Structure, Synthesis, and Properties of Some Persubstituted 1,2-Dinitroethanes. In Quest of Nitrocyclopropyl-Anion Derivatives

Article abstract of DOI:10.1002/hlca.19820650114

Attempts to deprotonate nitrocyclopropane led to solutions which showed strong ESR. signals (Fig. 1) and from which 1-nitro-1'-nitroso-bicyclopropyl (3) and 1,1'-dinitro-bicyclopropyl (2) were isolated.The activation energy for rotation about the central C,C-bond of 2 is estimated to be about 12 kcal/mol (1H-NMR. spectra in Fig. 2).In contrast, the open-chain analoque 2,3-dimethyl-2,3-dinitrobutane (1) shows a metyl singlet down to -70 deg C.Low-temperature X-ray analyses of 1, 2, 3, and also of 1,1'-dinitro-bicyclobutyl (4) show that all four molecules have gauche-conformations but reveal striking structural differences between the open-chain and the cyclic derivatives (Fig. 4-6): the central C,C-bond is long in 1 (1.575 Angstroem), short in 2 (1.479 Angstroem); the C,N-bonds are long in 1 (1.549 Angstroem), short in 2 (1.488 Angstroem); the orientation of the nitro groups is bisected in 2 and perpendicular in 1.The crystal structure of the nitro-nitroso compound 3 is isimorphous with that of the dinitro compound 2 and thus disordered (Fig. 15-16).The effect of the nitro group as ?-electron acceptor on the molecular conformations and bond lengths is discussed.From analysis of the anisotropic vibrational parameters of 2 the root-mean-square librational amplitude of the nitro groups about their C,N-bonds is estimated to be about 5.8 deg at 95 K, corresponding to a rotational barrier of about 9 kcal/mol, i. e. the same order of magnitude as the NMR. estimate of about 12 kcal/mol for C,C-rotation.