E + ZPE_Anh, energy profile for the reaction between propargyl radical (1) and vinyl radical (2). The dashed orange and blue profiles correspond to the formation of cis-C₅H₅ and trans-C₅H₅, respectively; the solid black and dashed yellow profiles correspond to the minimum energy paths for the formation of 5 and a-C₃H₄ + C₂H₂, respectively, and the dashed green and red lines correspond to the exit channels leading to 3 and 4, respectively. Energy values are given in kcal mol⁻¹.