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1.
Existing experimental data on positional selectivity in electrophilic substitution reactions of π-excessive heterocycles are classified. These data are discussed basing on the results of the authors' quantum-chemical calculations [RHF/6-31G(d), MP2/6-31G(d), and B3LYP/6-31G(d)] of the σ-complexes formed during attack of electrophiles such as H+, Me+, Me3Si+, Br+, NO2 +, MeCO+, and SO3 at the α- and β-positions of furan, thiophene, selenophene, pyrrole and its N-substituted derivatives, N-R-pyrroles (R = Me, t-Bu, SiMe3, Si(i-Pr)3, C6H4(p-NO2), SO2Ph, CHO, CO2Me), and the corresponding α- and β-substituted electrophilic substitution products. The differences in energies of the α-and β-isomers of the σ-complexes characterize the preferred direction of electrophilic attack, while the differences in the energies of the isomeric products make it possible to assess the energy preference of one of them. Analysis of the obtained data demonstrates the effects of the studied heterocycles' structure, the nature of the electrophile, and the thermal and steric factors on the positional selectivity (α/β ratio) in electrophilic substitution reactions of π-excessive five-membered heteroaromatic compounds.  相似文献   

2.
The Production of NO+- and NO2+- intermediate complexes formed by nitration of aromatic compounds by means of ion-molecule reactions in the gas phase were attempted. The experiments were performed with benzene, pyridine and toluene respectively and with NO+, NO2+ CH3NO2+ and CH2ONO2+ als ‘nitration’ ions. Aromatic NO+-as well as NO2+-complexes were observed with varying reaction cross-sections. The determined lower limit of bonding energy of 16 kcal/mol for to be σ-complexes. This fact was regarded as additional support for the analogy between electrophilic substitution reactions and ion-molecule reactions.  相似文献   

3.
D. Heidrich  M. Grimmer  B. Sommer 《Tetrahedron》1976,32(16):2027-2032
The [H,CH3]-σ-complexes of toluene and the three isomeric xylenes formed by electrophilic H+-attack on substituted positions or by H-shifts from the isomeric σ-complexes are studied by the CNDO/2-FK MO method. These complexes (ipso-adducts) occur as minima on the energy surfaces in agreement with the results for [H,H]-σ-complexes. Their geometrical structure and tendencies of formation are presented and a comparison with experimental results in solution is given. Suggestions for different stabilization of the isomeric σ-complexes of substituted benzene by solvent molecules are found.  相似文献   

4.
The temperature dependence of the ratios of the rate constants k(C5H10)/k(C6H12) and k(C6H12)/k(C6D12) for the reaction of the cycloalkanes C5H10, C6H12, and C6D12 with OH+ cations in the system (NH4)2S2O8 (0.1 mol/kg)-H2SO4 (94.4 mass %) in the 6–50 °C range has been studied. The activation energies found E(C6H12) − E(C5H10) = − 5.3 ± 0.3 and E(C6D12) − E(C6H12) = 7.9 ± 0.7 (kJ/mol) permits the comparison of OH+ to a group of reagents (NO+2, Pd2+, HSO+3) which interact with the C-H bond via an electrophilic substitution mechanism. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 6, pp. 354–358, November–December, 2008.  相似文献   

5.
Adenine complexes with nitrosonium ion have been studied by the RI-MP2/L1 quantum-chemical method. Addition of nitrosonium ion to adenine tautomers produces a set of nitrosonium complexes of different types (1??C3??). n-Complexes involving NO+ coordination to nitrogen atoms are more energetically favorable than ??-complexes. The global minimum on the potential energy surface is occupied by the complex of 7H-adenine tautomer with nitrosonium ion coordinated at the N3 atom.  相似文献   

6.
The hydrolysis of PhN+Me2CH2SO3? (2) is so slow that a proposed mechanism of hydrolysis of PhNHCH2SO3? Na+ involving SN2 attack of H2O on PhN2+CH2SO3? may be discounted.  相似文献   

