Zdzisław Daszkiewicz

Charge-density analysis of 1-nitroindoline: refinement quality using free R factors and restraints

Nitramines and related N-nitro compounds have attracted significant attention owing to their use in rocket fuel and as explosives. The charge density of 1-nitroindoline was determined experimentally and from theoretical calculations. Electron-density refinements were performed using the multipolar atom formalism. In order to design the ideal restraint strategy for the charge-density parameters, R-free analyses were performed involving a series of comprehensive refinements. Different weights were applied to the charge-density restraints, namely the similarity between chemically equivalent atoms and local symmetry. Additionally, isotropic thermal motion and an anisotropic model calculated by rigid-body analysis were tested on H atoms. The restraint weights which resulted in the lowest values of the averaged R-free factors and the anisotropic H-atom model were considered to yield the best charge density and were used in the final refinement. The derived experimental charge density along with intra- and intermolecular interactions was analysed and compared with theoretical calculations, notably with respect to the symmetry of multipole parameters. A comparison of different refinements suggests that the appropriate weighting scheme applied to charge-density restraints can reduce the observed artefacts. The topological bond orders of the molecule were calculated.

Halogen effect on structure and 13C NMR chemical shift of 3,6-disubstituted-N-alkyl carbazoles.

Structures of selected 3,6‐dihalogeno‐N‐alkyl carbazole derivatives were calculated at the B3LYP/6‐311++G(3df,2pd) level of theory, and their 13C nuclear magnetic resonance (NMR) isotropic shieldings were predicted using density functional theory (DFT). The model compounds contained 9H, N‐methyl and N‐ethyl derivatives. The relativistic effect of Br and I atoms on nuclear shieldings was modeled using the spin–orbit zeroth‐order regular approximation (ZORA) method. Significant heavy atom shielding effects for the carbon atom directly bonded with Br and I were observed (~−10 and ~−30 ppm while the other carbon shifts were practically unaffected). The decreasing electronegativity of the halogen substituent (F, Cl, Br, and I) was reflected in both nonrelativistic and relativistic NMR results as decreased values of chemical shifts of carbon atoms attached to halogen (C3 and C6) leading to a strong sensitivity to halogen atom type at 3 and 6 positions of the carbazole ring. The predicted NMR data correctly reproduce the available experimental data for unsubstituted N‐alkylcarbazoles. Copyright

4-Chloro-N-methyl-N-nitroaniline

The molecular structure of (p-ClC 6 H 4 )(CH 3 )NNO 2 (or C 7 H 7 ClN 2 O 2 ) contains a planar NNO 2 nitroamino group which is twisted about the N-C phenyl bond by ca 68° from the plane of the aromatic ring. The structural data are in agreement with the spectral results and indicate that there is no conjugation between the aromatic sextet and the nitroamino group. There are no specific intermolecular interactions.

Nitration in the carbazole series

Abstract Nitration of9-tosylcarbazole in acetic anhydride solution gives l-nitro (28%), 2-nitro (19%) and 3-nitro (53%) derivatives. The mixture of the nitro compounds obtained from 9-acetylcarbazole contains 10%, 48% and 42% of the isomers, respectively. Under similar conditions 9-nitrosocarbazole shows a different isomer distribution: 34% of 1-nitro and 66% of 3-nitrocarbazole. Nitration of carbazole is a two step process involving formation and rearrangement of 9-nitrocarbazole. The hypothesis was supported by the results of 1,3,6,8-tetrachlorocarbazole nitration and oxidation of 9-nitrosocarbazole and rearrangement of 9-nitrocarbazole in the nitration conditions.

By-products in the rearrangement of N-methyl-N-phenylnitramine

Abstract N-Methyl-N-phenylnitramine was rearranged in the aqueous dioxane — sulphuric acid mixture to 2-nitro- and 4-nitro-N-methylanilines. The isomer ratio was independent of the acidity within the range of −0.3 > Ho > −2.8. Some by-products were isolated and identified e.g. N-methyl-N-nitrosoaniline, its 2-nitro and 4-nitro derivatives, nitrosobenzene and 4′,4″-bis-(N-methylamino)-3′,3″-dinitrodiphenylmethane. The mechanism of the nitramine rearrangement is discussed.

