Quantum Chemical Study on the Reaction Mechanism of OBrO Radical with OH Radical

The reaction mechanism of OBrO with OH has been studied using the B3LYP/6-311 G(d,p) and the high-level electron-correlation CCSD(T)/6-311 G(d,p) at single-point. The results show that the title reaction could probably proceed by four possible schemes, generating HOBr O2, HBr O3, BrO HO2 and HOBrO2 products, respectively. The main channel is the one to yield HOBr O2. The whole reaction involves the formation of three-membered, four-membered and five-membered rings, followed by the complicated processes of association,H-shift, Br-shift and dissociation. All routes are exothermic.     

UV Photoionization Study of the Ethyl Radical

Introduction Ashighlyreactivebuildingblocksandfundamen talreactionintermediatesinorganicsynthesis,thealkyl radicalfamilyplaysacentralroleinadiversearrayof importantprocessesrangingfromcombustion[1]toat mosphericchemistry[2].Amongalkylradicals,theeth ylrad…     

Ultrafast Radical Photogeneration Pathways in Eumelanin†

Eumelanin is a ubiquitous biological pigment that rapidly and efficiently deactivates excited states created by UV or visible radiation. Paradoxically, photoirradiation of eumelanin also generates radicals and harmful reactive oxygen species, but the relationship between these pathways and excited-state deactivation is uncertain. Here, greatly expanding the excitation tuning range (225–620 nm) and probing window (400–1500 nm) in femtosecond transient absorption spectroscopy of the synthetic eumelanin, DOPA melanin, enables the detection of photogenerated radials with ultrafast time resolution for the first time. Despite its heterogeneous nature, the transient absorption signals can be modeled by two spectral components assigned to solvated electrons and photogenerated radicals. Radical absorbance measured several nanoseconds after excitation increases exponentially with increasing photon energy, matching the trend in radical yields measured in electron paramagnetic resonance spectroscopy experiments. Spectral modeling of the transient signals reveals two radical generation mechanisms: (1) photoionization by UV light; and (2) photoinduced charge transfer among eumelanin chromophores by UVA and visible wavelengths capable of reaching the pigment in skin. Concurrent ultrafast relaxation and radical generation underlie the ability of eumelanin to be both photoprotective and photodamaging, and the branching between these pathways likely depends on the wavelength of the absorbed light.     

Free Radical–Mediated Chemoselective Reduction of Enones

A novel methodology has been devised for the chemoselective reduction of enones involving the use of ⁿ Bu₃SnH and azobisisobutyronitrile. The 1,4-reduction of variously substituted α,β-unsaturated cyclic and acyclic enones has been successfully carried out under free radical reaction conditions. The reaction has been determined to proceed via single-electron transfer.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications^® for the following free supplemental resource(s): Full experimental and spectral details.]     

α-Carbonyl Radical Cyclizatio n in Organic Synthesis

Intramolecular radical cyclization reactions are now used routinely to synthesize carbocyclic and heterocyclic structures. We have reported that α-carbonyl radicals 1, generated from the corresponding iodo ketones or enones, underwent intramolecular radical cyclization smoothly to afford products 2.1, 2,3     

Rod-like Schiff Base Magnetic Liquid Crystals Bearing Organic Radical

4 novel rod-like Schiff base magnetic liquid crystals have been prepared in which trans-bicyclohexyl or trans-cyclohexyl phenyl and biphenyl carboxylic acid phenol ester mesogenic cores with n-propyl and n-pentyl subsfituents were terminated by 4-amino-TEMPO （TEMPO=2,2,6,6-tetramethylpiperidine-l-oxyl）. Of these compounds the silk-like and schlieren textures were found from 4e and 4d by POM （Polarizing Optical Microscope）. DSC （Differential Scanning Calorimeter） measurements show that the mesophase exists from 4-6℃. EPR spectra reveal their paramagnetic properties.     

Hydrocarbon Oxidation by a Porphyrin-π-Cation Radical Complex

Heme and chlorin π-cation radical oxidants are widely implicated in biological and synthetic oxidation catalysis. Little insight into the role of π-cation radicals in proton coupled electron transfer (PCET) oxidation is available. We prepared a Ni^II-porphyrin-π-cation complex ([Ni^II(P⋅⁺)]) and found it to be capable of the oxidation of a variety of simple hydrocarbon substrates. Interestingly, some of the products were hydroxylated, with ([Ni^II(P⋅⁺)]) working in concert with atmospheric O₂ to yield hydroxylated hydrocarbons. Kinetic data suggested that the porphyrin-π-cation radical species oxidised substrates through a concerted PCET mechanism, where the porphyrin-π-cation radical accepted the electron, and the proton was transferred to a free anion. Our findings highlight the potential role of π-cation radicals as hydrocarbon activators, demonstrating that porphyrin ligand non-innocence could be a readily manipulated resource for oxidation catalyst development.     

