Resumo

SANCHEZ-VIESCA, Francisco  e  GOMEZ, Ma. Reina. Autogenic electromeric effect in pyridine N-oxide and its nitration. TIP [online]. 2014, vol.17, n.1, pp.56-61. ISSN 1405-888X.

Linton found out that the dipole moment of pyridine N-oxide is appreciably smaller than the expected theoretical value. Thus, he postulated the contribution of three 'excited structures', with a negative electric charge at the 2-, 4- and 6-position. However, a typical electrophilic substitution such as nitration, afforded only the 4-nitro derivative. This discrepancy between theory and experiment prompted us to study the pyridine N-oxide physical properties, since its reactivity is derived from them. Besides, these negative charged rings require an unexpected polarization and a reaction mechanism must be provided. We propose intermolecular induced polarization as a viable path. We uncovered that only one of the three structures before mentioned is supported by the observed reactivity and by ¹³C nuclear magnetic resonance data. On rejecting 2 of the Linton's 'excited structures', we have explained the regioselectivity found in pyridine N-oxide nitration.

Palavras-chave : Autogenic electromeric effect; resonance structures; reaction mechanisms; pyridine N-oxide nitration.

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