“…However for component of NH 2 (CH 2 ) 6 NH 2 CB [7] complex, still no carbamate intermediate could be detected under the same concentration. The proton signals of bicarbonate product corresponding to bound amine shifted from 0.67, 0.86, 2.37 ppm to 0.61, 0.89, 2.51 ppm, whereas the signal shifts appeared and the conversion stayed complete since 45 s based on integration of the resonance signal at 0.61, 0.89 or 2.51 ppm (Figure 3b) The absence of carbamate product for bound amine whether or not in a mixture with free amine could be mostly ascribed to the deshielding effect [13,14] in that nucleophilicity of bound amine to attack CO 2 decreases as influenced by the electronegative portal oxygens, while the steric effect also inhibits the formation of carbamate to some extent. On the other hand, increased electrophilicity of bound amine caused by the deshielding effect favors the acid-base neutralization towards bicarbonate product, thus resulting in higher selectivity and faster reaction rate for bound amine compared to free amine.…”