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1.
M. Laura Dántola 《Tetrahedron》2008,64(37):8692-8699
In vitiligo, a common skin disorder that produces white patches of depigmentation, 7,8-dihydropterins accumulate in the presence of high concentration of H2O2. In this work, we present a study of the reaction between 7,8-dihydropterins and H2O2. The rate of the reaction, as well as the products formed, strongly depend on the chemical structure of the substituents. Electron-donor groups as substituents are the most reactive derivatives and undergo oxidation of the pterin moiety. The corresponding bimolecular rate constants at 37 °C in neutral aqueous solutions are reported. The biological implications of the results obtained are also discussed. 相似文献
2.
The second-order rate constants at three different temperatures have been determined for nucleophilic substitution reactions
of ethyl bromoacetate with various substituted aliphatic carboxylate ions (XCH2COO−) in 90% acetone-10% water (v/v) mixture and the activation parameters have been evaluated. The rate data have been analysed
in terms of electronic and steric effects by using various single and multi-parameterequations. Analysis of the results shows
that localized and steric effects are more important than the delocalized effect. The regression coefficient of the inductive
component is negative indicating that inductively electron-releasing substituents accelerate the reaction and electron-withdrawing
substituents retard it. The steric component corresponds to the reaction being subject to steric acceleration by the substituents.
The per cent steric effect has been calculated. The Br?nsted type correlation is fair, and theβ
N value has been determined. 相似文献
3.
The inductive and resonance effects of silicon-, germanium-, tin-, and lead-containing and some organic substituents on the
HOMO energies (E
HOMO) for 43 monosubstituted andp-disubstituted benzene derivatives were analyzed in the Koopmans approximation. A linear dependence between the perturbation
energy δE and the resonanceσ
R
+
parameters of the substituents was established. The Koopmans approximation is a rough approximation for the compounds studied,
since to provide for its rigorous fulfilment, the δE values must depend on the σ
R
0
parameters of the substituents. The principal regularities of increasing the σ,π-conjugation between the organoelement substituents
and the π-system caused by a positive charge on the benzene ring were established.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 70–75, January 1997. 相似文献
4.
N. A. Buina G. M. Husnullina I. A. Vuretdinov A. E. Arbuzov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract This communication deals with a simple method for preparation of X-phosphorylated sugars by the reaction of trivalent phosphorus derivatives with 1-α,β-azides of 2,3,4,5-tetraacetylated and 2,3,4,6-tetra(trimethyl)silylated glycose. It has been established that ohosphimine derivatives, obtained as a result of the Staudinger reaction, can be easily hydrolyzed to give derivatives of acetylated glucosaminphosphoric acids. It has been discovered that susceptibility to hydrolysis depends on the phosphorus suhstituents. When using esters of trivalent phosphorus the rate of hydrolysis for compounds with alkyl substituents decreases in order C3H7 > C2H5O >> CH3O This can probably be explained by the electronic and steric influence of the alkyl groups. 相似文献
5.
The rearrangement of 3-(N-acylamino)-substituted caran-4-one oximes in the presence of sulfuric acid affords 2-oxa-4-azabicyclo[3.3.1]non-3-en-6-one
derivatives. 3-Aminocaran-4-one oximes, in which the amino group contains such substituents as acetyl, propionyl, chloroacetyl,
1-adamantylcarbonyl, benzoyl, 2-thienylcarbonyl, or anilinocarbonyl, undergo this reaction. N-Acyl derivatives of higher fatty (heptanoic and nonadecanoic) acids do not undergo this reaction. The reaction with D2SO4 leads to the replacement of all hydrogen atoms of the isopropyl group by deuterium. The mechanism of this rearrangement is
proposed.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1837–1844, August, 2005. 相似文献
6.
The synthesis of novel 5-(phenylamino)-, 5-(benzylamino)-, and 5-(phenethylamino) derivatives of 1-benzyluracil-containing
different substituents in the aromatic nucleus has been carried out. Using the Hilbert-Johnson reaction it was found that
N(1)-monosubstitution can be achieved via alkylation of trimethylsilyl derivatives of 5-(arylamino)uracils using benzyl bromide.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 887–892, June, 2005. 相似文献
7.
