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1.
The ESR spectra of -irradiated, at –196 °C, solutions of acetic acid and acetic anhydride were studied depending on their concentrations in CFCl3. The structure of thus produced radical cations is confirmed with the deuterium substituted analogues. It has been shown that the ion-molecular reaction of the radical cation CH2COOH+ in the isolated dimer takes place for the dilute solutions of acetic acid in CFCl3 resulting in the formation of CH3COO follwed by its decomposition to CH3+CO2 while the radicals CH2COOH are formed via secondary processes. The reactions of radical cations of acetic oxide have been also studied.  相似文献   

2.
The hitherto unknown radical cation of cyclobutene ( 2 ) has been generated in a CFCl3 matrix by γ rays at 77 K. The coupling constants, as determined from the ESR spectrum of 2 +, are 2.80 and 1.11 mT for the four CH2 and the two CH = protons, respectively. Photo-induced ring opening of 2 + yields a radical cation which exhibits the same ESR and ENDOR spectra as those observed upon direct ionization of s-trans-buta-1, 3-diene (s-trans -1 ). The radical cation s-trans -1 +, should, therefore, be the final product of this conversion.  相似文献   

3.
It is found that an oxygen-centred nπ radical of HCOOCH3 is produced radiolytically in CFCl3 at 4.2 K without forming a σ* complex with a matrix molecule. This cation converts into the carbon-centred radical cation HC+(OH)OCH2 by an intramolecular hydrogen-atom transfer upon warming to 77 K. This is clear experimental evidence for a McLafferty rearrangement of ester radical cations.  相似文献   

4.
The structure of the methyl tert-butyl ether (MTBE) radical cation and mechanism of its thermal and photochemical reactions in irradiated freons (CFCl3, CF2ClCFCl2, and CF3CCl3) were studied. Radical products of MTBE radiolysis in the liquid phase were investigated by the spin trapping technique. The quantum-chemical calculations of the structure of MTBE radical cations and products of their transformations were carried out by density functional theory (DFT) and ab initioMP2 methods. The primary MTBE radical cations are stabilized in dilute solutions in CFCl3and CF3CCl3. The ion–molecule reaction (proton transfer from the radical cation) was found to occur in concentrated solutions in CFCl3immediately during irradiation. The action of light ( = 436 to 546 nm) at 77 K on the MTBE radical cation in CFCl3and CF3CCl3matrices results in intramolecular migration of the methyl group to yield the distonic radical cation (CH3)2 .CO+(CH3)2. The primary MTBE radical cations undergo an irreversible transformation with methane elimination resulting in formation of the 2-methoxypropene radical cation .CH2=+(3)3in CFCl3and CF3CCl3matrices in the temperature range 110–130 K. In the case of CF2ClCFCl2matrix, such a reaction occurs during irradiation at 77 K. Using the spin trapping technique, it was shown that the liquid-phase radiolysis of the neat ether resulted in the formation of fragmentation products (.CH3,CH3., and t-BuO. radicals) from the primary radical cations, as well as the products of their rearrangements and ion–molecule reactions.  相似文献   

5.
《Tetrahedron》1986,42(22):6315-6323
The σ radical cations of most typical bicycloalkanes such as norbornane and bicyclo[2,2,2]octane are radiolytically produced at 4 K in halogenocarbon matrices and are studied by ESR spectroscopy. Their electronic and geometrical structures as well as their dynamical behaviors have been elucidated from the hyperfine structures and their temperature changes. The semi occupied molecular orbital (SOMO) of the former cation is 4a2, in which the unpaired electron delocalizes over the four exo C-H bonds giving large hyperfine coupling. The latter is a Jahn-Teller active species and exhibits static distortion from D3h to C2v at 4 K in CFCl3, and the SOMO is likely to be 6b2, in which the unpaired electron delocalizes over the four endo C-H bonds giving large proton coupling, although a dynamically averaged structure with 12 equivalent methylene protons is observed in C-C6F12 as well as in CFCl2CF2Cl matrices at 77 K. The unpaired electron distribution in bicycloalkane radical cations is similar to that in cycloalkane radical cations previously studied. Upon warming both the cations undergo deprotonation to give 2-yl alkyl radicals from the exo or endo C-H bond, at which the higher unpaired electron density is populated. In addition to these radical cations, the structures and reactions of the radical cations of the related bicycloalkenes such as norbornadiene, quadricyclane, and bicyclo[2,2,2]octene have also been studied. The hydride ion transfer to an olefinic radical cation to form an alkyl radical is observed for the bicyclo[2,2,2]octene radical cation as the first example observed by ESR.  相似文献   

