For (Z)-(Z)-N-(λ5-phosphanylidene) formohydrazonic formic anhydride, Aza-Wittig reaction
and Mumm rearrangement are studied using both density functional and coupled cluster theories.
For this purpose, two different products starting from one substrate are considered that are competing
with each other. The obtained products, P1 and P2, are thermodynamically favorable. The product of
the aza-Wittig reaction, P1, is more stable than the product of Mumm rearrangement (P2). For the mentioned
products, just one reliable pathway is separately proposed based on unimolecular reaction.
Therefore, the rate constants based on RRKM theory in 300-600 K temperature range are calculated.
Results show that the P1 generation pathway is a suitable path due to low energy barriers than the path
P2. The first path has three steps with three transition states, TS1, TS2, and TS3. The P2 production
path is a single-step reaction. In CCSD level, the computed barrier energies are 14.55, 2.196, and 10.67
kcal/mol for Aza-Wittig reaction and 42.41 kcal/mol for Mumm rearrangement in comparison with the
corresponding complexes or reactants. For final products, the results of the computational study are in
a good agreement with experimental predictions.