Monomer Radical Cations Research Articles

Singlet O2 Oxidation of the Radical Cation versus the Dehydrogenated Neutral Radical of 9-Methylguanine in a Watson-Crick Base Pair. Consequences of Structural Context.

In DNA, guanine is the most susceptible to oxidative damage by exogenously and endogenously produced electronically excited singlet oxygen (1O2). The reaction mechanism and the product outcome strongly depend on the nucleobase ionization state and structural context. Previously, exposure of a monomeric 9-methylguanine radical cation (9MG•+, a model guanosine compound) to 1O2 was found to result in the formation of an 8-peroxide as the initial product. The present work explores the 1O2 oxidation of 9MG•+ and its dehydrogenated neutral form [9MG - H]• within a Watson-Crick base pair consisting of one-electron-oxidized 9-methylguanine-1-methylcytosine [9MG·1MC]•+. Emphasis is placed on entangling the base pair structural context and intra-base pair proton transfer with and consequences thereof on the singlet oxygenation of guanine radical species. Electrospray ionization coupled with guided-ion beam tandem mass spectrometry was used to study the formation and reaction of guanine radical species in the gas phase. The 1O2 oxidation of both 9MG•+ and [9MG - H]• is exothermic and proceeds barrierlessly either in an isolated monomer or within a base pair. Single- and multi-referential theories were tested for treating spin contaminations and multi-configurations occurring in radical-1O2 interactions, and reaction potential energy surfaces were mapped out to support experimental findings. The work provides a comprehensive profile for the singlet oxygenation of guanine radicals in different charge states and in the absence and the presence of base pairing. All results point to an 8-peroxide as the major oxidation product in the experiment, and the oxidation becomes slightly more favorable in a neutral radical form. On the basis of a variety of reaction pathways and product profiles observed in the present and previous studies, the interplay between guanine structure, base pairing, and singlet oxygenation and its biological implications are discussed.

Electrochemical and Spectroelectrochemical Studies on the Reactivity of Perimidine-Carbazole-Thiophene Monomers towards the Formation of Multidimensional Macromolecules versus Stable π-Dimeric States.

During research on cross-linked conducting polymers, double-functionalized monomers were synthesized. Two subunits potentially able to undergo oxidative coupling were used—perimidine and, respectively, carbazole, 3,6-di(hexylthiophene)carbazole or 3,6-di(decyloxythiophene)carbazole; alkyl and alkoxy chains as groups supporting molecular ordering and 14H-benzo[4,5]isoquinone[2,1-a]perimidin-14-one segment promoting CH⋯O interactions and π–π stacking. Electrochemical, spectroelectrochemical, and density functional theory (DFT) studies have shown that potential-controlled oxidation enables polarization of a specific monomer subunit, thus allowing for simultaneous coupling via perimidine and/or carbazole, but mainly leading to dimer formation. The reason for this was the considerable stability of the dicationic and tetracationic π-dimers over covalent bonding. In the case of perimidine-3,6-di(hexylthiophene)carbazole, the polymer was not obtained due to the steric hindrance of the alkyl substituents preventing the coupling of the monomer radical cations. The only linear π-conjugated polymer was obtained through di(decyloxythiophene)carbazole segment from perimidine-di(decyloxythiophene)-carbazole precursor. Due to the significant difference in potentials between subsequent oxidation states of monomer, it was impossible to polarize the entire molecule, so that both directions of coupling could be equally favored. Subsequent oxidation of this polymer to polarize the side perimidine groups did not allow further crosslinking, because rather the π–π interactions between these perimidine segments dominate in the solid product.

Three-dimensional carambola-like MXene/polypyrrole composite produced by one-step co-electrodeposition method for electrochemical energy storage

Two-dimensional (2D) MXenes have been extensively investigated for electrochemical energy storage because of their excellent electronic properties. In this work, a facile and effective method was developed to fabricate MXene/polypyrrole (MXene/PPy) composite film electrodes via one-step co-electrodeposition. In this process, 2D Ti3C2Tx-MXene nanosheets acted as a core polymer because of the functional groups, such as –F, –OH, or –O, on their surface, and pyrrole monomer radical cations (Py·+) would gradually polymerize on the surface and layer space of the 2D MXene nanosheets to form three-dimensional (3D) carambola-like MXene/PPy composite films. The 3D structure composite facilitated electron transfer and ionic diffusion, so the MXene/PPy composite film electrodes exhibited an outstanding electrochemical performance with a high gravimetric capacitance of 416 F g−1 at a current density of 0.5 A g−1 in a three-electrode system. The as-fabricated symmetric supercapacitors of ITO-glasses coated with MXene/PPy composite films also exhibited a high specific capacitance (184 F g−1 at a scan rate of 10 mV s−1), excellent reliability and good cycling stability (approximately 86.4% retention after 5000 cycles, at 5 A g−1).

