Theoretical study on the nucleophilic fluoroalkylation of propylene oxide with fluorinated sulfones

The path of nucleophilic fluoroalkylation reaction of propylene oxide with PhSO2CYF- (Y=F,H, and PhSO2, respectively) in gas phase and in Et2O solvent were studied theoretically. The nucleophilic fluoroalkylation of propylene oxide with fluorinated carbanions was probed by the reactivity comparison between (benzenesulfonyl)monofluoromethyl anion (PhSO2CHF-), (benzenesulfonyl) difluoromethyl anion (PhSO2CF2-), and bis(benzenesul-fonyl) monofluoromethyl anion ((PhSO2)2CF-). The nucleophilicity reactivity order of PhSO2CYF- (Y = F, H, and PhSO2) is [(PhSO2)2CF-] > PhSO2CHF- > PhSO2CF2-, which indicates that introducing another electron-withdrawing benzenesulfonyl group is an effective way to significantly increase the nucleophilicity of the fluorinate carbanions. For comparison, we also studied the nucleophilic addition reactions of propylene oxide with chlorine substituted carbanion PhSO2CHCl-. The calculated results show that the nucleophilicity of PhSO2CYF- is better than that of PhSO2CHCl- for the ring opening reaction with propylene oxide. The calculated results are in good agreement with the available experiments

Acceleration of Nucleophilic CH Activation by Strongly Basic Solvents

(IPI)Ru(II)(OH)_n(H_2O)_m, 2, where IPI is the NNN-pincer ligand, 2,6-diimidizoylpyridine, is shown to catalyze H/D exchange between hydrocarbons and strongly basic solvents at higher rates than in the case of the solvent alone. Significantly, catalysis by 2 is accelerated rather than inhibited by increasing solvent basicity. The evidence is consistent with the reaction proceeding by base modulated nucleophilic CH activation

Theoretical insight on the treatment of ß-hexachlorocyclohexane waste through alkaline dehydrochlorination

The occurrence of 4.8–7.2 million tons of hexachlorocyclohexane (HCH) isomers stocked in dumpsites around the world constitutes a huge environmental and economical challenge because of their toxicity and persistence. Alkaline treatment of an HCH mixture in a dehydrochlorination reaction is hampered by the low reactivity of the ß-HCH isomer (HCl elimination unavoidably occurring through syn H–C–C–Cl arrangements). More intriguingly, the preferential formation of 1, 2, 4-trichlorobenzene in the ß-HCH dehydrochlorination reaction (despite the larger thermodynamical stability of the 1, 3, 5-isomer) has remained unexplained up to now, though several kinetic studies had been reported. In this paper, we firstly show a detailed Density Functional study on all paths for the hydroxide anion-induced elimination of ß-HCH through a three-stage reaction mechanism (involving two types of reaction intermediates). We have now demonstrated that the first reaction intermediate can follow several alternative paths, the preferred route involving abstraction of the most acidic allylic hydrogen which leads to a second reaction intermediate yielding only 1, 2, 4-trichlorobenzene as the final reaction product. Our theoretical results allow explaining the available experimental data on the ß-HCH dehydrochlorination reaction (rate-determining step, regioselectivity, instability of some reaction intermediates). © 2021, The Author(s)

Synthetic Applications and Mechanistic Studies of the Hydroxide-Mediated Cleavage of Carbon-Carbon Bonds in Ketones

The hydroxide-mediated cleavage of ketones into alkanes and carboxylic acids has been reinvestigated and the substrate scope extended to benzyl carbonyl compounds. The transformation is performed with a 0.05 M ketone solution in refluxing xylene in the presence of 10 equiv of potassium hydroxide. The reaction constitutes a straightforward protocol for the synthesis of certain phenyl-substituted carboxylic acids from 2-phenylcycloalkanones. The mechanism was investigated by kinetic experiments which indicated a first order reaction in hydroxide and a full negative charge in the rate-determining step. The studies were complemented by a theoretical investigation where two possible pathways were characterized by DFT/M06-2X. The calculations showed that the scission takes place by nucleophilic attack of hydroxide on the ketone followed by fragmentation of the resulting oxyanion into the carboxylic acid and a benzyl anion

