Influence of the chloro substituent position on the triplet reactivity of benzophenone derivatives: a time‐resolved resonance Raman and density functional theory study

A nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic investigation of the photoreduction reactions and ability of several chloro‐substituted benzophenone (Cl‐BP) triplets is described. The TR³ results show that the 3‐chlorobenzophenone (3‐Cl‐BP), 4‐chlorobenzophenone (4‐Cl‐BP) and 4,4′‐dichlorobenzophenone (4,4′‐dichloro‐BP) triplets exhibit similar hydrogen abstraction ability with the parent BP triplet. In 2‐propanol, the 3‐Cl‐, 4‐Cl‐ and 4,4′‐dichloro‐diphenylketyl (DPK) radicals were observed and they appear to react with dimethylketyl radicals at the para‐position to form a light absorption transient species. These transient species were characterized with TR³ spectra, and identified with the help of results from density functional theory calculations. In an acetontitrile/water (MeCN:H₂O) 1:1 mixed solvent, these DPK radicals were also observed but with slower formation rates. However, the 2‐Cl‐DPK radical was observed to form with a lower yield and a significantly slower formation rate than the other chloro‐substituted benzophenones examined here in 2‐propanol under the same experimental conditions. These results reveal that the 2‐chloro substituent reduces the hydrogen abstraction ability of the substituted BP triplet, which was not as expected based on the assumption that the electron‐withdrawing group could increase its photoreduction ability. This unusual ortho effect of the chlorine substitution is briefly discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Time‐resolved spectroscopic and density functional theory investigation of the photochemistry of suprofen

The photochemistry of suprofen (SPF) was investigated by femtosecond transient absorption (fs‐TA), resonance Raman (RR) and nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic methods to gain additional information so as to better elucidate the possible photochemical reaction mechanism of suprofen in several different solvents. In neat acetonitrile (MeCN), the fs‐TA and ns‐TR³ experimental data indicated that the lowest lying excited singlet state S₁ (nπ*) underwent an efficient intersystem crossing process (ISC) to the excited triplet state T₃ (ππ*), followed by an internal conversion (IC) process to T₁ (ππ*). In the aqueous solution, a triplet biradical species (³ETK‐1) was obtained as the product of a decarboxylation process from triplet suprofen anion (³SPF⁻) and the reaction rate of the decarboxylation process was determined by the concentration of H₂O. A protonation process for ³ETK‐1 leads to formation of a neutral species (³ETK‐3) that was directly observed by ns‐TR³ spectra, then this ³ETK‐3 species decayed via ISC process to generate final product. Copyright © 2014 John Wiley & Sons, Ltd.     

Catalysis by hydrogen chloride in the gas‐phase elimination kinetics of 2‐phenyl‐2‐propanol and 3‐methyl‐1‐buten‐3‐ol

A homogeneous, molecular, gas‐phase elimination kinetics of 2‐phenyl‐2‐propanol and 3‐methyl‐1‐ buten‐3‐ol catalyzed by hydrogen chloride in the temperature range 325–386 °C and pressure range 34–149 torr are described. The rate coefficients are given by the following Arrhenius equations: for 2‐phenyl‐2‐propanol log k₁ (s^?1) = (11.01 ± 0.31) ? (109.5 ± 2.8) kJ mol^?1 (2.303 RT)^?1 and for 3‐methyl‐1‐buten‐3‐ol log k₁ (s^?1) = (11.50 ± 0.18) ? (116.5 ± 1.4) kJ mol^?1 (2.303 RT)^?1. Electron delocalization of the CH₂?CH and C₆H₅ appears to be an important effect in the rate enhancement of acid catalyzed tertiary alcohols in the gas phase. A concerted six‐member cyclic transition state type of mechanism appears to be, as described before, a rational interpretation for the dehydration process of these substrates. Copyright © 2007 John Wiley & Sons, Ltd.     