Photoinduced One-Electron Oxidation of Aromatic Selenides: Effect of the Structure on the Reversible Dimerization Reaction.

The photochemical one-electron oxidation of alkyl aryl selenides was studied by means of laser flash photolysis (355 nm). Quenching of the sensitizers in their excited state leads to selenide radical cation in the presence of selenium derivatives. The π-type dimer of methyl phenyl selenide radical cation was detected at 630 nm at expenses of the monomeric radical cation (530 nm). The effect of modification of the aryl and alkyl substituents was also studied, resulting that the formation of dimers depends on both, the electronic properties and steric hindrance of the substituents. Both effects, an increase in steric hindrance in the alkyl moiety or the presence of strongly electron donor groups in the aromatic substituent that stabilizes the radical cation, prevent the dimer formation.

Reversible σ-Bond Formation in Bowl-Shaped π-Radical Cations: The Effects of Curved and Planar Structures.

The reversible formation of σ-bonds between organic radicals has been widely investigated. However, reports on the formation of σ-dimers from delocalized π-radical cations are scarce. Herein, we report the reversible σ-dimerization behavior of a bowl-shaped π-radical cation generated from a nitrogen-embedded buckybowl, both in the crystalline state and in solution. The detailed structure of the σ-dimer in the crystalline state was determined by a single-crystal X-ray diffraction analysis. The monomeric radical cation exists predominantly in solution at room temperature, while dimerization of the radical cations occurs through carbon-carbon σ-bond formation upon reducing the temperature. 1H NMR and optical spectroscopy measurements confirmed the formation of a σ-dimer at low temperature. Comparative studies with a similar yet planar π-conjugated system suggested that the curved structure of the bowl-shaped π-radical cation facilitates the σ-dimerization at one of the internal sp2-hybridized carbon atoms. This trend was also observed for the nucleophilic addition reaction of methanol to the π-radical cations. The methoxylation reaction proceeded only for the curved π-radical cation. Theoretical calculations revealed that the large relief of structural strain at the α-carbon atom during the dimerization or nucleophilic addition reactions accelerated the bond formation at the internal carbon atom of the curved radical cation.

Photoinitiation with boron clusters

Polymer Chemistry Nonmetallic photoinitiators of polymerization are gaining interest for biomedical and electronics applications in which metal compounds are toxic or their presence reduces performance. Messina et al. report on boron clusters [B12(OR)12, where R is a phenyl or pentafluorophenyl group] that act as photoinitiators with blue light for the polymerization of olefins. These compounds photoionize and can initiate the reaction via one-electron transfer (creating a cluster radical anion and a monomer radical cation) to both electron-rich and electron-deficient styrene monomers at very low loadings (0.005 mol %). Even monomers such as isobutylene yielded highly branched polymers when the highly electron-withdrawing fluorinated initiator was used. J. Am. Chem. Soc. 10.1021/jacs.6b03568 (2016).

A new concept of the kinetics and mechanism of the oxidative polymerization of aromatic amines

A mechanism of the oxidative polymerization of aromatic amines, including the step of formation of a complex with charge transfer between quinonediimine fragments of oligomer chains and the monomer, is proposed. Quantitative characteristics of the kinetics of the oxidative polymerization of aromatic amines are theoretically justified and experimentally confirmed. It is demonstrated that the growth of chains during the oxidative polymerization occurs exclusively due to the recombination of the cation-radicals of oligomers of the aromatic amines with monomer cation-radicals.

