Electron paramagnetic resonance triplet carbenes

Thermolysis of diazoalkynes yields alkynyl carbenes like vinyl carbenes, these undergo carbene-to-carbene rearrangements very readily. Propargylene (241) was prepared in 1971, and it was found that the singlet form reacted with alkenes only at Ci, the position vacated by nitrogen, but the triplet form reacted at either Ci or C3. Propargylene and its methyl and phenyl derivatives showed electron paramagnetic resonance, and the predicted structure is of C2 symmetry, best described in terms of a diradical valence structure. 

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