A force field study of the chemical reaction between ethylene and cis-N2H2

The fully optimized geometry of the activated complex which occurs as an intermediate in the concerted H-transfer reaction between C₂H₄ and cis-N₂H₂ has been determined using the ab initio FORCE method of Pulay. The activation energy for the synchronous transfer of two hydrogen atoms from cis-N₂H₂ to ethylene is found to be 18.8kcal/mol, i.e. substantially lower than the previously estimated energy barrier of around 60 kcal/mol. The same method applied to trans-N₂H₂ and semilinear N₂H₂ gave an isomerization energy of 49.7 kcal/mol indicating that the isomerization of trans-N₂H₂ to the cis form might be the overall rate-controlling step.