Functionalization of Rhenium Aryl Bonds by O-Atom Transfer

Aryltrioxorhenium (ArReO_3) has been demonstrated to show rapid oxy-functionalization upon reaction with O-atom donors, YO, to selectively generate the corresponding phenols in near quantitative yields. (18)^O-Labeling experiments show that the oxygen in the products is exclusively from YO. DFT studies reveal a 10.7 kcal/mol barrier (Ar = Ph) for oxy-functionalization with H_2O_2 via a Baeyer-Villiger type mechanism involving nudeophilic attack of the aryl group on an electrophilic oxygen of YO coordinated to rhenium

Cyclopropenyl Cation - the Simplest Huckel's Aromatic Molecule - and its Cyclic Methyl Derivatives in Titan's Upper Atmosphere.

International audienceThe recent measurements by Cassini Ion Neutral Mass Spectrometer (INMS) showed the presence of numerous carbocations and shed light on their composition in Titan's upper atmosphere. The present research identifies an important class of ion-molecule reactions proceeding via carbocation collision complexes, and its implications in the chemistry of Titan's thermosphere and ionosphere. An analysis (based on the kinetics and dynamics of the elementary chemical processes identified) of the Cassini measurements reveals the mechanism of formation of the three- membered Huckel aromatic rings-Cyclopropenyl cation and its cyclic methyl derivatives. For carbocations, a nonclassical three-carbon-center two-electron-bond structure is no longer a controversial topic in chemistry literature. Emphasis has been placed on a future coordinated effort of state-of-the-art laboratory experiments, quantum-chemical calculations, and astronomical ALMA and JWST observations including planetary in situ measurements at millimeter and submillimeter wavelengths to elucidate the structure, energetics and dynamics of the compositions of carbocations detected by Cassini cationic mass spectrometry. The cabocation chemistry in Titan's upper atmosphere has a possible bearing on the organic chemistry and aromaticity in the atmosphere of primitive earth

Characterization and Investigation of Benzylic Carbenium Ion and Carbanion Ion-Diradical Intermediates With 3,5-Disubstituted (pi)-Donors/Acceptors

High-spin magnetic materials have been based on monomeric units that contain metals. Far less research has been done to develop and characterize alternative high-spin building blocks consisting of mostly organic subunits. To date, there exists a small class of known high-spin organomagnetic building blocks. These organic building blocks are comprised of neutral intermediates such as diradicals, nitrenes, and carbenes. The work presented in this text will show that a novel class of high-spin intermediates also exists that derives from ionic rather than neutral intermediates. Previous density functional theory (DFT) computations by Winter and Falvey identified a number of ion-diradicals that have favorable triplet ground states. For instance, the 3,5-bis(dimethylamino)benzyl carbenium ion, and 2-(3,5-dinitrophenyl)-1,3-dithiane carbanion, have singlet-triplet energy gaps (ΔESTs) of +1.9 and +0.3 kcal/mol, respectively. Ion-diradicals are based on a general framework whereby either an electron deficient or electron rich exocyclic center is attached to a benzene ring that contains two π-electron withdrawing or donating groups meta with respects to this site. The objective of chapter 2 is to identify the electronic spin state of the 3,5-bis(dimethylamino)benzyl carbenium ion. We have shown that this carbenium ion can be generated from C-O bond heterolysis of 3,5-bis(dimethylamino)benzyl esters and alcohols when photolyzed in polar protic solvents (e.g. methanol, 2-propanol, 2,2,2-trifluoroethanol). Our product studies show that indeed the 3,5-bis(dimethylamino)benzyl ethers are formed from this process, however an unexpected reduction product (3,5-bis(dimethylamino)toluene) is also observed. The reduction product here aptly demonstrates how an ion-diradical could be generated. Formal one electron transfer from a NMe2 group to the exocyclic benzylic carbenium ion center, creates a triplet cation diradical (ion-diradical) intermediate, which eventually leads to the formation of the 3,5-bis(dimethylamino)toluene product observed in all photolysis experiments. Chapters 4-6 investigates whether ion-diradicals can be generated from anionic exocyclic centers that have meta π-acceptor groups (e.g. NO2, CN, CO2R). Computations, NMR, UV-Vis, chemical trapping, H/D exchange, and Evans method magnetic susceptibility experiments demonstrate that the 2-(3,5-dinitrophenyl)-1,3-dithiane carbanion is a persistent and paramagnetic species. Chapters 5 and 6 focuses primarily on characterizing the electronic spin-states to similar anionic systems such as the 3,5-dinitroanilide anion, and 3,5-dinitrobenzyl methoxy ether carbanion

