Showing papers on "Homolysis published in 2013"
TL;DR: Mechanistic assessments based on kinetic and isotopic methods combined with density functional theory are used to probe the diverse pathways by which C-H bonds in CH4 react on bare Pd clusters, Pd cluster surfaces saturated with chemisorbed oxygen (O*), and PdO clusters.
Abstract: Mechanistic assessments based on kinetic and isotopic methods combined with density functional theory are used to probe the diverse pathways by which C–H bonds in CH4 react on bare Pd clusters, Pd cluster surfaces saturated with chemisorbed oxygen (O*), and PdO clusters. C–H activation routes change from oxidative addition to H-abstraction and then to σ-bond metathesis with increasing O-content, as active sites evolve from metal atom pairs (*–*) to oxygen atom (O*–O*) pairs and ultimately to Pd cation-lattice oxygen pairs (Pd2+–O2–) in PdO. The charges in the CH3 and H moieties along the reaction coordinate depend on the accessibility and chemical state of the Pd and O centers involved. Homolytic C–H dissociation prevails on bare (*–*) and O*-covered surfaces (O*–O*), while C–H bonds cleave heterolytically on Pd2+–O2– pairs at PdO surfaces. On bare surfaces, C–H bonds cleave via oxidative addition, involving Pd atom insertion into the C–H bond with electron backdonation from Pd to C–H antibonding states a...
240 citations
TL;DR: 2-isocyanobiphenyls react with aromatic aldehydes via base promoted homolytic aromatic substitution (BHAS) to give 6-aroylated phenanthridines through addition of acyl radicals to the isonitrile functionality and subsequent intramolecular BHAS of the intermediate imidoyl radicals.
154 citations
TL;DR: The o-, m- and p- substituted ArI, as well as the electron-donating and electron-withdrawing nature of the substituents were found be good to excellent substrates and double C-H arylation was successfully achieved.
141 citations
TL;DR: Direct arylation of unactivated arenes or heteroarenes with aryl halides could be carried out in the presence of potassium tert-butoxide and dimethyl sulfoxide under visible-light irradiation.
125 citations
TL;DR: This protocol offers an inexpensive, yet efficient route to aromatic C-C bond formations since transition metal catalysts and impurities can be avoided by using this reaction system.
Abstract: Transition-metal-free cross-coupling reactions have been a hot topic in recent years. With the aid of a radical initiator, a number of unactivated arene C-H bonds can be directly arylated/functionalized by using aryl halides through homolytic aromatic substitution. Commercially available or specially designed promoters (e.g. diamines, diols, and amino alcohols) have been used to make this synthetically attractive method viable. This protocol offers an inexpensive, yet efficient route to aromatic C-C bond formations since transition metal catalysts and impurities can be avoided by using this reaction system. In this article, we focus on the significance of the reaction conditions (e.g. bases and promoters), which allow this type of reaction to proceed smoothly. Substrate scope limitations and challenges, as well as mechanistic discussion are also included.
104 citations
TL;DR: In this article, a single-electron reduction of the Pacman uranyl complex [UO2(py)(H2L)] by the rare-earth complexes Ln(III)(A)3 (A = N(SiMe3)2, OC6H3Bu(t)2-2,6) via homolysis of a Ln-A bond was proposed.
Abstract: The heterobimetallic complexes [{UO2Ln(py)2(L)}2], combining a singly reduced uranyl cation and a rare-earth trication in a binucleating polypyrrole Schiff-base macrocycle (Pacman) and bridged through a uranyl oxo-group, have been prepared for Ln = Sc, Y, Ce, Sm, Eu, Gd, Dy, Er, Yb, and Lu. These compounds are formed by the single-electron reduction of the Pacman uranyl complex [UO2(py)(H2L)] by the rare-earth complexes Ln(III)(A)3 (A = N(SiMe3)2, OC6H3Bu(t)2-2,6) via homolysis of a Ln-A bond. The complexes are dimeric through mutual uranyl exo-oxo coordination but can be cleaved to form the trimetallic, monouranyl "ate" complexes [(py)3LiOUO(μ-X)Ln(py)(L)] by the addition of lithium halides. X-ray crystallographic structural characterization of many examples reveals very similar features for monomeric and dimeric series, the dimers containing an asymmetric U2O2 diamond core with shorter uranyl U═O distances than in the monomeric complexes. The synthesis by Ln(III)-A homolysis allows [5f(1)-4f(n)]2 and Li[5f(1)-4f(n)] complexes with oxo-bridged metal cations to be made for all possible 4f(n) configurations. Variable-temperature SQUID magnetometry and IR, NIR, and EPR spectroscopies on the complexes are utilized to provide a basis for the better understanding of the electronic structure of f-block complexes and their f-electron exchange interactions. Furthermore, the structures, calculated by restricted-core or all-electron methods, are compared along with the proposed mechanism of formation of the complexes. A strong antiferromagnetic coupling between the metal centers, mediated by the oxo groups, exists in the U(V)Sm(III) monomer, whereas the dimeric U(V)Dy(III) complex was found to show magnetic bistability at 3 K, a property required for the development of single-molecule magnets.
