# The First Stages of Chemical and Electrochemical Aniline Oxidation--Spectroscopic Comparative Study
## 3 Results
### UV--Visible Absorption Spectroscopy of Chemically Oxidated Aniline
Raman spectra obtained on SERS electrodes removed at various times from the reaction mixture of aniline oxidation starting at pH 1 (Figure 6a, Table 3) are in line with the known pernigraniline route of aniline oxidation. At the beginning (electrode just dipped into the reaction mixture and rinsed with water right away) and after 2 s, the spectra corresponding to linear AOs (1627, 1584, 1390/1370, 1175 cm\({}^{-1}\)) are observed [39; 46; 61] (Figure 7). Samples removed in the 2-20 min time window reflect the pernigraniline salt intermediate (1627, 1584, 1495, 1415, 1382, 1333, 1225, 1175 cm\({}^{-1}\)) [63; 67]. The final spectrum represents the emeraldine salt (1627, 1603, 1516, 1382/1333, 1175 cm\({}^{-1}\)) [39; 61]. In the spectra obtained with the 633 nm excitation line (Figure 6b, Table 3), the spectral features of the quinonoid pernigraniline structure (mainly 1582 and 1491/1482 cm\({}^{-1}\)) are resonantly enhanced, thus, the spectrum \begin{table}
\begin{tabular}{c c c c c} \hline
**633 nm** & **785 nm** & **Assignment** & **Typical Product** & **Reference** \\ \hline
1150/1155 & & d(C-H), Phz &
\begin{tabular}{c} benzenoid ring, \\ phenazine-like structure \\ \end{tabular} & [18; 28; 46; 57] \\ \hline
1055 & & H2 SO4 & H2 SO4 & [68] \\ \hline
1010 & 1010 & H2 SO4 & H2 SO4 & [68] \\ \hline
1000 & 1000 & H2 SO4, aniline & H2 SO4, aniline +** & [60] \\ \hline
960 & 970/980 & d(ring), B or polaron & linear chain & [46] \\ \hline
880 & 880 & d(ring), Q or polaron pair & linear chain & [46] \\ \hline  & 868 & d(ring), Q or polaron pair & linear chain & [46] \\ \hline
840 & 850 & d(ring), Q or polaron pair & linear chain & [58; 61] \\ \hline  & 830 & d(ring) & linear chain & [46] \\ \hline
810 & 810 & d(ring) & linear chain, aniline & [57; 60; 61; 62; 69] \\ \hline  & 805 & d(ring) & linear chain & [57; 61; 62; 69] \\ \hline
735 & 740 & d(C=N-C) & linear chain bases & [46; 57] \\ \hline
715 & 720 & d(C=N-C) & linear chain bases & [46; 57] \\ \hline
690 & 695 & & & \\ \hline
655 & 660 & g(ring) SQ & linear chain & [39] \\ \hline
640 & 645 & g(ring), localized polaron & linear chain & [49; 58] \\ \hline
610 & 610 & g(ring), Phz & phenazine-like structure & [28; 58; 61] \\ \hline
590 & 595 & & phenazine-like structure & [65; 70] \\ \hline
590 & 585 & g(ring), Q & linear chain & [46] \\ \hline
575 & 575 & g(ring), polaron pair &
\begin{tabular}{c} linear chain bases, \\ phenazine-like structure \\ \end{tabular} & [71] \\ \hline
550 & 545 & g(ring) & linear chain, aniline & [60] \\ \hline
530 & 525 & g(ring), Q or polaron pair & linear chain & [65; 69; 72] \\ \hline
515 & 515 & g(N-H), Q or polaron pair & linear chain & [58; 61] \\ \hline
495/505 & 495 & g(ring) &
\begin{tabular}{c} linear chain bases, \\ phenazine-like structure \\ \end{tabular} & [63; 65; 69] \\ \hline
465 & & g(ring) & \\ \hline
430 & 425 & g(C-H), Q, t(C-\(N\)-C) & linear chain & [58; 61] \\ \hline
410 & 410 & g(C-H) &
\begin{tabular}{c} linear chain bases, \\ phenazine-like structure \\ \end{tabular} & [58; 61; 63; 69; 73] \\ \hline
395 & 375 & g(ring), Q & linear chain & [58; 61] \\ \hline
295 & & g(C-\(N\)-C) &
\begin{tabular}{c} linear chain bases, \\ phenazine-like structure \\ \end{tabular} & [69] \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._of the final film is not dramatically different from the spectrum obtained after 20 minutes - residual overoxidated units are still detected.