March 5 , 19G4
COMMUNICATIONS TO THE EDITOR
959
distinguishcs them from these other radicals. One of McConnell and Robertson’s generalizations6 originally applied to aromatic radicals, i . e . , the g value of a radical increases with the spin orbit coupling parameter, j-, of the atoms that have significant spin density, applies also to this case. To remove some spin density from the terminal oxygen atom and distribute i t to any extent on the R group requires the polarization of the 0-0 bond so ( 7 ) IZ 1- VandeU’iele, P C. hiacDonald, E. Gurpide, and S Lieberman, as to make the terminal oxygen more negatively Recent Progv. Hovmone R e s . . 19, 275 (1963) ( 8 j Predoctoral Research Fellow, National Institutes of Health charged. For this reason radicals with electron-with(9) Career Scientist. Health Research Council, City oi New York drawing groups in R , such as the radical of Lontz, KENNETH D. ROBERTS should have the greatest spin density on the terminal DEPARTMENTS OF BIOCHEMISTRY AND OBSTETRICS ASD GYNECOLOGY LAJOSBASDI oxygen atom and therefore the highest g value. In COLUMBIA UNIVERSITY HAROLD I . CALVIN^ solution this radical would have the averaged g value D E P A RM~E N T OF MEDICINE WILLIAM D. DRUCKERg A-E‘~vYORKUSIVERSITY SEYMOUR LIEBERMAN of 2.0187. SEIV YORK,XE\VYORK Our microwave frequency was measured by a HewRECEIVED J A N U A R Y 6, 1964 lett-Packard 524C counter with a Hewlett-Packard 540B transfer oscillator. The magnetic field was determined by proton magnetic resonance using a marginal oscillator whose frequency was measured on the same Identification of Peroxy Radicals by Electron 524C counter. The line broadening effect of the presParamagnetic Resonance ence of molecular oxygen was a principal source of Sir : error in the g value measurement. In e.p.r. studies free radicals are identified by their ( 6 ) H M McConnell and R . E. Robertson, J . P h y s . Chem., 61, 1018 characteristic hyperfine splittings, their g values (line (19571, ( 7 ) University of Toronto, Toronto, Canada. positions), and their relaxation times in a particular milieu. The last parameter is the least specific and CALIFORNIA RESEARCH CORPORATION MALCOLM BERSOHN’ the first parameter gives the most information. Peroxy RICHMOND, CALIFORNIA J . R. THOMAS RECEIVED JANUARY 8, 1964 radicals, ROz,, have no hyperfine structure detectable by present methods except that due to O17. Because of the difficulty of 0 1 7 labeling only one experiment on Studies of Reactions of Atomic Carbon by a Double the OI7 hyperfine splittings of free radicals has been reported,’ so that method is not yet broadly applicable. Tracer Technique We wish to report evidence that the g values of perSir : oxy radicals easily distinguish them from RO. and Reaction mechanisms of atomic carbon have recently R.. We have measured the g value of the cumyl been studied using C” (20.5 min.) as produced by peroxy radical which is 2.()155 f 0.0005. Lontz2 nuclear transformation. 1-4 The C’l, being radioactive, found that the radical CF3CFCONH2 reacts in the serves as its own tracer. However, it would also be solid state with molecular oxygen to form a free radical greatly desirable to trace the origin of the atoms without noticeable hyperfine splitting and with g with which the C” combines. Because the nuclear values measured along the three principal axes of 2.0102, recoil technique provides only a small number of carbon 2.0193, and 2.026’7. He assumed this is the correspondatoms ( ~ 1 0 and ~ ) hence of product molecules, this has ing peroxy radical CF3CFCONH2. Fessenden and not been practical thus far. Labeling the molecules with which the carbon reacts with another radioisotope 02 is not feasible because the amount of such a secondary Schuler3 found that alkanes irradiated with fast label which could be incorporated in the product is electrons in the absence of oxygen formed hydrogen too small to d e t e ~ t . ~ atoms plus readily identifiable alkyl radicals. In the The use of stable isotopes, such as deuterium, as presence of oxygen under the same conditions radicals secondary tracers has faltered on the formidable probwithout noticeable hyperfine splitting were produced. lem of product analysis. Mass spectrometric separaThe g values of these latter radicals ranged from 2.0155 tion of isotopic deuterated molecules followed by when pentane was used to 2.0148 for paraffin oil, the counting of their Cll content is possible in principle, g value decreasing with increasing molecular weight but very difficult in practice.6 The alternative, of the parent alkane. These were also presumed to gas chromatographic separation of isotopic molecules be peroxy radicals. followed by C” radioassay, has been restricted by the Our cumyl peroxy radicals were produced in benzene unavailability of columns of sufficient resolving power. solution as a result of the reaction of cumene with With the recent publication by Cvetanovic, et al. , 7 oxygen in the presence of azobisisobutyronitrile. N o of a technique for separation of deuterated light olefins other radicals were detected in this system by e.p.r. Evidence that the principal radical formed in this (1) C. M a c K a y , et al.. J . A m . Chem. So
