Carbamate formation is one of the major chemical reactions that can occur in solution in the capture of CO2 by amine-based solvents, and carbamate formation makes a significant enthalpy contribution to the absorption-desorption of CO2 that occurs in the absorber/stripper columns of the PCC process. Consequently, the formation of carbamates of selected series of primary and secondary amines over the temperature range (288 to 318) K has been investigated by equilibrium H-1 NMR studies, and the stability constants (K-9) for the equilibrium: RNH2 + HCO3- reversible arrow(K9) RNHCOO- + H2O are reported. van't Hoff analyses have resulted in standard molar enthalpies, Delta H-m(o), and entropies, Delta S-m(o), of carbamate formation. A Delta H-m(o) - Delta S-m(o) plot generates a linear correlation for carbamate formation (providing a mean standard molar free energy, Delta G(m)(o), for carbamate formation of about -7 kJ . mol (1)), and this relationship helps provide a guide to the selection of an amine(s) solvent for CO2 capture, in terms of enthalpy considerations. A linear Delta H-m(o) - Delta S-m(o) plot also occurs for carbamate protonation. The formation of the carbamates has been correlated with systematic changes in composition and structure, and steric effects have been identified by comparing molecular geometries obtained using density functional B3LYP/6-311++G(d,p) calculations. Trends in steric effects have been identified in the series of compounds monoethanolamine (MEA), 1-amino-2-propanol, 2-amino-1-propanol (AP) and 2-amino-2-methyl-1-propanol (AMP). In the case of 2-piperidinemethanol, 2-piperidineethanol and 3-piperidinemethanol, strong intramolecular hydrogen bonding is shown to be the likely cause for lack of carbamate formation, and in the ring systems of pyrrolidine, morpholine, piperidine and thiomorpholine trends in carbamate formation (as given by K-9) have been correlated with the internal ring angle at the amine nitrogen, as well as the planarity of the environment around the nitrogen atom. (C) 2012 Elsevier Ltd. All rights reserved.