A COMPUTATIONAL STUDY OF THE STRUCTURES AND ELECTROSTATIC POTENTIALS OF SOME AZINES AND NITROAZINES
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An ab initio SCF computational approach is used to study six azines (azabenzenes) and their mononitro derivatives. Our primary interest is in determining how the reactive properties of the azines are affected by the introduction of the nitro group. All structures are optimized at the 3-21G level, and these are then used to compute the STO-5G molecular electrostatic potentials. Among the various isomers, those having two adjacent ring nitrogens are by far the least stable. The nitro derivatives are most stable when the substituent is to a ring nitrogen and least when it is . The dominant features of the electrostatic potentials of these molecules are the large and strong negative regions, centered in the molecular planes, that are associated with the ring nitrogens and are indicative of their basic characters. These negative potentials, and correspondingly the basicities, become weaker as the number of ring nitrogens increases and also with the substitution of the electron-withdrawing nitro group. The regions above and below the rings become increasingly positive in going from the mono- to the tetra-azine and with the introduction of the -NO2 group, suggesting enhanced susceptibility to nucleophilic attack. 1989.
