A theoretical investigation on the potential energy surface of CN2H rotation of the encapsulated 1-bicyclo[2.2.1]heptyldiazirine

The potential energy surface (PES) of CN₂H rotation of the encapsulated 1-bicyclo2.2.1]heptyldiazirine (BHD) inside a molecular container: Cram’s hemicarcerand (CH) was explored using two different DFT involved ONIOM methods: B3LYP/6-31G^**//ONIOM(B3LYP/6-31G^*: AM1) and B971/6-31G^**//ONIOM(B971/6-31G^*: AM1). The free-state PES of CN₂H rotation was also calculated, respectively by B3LYP/6-31G^**//B3LYP/6-31G^* and B971/6-31G^**//B971/6-31G^* methods for comparison. The findings in this study have shown that the PES profiles differ from each other notably in the two states. In the encapsulated state the rotation barrier corresponding to the free-state conversion with the largest rotation barrier increases by about 2 kcal/mol, which has exceeded the largest rotation barrier in the free-state. The conformational preference behavior towards certain BHD isomers, which might be in better conformational compatibility with the container, has been demonstrated.