Pentadiene reacted when flowed through a 13.6 MHz gaseous discharge forming vinylcyclopropane, cyclopentene and cyclopentadiene; 3-phenylpropene reacted similarly producing cyclopropylbenzene and indene. The plasma generated by a radio-frequency discharge provides an unique reaction medium, and therefore the plasmolysis of organic compounds often leads to novel transformations1 which are not achieved by ordinary chemical methods. In the present investigation we set out to discover photochemical analogues in plasma chemistry. The di-n-methane isomerization2 was chosen as an intriguing and appropriate photochemical reaction, which might be mimicked in a gaseous plasma. Although a variety of complex reactants undergo this photoisomerization, it seemed desirable to begin our search using simple dienes. We report that 1,4-pentadiene and 3-phenylpropene are isomerized by electron impact in the plasma phase. The respective products vinylcyclopropane and cyclopropylbenzene arise from apparent di-n-methane isomerizations. The inductively coupled plasma apparatus used in the present study was very similar to that described previously.3 The starting 1,4-diene was distilled through the discharge zone produced by an rf generator at 13.56 MHz. Products and unreacted starting materials were collected in a cold trap at -70°C and were analyzed by GLC. The products were isolated by preparative GLC and identified by spectral means, by comparison with authentic samples. Their yields were determined by GLC with an internal standard. Plasmolysis of L at an applied power of 40W with a flow rate of 3.48 mmol/min converted to 43% of ,l, into the products vinylcyclopropane (3: 5%), cyclopentadiene (5,: 21%), and cyclopentene (Q: 18%). Butadiene, butene, and 1,3-pentadiene were also detected. -rf*A + Q +Q Plasmolysis of $ gave phenylcyclopropane (2) and indene (8) as the major products. The formation of small amounts of indan, 1-phenylpropene, cumene, propylbenzene, styrene, toluene, and benzene were also detected.