Effect of carboxyl and carboxamide substituent groups on fluorinated pyrazine species with antitubercular activities

Abstract

The structural, electronic, topological and vibrational properties were studied for F-pyrazine, 3-fluoropyrazine-2-carboxilic acidand 3-fluoropyrazine-2-carboxamide in gas phase by using the hybrid B3LYP/6-311++G** level of theory. Theoretically, twoconformations were found for both acid and amide species being their C2 conformations, with C symmetries, the most stable. SThe NBO study reveals the high stability of the acid species due to the two DET and DET interactions not observed in the amide LP* LP LP*species. The AIM analysis supports the high stabilities of both C2 conformers due to the halogen bonds formation where thetopological properties are higher for the acid species, in very good concordance with the higher total energy observed by NBOcalculations. The frontier orbitals predict a higher reactivity for the amide species while the descriptors evidence the highernucleophilicity and electrophilicity indexes for the acid species. On the other hand, the C2-N3 stretching mode in FP is predicted athigher wavenumbers than pyrazine while in the acid and amide species this stretching mode is predicted with partial double bondat lower wavenumbers. The tentative assignments for the acid and amide species were performed. The force constants calculatedshow strongly dependence from their geometrical parameters.