Conjugated polyaniline as a result of the benzidine rearrangement

AbstractThe mechanism of the oxidative polymerization of aniline is reviewed on the basis of the experimental evidence and reaction schemes proposed in the literature. It is demonstrated that the balance between the non‐protonated and protonated forms of the monomer and the growing chain is responsible for the diversity of the molecular structure, morphology and properties of aniline oxidation products. Various forms are oxidized by two oxidation mechanisms: (1) chain reaction of electrophilic substitution and (2) coupling of cation‐radical centres. At pH > 2.5, the non‐protonated reagents are oxidized with a chain reaction controlled by electrophilic substitution of the aromatic ring. The reaction leads to the formation of non‐conducting aniline oligomers with heterogeneous molecular structures. At pH = 2.5–4, the electrophilic substitution is reduced because of the protonation of the aniline, and the cyclic dimer, phenazine, becomes the main product of the oxidation. The growth of the conjugated chain proceeds at pH < 2.5, when the reactants are protonated. The reaction proceeds through coupling between the terminal cation radical and the monomer cation radical with formation of a π‐complex. The transformation of the π‐complex into a para‐substituted monomer unit is thermodynamically controlled and is produced through an intramolecular benzidine (semidine) rearrangement. The regular structure of the growing chains is a result of the high regioselectivity of the sigmatropic rearrangements and significant energy gain attained by the formation of protonated polyconjugated chains in the agglomerated state. © 2015 Society of Chemical Industry

Pulse radiolysis studies of 3,5-dimethyl pyrazole derivatives of selenoethers.

One electron redox reaction of two asymmetric 3,5-dimethyl pyrazole derivatives of selenoethers attached to ethanoic acid (DPSeEA) and propionic acid (DPSePA) were studied by pulse radiolysis technique using transient absorption detection. The reaction of the hydroxyl ((•)OH) radical with DPSeEA or DPSePA at pH 7 produced transients absorbing at 500 nm and at 300 nm, respectively. The absorbance at 500 nm increased with increasing parent concentration indicating formation of dimer radical cations. From the absorbance changes, the equilibrium constants for the formation of dimer radical cation of DPSeEA and DPSePA were estimated as 2020 and 1608 M(-1), respectively. The rate constants at pH 7 for the reaction of the (•)OH radical with DPSeEA and DPSePA were determined to be 9.6 × 10(9) and 1.4 × 10(10) M(-1) s(-1), respectively. The dimer radical cation of DPSeEA and DPSePA decayed by first order kinetics with a rate constant of 2.8 × 10(4) and 5.5 × 10(3) s(-1), respectively. The yield of radical cations of DPSeEA and DPSePA were estimated from the secondary electron transfer reaction, which corresponds to 38% and 48% of (•)OH radical yield, respectively. Some fraction of monomer radical cation undergoes decarboxylation reaction, and the yield of decarboxylation was 25% and 20% for DPSeEA and DPSePA, respectively. These results have implication in understanding their antioxidant activity. The reaction of trichloromethyl peroxyl radical, glutathione, and ascorbic acid further support their antioxidant behavior.

Dissociative Photoionization of Glycerol and its Dimer Occurs Predominantly via a Ternary Hydrogen-Bridged Ion–Molecule Complex

The photoionization and dissociative photoionization of glycerol are studied experimentally and theoretically. Time-of-flight mass spectrometry combined with vacuum ultraviolet synchrotron radiation ranging from 8 to 15 eV is used to investigate the nature of the major fragments and their corresponding appearance energies. Deuterium (1,1,2,3,3-D5) and (13)C (2-(13)C) labeling is employed to narrow down the possible dissociation mechanisms leading to the major fragment ions (C3H(x)O2(+), C2H(x)O2(+), C2H(x)O(+), CH(x)O(+)). We find that the primary fragmentation of the glycerol radical cation (m/z 92) occurs only via two routes. The first channel proceeds via a six-membered hydrogen-transfer transition state, leading to a common stable ternary intermediate, comprised of neutral water, neutral formaldehyde, and a vinyl alcohol radical cation, which exhibits a binding energy of ≈42 kcal/mol and a very short (1.4 Å) hydrogen bond. Fragmentation of this intermediate gives rise to experimentally observed m/z 74, 62, 44, and 45. Fragments m/z 74 and 62 both consist of hydrogen-bridged ion-molecule complexes with binding energy >25 kcal/mol, whereas the m/z 44 species lacks such stabilization. This explains why water- or formaldehyde-loss products are observed first. The second primary fragmentation route arises from cleaving the elongated C-C bond. Also for this channel, intermediates comprised of hydrogen-bridged ion-molecule complexes exhibiting binding energies >24 kcal/mol are observed. Energy decomposition analysis reveals that electrostatic and charge-transfer interactions are equally important in hydrogen-bridged ion-molecule complexes. Furthermore, the dissociative photoionization of the glycerol dimer is investigated and compared to the main pathways for the monomeric species. To a first approximation, the glycerol dimer radical cation can be described as a monomeric glycerol radical cation in the presence of a spectator glycerol, thus giving rise to a dissociation pattern similar to that of the monomer.

