THE CHEMISTRY OF SINGLET AND TRIPLET METHYLENE

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Abstract
Results are reported for the photolysis of small, fixed amounts of diazomethane and cis-butene-2 in the presence of increasing pressures of the inert gases He, Ar, Xe, N2, and CF4. The variation in the percentage yield of the trans-dimethylcyclopropane as a function of the inert gas pressure indicates that two basic mechanisms, with opposite dependencies on the inert gas pressure, are responsible for its formation. An initial decrease in the percentage yield of this trans isomer with increasing pressure indicates that a source is an isomerization of energized molecules. These excited molecules result from the addition of methylene in a singlet state to cis-butene-2. A subsequent rise in the yield of the trans isomer with further increases in the pressure indicates that another mechanism, one whose rate is increased by an increase in pressure, must be present. This is attributed to a mechanism involving triplet methylene. The pressure regions for the observation of the singlet or triplet behavior of methylene are thus known and the modes of formation of the other C5 products may be determined.

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