# The First Stages of Chemical and Electrochemical Aniline Oxidation--Spectroscopic Comparative Study
## 3 Results
### UV--Visible Absorption Spectroscopy of Chemically Oxidated Aniline
However, they appear after ca 100 s of reaction, not immediately (Figure 5). A C=O stretching band of benzoquinone-based AOs is observed at 1650 cm\({}^{-1}\). The spectra obtained after 5 and 15 s of reaction reflect the formation of mainly linear AOs (typical bands at 1628, 1590, 1343 and 1177 cm\({}^{-1}\)). This might mean that phenazinium cations are formed later on, or that the phenazine-like AOs is protonated at later phases of the reaction after the pH drops (Figure 1b). As the  
Figure 4: UV-Visible absorption spectra of chemically oxidized aniline films on glass removed from the reaction mixture of starting pH 1 (**a**) and 7 (**b**) at various times after mixing. The spectra are normalized for clarity. Figure 5: Raman spectra of gold, surface-enhanced Raman scattering (SERS) electrodes removed from the reaction mixture of starting pH 7 at various times. Excitation 785 nm (**a**) and 633 nm (**b**). resonant enhancement is operative only for the protonated species, the neutral \(N\)-phenylphenazine structure may not be detected. At later stages of the reaction, a complex spectrum of the AO mixture is observed: typical bands of \(N\)-phenylphenazinium cation (1388/1363, 608, 575 cm\({}^{-1}\)) and linear emeraldine (1628, 1590, 1343 and 1177 cm\({}^{-1}\)) are observed. \begin{table}
\begin{tabular}{c c c c c} \hline
**633 nm** & **785 nm** & **Assignment** & **Typical Product** & **Reference** \\ \hline
1700 & & C=O stretching (overoxidation) & & [43] \\ \hline
1650 & & n(C=O) RQ & degradation products & [43; 56] \\ \hline
1625 & 1625 & n(ring) of the B ring next to the Q ring in a Q structure & linear chain, monomer & [39; 49; 57; 58; 59] \\ \hline
1620 & & n(C-N) & monomer & [60] \\ \hline
1605 & 1600 & n(ring) of B ring in the SQ structure & linear chain & [46; 57; 58; 61] \\ \hline
1595 & & SQ n(ring) & linear chain & [39; 57] \\ \hline
1585 & 1585 & n(ring) of the B ring in the B structure & linear chain, aniline cation, paralazine-like structure & [28; 46; 49; 57; 60; 61] \\ \hline
1565 & 1555 & n(ring) B & linear chain bases & [46; 57; 62] \\ \hline
1540 & 1535 & n(ring) B & end-chain B & [63; 64] \\ \hline
1520 & 1520 & d(\(N\)-H) & linear chain & [49; 57; 58; 61] \\ \hline
1505 & & d(\(N\)-H) & Charged phenazine-like structures & [65] \\ \hline
1490 & 1495 & n(C=N) & emeraldine base & [46; 57; 66] \\ \hline
1480 & 1480 & n(C=N)/d(C-H) + n(C-C) & emeraldine or pernigraniline & [46; 57; 60; 66] \\ \hline
1475/1485 & & n(C-N) & Charged phenazine & [28] \\ \hline
1470 & & n(C=N) & linear chain bases & [28; 46; 66] \\ \hline
1460 & 1455 & n(C=N) & linear chain bases, phenazine-like structure & [46; 63; 66] \\ \hline
1450 & 1450 & d(C-H) + n(ring) & linear chain & [46; 59] \\ \hline
1410/1425 & 1400/1415 & n(C-N)/n(ring) Q/neutral phenazine & linear chain bases & [46; 57; 65] \\ \hline
1390 & 1385/1390 & n(C-N), polaron pair & highly doped linear chain, phenazine-like structure & [59; 66] \\ \hline
1380 & 1380 & n(C-N), localized polaron & linear chain, aniline cation radical & [59; 60] \\ \hline
1365 & 1370 & n(C-N), localized polaron & phenazine-like structure & [28] \\ \hline
1335/1355 & 1335/1340 & n(C-N), delocalized polaron; d(C-H) B & linear chain/base & [46; 49; 57; 58; 61] \\ \hline
1320 & & n(C-N), delocalized polaron & linear chain & [49; 57; 58; 61] \\ \hline
1280 & & d(C-H) B & linear chain, aniline & [46; 60] \\ \hline
1260/1270 & 1270 & d(C-H) Q + P & linear chain bases, phenazine-like structure & [46] \\ \hline
1230/1235 & 1230/1235 & n(C-N), B or polaron & linear chain & [46] \\ \hline  & 1225 & n(C-N), B or polaron & linear chain & [46; 57; 59; 67] \\ \hline
1185 & 1190 & d(C-H), Q or polaron pair & linear chain, aniline cation radical & [49; 57; 58; 60; 61] \\ \hline
1175/1160 & 1175 & d(C-H), B and SQ & linear chain & [46; 57] \\ \hline \end{tabular}
\end{table} 
Table 3: Summary of observed Raman peaks—peak positions are rounded to 5 cm\({}^{-1}\).