Conformational dynamics of 4-formylaminoantipyrine based on NMR and theoretical calculations.

We investigated the metamizole metabolite 4-formylaminoantipyrine (4-FAA) by 1 H dynamic nuclear magnetic resonance. 4-FAA exhibits a carbon-nitrogen partial double bond that rotates slowly enough, on a resonance time scale, to provide the simultaneous spectra of two rotamers. We examined various solvents in an attempt to understand how protic and aprotic environments influence the anti and syn rotamer equilibriums. Moreover, we compared experimental data and theoretical calculations to evaluate the thermodynamic parameters of the rotational process. [ABSTRACT FROM AUTHOR]