J. Báscuas L. García-Río J. R. Leis M. Méndez-Pérez 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):603-606
A kinetic study was carried out on the solvolysis of ortho benzoyl chlorides in the presence of α-, β- and γ-Cyclodextrin (CD). The solvolysis mechanism of benzoyl chlorides is sensitive
to the substituents, and to the solvent in which the reaction takes place. In water, the behaviour exhibited by benzoyl chlorides
which have electron-attracting groups, is consistent with an associative mechanism whilst electron-donating substituents induce
a dissociative mechanism. The results obtained in the presence of CD show a decrease in the observed rate constant, k
obs, as the CD concentration increases. This behaviour can be explained if these substrates undergo solvolysis through a dissociative
path in the presence of α-, β- and γ-CD. 相似文献
8.
A. Ebrahimi S. M. Habibi Khorassani H. Delarami H. Esmaeeli 《Journal of computer-aided molecular design》2010,24(5):409-416
The substituent effects on the geometrical parameters and the individual hydrogen bond (HB) energies of base pairs such as
X–adenine–thymine (X–A–T), X–thymine–adenine (X–T–A), X–guanine–cytosine (X–G–C), and X–cytosine–guanine (X–C–G) have been studied by the quantum mechanical calculations at the B3LYP and MP2 levels with the 6–311++G(d,p) basis set. The
electron withdrawing (EW) substituents (F and NO2) increase the total binding energy (ΔE) of X–G–C derivatives and the electron donating (ED) substituent (CH3) decreases it when they are introduced in the 8 and 9 positions of G. The effects of substituents are reversed when they are located in the 1, 5, and 6 positions of C, with exception of CH3 in the 1 position and F in the 5 position, which in both cases the ΔE value decreases negligibly small. With minor exceptions (X=8–CH3, 8–F, and 9–NO2), both ED and EW substituents increase slightly the ΔE values of X–A–T derivatives. The individual HB energies (∆E
HBs) have been estimated using electron densities that calculated at the hydrogen bond critical points (HBCPs) by the atoms
in molecules (AIM) method. Most of changes of individual HBs are in consistent with the ED/EW nature of substituents and the
role of atoms entered H-bonding. The remarkable change is observed for NO2 substituted derivative in each case. 相似文献
9.
R. V. Andreev G. I. Borodkin V. G. Shubin 《Russian Journal of Organic Chemistry》2011,47(11):1703-1709
With the use of Hartree-Fock and DFT methods we demonstrated that for the benzene derivatives with the substituents Me, Et,
Pr, i-Pr, t-Bu, CF3, F, and Cl π-complexes are more favorable by energy, whereas with the substituents CHO, MeCO, PhCO, CN, NO, and NO2
n-complexes are more feasible. The affi nity of aromatic compounds to the nitrosonium-cation (ANO+) at the formation of the π-complexes grows with the growing donor character of the substituents in the ring and with their
number. The best agreement between the calculated and experimental ANO+ values for benzene was obtained with the use of RI-MP2/L1 method. 相似文献
10.
I. A. Opeida M. A. Kompanets O. V. Kushch A. G. Matvienko 《Theoretical and Experimental Chemistry》2010,46(2):107-111
The kinetics of the decomposition of the phthalimid-N-oxyl radical (PINO) in acetic acid has been studied. The rate constants
of the addition of the radical to T bonds of molecules of vinyl compounds – styrene, methyl methacrylate, acrylonitrile, and
methyl acrylate – have been measured. It was shown that electron-donor substituents in the monomer molecule increase, while
electron-acceptor substituents decrease the rate of addition. The reactivity of monomers in the elementary step of addition
of the PINO radical decreases in the order CH2=C(CH3)C6H5 > CH2=CHC6H5 > CH2=C(CH3)COOCH3 > CH2=CHCOOCH3 > CH2=CHCN. 相似文献
11.
Ru(III) acts an efficient catalyst in the oxidation of substituted 4-oxo-4-arylbutanoic acids (4-oxo acids) by bromate in
sulfuric acid medium, giving the corresponding benzoic acids in quantitative yields. The reaction shows first-order dependence
in both [bromate] and [H2SO4], and a non-linear dependence on both [oxo acid] and [catalyst]. Changing solvent from H2O to D2O increases the rate. The rate is not affected by ionic strength but decreases with increase in dielectric constant of the
medium. Electron-releasing substituents in the phenyl ring of the substrate greatly accelerate the rate, whereas the retardation
by electron-withdrawing substituents, though perceptible, is small. The linear free-energy relationship is characterized by
smooth curves in Hammett plots of log k versus σ; however, linear plots are obtained with excellent correlation coefficients at all the studied temperatures, when
Brown’s σ+ values are used. The reaction constant is negative and decreases with increase in temperature. From the intersection of the
lines in the Hammett and Arrhenius plots, the isokinetic relationship is evaluated. A mechanism involving a cyclic oxidant–substrate–catalyst
ternary complex is proposed, in which both C–C bond-breaking and C–O bond formation are involved, and the oxidation state
of Ru(III) remains unchanged. A rate law explaining all the kinetic results has been derived and verified. The reaction is
an example of neighboring group participation in intramolecular catalysis and is potentially useful for the synthesis of substituted
benzoic acids. 相似文献
12.
