Paramagnetic resonance spectra of free radicals in liquids have been studied during the course of intense irradiation with ultraviolet light. Equipment is described in which the liquid sample flows through the microwave cavity of the spectrometer and is photolyzed as it passes the sensitive region of the cavity. In this way the steady-state concentration of short-lived radicals have been observed. Temperatures from about −70° to 60°C have been used. A number of alcohols containing up to 1% H2O2 have been studied. In the absence of dissolved oxygen the main products are the radicals formed by abstraction of a hydrogen from the position alpha to the hydroxyl group. The radicals RĊHOH where R is H, CH3, C2H5, C3H7, (CH3)2CH, and C6H5 have values of aα near room temperature ranging from 14.7 to 17.4 G and g values ranging from 2.00298 to 2.00334. Those radicals with beta hydrogens have values of aβ ranging from 20.0 to 22.2 G. The ring protons of C6H5ĊHOH are inequivalent. When the alpha hydrogen is abstracted from allyl alcohol two radicals are formed that are geometric isomers with the relative abundances depending on temperature. Coupling values for all hydrogens in each isomer are given. All couplings are also given for the radicals formed from ethylene glycol and isopropyl alcohol. In many cases couplings have been measured at several temperatures. Values for hydrogens in hydroxyl groups are strongly temperature dependent and in some cases become zero. Alpha and beta coupling constants are less temperature dependent. The various results are discussed. In the presence of dissolved oxygen, peroxy radicals are formed and their spectra are discussed. Their linewidths are strongly dependent on temperature and on concentration of dissolved oxygen. Radicals have been seen in photolyzed hydrogen peroxide solutions for concentrations ranging from 10% to 45%. In the presence of acid a single absorption line is observed. Without the acid the spectra are complex. These results are also discussed.

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Paramagnetic resonance spectra in liquid acetone and acetone solutions were studied during the course of intense irradiation with ultraviolet light. In the presence of RH, an alcohol or ether, which served as a good hydrogen donor, both radicals of the reaction CHaCOCHs+RH--> (CHs) l::OH+R were seen. The abstracted H atom was taken from the carbon alpha to the 0 atom of the alcohol or ether. When pure liquid acetone was photolyzed, both radicals of the reaction CHaCOCHa+CHaCOCHs--> (CHa)l::OH +C)H2COCHa were seen. In addition some CHa was seen. Higher concentrations of CH2COCHa and CH3 were produced by photolyzing acetone containing 1 % H20 2. In the latter case, it is believed that the radical OH was produced from the H202. The OH radical then abstracted an H atom from acetone to give CH2COCH3• It is thought that CHa resulted from the reaction CH2COCHa-->H2C=C=o+CHa.Accurate measurements were made of the g values and hyperfine parameters for (CHahCOH, CH20H, and CHaCHOH in both water-rich and acetone-rich solutions at room temperature; for CHaCHOCH2CH s in acetone solution at room temperature; for CHa in acetone at -53°C; for CH2COCHa in acetone at room temperature and at -49.5°C; and for the radical resulting from the loss of one of the H atoms of d~oxane in acetone solution at room temperature. It was found that the OH-proton hyperfine coupling of CHaCHOH in aqueous solution could be carried through the value zero by changing the temperature. Effects due to acid-catalyzed proton exchange of the OH proton of CH20H and of (CHahCOH with solvent protons were studied in aqueous solutions. These studies gave values for the mean lifetime of a radical between exchanges.

ESR equipment has been developed for directly observing labile free radicals that are present a t high temperatures.A pressurized fluid is heated as it slowly flows through the microwave cavity of the spectrometer. Temperatures to 566 "C and pressures to 140 kg/cm2 have been used. Radicals are identified from well-resolved hyperfine structure. Spectra of cyanoisopropyl from the decomposition of azobisisobutyronitrile in solution a t 155-185 " C and hydroxyisopropyl from 2% di-tert-butyl peroxide in isopropyl alcohol at 173-258 OC are reported. Indenyl is reported from indene in benzene at 533 "C and in tetralin a t 471 "C. 1,2-Diphenylethyl has been observed from solutions of 1,2-diphenylethane in benzene from 460 to 560 "C. For dilute solutions of 1,2-diphenylethane in toluene the benzyl radical is obtained, while for more concentrated solutions a mixture of radicals is presen! in the following equilibrium for which K = I O f 3 at 560 "C and 105 kg/cm2: C~H~C H~C H~C~H S + C6HsCHz s C6H=,CHCH2C6H5 + C6HsCH3. Diphenylmethyl is obtained from the dissociation of tetraphenylethane as a