A multistep synthesis of [4.7-13C2] azulene (10) using Na13CN as source for the labelled carbon atom is described. The electron impact induced elimination of acetylene from the molecular ions of 10 proceeds with almost statistical participation of the carbon atoms, thus indicating an extensive scrambling of the azulene carbon skeleton prior to fragmentation. From the 13C NMR spectrum of 10, 13C13C spin spin coupling constants have been determined. The measured values confirm our earlier interpretation of the transmission of the 13C13C spin spin coupling constants in terms of a π-mechanism.
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