6.
《Chemical physics letters》1986,123(4):337-340
Ab initio calculations have been performed on the cyclopropane radical cation and the trimethylene radical cation. The former radical cation has been claimed to undergo irreversible ring opening to the latter in CFCl2CF2Cl matrices at 80 K. However, the computational results reported here show that the energy of the cyclopropane radical cation is much lower than that of the (0,0) trimethylene radical cation, thus casting doubt on the possibility of irreversible ring opening of the former to the latter. It is suggested that the ring-opened species that is observed in the matrix by EPR has a nucleophile strongly coordinated to the carbocationic center.  相似文献   

7.
Structure and mechanism of thermal and photochemical reactions of radical cations of methyl n-propyl ether (MPE) were studied in irradiated freonic matrices CFCl3, CF2ClCFCl2, and CF3CCl3 at 77 K. The quantum chemical calculations of the structure of radical cations and products of their transformations were carried out with methods based on the density functional theory (DFT). Experimental and calculation results show that the MPE radical cations are characterized by substantial delocalization of spin density to the propyl group. The action of light on the MPE radical cations in a CF3CCl3 matrix at 77 K results in intramolecular rearrangement yielding the distonic radical cation .CH2CH2CH2(OH+)CH3. It was found that the primary MPE radical cations underwent irreversible transformation to CH3CH2CH2OCH 2 . radical as a result of an ion-molecule reaction that occurred in a CF2ClCFCl2 matrix upon heating the sample to 110–120 K or in a CFCl3 matrix upon increasing the solute concentration.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 2, 2005, pp. 105–113.Original Russian Text Copyright © 2005 by Belevskii, Feldman, Tyurin.This revised version was published online in April 2005 with a corrected cover date.  相似文献   

8.
ESR spectra of -irradiated, at 77 K, acetone and CH3COEt solutions /0.1–22%/ in CFCl3 were studied. The yields of monomer and dimer radical cations of ketones and RCHCOCH3 radicals depend on ketone concentration in CFCl3. When exposed to light the dimeric radical cations are transformed into RCHCOMe, while the monomeric radical cations disappear without further radical production. Different types of solid phase ion-molecular reaction for monomer and dimer radical cations are discussed.  相似文献   

9.
《Tetrahedron》1986,42(22):6301-6314
The radical cations of cyclopropane and several of its methyl derivatives have been characterized by ESR spectroscopy following their generation by γ irradiation of dilute solutions of the parent compounds in Freon matrices at 77 K. In the CFCl3, CF3CCl3, and CF2ClCCl3, matrices, only the ring-closed species is usually observed in the accessible temperature range up to ca 160 K. In the CFCl2CF2Cl matrix, however, the ring-closed radical cations initially formed at 77 K undergo ring opening between 83 and 110 K, the more highly substituted radical cations requiring a higher temperature for this transformation. The ring-closed radical cations are 2A1 species for C2v symmetry, the most substituted cyclopropane C-C bond being elongated with the spin density largely confined to the basal carbons in a face-to-face (90°, 90°) structure. In the ring-opened radical cations, the radical center is localized on the most substituted carbon atom following the breaking of the weakened C-C bond of the ring-closed species. The radical conformations of the ring-opened species have been determined, the RCH2CH2· center produced from cyclopropane having a bisected conformation while the RCH2CMe2· center obtained from 1,1,2,2-tetramethylcyclopropane is eclipsed, as expected for the presence of α-methyl substituents at the radical site. The nature of the putative carbocation center in the ring-opened radical cations is discussed with reference to recent proposals that this center is strongly coordinated to an electrophile (Cl- or RCl) thereby negating the requirement for an orthogonal structure. Consideration of the strong matrix dependence of the ring-opening reaction suggests a possible solvation effect, however, in which the CFCl2CF2Cl matrix assists the twisting of one of the CR1R2 groups at the most substituted bond, leading to the rupture of this one-electron σ bond. A strong solvation effect also explains why ring-opening can occur in a suitable polar solvent despite theoretical calculations of unfavourable energetics for a similar gas-phase reaction. Experiments are also described on spiro[2.5]octane, the cyclopropane ring undergoing scission at the CH2-CH2 bond of this radical cation to give an RCH2· radical center. this radical then undergoes a H-atom abstraction with a neutral spiro[2.5]octane molecule in the CFCl2CF2Cl matrix at higher temperature to give the spiro[2.5]oct-6-yl radical.  相似文献   

