Thermal decomposition of a series of 1,2-diazetines.
A homologous series of tricyclic diazetines (6a-c), differing by the number of methylene groups in the saturated bridges of the fused carbon bicycles, was synthesized. The DeltaH++ of decomposition for each of the diazetines to afford N2 and the corresponding alkene was determined experimentally: 6a, 31.7; 6b, 39.3; 6c, 38.8 kcal/mol. The ground-state strain energy of each diazetine was estimated utilizing computationally obtained DeltaHf's for each of the experimentally investigated diazetines as well as several other diazetines whose DeltaH++'s had been previously reported in the literature. The sum of the ground-state strain energies and DeltaH++'s of decomposition for all of the diazetines was nearly constant, with an average value of 59 kcal/mol, suggesting that all of the diazetines decompose via the same mechanism. Generally, the higher the ground-state strain energy of the diazetine, the less the DeltaH++ for decomposition. The decomposition transition states for 6a-c and 7 were modeled computationally at the RB3LYP/6-311+G(3df,2p)//UB3LYP/6-31+G(d,p) level. The agreement of the experimentally determined DeltaH++ values with transition-state energies obtained computationally supports the reaction mechanism originally proposed by Yamabe that the elimination process occurs by an unsymmetrical, yet concerted, transition state with strong biradical character.
Department of Chemistry, Berry College, PO Box 495016, Mount Berry, Georgia 30149, USA. gbreton@berry.edu
Gary W
GW
Breton
John H
JH
Shugart