Scheme 2. Proposed Mechanisms for Chemisorption of CO₂ on Silica Modified with n-Propylamine.

Silylpropylcarbamate forms slowly on single amine groups where a neighboring amine group is not available. If water is present, silylpropylcarbamate does not form. IR frequencies for C=O and COO^– groups are given below the species. (I) and (II) are two possibilities for hydrogen bonds.