100 citations
TL;DR: A simple and efficient direct radical arylation of unactivated arenes is described which uses cheap and commercially available phenyl hydrazine as an initiator and offers a practical approach for preparation of an array of substituted biaryls.
99 citations
TL;DR: In the presence of an N-heterocyclic carbene as an unsaturated organic substrate, the fragile phosphasilene 8 acts as a :PH transfer reagent, resulting in the formation of silylene 9 and phosphaalkene 11 bearing a terminal PH moiety.
Abstract: The simplest parent phosphinidene, :PH (1), has been observed only in the gas phase or low temperature matrices and has escaped rigorous characterization because of its high reactivity. Its liberation and transfer to an unsaturated organic molecule in solution has now been accomplished by taking advantage of the facile homolytic bond cleavage of the fragile Si═P bond of the first zwitterionic phosphasilene LSi=PH (8) (L = CH[(C═CH2)CMe(NAr)2]; Ar = 2,6-iPr2C6H3). The latter bears two highly localized lone pairs on the phosphorus atom due to the LSi═PH ↔ LSi+–PH– resonance structures. Strikingly, the dissociation of 8 in hydrocarbon solutions occurs even at room temperature, affording the N-heterocyclic silylene LSi: (9) and 1, which leads to oligomeric [PH]n clusters in the absence of a trapping agent. However, in the presence of an N-heterocyclic carbene as an unsaturated organic substrate, the fragile phosphasilene 8 acts as a :PH transfer reagent, resulting in the formation of silylene 9 and phosphaalk...
99 citations
TL;DR: The geometric and electronic structures and reactivity of an S = 5/2 (HS) mononuclear nonheme (TMC)Fe(III)-OOH complex are studied by spectroscopies, calculations, and kinetics and compared with the results of previous studies to understand parallels and differences in mechanisms of O-O bond homolysis and electrophilic H-atom abstraction reactions.
Abstract: The geometric and electronic structures and reactivity of an S = 5/2 (HS) mononuclear nonheme (TMC)FeIII–OOH complex are studied by spectroscopies, calculations, and kinetics and compared with the results of previous studies of S = 1/2 (LS) FeIII–OOH complexes to understand parallels and differences in mechanisms of O–O bond homolysis and electrophilic H-atom abstraction reactions. The homolysis reaction of the HS [(TMC)FeIII–OOH]2+ complex is found to involve axial ligand coordination and a crossing to the LS surface for O–O bond homolysis. Both HS and LS FeIII–OOH complexes are found to perform direct H-atom abstraction reactions but with very different reaction coordinates. For the LS FeIII–OOH, the transition state is late in O–O and early in C–H coordinates. However, for the HS FeIII–OOH, the transition state is early in O–O and further along in the C–H coordinate. In addition, there is a significant amount of electron transfer from the substrate to the HS FeIII–OOH at transition state, but that does...
96 citations
TL;DR: In this paper, thermolysis of 2 in an attempt to favor a monomeric ketyl radical species unexpectedly led to cleavage of the C-O bond to generate a Zr/Co μ-oxo species featuring an unusual terminal Co−CPh2 carbene linkage.
Abstract: Single electron transfer from the ZrIIICo0 heterobimetallic complex (THF)Zr(MesNPiPr2)3Co–N2 (1) to benzophenone was previously shown to result in the isobenzopinacol product [(Ph2CO)Zr(MesNPiPr2)3Co–N2]2 (2) via coupling of two ketyl radicals. In this work, thermolysis of 2 in an attempt to favor a monomeric ketyl radical species unexpectedly led to cleavage of the C–O bond to generate a Zr/Co μ-oxo species featuring an unusual terminal Co═CPh2 carbene linkage, (η2-MesNPiPr2)Zr(μ-O)(MesNPiPr2)2Co═CPh2 (3). This complex was characterized structurally and spectroscopically, and its electronic structure is discussed in the context of density functional theory calculations. Complex 3 was also shown to be active toward carbene group transfer (cyclopropanation), and silane addition to 3 leads to PhSiH2O–Zr(MesNPiPr2)3Co–N2 (5) via a proposed Co–alkyl bond homolysis route.