10.
ESR spectra for -irradiated at 77 K solutions /0.02–16%/ of tetramethylurea /TMU/ in CFCl3 and Freon-113 have been studied. TMU+. radical cations radiolytically produced in dilute solutions have been shown to undergo intramolecular hydrogen transfer upon photobleaching resulting in CH2N= type radical. Evidence for intermolecular proton transfer in TMU+. radical cations after annealing to phase transition temperature /110–120 K/ in Freon-113 was obtained. Primary radical cations of TMU+. at their ground state take part in ion-molecular reaction via proton transfer. Molecular cations in their excited states may undergo fragmentation producing Me2N radicals, which were trapped in liquid phase by t-BuNO as a spin trap.  相似文献   

11.
A 4 K matrix ESR study shows that the molecular radical cations of isopropyl formate and acetate, produced radiolytically in halocarbon matrices at 4.2 K, undergo spontaneous rearrangement due to a selective intramolecular hydrogen shift from the tertiary CH bond in the isopropyl group to the carbonyl oxygen atom giving RC+(OH)OC(CH3)2, where R = H or CH3. The radical cation of tert-butyl acetate undergoes further fragmentation at the ester CO bond following a similar rearrangement to give an isobutene radical cation in CFCl3.  相似文献   

12.
Precise values of the proton coupling constants have been determined from the ENDOR spectra of the radical cation of s-trans-buta-1,3-diene generated from the neutral compound by γ irradiation in a CFCl3 matrix at 77 K. These values are 1.119 and 1.050 mT for the pairs of exo- and endo-protons in the 1,4-positions, respectively, and 0.283 mT for the pair of protons in the 2,3-positions. A general TRIPLE resonance spectrum proves that all coupling constants have the same sign which should be negative by theory, Evidence by experiment and theory indicate that the s-trans-configuration of the neutral compound is retained upon ionization.  相似文献   

13.
《Chemical physics letters》1987,133(3):207-213
In order to study radical cation rearrangements, the species generated by γ-irradiation of 1,2-diphenyl-3,3,4, 4-tetramethylcyclobutene (CB) and 3,4-diphenyl-2,5-dimethyl-2,4-hexadiene (BD) in frozen Freon solutions were studied by monitoring their EPR and visible absorption spectra. The optical and EPR spectra are indicative of CB+ and BD+ Conversion of CB+ to BD+ is not a dominant process at low temperatures in CFCl3 or the Freon mixture (50:50 CFCl3:CF2BrCF2Br) but can be assisted photochemically.  相似文献   

14.
The rate constant for the reaction of CFCl2 with oxygen is measured in the pressure range 0.2–12 Torr using pulsed-laser photolysis and time-resolved mass spectrometry. CFCl2 radicals are generated by photolysis of CFCl3 at 193 nm. The reaction kinetics are recorded by monitoring the build-up of the CFCl2O2 radical concentration. The reaction is in its fall-off region, and the parameters of the relation for the treatment of the fall-off are for M = N2: k(0) = (5.0 ± 0.8) × 10?30 cm6 molecule?2 s?1. k(∞) = (6.0 ± 1.0) × 10?12 cm3 molecule?1 s?1. This value of k(∞) is consistent with results obtained at low pressure taking Fc = 0.6, but the uncertainty in the high-pressure limit is much higher. The results are compared to measurements performed with CH3 and CF3. Estimates of the relative third-body efficiencies of He and N2 are given for CFCl2 and CF3.  相似文献   

15.
Three reaction paths, namely, molecule‐induced homolytic, free radical, and electrophilic, were modeled computationally at the MP2 level of ab initio theory and studied experimentally for the reaction of F2 with the terminal dienes of bicyclo[3.3.1]nonane series. The addition of fluorine is accompanied by transannular cyclization to the adamantane derivatives in which strong evidence for the electrophilic mechanism both in nucleophilic (acetonitrile) and non‐nucleophilic (CFCl3, CHCl3) solvents were found. The presence of KF in CFCl3 and CHCl3 facilitates the addition and substantially reduces the formation of tar products.  相似文献   

16.
ESR spectra for -irradiated, at –196 °C, solution of Me2NH, Me3N, and EtNH2 in CFCl3 /0.05÷100% amine/ have been studied. Radical cations Me2NH+., Me3N+. and EtNH 2 +. were trapped in dilute solutions /less than 1% amine in CFCl3/. The yields of radical cations decrease and those of neutral radicals /Me2 N, CH2NMe2, Et NH/ correspondingly increase as the amine concentration increases. Radical cations Me2NH+. are transformed to Me2 N as well as Me3N+. to C H2NMe2 via proton transfer reaction, which is described by the reaction volume model.  相似文献   

