The technique of spin trapping has been applied to the gas phase of cigarette smoke to identify and quantify the radicals present. It was found that radicals could be trapped only if the smoke was filtered. Three spin traps were used: N-tert-butyl-alpha-phenyl nitrone (PBN). 5,5-dimethyl-delta1-pyrroline-1-oxide (DMPO) and alpha-[3,5-di-tert-butyl-4-hydroxyphenyl)-N-tert-butyl nitrone (OHPBN). From the electron spin resonance (ESR) splitting constants of the radicals produced by the reaction of smoke radicals with the spin traps and also from the effec of varying the path length between the cigarette and the spin trap solution, it is concluded that three types of signals are observed. Type I signals indicate the presence of oxygenated radicals which appear to be a mixture of alkoxy radicals (RO) and aroyloxy (ArCO2-) radicals. Our data do not allow conclusions about the nature of the R or Ar groups in these two oxy radicals; however, considerations based on lifetimes suggest that the R group probably is tertiary. Type II and III signals are not typical spectra of spin adducts. Instead, we believe they result from reaction of smoke (and probably radicals in smoke) with the PBN spin trap and indicate that smoke has the ability to effect one-electron oxidations. Only type I signals are observed with DMPO and OHPBN. A quantitative study shows that 4 x 10(14) spins/puff are present in the smoke, in contrast with the result of a recent study which used a very different method for determining the radical content of smoke. A discussion of the nature of the radicals in smoke and some tentative conclusions are presented.

The photochemical behavior of several dialkyl benzoylphosphonates and para-substituted benzoylphosphonates in various solvents has been studied using product isolation, ultravioletspectral change, the electron spin resonance (ESR) technique, and quantum yield measurements. Upon irradiation to a degassed solution of these benzoylphosphonates through a Pyrex filter, the photo-pinacolization reaction was observed, except in the case of diethyl benzoylphosphonate; it was effectively quenched by 1,3-pentadiene or oxygen. On the other hand, the ESR spectra of photo-irradiated aroylphosphonates at 77°K have a large anisotropic doublet of 53–128 gauss separation; this separation is thought to be due to the interaction between an unpaired electron and the phosphorus nucleus. The structure of these radicals is also discussed. From these observations, it can be considered that the photochemical reaction proceeds via the ketyl radical formed by the hydrogen abstraction of the lowest excited triplet state of these aroylphosphonates. Irradiation to the diethyl benzoylphosphonate solutions in various solvents gave, not the pinacolized product, but 2,4,6-triphenyl-2,4,6-tris[diethylphosphoryl]-1,3,5-trioxane almost quantitatively. The quantum yields (Φ) of the disappearance of several para-substituted derivatives are highly sensitive to the electron-inductive abilities of the substituents; that is, Φ drops from 2.10 in the p-methoxybenzoylphosphonate derivative to 1.79 in the p-chloro derivative at room temperature. Such a substituent effect can be considered to result in the difference in the conformation between the carbonyl and phosphoryl groups. On the basis of these studies, the mechanism of the photochemical reaction of aroylphosphonates is described and discussed.

The technique of spin trapping has been applied to the gas phase of cigarette smoke to identify and quantify the radicals present. It was found that radicals could be trapped only if the smoke was filtered. Three spin traps were used: N-tert-butyl-a-phenyl nitrone (PBN), 5,5-dimethyl-A'-pyrroline-l-oxide (DMPO) and a-43,5-di-tert-butyl-4-hydroxyphenyl)-N-tertbutyl nitrone (OHPBN). From the electron spin resonance 4ESR) splitting constants of the radicals produced by the reaction of smoke radicals with the spin traps and also from the effect of varying the path length between the cigarette and the spin trap solution, it is concluded that three types of signals are observed. Type I signals indicate the presence of oxygenated radicals which appear to be a mixture of alkoxy radicals RO and aroyloxy (ArCO2 I radicals. Our data do not allow conclusions about the nature of the R or Ar groups in these two oxy radicals; however, considerations based on lifetimes suggest that the R group probably is tertiary. Type II and III signals are not typical spectra of spin adducts. Instead, we believe they result from reaction of smoke land probably radicals in smoke) with the PBN spin trap and indicate that smoke has the ability to effect one-electron oxidations. Only type I signals are observed with DMPO and OHPBN. A quantitative study shows that 4 x 1014 spins/puff are present in the smoke, in contrast with the result of a recent study which used a very different method for determining the radical content of smoke.A discussion of the nature of the radicals in smoke and some tentative conclusions are presented.

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