THERMAL REARRANGEMENTS .23. THE THERMOGRA M OF A C6H6 CHEMISTRY IN THE TEMPERATURE-RANGE FROM 450-DEGREES-C TO 730-DEGREES-C

The thermal isomerization of 1,5-hexadiyne (1) and its [1,6-D-2]-label ed derivative (1a) was studied in the temperature range 450-730 degree s C and in the presence of different carrier gases (N-2, H-2, D-2, N-2 /toluene). By detailed analysis (GC, GC MS, NMR) all volatile reaction products were identified and determined quantitatively by using hexaf luorobenzene as an internal standard. The experimental data show clear ly that the reaction products are formed by two different routes: (i) electrocyclization leading to dimethylene cyclobutene (3) at temperatu res up to about 600 degrees C and (ii) radical reaction leading to ben zene (4) and pentafulvene (5) at temperatures above 550 degrees C. Cyc lopentadienylmethyl radicals are supposed to be the essential radical intermediates.