The low reactivity of pyridine, pyridazine, pyrazine, and pyrimidine towards electrophilic substitution reactions can be explained assuming a frontier orbitals control of the reaction. In fact, DFT study of the molecular orbitals of these molecules shows that the HOMOs of these substrates are not π orbitals. Furthermore, the change in the reactivity observed in pyridine-N-oxide can be explained considering that, in this case, the HOMO is an aromatic orbital.
Keywords: pyridine, pyrazine, pyridazine, pyrimidine, electrophilic substitution, dft
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