Detection of ketyl radicals using 31P NMR spin trapping

Our recent work has allowed the development of ³¹P NMR spin trapping techniques for the detection and, at times, absolute quantification of many oxygen‐ and carbon‐centered free radical species. These methods are based on the ability of the nitrone phosphorus compound, 5‐diisopropoxy‐phosphoryl‐5‐methyl‐1‐pyrroline‐N‐oxide (DIPPMPO), to react with free radical species and form stable radical adducts, which are suitably detected and accurately quantified using ³¹P NMR. Our continuing efforts have now been focused on the application of this powerful system for the trapping of ketyl radicals, which are very difficult intermediates to be detected and quantified with traditional techniques (i.e., EPR). Ketyl radicals were initially produced using photochemical reactions of acetophenone, whose excited triplet state is able to abstract hydrogen from an H donor. As such, the ³¹P NMR signals for the radical adducts of the DIPPMPO spin trap with the ketyl radicals were assigned. Furthermore, in an effort to confirm the structure of these adducts, their mass spectra and fragmentation patterns were carefully examined under Gas Chromatography–Mass Spectrometry (GC–MS) conditions. Subsequently, the DIPPMPO spin trapping system was applied to the oxidation of 1‐(3,4‐dimethoxyphenyl)ethanol in the presence of horseradish peroxidase (HRP), hydrogen peroxide, and 1‐hydroxybenzotriazole (HBT) as the electron carrier (mediator). Our work confirmed that the mechanism consists of a hydrogen abstraction reaction from the α position, involving the ketyl radical: during the oxidation, the hydroxyl, hydroperoxyl, and ketyl radical intermediates were all detected. These efforts demonstrate the efficacy of our methodology that provides for the first time a facile means for the detection of the otherwise elusive ketyl radical species, with important implications in biology, chemistry, and biochemistry. Copyright © 2009 John Wiley & Sons, Ltd.     

Solvent effects on the structure of the triplet excited state of xanthone: a time‐resolved resonance Raman study

Solvent effects, especially intermolecular hydrogen bonding, play a central role in the photophysics and photochemistry of aromatic ketones. To gain insight into the solute–solvent interactions and their implications for structure and reactivity, we studied xanthone (XT) in two different solvents of similar dipolarity: acetonitrile (ACN; aprotic) and methanol (MeOH; protic), using time‐resolved resonance Raman (TR³) spectroscopy in conjunction with time‐dependent density functional theory calculations. Raman excitation profiles of XT in ACN followed the triplet‐triplet absorption band with a shoulder at the blue end, but for MeOH, they followed the triplet‐triplet absorption band quite closely; therefore, we propose that the resonance enhancement of Raman peaks are from two states in ACN and from a single state in the MeOH solvent. Furthermore, a resonance Raman peak at 614 cm⁻¹ (a₂ symmetry) that appeared in ACN but not in the MeOH solvent has been identified as a vibronic active mode that could be involved in coupling the two lowest 1³ππ* (1³A₁) and 1³nπ* (1³A₂) excited states. This was further confirmed by depolarization ratio measurements of some of the representative TR³ peaks in ACN, which showed a depolarized intensity for the 614 cm⁻¹ peak while the other peaks were polarized. Interestingly, we also observed blue shifting of some of the vibrational frequencies of XT in the 1³ππ* state compared with the ground state with increasing solvent polarity. This anomalous blue shift casts doubt on the general use of the resonance canonical structure to explain the structure of the excited states. In summary, we propose that the different hydrogen bonding mechanisms exhibited by the two lowest triplet states of XT separate them further in energy and that this can contribute to its low reactivity towards H atom abstraction in protic solvents. Copyright © 2016 John Wiley & Sons, Ltd.     

