STUDIES OF THE TRIPLET SENSITIZED DECOMPOSITION OF AZOALKANES AND OF THE THERMOLYSIS OF STABLE CIS ALKYLDIAZENES

[摘要] The triplet sensitized photolysis of methylazo-(1,1-dimethyl-2-propene) (3) and azo-bis-(1,1-dimethyl-2-propene) (4) have been examined due to their unique ability to decompose under those conditions. The cis isomer was found by two independent experiments not to lie on the triplet sensitized decomposition pathway. Instead, the azo triplet decomposes directly to radicals plus N(,2). This result encouraged an attempt to observe a SCE (spin correlation effect). By means of a crossover experiment, it was established that the cage effect was substantially lower for triplet sensitized decomposition than for direct irradiation, which is consistent with a SCE. However, the data are also ;;consistent;; with a number of other hypotheses as well. These alternate proposals are discussed in some detail; from this discussion emerges a hybrid postulate that incorporates an SCE and a long-lived diazenyl radical in the triplet sensitized decomposition of these azo compounds. Two stable cis azoalkanes were isolated (azoadamantane and azonorbornane). The activation parameters for the disappearance of the cis isomer of both compounds were determined. These activation parameters for cis-azoadamantane disappearance were compared to those obtained by others. The postulate that decomposition of azoalkanes is sensitive to the nature of the incipient radical is bourne out by our results. Finally, an interesting discrepancy was noted in which the 1-adamantyl radical is estimated as unfavorable due to the reluctance of azoadamantane to decompose thermally. On the other hand, the 1-adamantyl radical is judged as similar to the t-butyl radical by other means.

[发布机构] Rice University