The theoretical calculations of compounds1−4 were performed using Gaussian 09.Conformational analysis wasinitially carried out using Maestro7.5 conformational searching,together with the OPLS_2005 molecular mechanics methods. The optimized conformation geometries, important dihedral angles,thermodynamic parameters, and populations of all conformations are provided in the Supporting Information (Tables S1−4). The OPLS_2005 conformers were then optimized at the B3LYP/6-31G(d, p) level. Room-temperature equilibrium populations were calculated according to the Boltzmann distribution law. The theoretical calculation of ECD was performed using TDDFT
6,7 at the B3LYP/6-31G (d, p) level in MeOH with the PCM model and in the gas phase, respectively. The ECD spectra of compounds1−4were obtained by weighing the Boltzmann distribution rate of each geometric conformation.
The orbital information (NBO plotfiles) was generated using the NBO program of Gaussian 09. The predominantly populated conformers were selected for MO analysis.NBO plotfiles were used to generate corresponding Gaussian-type gridfiles using Multiwfn 2.4.After that, the isosurface of generated grid data was generated by VMD software.