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21.
V. K. Shevtsov P. I. Zakharov V. P. Zvolinskii V. G. Pleshakov G. V. Grigor'ev M. Zainul Abedin N. S. Prostakov 《Chemistry of Heterocyclic Compounds》1981,17(7):697-702
The dissociative ionization of 13 nitro derivatives of 2(4)-azafluorenes and 2(4)-azafluorenones was investigated. The introduction of an electron-acceptor nitro group into the molecule markedly reduces the stability of the molecular ions and suppresses the fragmentation pathways that are characteristic for azafluorenes. Nitro-nitrite rearrangement proceeds more readily in nitro-substituted 4-azafluorenes than in nitro-substituted 2-azafluorenes. A characteristic feature of the fragmentation of azafluorenes that do not contain nitro and methyl groups in a vicinal orientation is elimination of a OH particle by the molecular ions. It was established by deuterium labeling that in this case the formation of an [M — OH]+ ion is due to the presence of a methylene group attached to the C9 atom in the molecule.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 941–947, July, 1981. 相似文献
22.
P. I. Zakharov V. P. Zvolinskii S. G. Poshivalov V. G. Pleshakov T. S. Seitembetov 《Chemistry of Heterocyclic Compounds》1979,15(5):535-540
The mass spectra of 15 compounds of the 4-azaphenanthrene series and their deutero analogs with bulky R substituents (R=-CCPh, -CH=CHPh, CHBr-CHBrPh,-CH=CHC6H4OCH3-p, -COOH, -COOC2H5, and -CONHNH2) in the ortho position relative to the nitrogen atom were studied. An intense [M-H]+ ion peak, the appearance of which is evidently due to a process involving cyclization of the carbon atom of the side chain with the nitrogen atom, is formed in the fragmentation of the styryl derivatives. The fragmentation of the compounds with a methyl group in the ortho position relative to the styryl grouping is accompanied by the formation of an intense [M-Ph]+ ion peak. An ortho effect of the carboxyl and carbethoxy groups adjacent to the methyl substituent is observed in the mass spectra of the investigated compounds. The data obtained make it possible to establish the structures of bulky substituents in the ortho position relative to the ring nitrogen atom and the position of the methyl group in the pyridine ring of monomethylated azaphenahthrenes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 659–665, May, 1979. 相似文献
23.
V. K. Shevtsov P. I. Zakharov V. P. Zvolinskii V. G. Pleshakov T. S. Seitembetov N. S. Prostakov 《Chemistry of Heterocyclic Compounds》1979,15(3):328-332
The M+ and [M-H]+ ion peaks are the peaks of maximum intensity in the mass spectra of Schiff bases belonging to the 4-aza-9-fluorenylidenearylamine series. The dependence of the relative intensity of the [M-H]+ fragment on the structures of the I–XI molecules provides evidence for the possibility of the occurrence of rearrangement processes involving the formation of this ion. The formation of [M-CH3]+, [M-HCN]+, [M-Ar]+, and [M-CNAr]+ ions is also characteristic for the fragmentation of the investigated compounds. It was found that, in contrast to other types of Schiff bases, the ejection of an HCN molecule during the mass-spectrometric fragmentation of the investigated compounds occurs without participation of the nitrogen atom of the azomethine group. The elimination of a CNAr particle by the molecular ions is a distinctive feature of the investigated series of Schiff bases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 397–402, March, 1979. 相似文献
24.
Suppose that a continuous 2π-periodic function f on the real axis ? changes its monotonicity at different ordered fixed points y i ∈ [? π, π), i = 1, …, 2s, s ∈ ?. In other words, there is a set Y:= {y i } i∈? of points y i = y i+2s + 2π on ? such that, on [y i , y i?1], f is nondecreasing if i is odd and nonincreasing if i is even. For each n ≥ N(Y), we construct a trigonometric polynomial P n of order ≤ n changing its monotonicity at the same points y i ∈ Y as f and such that $$ \left\| {f - P_n } \right\| \leqslant c\left( s \right)\omega _2 \left( {f,\frac{\pi } {n}} \right), $$ where N(Y) is a constant depending only on Y, c(s) is a constant depending only on s, ω 2(f, ·) is the modulus of continuity of second order of the function f, and ∥ · ∥ is the max-norm. 相似文献
25.
Severin A. V. Berezin Ia. A. Orlova M. A. Trofimova T. P. Lupatov A. Yu. Egorov A. V. Pleshakov V. M. 《Russian Chemical Bulletin》2020,69(4):665-670
Russian Chemical Bulletin - Specific features of the interaction between bismuth(iii) and hydroxyapatite (HAP) of various morphologies during its sorption and co-crystallization binding were... 相似文献
26.
I. V. Pleshakov 《Physics of the Solid State》2005,47(9):1692-1696
This paper reports on the results of investigations into the magnetoelastic vibrations excited by radio pulses in thin single-crystal hematite plates according to the scheme of parallel parametric pumping. It is demonstrated that this technique can be used to examine the multimode spectrum of natural vibrations of crystals in weak external magnetic fields H0 < 200 Oe and to measure some acoustical quantities in this range. By using the parametric amplification of sound, it is established that an increase in the magnetic field is accompanied by the appearance of weakly damped low-intensity modes in the spectrum of natural vibrations. 相似文献
27.
V. K. Belsky A. I. Stash O. V. Koval'chukova S. B. Strashnova L. S. Shebaldina B. E. Zaitsev V. G. Pleshakov 《Crystallography Reports》2003,48(4):606-609
6-Methyl-5-acetyl-4-α-furyl-2-keto-1,2,3,6-tetrahydropyrimidine (I) and 6-methyl-5-acetyl-4-γ-bromophenyl-2-thio-1,2,3,6-tetrahydropyrimidine (II) are prepared by the modified Biginelli reaction, and their crystal and molecular structures are studied. It is shown that, in crystals I and II, the pyrimidine ring has an amide tautomeric form and adopts a sofa conformation. The IR absorption spectra are analyzed, and the stability of the tautomers of the pyrimidine fragments is evaluated using quantum-chemical calculations. 相似文献
28.
M. G. Pleshakov 《Journal of Approximation Theory》1999,99(2):519
Let 2s points yi=−πy2s<…<y1<π be given. Using these points, we define the points yi for all integer indices i by the equality yi=yi+2s+2π. We shall write fΔ(1)(Y) if f is a 2π-periodic continuous function and f does not decrease on [yi, yi−1], if i is odd; and f does not increase on [yi, yi−1], if i is even. In this article the following Theorem 1—the comonotone analogue of Jackson's inequality—is proved.
1. If fΔ(1)(Y), then for each nonnegative integer n there is a trigonometric polynomial τn(x) of order n such that τnΔ(1)(Y), and |f(x)−πn(x)|c(s) ω(f; 1/(n+1)), x
, where ω(f; t) is the modulus of continuity of f, c(s)=const. Depending only on s. 相似文献
29.
Mazur A. S. Karpunin A. E. Proskurina O. V. Gerasimov V. I. Pleshakov I. V. Matveev V. V. Kuz’min Yu. I. 《Physics of the Solid State》2018,60(7):1468-1470
Polyhydroxylated fullerene C60(OH)n (with an estimated number of hydroxyl groups n = 38–44) synthesized from pure fullerene by mixing a benzene solution of C60 with a NaOH aqueous solution in the presence of a catalyst was studied with 1H and 13C solid-state nuclear magnetic resonance. Possible features of the structure of a molecule shell were revealed from 1H NMR data. The 13C spectrum showed a peak splitting with an increase in temperature, which is probably due to fullerenol isomers.
相似文献30.