Abstract: ¹³C NMR chemical shifts of a new drug for antitutor-β-elemene have been studied by quantum chemical calculation. The calculations both at the ab initio Hartree-Fock and B3LYP density function level of theory (6-31G^*) at the molecular mechanics MMX and Quantum chemistry RHF/6-31G^*(or B3LYP/6-31G^*) optimized geometry have been implemented. Comparisons of both error analysis and linear correlation analysis have been performed between the theoretical and experimental chemical shifts. The results using GIAO gauge transformation method are better than those using CSGT method. The results using GIAO-B3LYP/6-31G^*//B3LYP/6-31G^* level are the best, with RMS of 4.3ppm, correlation coefficient R₂ of 0.998, SD of 2.42ppm. GIAO B3LYP/6-31G^*//MMX is a good method of counterpoising between the computational expense and accuracy of results, with RMS of 4.9ppm, R₂ of 0.996, SD of 3.04ppm.

Key words: Chemical shift, β-elemene, Quantum chemical calculation, Molecular mechanics