Dynamic NMR spectroscopy of three 2,2′-dialkyl/aryl-1-picrylhydrazines in liquid solution

We have studied and compared the proton nuclear magnetic resonance spectra of a series of three 2,2′-di(alkyl/aryl)-1-(2,4,6-trinitrophenyl)hydrazines at 500 MHz in liquid toluene-d8, with a view to learning details of the internal conformation changes taking place, as a function of temperature. Herein “alkyl” denotes ‘methyl’, and “aryl” denotes ‘phenyl’. The synthesis and characterization of 2-phenyl,2′-methyl-1-picrylhydrazine is reported. One goal of the present study was to afford a comparison with the oxidation products, i.e., the three corresponding hydrazyl free radicals – which show striking differences. All the hydrazine molecules in liquid solution occur as interconverting enantiomorphic pairs (atropisomers). Advanced techniques for obtaining the relevant activation energies and pseudo-thermodynamic parameters (Arrhenius and Eyring) have been utilized, and these parameters are listed and discussed. The three hydrazines turn out be very similar with respect to their internal dynamics.