Based on literature data, and registered changes we can assume that 8AQ could be reduced to dihydro-8-aminoquinoline due to the band reduction in band intensity at 312 nm and bathochromic shift of whole spectrum to shorter wave lengths. To check which isomer is the most probable product of the reaction we carried out additional quantum chemical calculations. The results are shown in Figure . By comparing the spectra of six plausible 2-electron/2-proton reduction products (Red1-Red6) we found that only Red1 and Red2 provide spectra that match the experimentally observed changes with respect to non-reduced 8AQ. Interestingly, Red2 is the lowest energy isomer, with Red1 being 15.9 kcal/mol higher in energy. Therefore, we conclude that the most probable reduction product at pH 3 is 3,4-dihydroquinoline-8-amine. Theoretical spectra of 8AQ at pH 3 in two forms 2a (blue) and 2b (green), compared to spectra generated for six plausible 2e/2H + reduction products (Red1-Red6). Spectral regions around 332 and 247 nm are highlighted in yellow to reflect bands that build-up upon reduction (see Figure ). Only Red1 and Red2 reproduce experimental findings. We note that Red2 is the lowest energy isomer.