The first vertical ionization potentialsl
1 of molecules RπX (X=Ph, H2C=CH, and HC≡C) depend on the joint influence of the inductive, resonance, and polarizability effects of substituents X, which
are characterized by parameters σ1, σR+, and σα, respectively. The mechanism of conjugation in radical cations formed upon ionization of RπX is changed as compared to neutral RπX molecules, while the substituent X becomes polarized. The conjugation and polarizability effects are strenthened in the
sequence Ph < H2C=CH <HC≡C as Rπ changes from Ph to H2C=CH and HC≡C. The σR+ parameters of Si-, Ge-, and Sn-containing substituents X are dependent on the type of Rπ but are connected by linear dependences in the series of benzene, ethylene, and acetylene derivatives.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1481–1486, August, 1998. 相似文献
13.
The kinetics and mechanism of the reactions of diarylthallium, trifluoroacetates with molecular iodine in dioxane solutions
have been studied. The reaction has the overall second order with the first order with respect to each reagent. The effect
of substituents in the aromatic ring on the rate constant of iodination is described by the equation logk
2ρσ+(ρ=-1.60, r=0.97). The reaction is catalyzed by the iodide ion. The activation enthalpies and entropies of iodination of diarylthallium
trifluoroacetates in dioxane and di(p-anisyl)thallium trifluoroacetate in various solvents have been calculated. The effect of solvents on the rate constant of
iodination of di(p-anisyl)thallium trifluoroacetate has been studied. The reaction mechanism is considered as an electrophilicS
EC process.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 451–455, March, 1999. 相似文献
14.
D. B. Berezin O. V. Shukhto M. S. Reshetyan 《Russian Journal of General Chemistry》2010,80(3):518-526
The reaction kinetics of the metal exchange Cd(II)-Cu(II) and Cd(II)-Zn(II) in the cadmium complexes (CdP) with porphyrin
ligands (H2P) differing by degree of stiffness (tetraphenylporphin, N-methyltetraphenylporphin, and tetraphenyltetrabenzoporphin) in the DMSO medium, was studied using spectrophotometric method.
The rate of metal exchange reaction depends on the nature of the non-planatrity of H2P in the structure of CdP complexes, as well as on the additional screening of the reaction center MN4 by the extra-ligands and substituents. The reduction of the coordinating ability of the anion X− in the structure of the solvate-salt of incoming metal M’X2(Solv)
n−2 in a series: acetylacetonate > acetate > chloride > nitrate favors the metal exchange. In the most studied cases the reaction
of CdP proceeds along a combined associative-dissociative mechanism. The order of the metal exchange reaction is found to
be depending on temperature indicating a change in the contributions of associative and combined routes. The “pure” associative
reaction mechanism in a medium of DMSO was for the first time found for the labile complex CdTPTBP with the saddle-type nonplanar
ligand. 相似文献
15.
《Tetrahedron》2004,60(23):4983-4987
A series of 6-alkynyl-2,4-diaminopyrimidine derivatives bearing various substituents at alkynyl moiety was prepared by the Sonogashira cross-coupling reaction of 2,4-diamino-6-iodopyrimidine using Pd(PPh3)2Cl2 as catalyst. The same reaction was applied to 2-amino-4,6-dichloropyrimidine. This compound on reaction with 1 equiv. of alkyne gave 6-alkynyl-2-amino-4-chloropyrimidine derivatives as main products, while reaction with three equivalents of alkyne afforded predominantly 4,6-bis-alkynyl-2-aminopyrimidines. Some of the resulting alkynyl pyrimidines showed considerable cytostatic activity. 相似文献
16.
N. N. Basargin E. R. Oskotskaya I. N. Senchakova Yu. G. Rozovskii 《Russian Journal of Inorganic Chemistry》2009,54(10):1619-1624
Physicochemical properties of new reagents, azo-substituted pyrocatechol derivatives and their tin(II) complexes, are studied.
