By using density functional theory(DFT) method in B3 LYP on the 6-311 + G(d,p) basis set level combine PCM model,we have researched the geometric parameters,infrared spectroscopy,natural charge population,the molecular energy,the frontier orbital and Fukui function scanning about aspirin,ibuprofen,Phenacetin and acetaminophen.The calculation results show that the benzene ring in the molecule,which play a certain role in pharmacological activity,esther,amidogen,amino,hydroxyl and carboxyl radical also take out many effects.From the total ca...