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1.
The dipole moments of 2-alkylaminoand 2-alkylnitramino-3(or 5)-methyl-4-nitropyridines and their N-oxides have been measured, as well as calculated, using vectorial summation of the group moments and by ab initio method. The estimated interaction dipole moments, int, have been discussed in terms of the electronic and steric effects and intramolecular hydrogen bonding. Introduction of the NHCH3 group to position 2 in 4-nitropyridine strengthens the conjugation between the nitro group and ring nitrogen. The lack of such strengthening in 4-nitropyridine-N-oxides is explained as being due to formation of intramolecular hydrogen bond between the N-oxide group and the hydrogen of alkylamino group. Introduction of the nitramino group does not lead to marked modification of the charge distribution in a molecule. This fact may be explained by much weaker electron-donating ability of this group in comparison with the alkylamino group. 相似文献
2.
The 1H, 13C, and 15N NMR chemical shifts of ten 4-nitropyridine N-oxide derivatives are assigned. The shielding of the pyridine ring nitrogen is sensitive to ring substitution through inductive effects, steric effects by ortho-substituents, and the possibility for electron delocalisation (resonance energy). In solution, 3-ethylnitrosoamino-4-nitropyridine N-oxide has two tautomers. The proposed reason is the steric crowding between vicinal 4-nitro and 3-ethylnitrosoamino groups, causing a disturbance to amino nitrogen that can delocalize its lone pair to the oxygen atom of the nitroso group. 相似文献
3.
The formation of mixed adsorbed layers has been tested for ternary mixtures containing a specifically adsorbed component—acetone and binary solvent benzene +n-hepane. The specific excess adsorption isotherms from the liquid phase were measured on silica gel samples partially dehydroxylated. The competition of liquid components for silica surface is discussed on the basis of changes in the mixed solvent composition. 相似文献
4.
A novel class of non-classical fullerenes, having pentagon–heptagon pairs, as in azulene, is modeled. The various coverings,
sometimes alternating azulenic and benzenic units, are designed by some new sequences of map operations or generalized operations.
The hypothetical azulenic fullerenes are characterized by PM3 semiempirical data and POAV1 strain energy SE. Their aromaticity
is discussed in the light of several criteria. The HOMA index of aromaticity enabled evaluation of global and local aromaticity
of the designed fullerenes. 相似文献
5.
Aniela Puszko 《Journal of chemical crystallography》1993,23(1):23-31
UV spectra of 2-chloropicolines, their N-oxides and 2-chloro-4-nitropicoline N-oxides are presented and the influence of substituents on the raax and max of spectral bands are discussed. The electronic spectra were calculated by a modified INDO method. Transition energies, intensities and assignments were compared with UV spectra. The latter were recorded for the first time on all the title compounds. 相似文献
6.
The UV spectra of seven methyl derivatives of 4-nitropyridine N-oxide in ethanol have been examined. The electronic spectra were calculated by a modified INDO method. Transition energies, intensities and assignments were compared with UV spectra. Spectroscopic manifestations of intramolecular interaction indicate that methyl groups modify the electronic interaction between the N-oxide and NO2 groups mainly through a steric strain.Department of Organic Chemistry, University of Economics, Pl-53342 Wroclaw, Poland. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 786–793, June, 2000. 相似文献
7.
Zieba-Mizgała A Puszko A Regiec A Kuduk-Jaworska J 《Bioelectrochemistry (Amsterdam, Netherlands)》2005,65(2):113-119
Investigation of the reduction potential and calculation of the partition coefficient n-octanol/water allow the assessment of the potential suitability of nitropirydine N-oxide compounds in radiotherapy of cancer. Experiments were carried out using cyclic voltammetry with HMDE as working electrode. The electrode reduction of the investigated compounds is quite irreversible and strongly dependent on pH. 相似文献
8.
Aniela Pop Florica Manea Ciprian Radovan Plamen Malchev Adriana Bebeselea Cristina Proca Georgeta Burtica Stephen Picken Joop Schoonman 《Electroanalysis》2008,20(22):2460-2466
The assessment of an expanded graphite‐Ag‐zeolite‐epoxy composite (EG‐Z‐Ag‐Epoxy) electrode for the determination of 4‐chlorophenol (4‐CP) is described and compared to the corresponding expanded graphite‐epoxy composite (EG‐Epoxy) electrode. Cyclic voltammetry was used to characterize the electrochemical behavior and determination of 4‐CP at both electrodes in 0.1 M Na2SO4 and 0.1 M NaOH supporting electrolytes. A substantial enhancement of sensitivity for the determination of 4‐CP at the EG‐Z‐Ag‐Epoxy electrode was reached by applying a chemical preconcentration step prior to voltammetric quantification. Also, under these last conditions the lowest limit of detection of 1 μM illustrates the analytical versatility of this electrode in a concentration range where aquatic 4‐chlorophenol pollution is known to occur. 相似文献
9.
Electronic spectra of thirteen title compounds were measured and the substituent effect on max and max were discussed. It was found that there is a disturbance of mutual electronic interaction of substituent by a steric ortho-effect. The obtained results provide evidence that the investigated 2-akylamino compounds exist in amino form.Department of Organic Chemistry, Academy of Economics, Wroclaw PL-53-432. Published in Khimiya Geterot siklicheskikh Soedinenii, No. 9, pp. l228–l231, September, 1996. Original article submitted August 20, 1995. 相似文献
10.
Aniela Puszko 《Chemistry of Heterocyclic Compounds》1998,34(10):1148-1160
UV spectra of 2,4-dihalopicolines and their N-oxides are presented, and the influence of substituents on spectral parameters
is discussed. The electronic spectra were calculated by a modified INDO method. Transition energies, intensities, and assignments
were compared with UV spectra. The degree of intramolecular charge transfer in 2,4-dihalopicolines is greater than in 2-halopicoline
N-oxides and smaller than in 2-halo-4-nitropicoline N-oxides. Difference values of HOMO-LUMO energies point out that the susceptibility
on photochemical reaction lies in the order: 2-halo-4-nitropicoline N-oxides > 2,4-dihalopicoline N-oxides > 2-halopicoline
N-oxides > pyridine N-oxide.
Department of Organic Chemistry, University of Economics, PL-53-342 Wroclaw, Poland. Translated from Khimiya Geterotsiklicheskikh
Soedinenii, Vol. 34, No. 10, pp. 1352–1366, October, 1999. 相似文献