DFT studies of intramolecular double proton transfer of 3,6-dihydro-3,6-diimino(siliane or pyridine)-2,5-diamine
Intramolecular double proton transfer of 3,6-dihydro-3,6-diiminosiline-2,5-diamine (A) and 3,6-dihydro-3,6-diiminopyridine-2,5-diamine (B) at DFT (B3LYP) level of theory has been investigated. Two mechanisms, stepwise (TS1) and concerted (TS2), are proposed for the process of proton transfer. The stepwise mechanism itself includes two pathways, the pathway (1) and pathway (2), which involve the resonance forms from side of N-C-C-C-N and N-C-X-C-N atoms (X = Si-H or N), respectively. These results show that for both the compounds the process of proton transfer is through the stepwise mechanism. The results indicate that in the case of compound (A) the process is through pathway (1), while for compound (B) the pathways (1) and (2) were almost similar to each other. In addition, aromaticity of the two compounds has been evaluated based on the nucleus independent chemical shift values to predict dominant resonance structures and the charge distributions in the ring.
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