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

Abstract

Abstract1‐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 (S0) ethyl, phenylcarbene (1EPC) 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 S1 excited state (1EPC*). This state rearranges to E,Z‐1‐phenylpropenes in competition with relaxation to ground state 1EPC 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.