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Can. J. Chem. 65, 1775 (1987. ' The photooxygenation of nitrobenzyl derivatives 1-10 has been studied in aqueous solution as a function of pH. For m-nitrobenzyl ethers 2-4 and 9, stable a-hydroperoxy ethers (11)(12)(13) are the primary photochemical products. Acid hydrolysis of 11-13 gives m-nitrobenzaldehyde and hydrogen peroxide. Quantum yields for photooxygenation are reported for a number of derivatives as a function of pH. Acid and base catalyses of photooxygenation are observed for several compounds. A mechanism involving photogenerated nitrobenzyl carbanion intermediates is proposed.PETER WAN, S . MURALIDHARAN, IAIN MCAULEY et CHRISTOPHER A. BABBAGE. Can. J. Chem. 65, 1775 (1987. Operant en solutions aqueuses, on a CtudiC la photo-oxydation des dCrivCs nitrobenzyliques (1-10) en fonction du pH. Dans les cas des Cthers m-nitrobenzyliques (2-4 et 9), les produits photochimiques primaires sont les Cthers a-hydroperoxylCs stables (11-13). L'hydrolyse acide des composCs 11-13 conduit au m-nitrobenzaldkhyde et au peroxyde d'hydroghe. Dans les cas d'un certain nombre de derives, on rapporte les rendements quantiques pour la photo-oxygenation en fonction du pH.Dans les cas de plusieurs composCs, on a observe que la photo-oxygenation est soumise i une catalyse acidelbase. On propose un mCcanisme impliquant, comme intermkdiaires, des carbanions nitrobenzyliques gCnCrCs photochimiquement.[Traduit par la revue]The photochemistry of aliphatic and aromatic nitro compounds has received considerable attention and several reviews (1-4) have been published. Recently, we (5-7) and others (8, 9) have noted that some m-and p-nitro-substituted benzenes display unexpected reactivity when irradiated in aqueous solution, especially in the presence of hydronium and hydroxide ions as catalysts for the transformations (5-8). Whereas it is well known (1-4) that o-nitrobenzyl systems are photolabile due to the proximity to the substituent of the reacting nitro chromophore, resulting in initial intramolecular hydrogen abstraction via the n, T" triplet excited state, it had been assumed for many years that the corresponding meta and para derivatives should not be photolabile, except for simple photoreduction. However, in aqueous solution, a number of m-and p-nitro-substituted derivatives have been found to react via new photochemical processes (5-9). In a preliminary report (10) we had demonstrated that molecular oxygen can react with photoexcited nitrobenzyl derivatives, which represent an additional example of the rich and sometimes unpredictable photochemistry of m-and p-substituted nitroaromatic compounds. In this work, we report the generality and proposed mechanisms for the photooxygenation reaction of a variety of m-and p-nitro-substituted derivatives. In addition, the thermal aqueous chemistry of several photogenerated a-hydroperoxy m-nitrobenzyl ethers isolated in these studies will be presented. Results Product studiesThe compounds chosen for the study, 1-10, are shown below. Both m-and p-nitrobenzyl alcohols 1 and 7, respec...

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Carbon-13 chemical shifts of l-phenylsulphonyl-2-phenylaziridine and several of its m-and psubstituted derivatives have been determined. The substituent chemical shift (SCS) effects on the benzylic carbon C-2, and on the methylene carbon C-3 have been satisfactorily correlated with Hammett substituent parameters (a) for variation of the C-Zaryl ring substituent (with a arylsulphonyl ring), and for analogous variation of the arylsulphonyl ring (with a given C-Zaryl ring). The results reveal an inverse C-Zaryl SCS effect on C-2, whereas the effect on C-3 is nosubstituents on the arylsulphonyl ring have a normal effect on both C-2 and C-3, for which the SCS is to higher frequency with increasing electron-withdrawing power of the substituent.In conjunction with a continuing investigation of the kinetics of ring-opening reactions of three-membered heterocycles, we have had occasion to record the 13C NMR spectra of a wide range of l-arylsulphonyl-2-arylaziridines (A). The results are of particular interest since there have been relatively few reports of I3C NMR spectra for series of three-membered heterocycles.' Further, our investigation of the relationship between Hammett substituent parameters (a, and a , ) and the I3C chemical shifts of C-2 and C-3 has revealed an inversion of the dependence on substituents X for the two atoms; thus, an increase in the electron-withdrawing power of X causes the I3C resonances of C-2 and C-3 to move to lower frequency and to higher frequency, respectively. The chemical shift values for C-2 and C-3 are subject to almost identical downfield displacements with an increase in the electron-withdrawing power of substituent Y. EXPERIMENTAL MeasurementsC NMR spectra were determined in CDCl, (0.5 mmol cm-') containing 2.5% v/v of T M S as reference, on a JEOL FX90Q spectrometer fitted with a multinuclear probe insert operating at 22.50 M H z with deuterium lock (CDC1, signal) and resolution stabil- iser; conventional wide-band proton noise and offresonance decoupling modes were used in conjunction, where necessary, with the usual gated (NOE retained) coupled mode in the course of spectral assignment. A n excitation pulse of 10 p s (a = 30") and a repetition time of 1.182s were used with a 600Hz spectral width and 8K data table; between 1000 and 10 000 scans were accumulated as required. Chemical shifts are expressed as G(ppm) with respect to internal TMS . Compounds 1-Arylsulphonyl-2-arylaziridines (A)were prepared by base-induced cyclization of the corresponding N-arylsulphonyl-1-aryl-2-bromoethylamines. The general procedures for the formation and dehydrobrominative cyclization of the bromoalkylsulphonamides are to be published in Synthesis. RESULTS AND DISCUSSIONThe 13C signals for the aziridines A were readily assigned using the known chemical shift rules2 in conjunction with observations of the off -resonance decoupled spectra. The results are listed in Table 1, and details of the Hammett correlations observed between the varying substituent parameter ax (or a,) and the substituent ch...

Results are reported which show that the photodecarboxylation of benzanellated acetic acids (I) and (III) proceeds via carbanion intermediates and in addition, that eight‐electron (4n) carbanions (in a conjugated cyclic π‐system) are better accommodated than six‐electron (4n + 2) carbanions in the excited singlet state.