Abstract
The present work aims to compare two possible pathways of a pre-reaction complex in the reaction of transfer of a hydrogen atom from ammonia to a nitro compound forming. Nitrobenzene, nitromethane, and HNO2 were used as nitro compounds. The proposed paths are: nitro compound intersystem crossing with a subsequent search for a substrate, or the formation of a complex with its subsequent excitation. The calculations were performed using TDPBE0/TDA/aug-cc-pVDZ method in NWChem-6.8 program. For verification purposes, some additional calculations were performed using RASCI/aug-cc-pVDZ method in PSI4 program. The location of the levels and the geometry of the complexes shows that the triplet complex (exciplex) is more stable than the singlet complex. The weak coupling between molecules in the singlet complex indicates that the probability of its excitation is very small. Moreover, there are experimental data, where the quantum yields of such reactions reach 0.3. The presented calculations confirm the mechanism of the nitro compound intersystem crossing with a subsequent search for a substrate.
Highlights
Hydrogen transfer reactions involving excited nitro compounds have been studied for a long time
Formation energy are calculated as difference between absolute energy of complex and sum of separated molecules energies
Weak-coupled, both of them cannot exist for a long time
Summary
Hydrogen transfer reactions involving excited nitro compounds have been studied for a long time. It is known that in the triplet state, aromatic nitro compounds are able to hydrogen atom abstraction from amines and ketones [1,2]. According to the scheme ArNO + CH. The triplet nitro compound reacts with alcohol and yields the radical pair. The mechanism of such a reaction is complicated. It may include direct or sensitized photoexcitation. These may be dark radical processes or occur under the action of light. Initial electron transfer with the yield of ion-radicals is possible
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