Pulse radiolysis studies of 2‐ and 3‐hydroxybenzyl alcohols: inhibition of dehydration of ·OH‐(hydroxybenzyl alcohols) adducts by H2PO4− ions

Reactions of ·OH/O ^.? radicals and H‐atoms as well as specific oxidants such as Cl₂^.? and N₃· radicals have been studied with 2‐ and 3‐hydroxybenzyl alcohols (2‐ and 3‐HBA) at various pH using pulse radiolysis technique. At pH 6.8, ·OH radicals were found to react quite fast with both the HBAs (k = 7.8 × 10⁹ dm³ mol^?1 s^?1 with 2‐HBA and 2 × 10⁹ dm³ mol^?1 s^?1 with 3‐HBA) mainly by adduct formation and to a minor extent by H‐abstraction from ? CH₂OH groups. ·OH‐(HBA) adduct were found to undergo decay to give phenoxyl type radicals in a pH dependent way and it was also very much dependent on buffer‐ion concentrations. It was seen that ·OH‐(2‐HBA) and ·OH‐(3‐HBA) adducts react with HPO₄^2? ions (k = 2.1 × 10⁷ and 2.8 × 10⁷ dm³ mol^?1 s^?1 at pH 6.8, respectively) giving the phenoxyl type radicals of HBAs. At the same time, this reaction is very much hindered in the presence of H₂PO ions indicating the role of phosphate ion concentration in determining the reaction pathway of ·OH adduct decay to final stable product. In the acidic region adducts were found to react with H⁺ ions. At pH 1, reaction of ·OH radicals with HBAs gave exclusively phenoxyl type radicals. Proportion of the reducing radicals formed by H‐abstraction pathway in ·OH/O ^.? reactions with HBAs was determined following electron transfer to methyl viologen. H‐atom abstraction is the major pathway in O ^.? reaction with HBAs compared to ·OH radical reaction. H‐atom reaction with 2‐ and 3‐HBA gave transient species which were found to transfer electron to methyl viologen quantitatively. Copyright © 2010 John Wiley & Sons, Ltd.     

Time-resolved EPR study of the photoreduction of phthalic anhydride and chlorinated phthalic anhydrides in 2-propanol

The photoreduction of phthalic anhydride (PA), 3,6-dichlorophthalic anhydride (3,6-DCPA), 4,5-dichlorophthalic anhydride (4,5-DCPA) and tetrachlorophthalic anhydride (TCPA) in 2-propanol has been studied with time-resolved electron paramagnetic resonance. The chemically induced dynamic electron polarization spectra show that the reaction takes place through the excited triplet states. From PA, cyclohexadienyl-type hydrogen adduct and ketyl radicals were observed, whereas 3,6-DCPA produced the 3,6-DCPA anion and hydrogen adduct radicals. With 4,5-DCPA only the anion radical appeared, whilst the TCPA system showed no apparent anion and adduct radical formation. These data show that the hydrogen adduct formation occurs at the 4 position in the benzene ring, but that 4,5-DCPA and TCPA do not undergo this reaction. The anion radicals of PAs are formed in subsequent deprotonation reactions of the ketyl radicals. We propose that the hydrogen adduct radical formation in PA and 3,6-DCPA takes place through direct hydrogen abstraction by the excited triplet molecules, in competition with similar abstraction by the carbonyl group to form the ketyls.     

The effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer of 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone in methanol: A TD‐DFT study

Excited‐state intermolecular or intramolecular proton transfer (ESIPT) reaction has important potential applications in biological probes. In this paper, the effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer reaction of the 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone (MQ) dye in methanol solvent is investigated by the density functional theory and time‐dependent density functional theory approaches. Both the primary structure parameters and infrared vibrational spectra analysis of MQ and its benzo‐analogue 2‐methyl‐3‐hydroxy‐4(1H)‐benzo‐quinolone (MBQ) show that the intermolecular hydrogen bond O₁―H₂?O₃ significantly strengthens in the excited state, whereas another intermolecular hydrogen bond O₃―H₄?O₅ weakens slightly. Simulated electron absorption and fluorescence spectra are agreement with the experimental data. The noncovalent interaction analysis displays that the intermolecular hydrogen bonds of MQ are obviously stronger than that of MBQ. Additionally, the energy profile analysis via the proton transfer reaction pathway illustrates that the ESIPT reaction of MBQ is relatively harder than that of MQ. Therefore, the effect of benzo‐annelation of the MQ dye weakens the intermolecular hydrogen bond and relatively inhibits the proton transfer reaction.     

