Relation between the substituent effect and arom aticity in imidazole derivatives: a compar ative stud y

Aromaticity is one of the ke y concepts in chemistry which is studied time to time, by both experimental and theoretical chemists [۱,۲]. Numerous methods have been developed f or the measurement of t he extent of aromaticity since Kekule´ first intr oduced the c oncept ۱۴۷ years ago, b ut no single measure has gained universal acceptance. Part of the problem i s that aromaticity is a m ultidimensional property, composed of geometrical, energ etic and ma gnetic comp onents, whe reas most measures focu s on only one aspect [۳]. The imidazole ring s ystem is the most important substructures fo und in a large number of natu ral products and pharmacologically active com pound systems. Comp ounds containing imidazole moiety have many pharmacolo gical prope rties and play importa nt roles in biochemica l processes. [۴]. energies and arom aticity of a series of R substituted imidazoles [R = NH۲, OH, H, CH۳, F, Cl, CN NO, NO۲], their anions and protonated forms in the gas phase have been calculated with the D FT/B۳LYP and MP۲ me thods at the ۶-۳۱۱++G (d,p) level. We have ana lyzed the c hange of local aromaticity using several aromaticity indicat ors (Pozharsky Index, HOMA, NICS and pEDA) and found a considerable ring aromaticity for imidazoles, imidazolat e anions and their proton ated forms. In each cla ss anion for ms have the most aroma ticity and in neutral forms,۱- H imidazoles have less aromaticity character. Th e results of calculated aromaticities of imida zole derivatives substituted at ۲ position using various scal es presented in Table ۱,۲ and۳

کلیدواژه ها:

Aromaticity ، NICS ، NBO ، H OMA ، Imidazoles