89 citations
TL;DR: Triarylsulfonium salts are prompted to undergo efficient homolytic reduction by single electron transfer under mild photocatalytic conditions, and the liberated aryl radical can then participate in carbon-carbon bond formation processes with allyl sulfones and activated olefins as mentioned in this paper.
Abstract: Triarylsulfonium salts are prompted to undergo efficient homolytic reduction by single electron transfer under mild photocatalytic conditions. The liberated aryl radical can then participate in carbon-carbon bond formation processes with allyl sulfones and activated olefins. Triarylsulfonium salts emerge as a valuable and alternative source of aryl radicals for synthesis.
TL;DR: A new photochromic compound is synthesized, in which the stable colored species photochemically converts into the metastable colorless species via a short-lived radical, which has a 1,1'-binaphthyl moiety bridging the two diphenylimidazole units.
Abstract: We have synthesized a new photochromic compound that exhibits unusual negative photochromism, in which the stable colored species photochemically converts into the metastable colorless species via a short-lived radical. This compound has a 1,1'-binaphthyl moiety bridging the two diphenylimidazole units. Its photochemical properties were investigated by nanosecond laser flash photolysis. The colored species isomerizes to the colorless species upon exposure to visible light and thermally returns to the original colored species within 20 min at room temperature. Moreover, the photodecoloration reaction proceeds via a short-lived radical with a half-life of 9.4 μs in benzene at room temperature. Both the colored and colorless species show the photoinduced homolytic bond cleavage reaction of the C-N bond between the nitrogen atom of the imidazole ring and the carbon atom of the 1-position of the 1,1'-binaphthyl moiety and that of the C-C bond between each of the carbon atoms of the 2-position of the imidazole ring, respectively, followed by their formation by rapid radical coupling.
TL;DR: A physical organic approach to the problem of free radicals in biology and medicine is highlighted in this Perspective with stereochemical, kinetic, and extrathermodynamic probes applied to the study of mechanism.
Abstract: This Perspective describes advances from the author’s laboratory on the free radical reactions of organic compounds with molecular oxygen. Polyunsaturated fatty acids (PUFAs) and sterols are particularly prone to undergo radical chain oxidation, and evidence suggests that this process, known as lipid peroxidation, occurs in vivo under a variety of conditions that are the result of an oxidative stress. Cyclic peroxides, hydroperoxides, and epoxy alcohols are major products formed from peroxidation, and the basic mechanisms of product formation are now reasonably well understood. These mechanisms include reversible addition of oxygen to carbon radicals, rearrangement and cyclization of allyl and pentadienyl peroxyl radicals, and homolytic substitution of carbon radicals on the peroxide bond. A physical organic approach to the problem of free radicals in biology and medicine is highlighted in this Perspective with stereochemical, kinetic, and extrathermodynamic probes applied to the study of mechanism. A rad...
TL;DR: The first direct experimental evidence showing that a high-spin iron(III)-hydroperoxo complex bearing an N-methylated cyclam ligand can oxidize thioanisoles is reported.
Abstract: We report the first direct experimental evidence showing that a high-spin iron(III)-hydroperoxo complex bearing an N-methylated cyclam ligand can oxidize thioanisoles. DFT calculations showed that the reaction pathway involves heterolytic O-O bond cleavage and that the choice of the heterolytic pathway versus the homolytic pathway is dependent on the spin state and the number of electrons in the d(xz) orbital of the Fe(III)-OOH species.
TL;DR: The mechanism of the rate-limiting stage of alkanes oxidation with hydrogen peroxide, that is, formation of the hydroxyl radicals, catalyzed by aqua complexes, [M(H2O)n]3+ (1), was theoretically studied in detail at the DFT level as mentioned in this paper.
