Instituto de Química, Universidade Federal Fluminense, Campus do Valonguinho, CEP 24020-141, Niterói, Rio de Janeiro, Brazil.
Phys Chem Chem Phys. 2014 Aug 28;16(32):17213-9. doi: 10.1039/c4cp02254h.
The interaction between CO2 and 1,2-diaminoethane was computed using pure and hybrid density functionals. The CAM-B3LYP and wB97X-D functionals using a triple-ζ basis set that includes diffuse and polarization functions are the best functionals for calculating the relative energies of the zwitterion intermediate compared to a coupled-cluster with a single, double and non-iterative triple excitation (CCSD(T)) approach extrapolated to a complete basis set limit. With the two functionals and the triple-ζ basis set, the zwitterion is 1.70 kcal mol(-1) less stable than the reactants, and close to 1.63 kcal mol(-1) computed using the CCSD(T) approach. The inclusion of vibrational and thermal corrections and of entropic effects increases the relative energy of the zwitterion to 14.7 kcal mol(-1). Bending of the CO2 geometry increases its acidity due to a 1.09 eV reduction in the LUMO energy. Calculation of the CO2 interaction energy with a set of amines revealed that the interaction energies show a high correlation with their basicities, with the stronger bases stabilizing the zwitterion. For the most basic amine computed (3,4,6,7,8,9-hexahydro-2H-pyrimido[1,2-a]pyrimidine), the Gibbs free energy of the zwitterion is 15.8 kcal mol(-1) lower than the reactants. Therefore, for this highly basic amine, the zwitterion may have a longer lifetime, in contrast to 2-aminoethanol (MEA), where it is only a transient species.
采用纯和杂化密度泛函对 CO2 和 1,2-二氨基乙烷的相互作用进行了计算。与耦合簇单双加三激发（CCSD(T)）方法外推至完全基组极限相比，采用三重ζ基组（包括弥散和极化函数）的 CAM-B3LYP 和 wB97X-D 泛函更适合计算两性离子中间体的相对能量。对于两种函数和三重 ζ 基组，两性离子比反应物稳定 1.70 kcal/mol，与使用 CCSD(T)方法计算的结果接近 1.63 kcal/mol。考虑振动和热校正以及熵效应后，两性离子的相对能量增加到 14.7 kcal/mol。CO2 几何形状的弯曲由于 LUMO 能量降低 1.09 eV 而增加了其酸度。用一组胺计算 CO2 相互作用能表明，相互作用能与它们的碱性高度相关，碱性越强，两性离子越稳定。对于计算出的最碱性胺（3,4,6,7,8,9-六氢-2H-嘧啶并[1,2-a]嘧啶），两性离子的吉布斯自由能比反应物低 15.8 kcal/mol。因此，对于这种高度碱性的胺，两性离子可能具有更长的寿命，与 2-氨基乙醇（MEA）形成鲜明对比，MEA 中两性离子只是一种瞬态物种。
