AbstractQualitative NMR spectroscopy was used to study the species formed during CO2 absorption in aqueous solution of diamines. Three different systems, consisting of primary (ethylenediamine), primary/secondary (3-(Methylamino) propylamine) and secondary (piperazine) diamines were studied by 13C NMR and the main products were identified based on various 1D and 2D NMR techniques. The main compounds were observed and assigned to (primary/ secondary) carbamate, dicarbamate and carbonate/bicarbonate. The highest concentration of carbonate/bicarbonate and dicarbamate were observed in the PZ/CO2/H2O followed by MAPA/CO2/H2O and EDA/CO2/H2O. Both 1H and 13C NMR spectroscopy was used to quantitatively determine the speciation of amines but 13C-NMR, although slower, has the potential of being more accurate than the 1H-NMR. The diamines studied in the present work were found to have high CO2 absorption capacity compared to other amines described in the literature. This indicates that they are interesting for the further investigation.