Abstract: The mechanism of the rate-limiting stage of alkanes oxidation with hydrogen peroxide, that is, formation of the hydroxyl radicals, catalyzed by aqua complexes, [M(H2O)n]3+ (1), of the group III metals exhibiting a unique stable non-zero oxidation state (M = Ga, In, Sc, Y, or La) was theoretically studied in detail at the DFT level. The mechanism involves the substitution of a H2O ligand for H2O2, protolysis of the coordinated H2O2, substitution of another H2O ligand for H2O2, generation of the hydroxyl radical upon the homolytic O–O bond cleavage in the key complex [M(H2O)(n−2)(H2O2)(OOH)]2+, and closure of the catalytic cycle. The substitution steps proceed via the dissociative mechanism D (M = Ga and Y) or the associative mechanisms A [M = Sc, La, or In (second substitution)] or Ia [M = In (first substitution)]. The general catalytic activity of 1 is determined by three main factors, that is, (i) lability of the complexes, (ii) acidity of the metal-bound ligands, and (iii) the H2O2 activation toward the...
TL;DR: Reactions of 1,3-dimethylimidazol-2-ylidene-borane (diMe-Imd-BH3) and related NHC-boranes with diaryl and diheteroaryl disulfides provide diverse N HC-boryl monosulfides and NHC
Abstract: Reactions of 1,3-dimethylimidazol-2-ylidene-borane (diMe-Imd-BH3) and related NHC-boranes with diaryl and diheteroaryl disulfides provide diverse NHC-boryl monosulfides (diMe-Imd-BH2SAr) and NHC-boryl disulfides (diMe-Imd-BH(SAr)2). Heating in the dark with 1 equiv of disulfide favors monosulfide formation, while irradiation with 2 equiv disulfide favors disulfide formation. With heteroaryl disulfides, the NHC-borane in the primary NHC-boryl sulfide product migrates from sulfur to nitrogen to give new products with a thioamide substructure. Most substitution reactions are thought to proceed through radical chains in which homolytic substitution of a disulfide by an NHC-boryl radical is a key step. However, with electrophilic disulfides under dark conditions, a competing ionic path may also be possible.
TL;DR: H-H σ-bond activation promoted by Ni[MesB(o-Ph2PC6H4)2] (1(Mes)) was theoretically investigated with the density functional theory method and resulted in an unprecedented trans-nickel(II) hydridoborohydrido complex.
Abstract: H–H σ-bond activation promoted by Ni[MesB(o-Ph2PC6H4)2] (1Mes) was theoretically investigated with the density functional theory method. In 1Mes, the nickel 3d, 4s, and 4p orbital populations are similar to those of the typical nickel(II) complex. First, one H2 molecule coordinates with the nickel center to form a dihydrogen complex, 2, which induces an increase in the nickel 3d and 4p orbital populations and thus a decrease in the nickel oxidation state. Then, the H–H σ-bond is cleaved under the unusual cooperation of the electron-rich nickel center and the electron-deficient borane ligand in a polarized manner, leading to an unprecedented trans-nickel(II) hydridoborohydrido complex, 3. In the transition state, charge transfer (CT) occuring from the H2 moiety to the 1Mes moiety (0.683 e) is much larger than the reverse CT (0.284 e). As a result, cleavage of the H–H σ-bond affords two positively charged hydrogen atoms. In this process, the boron atomic population and the nickel 4p orbital population incre...
TL;DR: It is known that the H2 molecule dissociates heterolytically on stepped MgO surfaces with formation of protons bound to O2-anions (OH groups) and hydride ions bound to Mg cations (MgH groups).
Abstract: It is well-known that the H2 molecule dissociates heterolytically on stepped MgO surfaces with formation of protons bound to O2– anions (OH groups) and hydride ions bound to Mg cations (MgH groups)...
TL;DR: During photolysis of acetophenone O-allylcarbamoyl oxime, the corresponding oxazolidin-2-onylmethyl radical was detected by EPR spectroscopy, providing the first evidence that N-monosubstituted carbamoysloxyl radicals can hold their structural integrity.
Abstract: A set of oxime carbamates having N-alkyl and N,N-dialkyl substituents were prepared via carbonyldiimidazole intermediates. It was shown by EPR spectroscopy that they underwent clean homolysis of their N–O bonds upon UV photolysis. During photolysis of acetophenone O-allylcarbamoyl oxime, the corresponding oxazolidin-2-onylmethyl radical was detected by EPR spectroscopy, providing the first evidence that N-monosubstituted carbamoyloxyl radicals can hold their structural integrity. N,N-Disubstituted carbamoyloxyl radicals dissociated rapidly at the lowest accessible temperatures. Above room temperature, both types of oxime carbamate acted as selective new precursors for aminyl and iminyl radicals. Rate parameters were measured for 5-exo cyclization of N-benzyl-N-pent-4-enylaminyl radicals; the rate constant was smaller than for C-centered and O-centered analogues. Oxime carbamates derived from the volatile diethylamine afforded aryliminyl radicals that proved convenient for phenanthridine preparations.