17.
A flow injection gas phase chemiluminometer has been constructed for monitoring halogenated compounds which upon UV radiation consume ozone. The ozone concentration is followed by the ethylene-ozone chemiluminescent reaction and by UV absorption. The sensitivity depends on the ability of each compound to consume ozone and the limits of quantification vary from 9.6 and 25 nmol for CFCl3 and CF2Cl2 to 22.5 and 17.2 μmol for CHCl3 and CH3CCl3, respectively.  相似文献   

18.
Chemically activated CF3SH, CFCl2SH, and CF2ClSH were formed through combination of SH and CF3, CFCl2, and CF2Cl radicals, respectively. The SH radical was prepared by abstraction of an H‐atom from H2S by the halocarbon radical produced during photolysis of (CF3)2C=O, (CFCl2)2C=O, or (CF2Cl)2C=O. 1,2‐HX (X = F, Cl) elimination reactions were observed from CF3SH, CFCl2SH, and CF2ClSH with products detected by GC‐MS. The combination reaction of CF2Cl radicals with SH radicals prepared CF2ClSH molecules with approximately 318 kJ/mol of internal energy. The experimental rate constants for elimination of HCl and HF from CF2ClSH were 3 ± 3 × 1010 and 2 ± 1 × 109 s?1, respectively. Comparison to Rice–Ramsperger–Kassel–Marcus (RRKM) calculated rate constants assigned the threshold energies as 171 ± 12 and 205 ± 12 kJ/mol for the unimolecular elimination of HCl and HF, respectively. Theoretical calculations using the B3PW91, MP2, and M062X methods with the 6311+G(2d,p) and 6‐31G(d',p') basis sets established that for a specific method the threshold energies differ by only 4 kJ/mol between the two different basis sets. There was wide variation among the three methods, but the M062X approach appeared to give threshold energies closest to the experimental values. Chemically activated CF3SH and CFCl2SH were also prepared with about 318 kcal mol?1 of internal energy, and the HX (X = F, Cl) elimination reactions were observed. Only HCl loss was detected from CFCl2SH, but the rate was too fast to measure with our kinetic method; however, based on our detection limit the HF elimination channel is at least 50 times slower.  相似文献   

19.
The effect of CFCl3 (0.025–0.200 mbar) addition on the formation of ozone in 214 nm photolysis of oxygen (800–2000 mbar) was investigated. Kinetic analysis of the drastic reduction in ozone formation in the presence of CFCl3 shows that it proceeds by a chain mechanism with a chain length of 5.07 ± 0.21(2σ). This chain length is independent of CFCl3 and O2 pressures as well as incident light intensity and the mechanism of the chain reaction is governed by the Cl generating reactions of ClO radicals. A mechanism based only on the self reaction of these radicals: ClO + ClO → Cl2 + O2 (7), Cl + ClO2 (8), and Cl + OClO (9), followed by fast decomposition of ClO2 into Cl and O2, predicts a chain length which is considerably lower than the observed value. Incorporation of the reaction CFCl2O2 + ClO → CFCl2O + ClO2 (11) in the mechanism satisfactorily accounts for the observed chain length. A lower limit of 3 × 10?12 cm3 molecule?1 s?1 for k11 is estimated.  相似文献   

20.
The kinetics of oxidation of 2,2′-azinobis-(3-ethylbenzothiazole-6-sulphonate) (ABTS) by the inorganic peroxides, peroxomonosulphate, peroxodisulphate, peroxodiphosphate, and hydrogen peroxide were investigated in aqueous solution. The kinetics of formation of the radical cation, ABTS.+, on one-electron abstraction by these peroxides and the further reaction of ABTS.+ with higher concentrations of these peroxides at longer time scale were studied by following the growth and decay of the radical cation, ABTS.+ at 417 nm. The rate of formation of ABTS.+ was found to obey a total second-order, first-order each in [ABTS] and [peroxide], except for H2O2, which reacted through Michaelis-Menten kinetics. All the peroxides investigated were found to react with ABTS.+; however peroxodisulphate alone oxidized ABTS.+ to the dication (ABTS++), the other peroxides reacted via ionic mechanism, probably forming sulphoxide and sulphone as products. The kinetics of decay of the radical cation, ABTS.+, was also found to follow a total second-order, first-order each in [ABTS.+] and [peroxide], except peroxodiphosphate the reaction of which obeyed Michaelis-Menten kinetics. The effect of pH and temperature were also investigated in all the systems and the kinetic and thermodynamic parameters were evaluated and discussed with suitable reaction mechanisms.  相似文献   

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