A quantitative study on the stereoselectivity of sigmatropic shift reactions in acyclic systems

The semiempirical MINDO/3 method has been used to study sigmatropic [1,3] shifts in propene, [1,5] shifts in pentadiene and [1,7] shifts in heptatriene, occurring in the suprafacial and antarafacial way. Hydrogen, fluorine and methyl (with retention or inversion of configuration) were taken as the shifting goups. For the [1,3] shifts some STO-3G and 4-31G calculations have also been performed. Good correspondence has been obtained with the stereoselectivity predictions of the Woodward-Hoffmann theory. The activation energy for the allowed reactions is 8–21 lower than the value for the forbidden modes. The shift of a F atom proceeds via an inversion-type mechanism