Study of the transition state in the isomerization of trans-N₂F₂ to cis-N₂F₂ by extended Huckel theory

Abstract

The quantitative agreement with experimental barrier height and the extra stabilization energy of cis-N₂F₂ over trans-N₂F₂ may not be considered to be very good, but this is only to be expected as small differences between large quantities are being calculated. It appears from our present calculations that the use of Cusachs relation for evaluating the off-diagonal matrix elements in this system is open to question since the experimentally observed planarity of N₂F₂ is not correctly predicted by the use of this relation. We therefore prefer the use of the Wolfsberg-Helmholz relation in this system. A value of K= 1.75 appears to be preferable. The results of all the E.H.T. calculations made here for difluorodiazine clearly show that a twisted transition state is more probable than a linear one (LT or LC) in the isomerization of trans-N₂F₂ to cis-N₂F₂. This conclusion also receives further support from a consideration of the high preexponential factor in the rate equation [1] and the multiplicity of the transition state.