THE STRUCTURE AND SOME MOLECULAR PROPERTIES OF ACETONE-PICRYLHYDRAZONE

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) A, b = 7.7968(18) A, c = 8.0018(5) A, 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 ha...