TL;DR: In this paper, the potential barriers and the reaction heat were determined by basic density function theory (DFT) calculations to estimate whether the proposed radical pathway is possible, and the assessment and optimization of the process parameters for MnO 2 /PAA/US system to eliminate phenol was accomplished with experimental design.
TL;DR: The FeCl3-mediated reaction of [60]fullerene with N-benzhydryl sulfonamides afforded C60-fused indane derivatives using the high-speed vibration milling technique.
TL;DR: An accurate determination of the homolytic gas-phase Co-C bond dissociation energies in the related adenosyl- and methylcobinamides is reported utilizing an energy-resolved threshold collision-induced dissociation technique for benchmarking of electronic structure methods separate from (often ill-defined) solvent effects.
Abstract: Essential to biological activity of adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl) is the Co–C bond cleavage step. Hence, we report an accurate determination of the homolytic gas-phase Co–C bond dissociation energies in the related adenosyl- and methylcobinamides (41.5 ± 1.2 and 44.6 ± 0.8 kcal/mol, respectively) utilizing an energy-resolved threshold collision-induced dissociation technique. This approach allows for benchmarking of electronic structure methods separate from (often ill-defined) solvent effects. Adequacy of various density functional theory methods has been tested with respect to the experimentally obtained values.
TL;DR: It has been found that a low-lying dissociative (2)πσ* excited state exists in pyridinium, which can lead to the photodetachment of the hydrogen atom, and the H2O molecule can be dissociated into H˙ and OH˙ radicals by the absorption of two ultraviolet photons.
Abstract: The photochemistry of the hydrogen-bonded pyridine-water complex has been investigated with ab initio computational methods. Vertical excitation energies, excited-state reaction paths for proton transfer as well as structures and energies of conical intersections and reaction barriers have been determined with multi-configuration self-consistent-field and multi-reference perturbation methods, as well as with single-reference coupled-cluster and propagator methods. In the pyridine-water complex, the energies of two charge-separated excited states of (1)nπ* and (1)ππ* character are connected to the energies of the locally excited (1)nπ* and (1)ππ* states of the pyridine chromophore via a low energy barrier. The charge-separated excited states are strongly stabilized by the transfer of a proton from water to pyridine. The energies of the resulting biradical states intersect the potential-energy surface of the closed-shell ground state as a function of the proton-transfer coordinate. The resulting radical pair may dissociate to yield pyridinium and hydroxyl radicals. The photochemistry of the hypervalent pyridinium radical has been explored with the same computational methods. It has been found that a low-lying dissociative (2)πσ* excited state exists in pyridinium, which can lead to the photodetachment of the hydrogen atom. Overall, the H2O molecule can thus be dissociated into H˙ and OH˙ radicals by the absorption of two ultraviolet photons. The relevance of these results for solar water splitting and solar carbon dioxide reduction is discussed.
TL;DR: This article deals with two transformations, radical phosphination by addition across unsaturated C–C bonds and substitution of organic halides.
Abstract: Organophosphorus compounds are important in organic chemistry. This review article covers emerging, powerful synthetic approaches to organophosphorus compounds by homolytic substitution at phosphorus with a carbon-centered radical. Phosphination reagents include diphosphines, chalcogenophosphines and stannylphosphines, which bear a weak P–heteroatom bond for homolysis. This article deals with two transformations, radical phosphination by addition across unsaturated C–C bonds and substitution of organic halides.
TL;DR: In this article, the authors developed a series of fast photochromic imidazole dimers with a [2.2]paracyclophane ([2]PC) moiety that bridge diphenylimidazoles units and succeeded the acceleration of the thermal decoloration rate.
Abstract: Recently, we have developed a series of fast photochromic imidazole dimers with a [2.2]paracyclophane ([2.2]PC) moiety that bridge diphenylimidazole units and succeeded the acceleration of the thermal decoloration rate. The colorless [2.2]PC-bridged imidazole dimers show a photoinduced homolytic bond cleavage of the C–N bond between the imidazole rings to give a pair of colored imidazolyl radicals upon UV light irradiation, followed by the radical–radical coupling reaction to form the initial C–N bond between the imidazole rings. The decoloration reaction to give the initial imidazole dimer proceeds only thermally. The high quantum yield close to unity of the photochromic reaction and the large extinction coefficient of the radical achieve both high optical density at the photostationary state and rapid switching speed. The application to rapid fluorescence switching has been investigated to develop a new type of photochromic fluorescence switching molecule applicable to super-resolution microscopy. The w...