Reversible σ‐Dimerizations of Persistent Organic Radical Cations

A class of well-defined reversible σ-dimerizations of 9,10-dialkoxyanthracene radical cations are presented. Yellow crystals of the σ-dimerized dication dissociate to purple solutions of monomeric radical cations in solution. The identity and stability of radical cations were unequivocally confirmed, providing evidence for reversible σ-dimerizations of persistent radical cations of aromatic systems.

From Monomers to π Stacks, from Nonconductive to Conductive: Syntheses, Characterization, and Crystal Structures of Benzidine Radical Cations

Salts that contain radical cations of benzidine (BZ), 3,3',5,5'-tetramethylbenzidine (TMB), 2,2',6,6'-tetraisopropylbenzidine (TPB), and 4,4'-terphenyldiamine (DATP) have been isolated with weakly coordinating anions [Al(OR(F))(4)](-) (OR(F) = OC(CF(3))(3)) or SbF(6)(-). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of benzidine or its alkyl-substituted derivatives in CH(2)Cl(2). The salts were characterized by UV absorption and EPR spectroscopy as well as by their single-crystal X-ray structures. Variable-temperature UV/Vis absorption spectra of BZ(·)(+)[Al(OR(F))(4)](-) and TMB(·)(+)[Al(OR(F))(4)](-) in acetonitrile indicate an equilibrium between monomeric free radical cations and a radical-cation dimer. In contrast, the absorption spectrum of TPB(·)(+)SbF(6)(-) in acetonitrile indicates that the oxidation of TPB only resulted in a monomeric radical cation. Single-crystal X-ray diffraction studies show that in the solid state BZ and its methylation derivative (TMB) form radical-cation π dimers upon oxidation, whereas that modified with isopropyl groups (TPB) becomes a monomeric free radical cation. By increasing the chain length, π stacks of π dimers are obtained for the radical cation of DATP. The single-crystal conductivity measurements show that monomerized or π-dimerized radicals (BZ(·)(+), TMB(·)(+), and TPB(·)(+)) are nonconductive, whereas the π-stacked radical (DATP(·)(+)) is conductive. A conduction mechanism between chains through π stacks is proposed.

Specific Indolo[3,2,1-jk]carbazole Conducting Thin-Film Materials Production by Selective Substitution

Selectively substituted indolo[3,2,1-jk] carbazole (IC) molecules have been synthesized through flash vacuum pyrolysis (FVP) and then electro-oxidized, resulting in the formation of redox-active and electronically conducting thin films consisting exclusively of three highly luminescent dimer species, the 2,2'-, 2,10'-, and 10,10'-coupled dimers. DFT calculation has enabled both the accurate calculation of monomer oxidation potentials and the prediction of the nature of the resulting dimers through consideration of the coupling of the oxidized monomer radical cations. This demonstrates that substituted ICs represent a class of molecules able to form redox-active and conducting dimer films of controlled composition upon oxidation and that DFT calculations can be used to inform the synthesis of specific IC monomers most likely to both produce electronically conducting thin-film materials and yield specific luminescent dimers with desirable materials properties.

An EPR analysis of β‐dimerization in α‐blocked pyrroles in oxidant conditions

Electron paramagnetic resonance (EPR) analysis of neutral and acidic solutions of 2,5-dimethyl-1-phenylpyrrol (1) and meta-, para-, and ortho-bis(2,5-dimethylpyrrol-1-yl)benzenes (4-6) in the presence of Tl(III) trifluoroacetate as oxidant reveals the poor stability of their generated monomeric radical cations which dimerize through C(β)-C(β) bond formation. EPR spectra of the monomeric radical cations 4(•+) , 5(•+) , and 6(•+) coincide with that of 1(•+) , suggesting that the unpaired electron in these charged species is confined in one of the pyrrolic rings. The very twisted angles between pyrrolic and phenyl planes due to steric hindrance in the X-ray analysis of the molecular structure of 4 confirm the absence of extended conjugation in the π-system.