Homo‐Diels–Alder reaction of a very inactive diene,bicyclo[2,2,1]hepta‐2,5‐diene,with the most active dienophile, 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione. Solvent,temperature, and high pressure influence on the reaction rate

Solvent, temperature, and high pressure influence on the rate constant of homo‐Diels–Alder cycloaddition reactions of the very active hetero‐dienophile, 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione (1), with the very inactive unconjugated diene, bicyclo[2,2,1]hepta‐2,5‐diene (2), and of 1 with some substituted anthracenes have been studied. The rate constants change amounts to about seven orders of magnitude: from 3.95^.10^?3 for reaction (1+2) to 12200 L mol^?1 s^?1 for reaction of 1 with 9,10‐dimethylanthracene (4e) in toluene solution at 298 K. A comparison of the reactivity (ln k₂) and the heat of reactions (?_r‐nH) of maleic anhydride, tetracyanoethylene and of 1 with several dienes has been performed. The heat of reaction (1+2) is ?218 ± 2 kJ mol^?1, of 1 with 9,10‐dimethylanthracene ?117.8 ± 0.7 kJ mol^?1, and of 1 with 9,10‐dimethoxyanthracene ?91.6 ±0.2 kJ mol^?1. From these data, it follows that the exothermicity of reaction (1+2) is higher than that with 1,3‐butadiene. However, the heat of reaction of 9,10‐dimethylanthracene with 1 (?117.8 kJ mol^?1) is nearly the same as that found for the reaction with the structural C=C counterpart, N‐phenylmaleimide (?117.0 kJ mol^?1). Since the energy of the N=N bond is considerably lower (418 kJ/bond) than that of the C=C bond (611 kJ/bond), it was proposed that this difference in the bond energy can generate a lower barrier of activation in the Diels–Alder cycloaddition reaction with 1. Linear correlation (R = 0.94) of the solvent effect on the rate constants of reaction (1+2) and on the heat of solution of 1 has been observed. The ratio of the volume of activation (?V^≠) and the volume of reaction (?V_r‐n) of the homo‐Diels–Alder reaction (1+2) is considered as “normal”: ?V^≠/?V_r‐n = ?25.1/?30.95 = 0.81. Copyright © 2012 John Wiley & Sons, Ltd.     

Understanding halogen‐substituent assistance in H‐atom abstraction‐based reactions of CHCl•− with CH4 − nXn (X = H,F, Cl; n = 0–3)

The effect of halogen‐substituent on hydrogen abstraction mechanisms was studied by applying density functional theory functional calculations to the gas‐phase reactions between CHCl^?? and CH_{4 ? n}X_n (X = H, F, Cl; n = 0–3), and it is found that a heavier X substituent in the substrate results in a greater stabilization of corresponding complex, a lower activation energy, a faster H‐abstraction reaction, and greater exothermicity. However, CH₄– reaction is more reactive than CH₃F– reaction under the same condition because of dominant π‐donation from the electronegative F atom. We also explored the reactivity difference for the seven reactions in terms of factors derived from bond order, second‐order perturbative energy, and activation strain model analysis. The rate constants are evaluated over a wide temperature range of 298–1000 K by the conventional transition state theory. Copyright © 2014 John Wiley & Sons, Ltd.     

