Theoretical study on hydrogen bonding interaction of ureas and thioureas with imines

The hydrogen bonding interaction between ureas and thioureas with imines was investigated using the MP2 method. In combination with the catalytic reactions, we discussed two different hydrogen bonding patterns, which have the same typical hydrogen bonding feature of red shift effect. Based on it, the substituent effect of the more stable pattern was researched. The results indicated that electron-withdrawing groups on ureas or thioureas and electron-donating groups on imines can both facilitate the hydrogen bonding formation. We also studied the cis-trans isomerization of this pattern which is associated with the catalysis mechanism. The NBO analysis gave a more profound understanding of the hydrogen bonding interaction and appeared quite significant in view of their importance for understanding the intermolecular interaction leading to hydrogen bonding.