Gas-phase formation and reactions of radical cations of guanosine, deoxyguanosine and their homodimers and heterodimers

Electrospray ionisation of methanolic solutions containing a mixture of the nucleoside deoxyguanosine, dG, incubated with Cu(NO3)2 resulted in the formation of a range of ions, including doubly charged copper nucleoside complexes [CuIIdGn]2+, with n ranging from 2 to 10. Collision-induced dissociation of these complexes proceeds via a number of different pathways that depend on the size of the cluster, n. When n=3, monomeric radical cations are formed via redox processes. When n=4, dimeric radical cations are formed. Related complexes are formed for the nucleoside guanosine, Gs, and these [CuIIGsn]2+ complexes fragment in similar fashions to their [CuIIdGn]2+ counterparts. A key finding is that the radical cations of dG and Gs have fragmentation patterns that depend on the way they are formed. Thus radical cations, dG+ and Gs+, formed directly in the electrospray ionisation source or via collision-induced dissociation of [CuIIdG3]2+ and [CuIIGs3]2+ complexes fragment in the same way, giving the radical cation of the guanine base at m/z 151 via cleavage of the N-glycosidic bond. In contrast, the collision-induced dissociation spectra of radical cations formed via the sequences [CuIIdG4]2+→dG2+→dG+ and [CuIIGs4]2+→Gs2+→Gs+ are dominated by the loss of CH2O and further loss of C2H3O2 from the sugar moiety. These different fragmentation reactions are attributed to different tautomeric structures of the radical cations. Quantum chemical calculations were carried out on possible structures of the radical cation dimer of the model 9-methylguanine. Three low energy structures were found. Two of these represent base pairs of the kind found in supramolecular motifs of guanine derivatives, and one of these possesses a novel tautomeric structure that may have important biological implications.

Investigation of the electropolymerization of o‐toluidine and p‐phenylenediamine and their electrocopolymerization by in situ ultraviolet–visible spectroelectrochemistry

AbstractUnder the conditions of potentiostatic electrolysis, the electropolymerization of o‐toluidine (OT) and para‐phenylenediamine (PPDA) and the electrocopolymerization between OT and PPDA on an indium tin oxide (ITO) conductive glass electrode at potentials of 0.7, 0.8, and 0.9 V were studied in detail by in situ ultraviolet–visible (UV–vis) spectrometry in 0.5 mol/L sulfuric acid media. It was shown that both OT and PPDA could be electropolymerized on the ITO electrode, which depended on the applied electrolysis potential and the concentration of the monomer. Furthermore, in situ UV–vis spectra indicated that the electrocopolymerization between OT and PPDA could happen. The presence of PPDA not only promoted polymerization but also accelerated polymerization, which was attributed to the formation of an intermediate result from the coupling of PPDA and the toluidine monomer cation radical. PPDA could be incorporated into the copolymer to make the copolymer have a phenazine or phenazine‐like cyclic structure, which was proven by the reflectance Fourier transform infrared spectra of the polymer and copolymer. The scanning electron microscopy morphology images of the polymers obtained showed that, in addition to accelerating polymerization, PPDA also could change the method of nucleation for the polymer to make the copolymer possess a fibrous surface morphology. The diameter of the fibroid copolymer was about 100 nm, and the length of that reached about 1000 nm. In the article, a newer concerned mechanism of copolymerization was proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Calculation of the Redox Properties of Aromatics and Prediction of Their Coupling Mechanism and Oligomer Redox Properties

The B3LYP density functional theory method has been used to determine theoretical values for the peak oxidation potentials for a range of redox-active aromatics in acetonitrile at room temperature. Excellent agreement to within 37 mV is found between these values and those observed experimentally. The calculated electron spin density distributions of indole monomer and indole oligomer radical cations also enable a plausible mechanism to be advanced by which the experimentally observed asymmetric trimer product is formed. Theoretical values for the peak oxidation potential of the indole trimer also show excellent agreement with those observed previously in electrochemical studies, again consistent with this asymmetric trimer product. Together, with the previously demonstrated ability of this approach to predict the coupling mechanisms and redox properties of the oligomers formed from indolocarbazole, these calculations provide a method for the in silico screening of molecular properties to inform molecular materials design and electrosynthesis.

