The Brönsted Basicities of N-Heterocyclic Olefins in DMSO: An Effective Way to Evaluate the Stability of NHO–CO₂ Adducts

Abstract

A Brönsted basicity scale (∼24 p<i>K</i> units) for 85 commonly seen imidazole-, imidazoline-, triazole-, and thiazole-based N-heterocyclic olefins (NHOs) in DMSO was established using a well-examined computational model. The influence of substituents on the Brönsted basicities of these NHOs was investigated through basicity comparisons and rationalized by geometric analyses. The Gibbs energy (Δ<i>G</i>_r) of the reaction between NHO and CO₂ was also calculated, which linearly correlates with the basicity of the corresponding NHO, suggesting that the stability of NHO-CO₂ adducts can be evaluated by the basicity of NHOs and a stronger basicity leads to a more stable NHO-CO₂ adduct.