Free Radical–Induced Graft Copolymerization onto Natural Fibers

Surface modification of a natural cellulosic polymer system is required to improve the physicochemical properties of the fibers to be used as reinforcement for green composite applications. Surface modification through graft copolymerization improves the existing properties of the cellulosic fibers for a number of applications. Therefore, in the present study, an attempt was made to synthesize butyl acrylate (BA)-g-Saccaharum cilliare fibers using a redox initiator. Graft copolymers were characterized through FT-IR/SEM/TGA/DTA/DTG techniques, and the effect of grafting percentage on the water absorption properties of raw as well as grafted fibers was also investigated.     

Grafting of Hexafluoropropylene onto Polytetramethylene Glycol by Radical Reaction

A well-defined modification of polytetramethylene glycol （PTMG） was realized by radical grafting with hexafluoropropylene （HFP）. The structure of grafted product was confirmed by means of IR, ^1H NMR and ^13C NMR. The effects of the amount of initiator, reaction time and temperature on the grafting HFP onto PTMG were investigated.     

Radical scavenging properties of a flavouring agent–Vanillin

Using pulse radiolysis technique, the one-electron oxidation of vanillin (V-OH) with azide radicals, at pH 6 and 9 resulted in the formation of vanillin phenoxyl radical with k = 6.7 × 10⁷ and 2.5 × 10⁹ dm³ mol^-1 s^-1, respectively. The transient absorption spectra of the vanillin phenoxyl radical (V-O) formed either at pH 6 or 9, showed a _max at 410 nm. At pH 5, the OH radicals seem to form an adduct with vanillin, _max at 430 nm and k(OH + V-OH) = 3.3 × 10⁹ dm³ mol^-1 s^-1, while at pH 9, the OH radical reaction resulted in the formation of vanillin phenoxyl radical with _max at 410 nm and k(OH + V-O-) = 6.6 × 10⁹ dm³ mol^-1 s^-1. The reactivity of NO₂radicals with vanillin is lower by orders of magnitude signifying an incomplete reaction. In general, the rate constants for the reaction of OH, N, NO radicals with vanillin were higher at pH 9 than at the lower pH. Its reactivity with other one-electron oxidants like CCl₃OO, CHCl₂OO and CH radicals and the ability to chemically repair tryptophanyl and guanosyl radicals with k = 1.5 - 4 × 10⁷ dm³ mol^-1 s^-1 indicate its antioxidative behaviour.     

Free Radical Copolymerization of N‐Cyclohexylmaleimide with Cyclohexene

The radical copolymerization of cyclohexene (M₁) and N‐cyclohexylmaleimide (M₂) was carried out with 2,2′‐azobis(isobutyronitrile) as an initiator in various solvents at 55°C. The copolymerization of cyclohexene with N‐cyclohexylmaleimide in chloroform, dioxane and benzene proceeded in a homogeneous system to give an alternating copolymer when the monomer of cyclohexene was over 40 mol% in the feed. It was found that the initial rate of the copolymerization (R_p), as well as the number‐average molecular weight of copolymers, were dependent on the monomer composition and was at maximum at about 30 mol% of cyclohexene in the feed. The effects of solvents on the R_p and reactivity ratios were also investigated in this copolymerization system. The copolymerization in dioxane produced a higher R_p than that in chloroform and benzene, and the monomer reactivity ratios were found to be r₁=0, r₂=0.032 in chloroform; r₁=0, r₂=0.065 in benzene and r₁=0, r₂=0.14 in dioxane, respectively.     

