Dienyl and homodienyl 1,5-hydrogen shifts

INDO calculations on the sigmatropic [1, 5] H-Shift in 1,3-cyclohexadiene and 1,3,5-cycloheptatriene A homo-cyclopentadienyl transition state model

“…At this point, it can be concluded that the picture, outlined in this and in the previous paper, explains the relative activation parameters involved in [1,5] H-shifts in cyclic 1,3-dienes quite satisfactorily and in a mutually consistent manner.…”

“…The experimental activation enthalpies for [1,5] H-shifts in 1,3-cycloheptadiene and 1,3-cyclooctadiene are indeed lower than for 1,3-cyclohexadiene, see Table 2. At this point, it can be concluded that the picture, outlined in this and in the previous paper, explains the relative activation parameters involved in [1,5] H-shifts in cyclic 1,3-dienes quite satisfactorily and in a mutually consistent manner.…”

“…In Table 2 we compare the theoretical and the experimental activation enthalpies. The experimental value for cyclohexadiene, reported in this study, was obtained starting from 1,3-1D,4D-cyclohexadiene, using NMR-monitoring [4] 29 [5] 29 [6] 32 37 [7] 27 of the reaction mixtures. Reaction temperatures ranged from 303°C to 330 ° C. More experimental details will be published elsewhere [11].…”

“…In the previous study it was shown, how the stability of the cyclopentadienyl anion and -radical is reflected in the relatively low activation enthalpy for the [1,5] H-shift in cyclopentadiene. Furthermore, it appeared that the charge transfer from the moving hydrogen to the cyclopentadiene system can be correlated with the electron affinity of the cyclic conjugated cyclopentadienyl system.…”

“…Recently we reported a reaction pathway for the thermal sigmatropic [1,5] H-shift in cyclopentadiene [1]. A detailed study of the geometry of the activated complex yielded a partial electron transfer from the migrating hydrogen to the nascent cyclopentadienyl system.…”