DFT study on abstraction reaction mechanism of oh radical with 2‐methoxyphenol

Reaction mechanism of 2‐methoxyphenol (2MP) (guaiacol) with OH radical has been performed using density functional theory methods BH&HLYP and MPW1K method with 6‐311++G(d,p) basis set. Single‐point energy calculations were done using CCSD(T)/6‐311++G(d,p). The theoretical results reveal that the hydrogen abstraction from methoxy group is found to be the dominant reaction channel with an energy barrier of 9.31 kcal/mol. Also, time‐dependent density functional theory calculations have been performed using BH&HLYP/6‐311++G(d,p) level of theory, and the results reveal that the reactions occur in ground state than the excited state. The results of reaction force profile indicate that structural rearrangements are most influential with high percentage than the relaxation process. The calculated theoretical rate constants (12.19 × 10^?11 cm³ molecule^?1 s^?1) are in good agreement with the experimental rate constant. The atmospheric lifetime of 2‐methoxyphenol with respect to OH radicals is 2.27 hours, which implies that OH radical plays an important role in the degradation of 2MP. The Wiberg bond index of the abstraction reaction reveals that the bond order is concerted, partially synchronic. The reactant‐like transition state satisfies Hammond postulate, which eventually results in an exothermic reaction, and the product‐like transition state reveals in endothermic nature.     

Synthesis,properties, and solvatochromism of 1,3‐dimethyl‐5‐{(thien‐2‐yl)‐[4‐(1‐piperidyl) phenyl]methylidene}‐(1H,3H)‐pyrimidine‐2,4,6‐trione

A new merocyanine dye, 1,3‐Dimethyl‐5‐{(thien‐2‐yl)‐[4‐(1‐piperidyl)phenyl]methylidene}‐ (1H, 3H)‐pyrimidine‐2,4,6‐trione 3 , has been synthesized by condensation of 2‐[4‐(piperidyl)benzoyl]thiophene 1 with N,N′‐dimethyl barbituric acid 2 . The solvatochromic response of 3 dissolved in 26 solvents of different polarity has been measured. The solvent‐dependent long‐wavelength UV/Vis spectroscopic absorption maxima, v_max, are analyzed using the empirical Kamlet–Taft solvent parameters π* (dipolarity/polarizability), α (hydrogen‐bond donating capacity), and β (hydrogen‐bond accepting ability) in terms of the well‐established linear solvation energy relationship (LSER): (1) The solvent independent coefficients s , a , and b and (v_max)₀ have been determined. The McRae equation and the empirical solvent polarity index, E_T(30) have been also used to study the solvatochromism of 3 . Copyright © 2007 John Wiley & Sons, Ltd.     

The kinetics and mechanism of the homogeneous,unimolecular gas‐phase elimination of 2‐(4‐substituted‐phenoxy)tetrahydro‐2H‐pyranes

The gas‐phase elimination kinetics of tetrahydropyranyl phenoxy ethers: 2‐phenoxytetrahydro‐2H‐pyran, 2‐(4‐methoxyphenoxy)tetrahydro‐2H‐pyran, and 2‐(4‐tert‐butylphenoxy)tetrahydro‐2H‐pyran were determined in a static system, with the vessels deactivated with allyl bromide, and in the presence of the free radical inhibitor toluene. The working temperature and pressure were 330 to 390°C and 25 to 89 Torr, respectively. The reactions yielded DHP and the corresponding 4‐substituted phenol. The eliminations are homogeneous, unimolecular, and satisfy a first‐order rate law. The Arrhenius equations for decompositions were found as follows:

• 2‐phenoxytetrahydro‐2H‐pyran
• log k₁ (s^?1) = (14.18 ± 0.21) ? (211.6 ± 0.4) kJ mol^?1 (2.303 RT)^?1
• 2‐(4‐methoxyphenoxy)tetrahydro‐2H‐pyran
• log k₁ (s^?1) = (14.11 ± 0.18) ? (203.6 ± 0.3) kJ mol^?1 (2.303 RT)^?1
• 2‐(4‐tert‐butylphenoxy)tetrahydro‐2H‐pyran
• log k₁ (s^?1) = (14.08 ± 0.08) ? (205.9 ± 1.0) kJ mol^?1 (2.303 RT)^?1

The analysis of kinetic and thermodynamic parameters for thermal elimination of 2‐(4‐substituted‐phenoxy)tetrahydro‐2H‐pyranes suggests that the reaction proceeds via 4‐member cyclic transition state. The results obtained confirm a slight increase of rate constant with increasing electron donating ability groups in the phenoxy ring. The pyran hydrogen abstraction by the oxygen of the phenoxy group appears to be the determinant factor in the reaction rate.     

