To advance the optimal design of amines for postcombustion CO2 capture, a sound mechanistic under-standing of the chemical process of amines with good CO2 capture performance is advantageous. A stoically hindered alkanolamine, 2-(tert-butylamino)ethanol (TBAE), in ethylene glycol (EG) solution was recently reported to have better CO2 capture performance and unusual reactivity toward CO2, in Comparison with those of the prototypical. alkanolamines. However, the reaction mechanism of TBAE with CO2 in EG solution is unclear: Here, various quantum chemistry methods were employed to probe the reaction mechanism of TBAE With; CO2 in EG and aqueous solution. Six reaction pathways involving three kinds of possible reactive centers,of TBAE solution Were considered. The results indicated that the formation of, anionic hydroxyethyl carbonate by the attack of -OH of EG on CO2 is the most favorable, which is confirmed by Complementary high-resolution mass spectrum experiments.. This clarified that the speculated zwitterionic carbonate species is not the main product in EG solution. The reaction process of TBAE in aqueous solution is similar to that in BG solution, leading to bicarbonate, which agrees with experimental observations. On the basis of the unveiled reaction mechanisms of TBAE + CO2, the role of the key tert-butyl functional group of TBAE was revealed.