Wavelength‐dependent photochemistry of 1‐phenyl‐1‐diazopropane

1-Phenyl-1-diazopropane (PDP) was photolyzed in acetonitrile/methanol mixtures using either 520-nm light or 350-nm light. The main photoproducts were 1-methoxypropylbenzene and E,Z-1-phenylpropene. With 520-nm light, a plot of (1-methoxypropylbenzene)/(E,Z-1-phenylpropene) versus methanol concentration was linear. These results are consistent with the visible light induced fragmentation of PDP to dinitrogen and closed shell singlet (S-0) ethyl, phenylcarbene ((EPC)-E-1) which partitions between 1,2 hydrogen migration to form alkene, and reaction with methanol to form ether. The same plot generated with 350-nm light significantly deviates from linearity. It is proposed that 350-nm light generates the carbene in a vibrationally excited, open shell S-1 excited state ((EPC)-E-1*). This state rearranges to E,Z-1-phenylpropenes in competition with relaxation to ground state (EPC)-E-1 over a few tens of ps. As a result, methanol cannot completely suppress alkene formation upon photolysis of PDP with 350-nm light. The carbene excited state is a "non-trappable carbene" route to alkenes.