Consequence of one-electron oxidation and one-electron reduction for aniline

Abstract

Quantum-chemical calculations were performed for all possible isomers of neutral aniline and its redox forms, and intramolecular proton-transfer (prototropy) accompanied by π-electron delocalization was analyzed. One-electron oxidation (PhNH2 – e → [PhNH2]+•) has no important effect on tautomeric preferences. The enamine tautomer is preferred for oxidized aniline similarly as for the neutral molecule. Dramatical changes take place when proceeding from neutral to reduced aniline. One-electron reduction (PhNH2 + e → [PhNH2]-•) favors the imine tautomer. Independently on the state of oxidation, π- and n-electrons are more delocalized for the enamine than imine tautomers. The change of the tautomeric preferences for reduced aniline may partially explain the origin of the CH tautomers for reduced nucleobases (cytosine, adenine, and guanine).

DFT studies on the favored and rare tautomers of neutral and redox cytosine

“…Consequently, the geometry-based indices (HOMED6 and HOMED8) [21,52,53,58,59]. This indicates that all tautomeric conversions for cytosine (Scheme S1, Supplementary Material) are isoentropic processes in the gas phase.…”

“…Geometric and energetic consequences of prototropy have also been examined and compared to those observed earlier for 4APM and 2OHPM. For investigations, the DFT method [54] has been employed with the hybrid functional of Becke [55] and gradient correction of Lee et al (B3LYP) [56] and the 6-311?G(d,p) basis set [57] as previously described for adenine and its models [52,53,58,59]. The B3LYP functional has been recommended for charged radicals [60] and applied for the anionic states of nucleic bases [51].…”

Variations of the tautomeric preferences and π-electron delocalization for the neutral and redox forms of purine when proceeding from the gas phase (DFT) to water (PCM)

“…However, it has been found recently that they become very important for anionic forms of nucleobases, adenine and guanine [34–36], and for uric acid [37, 38]. They are also favored for reduced aromatic imidazole and aniline as well as for reduced aliphatic vinylamine-acetaldimine [39, 40]. For these reasons, the complete tautomeric mixture (including CH tautomers) has been considered for investigations of tautomeric equilibria for purine in the gas phase [32, 33].…”

“…They are also favored for reduced aromatic imidazole and aniline as well as for reduced aliphatic vinylamine-acetaldimine [39, 40]. For these reasons, the complete tautomeric mixture (including CH tautomers) has been considered for investigations of tautomeric equilibria for purine in the gas phase [32, 33]. …”

“…For calculations, the 6-311+G(d,p) basis set [46] with the diffuse and polarization functions was employed similarly as previously described for the gas phase purine structures [32, 33]. The B3LYP functional and the basis set with the diffuse and polarization functions have been recommended in the literature for charged radicals [47–49].…”