Effect of the 5-Substituent on the Tetrazole-Azide Isomerization in Tetrazolo[1,5-a] pyridines by Ab Initio Calculations

摘要

The effect of substituents CH_3,OH,Cl,OCH_3,NO_2 and COOH at the 5-alpyridines,on the tetrazoleazide equilibrium,was investigated at the 6-31G~**/MP2 level of theory.For both,the parent and 5-CH_3 compounds,the tetrazole forms are largely favored,while the other substituents-OH,Cl,OCH_3 and NO_2-stabilize the azide isomer.With the COOH group,the tetrazole and azide forms are preicted to be in equilibrium in nearly equal amounts.The influence of these groups on the transition state (TS) was also studied.In general it is observed that,groups which stabilize the azide isomer,lower the E_(act) of the isomerization reaction,and conversely,those that favor the tetrazole form,raise the E_(act) of this reaction,reltive to the unsubstituted compound.The TS has a close resemblance to the tetrazole structure.