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Infrared Fingerprints of nN → σ*NH Hyperconjugation in Hydrazides
Laize A F Andrade1, Josué M Silla1, Rodrigo A Cormanich2
1Department of Chemistry, Federal University of Lavras , 37200-000 Lavras, MG, Brazil.
Abstract:
An earlier study demonstrated that hyperconjugation operates in hydrazides by analyzing the N-H stretching mode in gas phase infrared (IR) spectroscopy, and then observing two very distinct bands corresponding to isolated isomers experiencing or not the nN → σ*N-H electron delocalization. The present work reports a chemical method to obtain insight on the hyperconjugation in hydrazide derivatives from solution IR spectroscopy. The analogous amides did not show a νN-H red-shifted band, as the electron donor orbital in the above hyperconjugative interaction does not exist. In addition, the effect of electron withdrawing groups bonded to a nitrogen atom, namely the trifluoroacetyl and the methanesulfonyl groups, was analyzed on the conformational isomerism and on the ability to induce a stronger hyperconjugation in the resulting compounds.
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