoxide carbon intramolecularly through an SN2 process; opening of the original three-membered ring occurs as a new epoxide closes at the neighboring position [1]. The product is therefore an isomeric hydroxy epoxide in which the oxygen functions have exchanged positional relationships. Backside attack causes inversion at the displaced epoxide carbon, and regioselectivity reflects substitution, stereoelectronic alignment, solvation, and trapping of one equilibrating alkoxide. The transformation is often described as epoxide migration, but no free epoxide fragment moves: ring opening and ring closure are coupled within one molecule. Related aza- and thia-Payne rearrangements replace the attacking oxygen nucleophile with nitrogen or sulfur [2]. It is distinct from simple epoxide opening because the intramolecular nucleophile simultaneously creates a new epoxide rather than yielding a permanently ring-opened product.
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Topic Review
Passerini Condensation
Passerini condensation is a three-component reaction of a carbonyl compound, a carboxylic acid, and an isocyanide that furnishes an α-acyloxy carboxamide. The carbonyl component may be an aldehyde or ketone, the acid supplies the acyloxy group, and the isocyanide carbon becomes the amide carbonyl carbon [1]. In the accepted nonionic or partially ionic pathway, hydrogen bonding activates the carbonyl and organizes addition of the isocyanide; the resulting nitrilium intermediate is trapped by carboxylate and undergoes acyl transfer to produce the ester–amide product. Modified sequences may generate the carbonyl partner in situ yet retain the same three-component bond construction [2]. The defining product is an α-acyloxy amide, not an α-acylamino acid. Passerini condensation differs from the Ugi reaction because no amine component is present; Ugi chemistry proceeds through an imine or iminium species and gives an α-acylamino amide rather than the oxygenated Passerini connectivity.
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Topic Review
Newman-Kwart Rearrangement
The Newman–Kwart rearrangement is an intramolecular thermal conversion of an O-aryl thiocarbamate into the corresponding S-aryl thiocarbamate. Heating promotes nucleophilic attack by sulfur at the aromatic ipso carbon bonded to oxygen, with simultaneous or stepwise displacement of the oxygen substituent through a four-membered or closely related cyclic transition arrangement [1]. The net result is migration of the aryl group from oxygen to sulfur without changing the aryl carbon skeleton. Electronic activation of the aromatic ring and steric effects near the reaction center strongly influence the rearrangement rate; steric acceleration relative to the related Chapman rearrangement has been documented [2]. Hydrolysis of the rearranged S-aryl thiocarbamate can reveal an aryl thiol, but that subsequent cleavage is not part of the rearrangement itself. The reaction is specifically an O-to-S aryl transfer and is not a radical conversion of thioethers into carbonyl compounds, nor should it be confused with the Smiles rearrangement, an intramolecular nucleophilic aromatic substitution involving a tethered nucleophile.
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Topic Review
Intramolecular Cyclocondensation
Intramolecular cyclocondensation is a ring-forming reaction in which two complementary functional groups within the same molecule combine and a small molecule is eliminated. One terminus acts as a nucleophile and the other as an electrophile, so the tether converts an otherwise intermolecular condensation into a unimolecular closure. Depending on the functional groups, elimination may release water, an alcohol, hydrogen halide, or another low-molecular-mass species, and the ring product may be carbocyclic or heterocyclic. Cyclocondensation of 4- and 5-oxocarboxylic acids forms five- and six-membered rings through internal carbonyl chemistry [1], whereas appropriately configured o-phenylallylbenzaldehydes undergo thermolytic intramolecular cyclocondensation to naphthalene frameworks [2]. The defining distinction from simple cyclization is the condensation component: bond formation is coupled to loss of a small molecule. It also differs from intramolecular cycloaddition, in which two π systems combine without obligatory elimination.
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Topic Review
Hydroxyamination
Hydroxyamination denotes formation of a carbon–nitrogen bond that installs an N-hydroxyamino unit, commonly by reaction of a carbon nucleophile, alkene, or enolizable carbonyl compound with a nitroso electrophile. In direct asymmetric α-hydroxyamination, an enolate or enamine attacks the nitrogen atom of a nitroso compound, giving an α-substituted carbonyl product bearing an N–OH-containing amino group; catalyst-controlled facial selection can establish a stereogenic carbon [1]. Allylic hydroxyamination can instead proceed by a nitroso–ene pathway in which an alkene forms a C–N bond while the double bond and an allylic hydrogen reorganize [2]. These variants share incorporation of the nitrogen atom together with retention of the N–O bond, rather than conversion of a carbonyl compound into an oxime. Hydroxyamination is therefore distinct from reductive amination, which replaces a carbonyl oxygen with an amine nitrogen, and from aminohydroxylation, which adds separate amino and hydroxy groups across a carbon–carbon multiple bond.
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