Safety of 3,5-Dimethyl-4-nitropyridine 1-oxide. Aromatic heterocyclic compounds can also be classified according to the number of heteroatoms contained in the heterocycle: single heteroatom, two heteroatoms, three heteroatoms and four heteroatoms. Compound: 3,5-Dimethyl-4-nitropyridine 1-oxide, is researched, Molecular C7H8N2O3, CAS is 14248-66-9, about Nucleophilic displacements in substituted pyridine N-oxides. I. Kinetics of the reactions between sodium ethoxide and 2- and 4-bromo-, 4-chloro-, 2-, 3-, and 4-nitro-, 4-chloro-3,5-dimethyl-, and 3,5-dimethyl-4-nitropyridine 1-oxide in anhydrous ethanol. Author is Johnson, Ronald Mark.
Rates of reaction of halo and nitro pyridine N-oxides with sodium ethoxide in anhydrous ethanol were measured and the Arrhenius parameters calculated and discussed. The reaction rates, entropies, and energies of activation for nitro group displacements all decrease in the order 2 > 4 > 3. With the bromopyridine N-oxides both the entropy and energy of activation decrease in the order 4 > 2, but the positional reactivity is 2 > 4. Two methyl groups adjacent to the leaving group retard the reactions of 4-bromo-and 4-nitro-3,5-dimethylpyridine 1-oxide (I). Low activation energies are attributed to hindrance of nitro group conjugation in the ground state, either by N-oxide, oxygen dipolar repulsion (for 2-nitropyridine 1-oxide) or steric inhibition (in I). Small neg. or small pos. values obtained for activation entropies are attributed to extensive desolvation in forming the transition state. The very high entropy of activation for the reaction of 2-nitropyridine 1-oxide is attributed to the increased freedom of rotation of the nitro group in the transition state compared to the restriction imposed by the N-oxide oxygen in the ground state.
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Reference:
Isoxazole – Wikipedia,
Isoxazole | C3H3NO – PubChem