The structure and some molecular properties of acetone-picrylhydrazone

Abstract

Various physical measurements and quantum-mechanical computations to characterize molecular 2-propanone(2,4,6-trinitrophenyl)hydrazone, alias acetone-picrylhydrazine (AH), are reported, including an X-ray diffraction structural determination, an 1H and 13C NMR study of its internal hindered reorientation, and a theoretical (SCF-MO) interpretation of these observations. The structure of AH was determined by X-ray crystallography. The space group is Pbar over 1, with a = 10.1768(9) Å, b = 7.7968(18) Å, c = 8.0018(5) Å, α = 92.102(6)°, β = 99.919(7)°, γ = 105.926(6)°, Z = 2, wR2(F2) = 0.1995 based on all 2748 unique reflections. The (picryl) proton NMR thermal work yielded a Gibbs activation energy ΔG‡ = 46.9 ± 0.4 kJ mol-1 in acetone-d6 and 48.1 ± 0.2 kJ mol-1 in chloroform-d, whereas 13C NMR (two pairs in the picryl ring) yielded 46.6 ± 1.0 and 46.4 ± 1.0 kJ mol-1 in acetone-d6. The SCF-MO computations yielded a detailed model of the conformerization path. Various model conformations and tautomers of AH have been considered, as has removal of H+ or of H0 from its hydrazinic linkage.Key words: dynamic NMR, picrylhydrazone, hindered rotation, activation parameters, SCF-MO model.

2,2-Dimethyl-1-(2,4,6-trinitrophenyl)hydrazine

“…2,2-Dimethyl-1-picrylhydrazine (DMPH-H) reported herein is the latest member of a series of closely related picrylhydrazines being investigated in an ongoing study of their internal rotations (conformerizations), as well as the acidity and oxidizability of the hydrazinic moiety (e.g. Brown et al, 1999;Tyson & Weil, 1990). Comparisons of the molecular structures, pseudo-thermodynamic conformerization activation parameters, chemical properties, and the results of molecular-orbital computations have been a vital component of this work (Brown et al, 1999;Wang et al, 1991).…”

“…Brown et al, 1999;Tyson & Weil, 1990). Comparisons of the molecular structures, pseudo-thermodynamic conformerization activation parameters, chemical properties, and the results of molecular-orbital computations have been a vital component of this work (Brown et al, 1999;Wang et al, 1991).…”

“…The structure of DMPH-H has an intramolecular hydrogen bond between the H atom on N1 and one of the O atoms on N2 (O21) [or N6 (O61)] to form a six-membered ring (Fig. 1), a structure found in all of the picryl hydrazines (Brown et al, 1999;Wang et al, 1991). The result is to put the plane of the N2 nitro group fairly close [22.62 (6) ] to the plane of the picryl ring {whereas the plane of the N6 nitro group adopts a conformation highly twisted [52.74 (6) ] relative to the plane of the picryl ring due to the proximity of atom N7} unlike the coplanar situation in DPPH-H (Wang et al, 1991).…”