Radical cyclisation studies of β-nitroamines from the nitro-Mannich reaction

A range of novel β-nitroacetamides with an alkenyl- or alkynyl tether were synthesized using the deprotonative or conjugate addition nitro-Mannich reaction. They were subjected to radical denitration-cyclisation with a 10 equivalent excess of tributyltin hydride, catalytic AIBN in refluxing benzene to explore the structural and electronic requirements for efficient cyclisation. Cyclisations of the β-nitroacetamides were successful in most cases, undergoing 5-exo-trig cyclisation to give the desired cyclopentyl or indanyl structures. Radical 1,4-translocation of a phenyl group was observed in several cases. Diastereoselectivity was low, with 2 or 3 of 4 possible diastereoisomers observed in most cases. Further purification by crystallisation allowed the isolation of some as single diastereoisomers. It was found that higher yields were obtained by increasing the substitution or reducing the degrees of freedom of the tether between the nitro group and the radical acceptor.     

Synthesis of Dendritic-Linear Block Copolymers by Atom Transfer Radical Polymerization

Polymers and copolymers with complex, yet well-defined architectures are drawing significant attentions in the search for materials with excellent properties. Of these macromolecular structures, dendritic-linear block copolymers consisting of covalently bound linear and dendritic segments have shown interesting solution, solid-state, and interfacial properties. As a novel polymerization approach, atom transfer radical polymerization (ATRP) has been attracting increasing interest recently, sin…     

Asymmetric Radical Oxyboration of β-Substituted Styrenes via Late-Stage Stereomutation

Herein, we report an unprecedented copper-catalyzed highly enantio- and diastereoselective radical oxyboration of β-substituted styrenes. The lynchpin of success is ascribed to the development of a late-stage stereomutation strategy, which enables enantioenriched cis-isomers among a couple of early-generated diastereomers to be converted into trans-isomer counterparts, thus fulfilling high diastereocontrol; while the degree of enantio-differentiation is determined by the borocupration process of the C=C bond. This reaction provides an efficient protocol to access enantioenriched trans-1,2- dioxygenation products. The value of this method has further been highlighted in a diversity of follow-up stereospecific transformations and further modifying complex molecules.     

Fluorescence Sensing of Glutathione Thiyl Radical by BODIPY-Modified β-Cyclodextrin

The fluorescence sensing of intracellular glutathione thiyl radical(GS·)is in great demand to seek the GS·-related pathophysiological events.Herein,boron-dipyrr...     

Theoretical Investigation on Radical—Coupling Reactivity of Indolinonic Aminoxyls

Indolinonic aminoxyls can effectively scavenge various radicals by directly coupling with them or by initatin superoxide dismutase.To better understand the radical-coupling reactions,DFT method B3LYP/6-31G(d,p) was employed to calculate variations of free energy for the coupling reactions and other physico-chemical parameters.The radical-coupling activity difference between aminoxyls was elucidated to a large extent in terms of elctronic properties of substituents.     

Radical reaction HCNO + 3NH: a mechanistic study

The complex triplet potential energy surface for the reaction of HCNO with NH is investigated at the G3B3 level using the B3LYP/6-311++G(d,p), and QCISD/6-311++G(d,p) geometries. Various possible isomerization and dissociation pathways are probed. The initial association between HCNO and NH is found to be carbon to nitrogen attack leading to HNCHNO 2a, which can convert to 2b, 2c, and 2d. Subsequently, 1,4-H-shift of 2a to form NCHNOH 3a followed by dissociation to P ₂ (¹HCN + ³HON) is the most feasible pathway. Much less competitively, 2d undergoes successive 1,3-H-shift and C-N cleavage to form HNCNOH 8b, and then to product P ₃ (¹HNC + ³HON), the second feasible pathway. 8b can alternatively isomerize to 8c followed by N–O bond rupture to generate P ₆ (²OH + ²HNCN), the lesser followed feasible pathway. In addition, 2b takes continuously 1,3- and 1,2-H-shift to form NC(H)NHO 6a, then to ONHCNH 7a which can convert to 7b. Eventually, 7b may take C-N bond fission to produce P ₅ (¹HNC + ³HNO), the least feasible pathway. The present paper may be helpful for future experimental identification of the product distributions for the title reaction, and may be helpful to deeply understand the mechanism of the title reaction.     

Quantum Chemical Study on Reaction of Acetaldehyde with Hydroxyl Radical

The reaction of acetaldehyde with hydroxyl radical was studied by means of quantum chemical methods. The geometries for all the stationary points on the potential energy surfaces were optimized fully, respectively, at the G3MP2, G3, and MP2/6-311 G(d,p) levels. Single-point energies of all the species were calculated at the QCISD/6-311 G(d,p) level. The mechanism of the reaction studied was confirmed. The predicted product is acetyl radical that is in agreement with the experiment.