Ring opening of 1-methylcyclopropene and cyclopropene: Matrix infrared spectroscopic identification of 2-butene-1,3-diyl and propene-1,3-diyl

Triplet 2-butene-1,3-diyl (T-11) was generated on irradiation of 1-methylcy clopropine (10) in a bromine-doped xenon matrix and was characterized by me ans of IR spectroscopy fur the first time. Experimental results suggest tha t triplet propene-1,3-diyl (T-3) is formed from cyclopropene (1) under simi lar conditions. In accordance with theoretical calculations, the experiment al data indicate that the reactions 1--> 3 and 10 -->11 are the lowest ener gy ground-state pathways for the ring opening of 1 and 10, respectively.