Abstract 7-methoxy-4’-p-toluenesulfonylisoflavone(L1) and 7- ethyl oxyacetate-4’-p-toluene -sulfonylisoflavone (L2) were synthesized and characterized by IR, 1H NMR and elemental analysis. Single crystals of L1 were determined by X-ray single crystal diffraction. The scavenging effect of L1 and L2 on DPPH• radical were detected by ultraviolet spectrophotometry. In addition , the semi-empirical method of quantum chemistry（AM1）and HF ab initio methods were used for calculating charge density of atoms in the molecule. The possible mechanism of eliminating DPPH• radical was explained. The experiment result shows that, the crystal [C23 H18 O6S] belongs to monoclinic space group P2 (1)/c with unit cell constants a = 20.041(5) Å , b = 6.0876(17) Å , c = 16.516(4) Å . The compound L2 can scavenge DPPH• radical more effectively than L1.

Key words: 7-methoxy-4'-p-toluenesulfonyloxyisoflavone, 7-ethoxyl carbonylmethoxy-4'-p-toluenesul- fonyloxyisoflavone, crystal structure, antioxidant, quantum chemistry