FT‐IR and FT‐Raman investigations of the chemosensing material para‐hexafluoroisopropanol aniline

As an important chemosensing material involving hexafluoroisopropanol (HFIP) for detecting nerve agents, para‐HFIP aniline (p‐HFIPA) has been firstly synthesized through a new reaction approach and then characterized by nuclear magnetic resonance and mass spectrometry experiments. Fourier transform infrared absorption spectroscopy (FT‐IR) and FT‐Raman spectra of p‐HFIPA have been obtained in the regions of 4000–500 and 4000–200 cm⁻¹, respectively. Detailed identifications of its fundamental vibrational bands have been given for the first time. Moreover, p‐HFIPA has been optimized and vibrational wavenumber analysis can be subsequently performed via density functional theory (DFT) approach in order to assist these identifications in the experimental FT‐IR and FT‐Raman spectra. The present experimental FT‐IR and FT‐Raman spectra of p‐HFIPA are in good agreement with theoretical FT‐IR and FT‐Raman spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

A DFT investigation into the structure and energetics for nonadiabatic proton transfer in the benzophenone/N,N‐dimethylaniline contact radical ion pair

For the past 60 years, the standard model for the interpretation of the mechanism for proton transfer has been based upon transition‐state theory, which posits that the transition state is found in the proton transfer coordinate involving the breaking and making of bonds. However, the observed dynamics of proton transfer within the triplet contact radical ion pair, derived from a variety of substituted benzophenones complexed with N,N‐dimethylaniline, cannot be accounted for within the standard model for proton transfer. Instead, the kinetic behavior is in accord with nonadiabatic proton transfer theory that has the transition state in the solvent coordinate. Evidence for the importance of the solvent coordinate comes from the existence of an inverted region; as the driving force for reaction increases, the rate of proton transfer decreases. This kinetic behavior is not found in the standard model. The present paper employs density function theory to examine the question as to whether the inverted region can be attributed to the transition state being in the solvent coordinate or whether the inverted region is an artifact produced by changes in the structure of the triplet contact radical ion pair with the placement of substituents upon the p,p′ positions of benzophenone. It is concluded that the inverted region is not an artifact of substituent effects upon structure. These results support the conclusion that the transition state for proton transfer resides in the solvent coordinate and challenges the validity of the standard model for interpreting the mechanism of proton transfer. Copyright © 2014 John Wiley & Sons, Ltd.     

Mechanistic study on silver(I)‐catalyzed aminofluorination of unactivated alkenes

A study has been performed on the mechanism for the Ag(I)‐catalyzed intramolecular aminofluorination of N‐arylpent‐4‐enamides with Selectfluor by means of density functional theory. According to the calculations, the whole catalytic cycle consists of a series of elementary reactions, including formation of the complex ( IMC ) of the substrate and Ag(H₂O)⁺ (derived from the ligation of H₂O to Ag(I)), oxidation of the complex IMC by Selectfluor, deprotonation, homolytic cleavage of the N–Ag(II) bond, intramolecular radical cyclization, and fluorine abstraction. It is suggested that the oxidation of the complex IMC should be the rate‐determining step and that the intramolecular radical cyclization determines the regioselectivity of the reaction. Different from that in the decarboxylative fluorination, herein, the deprotonation of the amide is initiated by Ag(II) rather than Ag(I).     