The acid-base properties of the hydroxy groups (pK′i, pK″i), parameters of complex formation reactions (pH, temperature, time), and instability constants of the complexes formed (pK
i) are determined. Quantitative correlations between the dissociation constants (pK′a) of the functional analytical group, and the electronic Hammett constant σ for a substituent (pK′a-pH50 of the complex formation reaction), as well as between pK′a and instability constants of the complexes (pK
a), are established. The quantitative correlations established allow the prediction of the physicochemical properties of the
reagents and tin(II) complexes with new reagents of this class with the same functional analytical group (FAG) but other substituents. 相似文献
17.
Oxidation kinetics of benzaldehyde and some of its ortho- and para-monosubstituted derivatives have been studied using cetylpicolinium dichromates, a class of novel phase transfer oxidants, in dichloromethane medium. The rate of reaction is first order with respect to oxidant and fractional order with respect to the substrates. The Michaelis–Menten type oxidation was observed with respect to the substrates. Benzaldehydes are found to be oxidized to their corresponding acids. The mechanism of oxidation reaction has been suggested based on the solvent isotope effect, Hammett plot, and thermodynamic study. The solvent isotope effect (kCHCl3/kCDCl3 = 1.57) indicates the involvement of hydrogen exchange with the medium during oxidation reactions. A strong influence of specific solute–solvent interactions on the rate of the reaction is observed. Both the electron-withdrawing and electron-releasing substituents on the substrates accelerate the rate of reaction. 相似文献
18.
V. K. Mavrodiev I. I. Furlei Sh. Sultanov Yu. S. Nekrasov Yu. A. Belousov 《Russian Chemical Bulletin》1997,46(6):1113-1115
Negative ion mass spectra of cyclopentadienyltricarbonylmanganese and-rhenium derivatives RC5H4M(CO)3 (R=H, CN, COOH, COMe, COOMe, CH2OH, CHO; M=Mn, Re) were studied. The subsequent detachment of carbonyl groups is the main process of the fragmentation of
these compounds under the conditions of the resonance capture of electrons. On going fron the rhenium complexes to manganese
derivatives, the maxima of the yields of the ions [M-nCO]− (n=1–3) shift to the lower energy region indicating that the stability of the Re−CO bond is higher than that of Mn−CO. The average
lifetimes of the molecular negative ions relative to the autodetachment of an electron (τa) and to dissociation (τd) were measured. It was found that electron-accepting substituents increase the τa value and decrease τd.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1161–1164, June, 1997. 相似文献
19.
A. A. Shubin R. S. Mitchenko T. V. Bezbozhnaya A. N. Vdovichenko 《Russian Chemical Bulletin》2005,54(10):2456-2459
A procedure was developed for the synthesis of previously unknown β-chlorovinyl derivatives of PtIV chloride complexes by chloroplatination of terminal alkynes catalyzed by PtII chloride complexes. The reaction is highly stereoselective and gives only the products of trans-anti-addition of platinum and chlorine atoms. The regioselectivity of the catalytic reaction formally corresponds to Markovnikov’s
rule, e.g., in alkynes containing electron-donating substituents, platinum attacks the terminal carbon atom. The σ-vinyl derivatives
of PtIV chloride complexes were characterized by IR spectroscopy and 1H and 13C NMR spectroscopy.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2380–2384, October, 2005. 相似文献
20.
Ralf Smounig C. Oliver Kappe Curt Wentrup Gert Kollenz 《Monatshefte für Chemie / Chemical Monthly》2003,134(4):509-518
Summary. Several new lariat-crown ethers bearing either bridged bisdioxine or tetraoxaadamantane units as chiral substituents are
prepared by reacting the corresponding amino-crown ether derivatives with the dimeric α-oxoketene, the latter obtained by
flash vacuum pyrolysis of a furan-2,3-dione precursor. Complexation properties towards differently charged metal ions are
investigated by 1H NMR titration to obtain complexation constants (K
c
-values for potassium/sodium rhodanides: 480–1100 mol dm−3), as well as extraction experiments to explore the metal ion transportation abilities of the new lariat crown derivatives.
In particular, a significantly increased ability to transport metal ions from water into chloroform was found with spherical
tetraoxaadamantyl derivatives when compared with the free amino-benzocrown ethers.
Corresponding author. E-mail: kollenz@kfunigraz.ac.at
Received July 5, 2002; accepted July 19, 2002 相似文献