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A new technique has been developed and used to redetermine the rates of H atom reactions at room temperature ,:"i.th a num~er of simple olefins. Hydrogen atoms are generated by the mercury photosensitized deco~posttion of H2 m the presence of small amounts of ethylene or its mixtures with an added olefin. The relatlve rate constants are determined from a comparison of the yields of n-butane in the two cases. The v~lue~ ob~aine~ are compared with the earlier determinations and with another independent recent redeter-mmatlOn m this laboratory. The values obtained by the three independent techniques are in very good agreement.

Reaction of oxygen atoms with 1,3-butadiene has been investigated a t rooin temperature. It is found that it conforms to the general rnechanisil~ established previously for the analogous reactions of rnonoolef~ls. 0111y 1,2-addition occurs, and the addition products, butadiene moi~oxide and 3-butenal, possess excess energy when formed as a result of high heats of reaction. The pressure dependence of the forlnation of the addition products yields the values of the "lifetimes" of the initially produced "hot" tliolecules.~The relative rate cotlstants have been determined a t 25 and 127" C and froin these the relatlve values of the A r r h e n i~~s parail~eters have been calculated.The general mechanism of reaction of oxygen atoms with allcenes has recently been established in this laboratory (1) and the trends in the relative rate constants (2) demonstrated the electrophilic character of the ground-state oxygen atoms in these reactions. As an extension of this work the present study of the analogous reaction with 1,3-butadiene, as the simplest representative of conjugated diolefins was carried out.The particular questions which the present investigation was hoped to ails\\-er are: first, whether conjugated diolefins in their reactions with oxygen atoms follo~v the general mechanisn~ established for monoolefins; secondly, whether only 1,2-or also l,4-addition products are formed; and lastly, ivllether the value of the rate constant of the reaction of oxygen atoms with 1,3-butadiene is such as inight be expected in view of the trends and relations established in the case of monoolefins (2). Affirmative answers to these questions have been obtained and only the tmo 1, 2-addition products predicted on the basis of the rules forinulated for the monolefins (I), butadiene monoxide and 3-butenal, the latter readily isomerizing to the more stable crotonaldehydc, have been observed. The 1,4-addition product, 2,s-dihydrofuran, is not formed.The pronounced pressure effect observed in the present work illustrates particularly \ d l initial formation of "hot" addition products and the consequent "pressure-dependent frngmentation" (1) in the reactions of oxygen atoms with olefins. As a result, in some of these reactions, including 1,s-butadiene itself, the addition products are essentially completely decomposed a t pressures of a few millin~eters and are then not observable experimentally. This feature and some other difficulties inherent in the electrical discharge method for production of oxygen atoms, as discussed recentl>. else\\~here (3), are believed to be responsible for the entirely different conclusions from the present ones arrived a t by Avralnenko and I

Mercury-photosensitized reaction of butene-1 has been studied at room temperature in the pressure range of 14 to 230 mm. Methyl cyclopropane is found to be formed by molecular rearrangement and its yield goes through a maximum at a pressure of about 65 mm. The dependence of the yield of this product on pressure is explained by postulating participation in the process of two excited states of equal lifetimes. These are, perhaps, the vibrationally excited triplets of butene-1 and of methyl cyclopropane, the latter being formed from the former by an internal 1,2- or approximately 1,4- migration of an H atom. Molecular rearrangement to butene-2 does not occur.

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