TL;DR: The ratio of heterolysis to homolysis increased gradually in all solvent systems, suggesting that [(TMP)Mn-OOC(O)R] species 2a is the major active species, and a Mn(V)=O intermediate generated from the heterolytic cleavage of 2b becomes a major reactive species.
Abstract: The participation of multiple active oxidants generated from the reactions of two manganese(III) porphyrin complexes containing electron-withdrawing and -donating substituents with peroxyphenylacetic acid (PPAA) as a mechanistic probe was studied by carrying out catalytic oxidations of cyclohexene, 1-octene, and ethylbenzene in various solvent systems, namely, toluene, CH(2) Cl(2) , CH(3) CN, and H(2) O/CH(3) CN (1:4). With an increase in the concentration of the easy-to-oxidize substrate cyclohexene in the presence of [(TMP)MnCl] (1a) with electron-donating substituents, the ratio of heterolysis to homolysis increased gradually in all solvent systems, suggesting that [(TMP)Mn-OOC(O)R] species 2a is the major active species. When the substrate was changed from the easy-to-oxidize one (cyclohexene) to difficult-to-oxidize ones (1-octene and ethylbenzene), the ratio of heterolysis to homolysis increased a little or did not change. [(F(20) TPP)Mn-OOC(O)R] species 2b generated from the reaction of [(F(20) TPP)MnCl] (1b) with electron-withdrawing substituents and PPAA also gradually becomes involved in olefin epoxidation (although to a much lesser degree than with [(TMP)Mn-OOR] 2a) depending on the concentration of the easy-to-oxidize substrate cyclohexene in all aprotic solvent systems except for CH(3) CN, whereas Mn(V)=O species is the major active oxidant in the protic solvent system. With difficult-to-oxidize substrates, the ratio of heterolysis to homolysis did not vary except for 1-octene in toluene, indicating that a Mn(V)=O intermediate generated from the heterolytic cleavage of 2b becomes a major reactive species. We also studied the competitive epoxidations of cis-2-octene and trans-2-octene with two manganese(III) porphyrin complexes by meta-chloroperbenzoic acid (MCPBA) in various solvents under catalytic reaction conditions. The ratios of cis- to trans-2-octene oxide formed in the reactions of MCPBA varied depending on the substrate concentration, further supporting the contention that the reactions of manganese porphyrin complexes with peracids generate multiple reactive oxidizing intermediates.
TL;DR: It is concluded that homolysis and heterolysis of the dioxygen bond with formation of compound II in AOS and compound I in 5,8-LDS are influenced by Asn and Gln residues, respectively, of the I-helices.
TL;DR: In this paper, the authors examined the bond dissociation behavior and aromatic ring architecture of basic nitrogen compounds in Sudan heavy petroleum fraction using both broadband and quadrupole isolation modes positive ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with collision induced dissociation (CID) techniques were used to characterize a low sulfur crude oil derived vacuum residuum (VR).
Abstract: This paper examined the bond dissociation behavior and aromatic ring architecture of basic nitrogen compounds in Sudan heavy petroleum fraction. Both broadband and quadrupole isolation modes positive-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with collision induced dissociation (CID) techniques were used to characterize a low sulfur crude oil derived vacuum residuum (VR). The appropriate CID operating condition was selected by comparing the molecular weight distributions of the basic nitrogen compounds under various CID operating conditions. Both odd- and even-electron fragment ions were observed from the mass spectrum, indicating that the heterolytic and homolytic bond cleavages occurred simultaneously during the CID process. The odd-electron fragment ions were predominant in each class species, indicating preferential heterolytic bond cleavages. At the optimal CID condition, the alkyl groups decomposed deeply and just left the aromatic cores of the nitrogen compounds. No significant variation in double bond equivalent (DBE) value was observed between the fragment and parent ions, revealing that the domination of single core structure.
TL;DR: Indolinic nitroxides derived from 2,2-diphenyl-3-phenylimino-2,3-dihydroindol-1-yloxyl (DPAIO) were designed to improve the bulk polymerization of methacrylate derivatives as discussed by the authors.
TL;DR: A range of mononuclear organomagnesates [RMgX2]− were generated in the gas phase by decarboxylation of the magnesium carboxylate precursors as discussed by the authors.