Structure and properties of some nitro derivatives of N-methyl-N-phenylnitramine

Abstract Ten mono-, di- and tri-nitro derivatives of N-methyl-N-phenylnitramine were prepared and investigated using spectral and electrooptical methods. Three of them, viz. N-(2, 5-dinitrophenyl)-N-methylnitramine (monoclinic, P21/c, a=8.248(2), b=11.655(2), c=10.404(2) A , β=102.57(2)°), N-(2,3-dinitrophenyl)-N-methylnitramine (monoclinic, P21/c, a=9.224(2), b=7.222(2), c=15.458(4) A , β=101.08(2)°)) and N-(3,5-dinitrophenyl)-N-methylnitramine (monoclinic, P21/n, a=9.814(2), b=12.000(2), c=8.865(2) A , β=114.94(2)°) were examined by the X-ray diffraction method. The nitramino group is nearly planar with the short N(7)–N(8) bond and strongly electron deficient N(8) atom. The nitramino group is twisted vs. the aromatic ring, there is no conjugation between the nitro and nitramino groups across the ring. The nitramino group is an electron withdrawing substituent due to the inductive effect. The number and positions of the Ar-nitro groups have no influence on the N-nitro group. Its migration ability cannot be explained in terms of the interaction between the migration origin and the ring substituents.

N-Methyl-N-(2-nitrophenyl)nitramine and N-methyl-N-(3-nitrophenyl)nitramine.

The structures of the two title isomeric compounds (systematic names: N-methyl-N,2-dinitroaniline and N-methyl-N,3-dinitroaniline, both C7H7N3O4) are slightly different because they exhibit different steric hindrances and hydrogen-bonding environments. The aromatic rings are planar. The -N(Me)NO2 and -NO2 groups are not coplanar with the rings. Comparison of the geometric parameters of the ortho, meta and para isomers together with those of N-methyl-N-phenylnitramine suggests that the position of the nitro group has a strong influence on the aromatic ring distortion. The crystal packing is stabilized by weak C-H...O hydrogen bonds to the nitramine group.

4-(N-Methylnitramino)pyridine 1-oxide

In the title compound, C 6 H 7 N 3 O 3 , the NNO 2 group is twisted ca 59° from the planar pyridine ring. The nitramino group is almost planar, with the N7 atom diverging 0.15 A from the C4-N8-C11 plane. The lone pair on N7 is included into the N-nitro group π-electron system resulting in two independent sets of multicenter π-orbitals. Significant anisotropy of the temperature dependence of thermal expansion is observed in the range 90-300 K.

SYNTHESIS AND REARRANGEMENT OF N-METHYL-N-(2-THIAZOLYL)-NITRAMINE

Methylation of N-(2-thiazolyl)-nitramine in alkaline solution gives 1,2-dihydro-3-methyl-2-nitriminothiazole which rear-ranges in concentrated sulphuric acid yielding small amount of 2-(N-methylamino)-5-nitrothiazole, identical with the product of rearrangement of N-methyl-N-(2-thiazolyl)-nitramine. The latter compound was obtained by the action of sodium hydride on 2-(N-methylamino)-thiazole followed by the nitration with n-butyl nitrate.

Rearrangement of N-(3-pyridyl)nitramine

Contrary to other N-(pyridyl)nitramines, the title compound cannot be rearranged to 3-amino-2-nitropyridine or other isomers. Hypothetical products of its transformation under influence of concentrated sulphuric acid, viz. 3-hydroxypyridine, 3,3′-azoxypyridine and 3,3′-azopyridine, were obtained from 3-nitro- and 3-aminopyridine in oxidation and reduction reactions. N-(3-Pyridyl)nitramine was prepared and rearranged in concentrated sulphuric acid. 3-Hydroxypyridine and 3,3′-azoxypyridine were isolated from the reaction mixture, other products were identified by the HPLC and GCMS methods. The results indicate that N-(3-pyridyl)hydroxylamine is an intermediate formed from N-(3-pyridyl)nitramine under the influence of concentrated sulphuric acid. The reaction path, leading to the final products, is discussed in context of the mechanism of nitramine rearrangement.