Monomer and Dimer Radical Cations of Benzene, Toluene, and Naphthalene

Pulse radiolytic generation of monomeric and dimeric cations of benzene, toluene, and naphthalene in aqueous acid media at room temperature and their spectrophotometric characterization is discussed. Results presented include measurements of each aromatic's solubility in H(2)O-H(2)SO(4) and H(2)O-HClO(4) media over the acidity range pH 1 to H(0) -7.0, facile oxidative generation, and real-time identification of appropriate cationic transients with respective lambda(max) (nm) and epsilon (M(-1) cm(-1)) values measured as follows: C(6)H(6)(*+) (443, 1145 +/- 75), C(6)H(5)CH(3)(*+) (428, 1230 +/- 90), C(10)H(8)(*+) (381, 3650 +/- 225, and 687, 2210 +/- 160), (C(6)H(6))(2)(*+) (860, 2835 +/- 235), (C(6)H(5)CH(3))(2)(*+) (950, 1685 +/- 155), and (C(10)H(8))(2)(*+) (1040, 4170 +/- 320). Kinetic measurements reveal the respective formation rates of monomeric cations to be near-diffusion controlled, while the forward rate values for the dimeric species generation are marginally slower. The proton activity corrected pK(a) values are found to remain between -2.6 and -1.3 for the ArH(*+) species (C(6)H(6)(*+) most acidic, C(10)H(8)(*+) least acidic), while the pK(a) values of (ArH)(2)(*+) species vary from -5.0 to -3.0 ((C(6)H(6))(2)(*+) most acidic, (C(10)H(8))(2)(*+) least acidic). In H(0) -5 in aqueous H(2)SO(4), the respective stabilization energy of (C(6)H(6))(2)(*+), (C(6)H(5)CH(3))(2)(*+), and (C(10)H(8))(2)(*+) is estimated to be 16.6, 15.0, and 13.7 kcal mol(-1). Thus, the aqueous acid solution emerges as an alternative medium for typical radical-cationic studies, while offering compatibility for the deprotonated radical characterization near neutral pH.

Electrochemical and spectroscopic characterization of poly(1,8-diaminocarbazole): Part I. Electropolymerization and determination of the polymer structure by FTIR studies and DFT calculations

Poly(1,8-diaminocarbazole) (PDACz) films on the Pt electrodes were obtained from acetonitrile (0.1 M LiClO 4) and acidic aqueous solutions (0.1 M HClO 4). The changes in the shape of polymerization curves in the two media are discussed in terms of a limited conductivity window of the fully oxidized PDACz. The polymer structure of the films obtained from acetonitrile and acidic aqueous solution was proposed on the base of FTIR spectra and the results of theoretical calculations. Density functional theory (DFT) was used to calculate a distribution of unpaired-electron spin density for monomer radical cations to predict the coupling positions during polymerization. This method allowed to resolve the problems concerning the monomer linkage, still present after analysis of FTIR spectra of the polymer.

Energies, Stability and Structure Properties of Radicals Derived from Organic Sulfides Containing an Acetyl Group after the •OH Attack: ab Initio and DFT Calculations vs Experiment

The mutual location of the sulfur atom and the acetyl group was found to affect significantly the (*)OH-induced oxidation mechanism of the organic sulfides containing either an alpha- or beta-positioned acetyl group. This phenomenon was reflected in formation of different intermediate products observed in pulse radiolysis experiments (Varmenot et al. J. Phys. Chem. A. 2004, 108, 6331-6346). In order to obtain a better support for the earlier interpretation of the experimental data, quantum mechanical calculations were performed using a density functional theory method (DFT-B3LYP) and the ab initio method (Møller-Plesset perturbation theory MP2) for optimizations and energy calculations of the parent molecules and radicals and radical cations derived from them. In accordance with experiments, it was found that the alpha-positioned acetyl group in S-ethylthioacetate (SETAc) destabilizes hydroxysulfuranyl radicals and monomeric sulfur radical cations. Instead, formation of stable C-centered radicals of the alpha-(alkylthio)alkyl-type was found energetically favorable, the H3C-(*)CH-S-C(=O)CH3 radical, in particular. On the other hand, the beta-positioned acetyl group in S-ethylthioacetone (SETA) does not destabilize hydroxysulfuranyl radicals, monomeric sulfur radical cations, and dimeric sulfur radical cations. Moreover, the alpha-(alkylthio)alkyl radicals of the type -S-(*)CH-C(=O)- were found to be particularly stabilized. The calculated transition states pointed toward the efficient direct conversion of the hydroxysulfuranyl radicals derived from SETAC and SETA radicals into the respective C-centered radicals. This reaction pathway, important in neutral solutions, is responsible for the absence of the dimeric radical cations of SETAc at low and high concentrations and of the dimeric radical cations of SETA at relatively low concentrations of the solute.