The chemisorption of CO2 by aqueous-hindered amines has been investigated experimentally and theoretically. Negative-ion ESI–MS analysis of solutions containing a sterically hindered amine and a source of 13CO2 reveals peaks corresponding to [M–H + 45]−. These ions readily lose 45 Da when subjected to collisional activation, and together with other key fragments confirms the generation of the 13C-labelled carbamate derivatives. The thermochemistry of the two key capture reactions: $$2.{\text{amine }} + {\text{ CO}}_{ 2} { \leftrightarrows }{\text{amine}} - {\text{CO}}_{ 2}^{ - } + {\text{ amine}} - {\text{H}}^{ + } {\kern 1pt} \quad 1:{\text{carbam}}$$ 2 . amine + CO 2 ⇆ amine - CO 2 - + amine - H + 1 : carbam $${\text{amine }} + {\text{ CO}}_{ 2} + {\text{ H}}_{ 2} {\text{O}}{ \leftrightarrows }{\text{HCO}}_{ 3}^{ - } + {\text{ amine}} - {\text{H}}^{ + } \quad 2:{\text{ bicarb}}$$ amine + CO 2 + H 2 O ⇆ HCO 3 - + amine - H + 2 : bicarb at 298 K was modelled using composite chemistry methods, CCSD(T), DFT, and SM8 free energies of solvation. The aqueous reaction free energies (ΔG 298) for reaction 1 are predicted to be more negative than ΔG 298 for reaction 2 when amine = ammonia, 2-aminoethanol (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-hydroxymethyl-propane-1,3-diol (tris), and 2-piperidinemethanol (2-PM). For AMP, tris, and 2-PM, activation free energies ΔG 298 ‡ for reaction 1 (SM8 + CCSD(T)/6-311 ++G(d,p)//M08-HX/MG3S: 38–67 kJ mol−1) are smaller than the corresponding values for 2 (109–113 kJ mol−1). For 2-PM, the computed carbamate ΔG 298 ‡ (38 kJ mol−1) is comparable to the MEA value (45 kJ mol−1), whereas the primary amines with tertiary alpha carbons have slightly larger values (60–70 kJ mol−1). The organic amine values are much lower than the value for ammonia (93 kJ mol−1). The results indicate CO2 chemisorption proceeds via a carbamate intermediate for all aqueous primary and secondary amines. Hindered carbamates are susceptible to further chemical transformations following their formation.