4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione in the ene reactions with cyclohexene, 1‐hexene and 2,3‐dimethyl‐2‐butene. The heat of reaction and the influence of temperature and pressure on the reaction rate

The values of the enthalpy (53.3; 51.3; 20.0 kJ mol^?1), entropy (?106; ?122; ?144 J mol^?1K^?1), and volume of activation (?29.1; ?31.0; ?cm³ mol^?1), the reaction volume (?25.0; ?26.6; ?cm³ mol^?1) and reaction enthalpy (?155.9; ?158.2; ?150.2 kJ mol^?1) have been obtained for the first time for the ene reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione 1 , with cyclohexene 4 , 1‐hexene 6 , and with 2,3‐dimethyl‐2‐butene 8 , respectively. The ratio of the values of the activation volume to the reaction volume (?V^≠_corr/ΔV_{r ? n}) in the ene reactions under study, 1 + 4 → 5 and 1 + 6 → 7 , appeared to be the same, namely 1.16. The large negative values of the entropy and the volume of activation of studied reactions 1 + 4 → 5 and 1 + 6 → 7 better correspond to the cyclic structure of the activated complex at the stage determining the reaction rate. The equilibrium constants of these ene reactions can be estimated as exceeding 10¹⁸ L mol^?1, and these reactions can be considered irreversible. Copyright © 2014 John Wiley & Sons, Ltd.     

NMR,IR, and ESR spectroscopic investigation of reaction of α‐silylamines with carbon tetrachloride

This paper reports about high reactivity of α‐silylamines in the reaction with CCl₄. Unlike Et₃N, α‐silylamines rapidly react with CCl₄ upon irradiation with daylight to form α‐silylamine hydrochloride salts in 92–98% yields. The influence of structure of α‐silylamines and solvent on the degree of conversion was displayed. The interaction of α‐silylamines with CCl₄ was studied by NMR, ESR, and IR spectroscopy. C‐centered radicals of α‐silylamines were detected by ESR spectroscopy with spin traps (MNP, ND, and PBN) in reaction mixtures in CH₃CN and C₆H₆ and it show the radical character of this reaction. Both CH₃CN and C₆H₆ serve as solvents as well as reagents for this reaction. A mechanism of an interaction between α‐silylamines and CCl₄ is discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Pulse-shift measurement: a direct observation of radical pair dynamics in a micelle

The hydrogen abstraction reactions of benzophenone in a micellar solution in the absence and presence of 1,4-cyclohexadiene are compared with time-resolved electron spin resonance (ESR) and optically detected (OD) ESR. “Pulse shift” measurement by OD-ESR, which observes the effect of a resonant microwave pulse at different delay times after laser excitation, reveals that the lifetime of the radical pair becomes much shorter in the presence of 1,4-cyclohexadiene. This explains the change of chemically induced dynamic electron polarization from spin-correlated radical pair polarization in the absence of 1,4-cyclohexadiene to conventional, E^*/A polarization in its presence. The rate constants determined by this technique indicate that the escaping rate of cyclohexadienyl radical is ten times larger than those of alkyl and benzophenone ketyl radicals.     

乙二醇均相溶液中苊醌三重激发态淬灭反应的TR-ESR研究

利用时间分辨电子自旋共振（TR-ESR）方法,研究了乙二醇（EG）均相溶液中稳定自由基TEMPO和生物抗氧化剂维生素C（VC）对苊醌（ACQ）激发三重态3ACQ*的淬灭反应。光解ACQ/EG体系,观察到苊醌中性自由基ACQH•和乙二醇烷基自由基的发射/吸收+发射（E/A+E）的CIDEP信号,ACQH•和CH2(OH)C•HOH由3ACQ*从EG上夺氢生成。光解ACQ/TEMPO/EG体系,3ACQ*与TEMPO相互作用将极化转移给TEMPO。光解ACQ/VC/EG体系,3ACQ*除了从EG上夺氢外,还从VC上夺氢生成VC负离子基As•-。较强的As•-的CIDEP信号表明VC对3ACQ*有明显的淬灭作用。