Some studies of the reactions of carbon nucleophiles with aromatic nitro compounds

Some reactions of aromatic nitro-compounds with carbon nucleophiles have been investigated. The techniques used include NMR spectroscopy, UV-visible spectroscopy and stopped-flow spectrophotometry. The initial rapid reactions of carbanions derived from ring-substituted phenylacetonitriles with 1,3,5-trinitrobenzene yield σ-adducts. Carbanions were generated from the phenylacetonitriles by reaction with sodium methoxide in methanol. Values of the equilibrium constants for the deprotonation reaction were determined spectrophotometrically. Rate constants for the σ-adduct forming reactions were measured in methanol using the stopped-flow method. With increasing carbanion reactivity rate constants for the C-C bond forming reaction increase to a limit of circa 10(^9) dm(^3) mol(^-1) s(^-1) close to the diffusion limit. Data were also obtained for reaction of the carbanions with 4-nitrobenzofuroxan and with 4-nitrobenzofurazan.An interesting slower reaction was observed in the reaction of carbanions with 1,3,5- TNB, 4-nitrobenzofuroxan and 4-nitrobenzofurazan. This yields coloured products and the nature of the process has been investigated. Attempts have been made to isolate the σ-adducts formed from carbanions. The adduct formed from 1,3,5-trinitrobenzene and phenylacetonitrile in the presence of triethylamine has been produced in crystalline form. NMR measurements in situ have indicated the formation of adducts from 4-nitrobenzofuroxan and from 4-nitrobenzofiirazan with deuterated nitromethane in the presence of triethylamine

Carbanion and enol intermediates in c-nitrosation and halogenation

A kinetic study of the mtrosation of ethyl cyanoacetate, diethyl malonate and malononitrile, in acidic water/dioxan solution, by nitrous acid, at 25ºC, was under taken. Catalysis of this reaction was obtained by the addition of nucleophilic catalysts; chloride ion, bromide ion, thiocyanate ion and thiourea. The results were consistent with a mechanism where malononitrile reacted exclusively via the carbanion intermediate. Within the pH range used, pH 0∙7 to pH 3∙3, ethyl cyano acetate and diethyl malonate reacted either through a carbanion intermediate, at higher acidity, or an enol intermediate, at lower acidity. Values of the second order rate constant for the attack of the nitrosating species upon the carbanions were obtained. The carbanions of malononitrile and diethyl malonate reacted at the diffusion limit, in the presence of catalysts. Nitrosation of ethyl cyanoacetate, via its carbanion, showed an already established trend in the reactivity of the nitro sating species, NOSC(NH(_2))(_2) < NOSCN < NOBr < NOCl. A kinetic study of the nitrosation of malonic and methylmalonic acids, and of the iodination and bromination of these two acids as well as ethylmalonic and phenylmalonic acids, in aqueous acidic solutions, at 25ºC, was also undertaken. At high acidity nitrosation was shown to proceed via an enol intermediate and at lower acidities via a carbanion. Nitrosation of the intermediate was rate determining. Under certain conditions, in nitrosation, it was possible to make the enolisation rate limiting. lodination and bromination, by the halogen molecules, involved rate determining enol formation. lodination by triiodide ion involved rate determining iodination of the enol. Values of the enolisation rate constant, kg, were obtained for all four of the acid substrates, these were in reasonable agreement for the different electrophilic processes. Between pH 0 and pH 2 the results fitted an intramolecular acid catalysed enolisation mechanism. At higher pH values (2 to 4) the results fitted a change in mechanism to include, additionally, base catalysed enolisation and enol carboxylate formation pathways