Study On Standard Enthalpies Of Formation Of Drug And Dye Molecules

Theoretical and computational chemistry play an important role in the field of chemistry with the rapid development of computer technology.There are studies based on theoretical methods to calculate the thermodynamic properties of compounds.Thermodynamic data can be obtained by theoretical calculation,which can be for any compound without restriction conditions such as reaction temperature,pressure,time.Standard enthalpy of formation of a compound is one of important thermodynamic properties,which is the important data used in calculating reaction enthalpy,equilibrium constants and theoretical yields of reactions when the substance is included.Drugs and dyes are important daily necessities,but their measurement data of standard enthalpies of formation is limited.Therefore,the theoretical methods are adopted to study enthalpies of formation of some drug and dye compounds.The enthalpies of formation for 22 Non-steroidal anti-inflammatory drug melecules and 22 azo-dyes molecules were calculated with B3LYP/6-31G?2df,p?,B3LYP/6-311G?2df,p?,WB97XD/6-31G?2df,p?,HF/6-31G?2df,p?and G4MP2 methods by means of designed isodemic reactions.Comparison the calculated values with the experimental values,the average deviation of above five methods is 15.45,18.62,13.12,39.33,26.14 k J·mol^-1,respectively,in which the average deviation calculated by the WB97XD/6-31G?2df,p?method is the smallest.The calculated values by the G4MP2method are the closest to the experimental values among the five methods,but the calculation does not converge when G4MP2 method is used to calculate the enthalpies of formation for the larger molecules.Therefore,the WB97XD/6-31G?2df,p?method with minimum calculation deviation is selected as the preferred method.There are 6 pairs chiral molecules among the 22 drug molecules,and the calculation results show that the enthalpies of formation of the S configuration molecules are smaller than those of R configuration molecules and the difference is 15 k J·mol^-1.When the group attached to the benzene ring of the main structure is an alkyl group or an aryl group,the enthalpies of formation of the molecules are relatively close.Dye molecules are divided into monoazo and disazo dye molecules.The calculation results show that enthalpies of formation of bisazo dye molecules are significantly larger than those of monoazo dye molecules.The results show that the enthalpy of formation reduces 15?30 k J·mol^-1for each number of methyl group being added to benzene ring.At the same time,the position of the substituent and different groups on the benzene ring affect the enthalpies of formation of molecules.Comparison above five methods of computer time,it is found that G4MP2 model is the slowest method for calculating enthalpy of formation,while B3LYP/6-31G?2df,p?method is the fastest one,and WB97XD/6-31G?2df,p?method has 1.5 times the computing speed of the B3LYP/6-31G?2df,p?method.Considering the calculation efficiency and accuracy of the five methods,WB97XD/6-31G?2df,p?method is suitable for calculating enthalpies of formation for larger molecules.At the same time,the reaction path of the new ionic energetic material TKX-50 was studied with DFT method.According to the reaction path of TKX-50,14 transition states?TSs?were searched,in which 6 TSs have lower energies than those of reactants.The energy barrier of the transition state determines the minimum energy required between the reactants and the product,and determines the ease of the reaction process.The equilibrium constant for each reaction were calculated and clarify the thermodynamic limits of each reaction.According to the calculated results,the equilibrium constant of each reaction of the reaction path of TKX-50 is less affected by temperature.