7.
The reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine (1) with conc. H2SO4 affords 4-nitropyrocatechol and that with conc. sulfonic acids (RSO3H where R = Me, CF3) affords 2-hydroxy-5-nitrophenyl-R-sulfonates in yields of 80?C85%. These reactions are assumed to proceed through an intermediate (phenoxy)oxodiazonium ion [NO2C6H4O-N=N=O]+, which eliminates the N2O molecule to form the aryloxenium ion [NO2C6H4O]+. The latter reacts with acid anions at the ortho-carbon atom of the phenyl ring. The thermodynamical parameters of the elementary reactions resulting in the formation of the (phenoxy)oxodiazonium ion [NO2C6H4O-N=N=O]+ and aryloxenium ion [NO2C6H4O]+ were calculated in the B3LYP/6?311+G(d) study of the combined molecular system (nitrohydroxylamine 1 + [H3SO4]+). The reaction of nitrohydroxylamine 1 with aqueous solutions of strong acids (??70% H2SO4, CF3SO3H) affords mainly 4-nitrophenol. It appears that the mechanism of this reaction does not involve the formation of the aryloxenium ion.  相似文献   

8.
Structures and enthalpies of formation have been calculated, in the MNDO approximation using UHF wave-functions for open shell species, for tetramethyldiphosphine, Me4P2, and the major ions in its mass spectrum: Me4P2+, Me3P2H+, Me3P2+, Me2P2H2+ (3 forms), Me2P2H+ (3 forms), Me2P2+ (3 forms), MePPCH2+ (3 forms), MeP2+ and MePCH2+, together with all the corresponding neutral fragments. Appearance potentials are calculated for all the ions, and possible fragmentation pathways deduced.  相似文献   

9.
The solid‐liquid equilibria in the quinary system Na+, K+//Cl?, SO2?4, B4O2?7‐H2O at 298 K had been studied experimentally using the method of isothermal solution saturation. Solubilities and densities of the solution of the quinary system were measured experimentally. Based on the experimental data, the dry‐salt phase diagram and water content diagram of the quinary system were constructed, respectively. In the equilibrium diagram of the quinary system Na+, K+//Cl?, SO2?4, B4O2?7‐H2O at 298 K, there are five invariant points F1, F2, F3, F4 and F5; eleven univariant curves E1F1, E2F2, E3F3, E4F5, E5F2, E6F4, E7F5, F1F4, F2F4 F1F3 and F3F5, and seven fields of crystallization saturated with Na2B4O7 corresponding to Na2SO4, Na2SO4·10H2O, Na2SO4·3K2SO4 (Gla), K2SO4, K2B4O7·4H2O, NaCl and KCl. The experimental results show that Na2SO4·3K2SO4 (Gla), K2SO4 and K2B4O7·4H2O have bigger crystallization fields than other salts in the quinary system Na+, K+//Cl?, SO2?4, B4O2?7‐H2O at 298 K.  相似文献   

10.
Regioselectivity of the reactions of lithium vinyl- and isopropenylcyclopentadienides C5H4C(R)=CH2 -Li+(R = H, Me) and lithium tetramethylvinylcyclopentadienide C5Me4CH=CH2 -Li+ with various electrophilic agents (Me3SiCl, Me3SnCl, Et2PCl, 2-chloro-1, 3-dioxaphospholane, and MeI) was studied. Two new monocyclopentadienyl zirconium complexes, [C5H4C(Me) = CH2]ZrCl3 · 2THF and [C5Me4CH=CH2]ZrCl3 · 2THF, were synthesized. Their crystal structures were established by X-ray diffraction. The results of quantum chemical calculations for the C5H4C(R) = CH2 - (R = H, Me) and C5Me4CH=CH2 - anions by the DFT method (RMPW1PW91) with the 6-311+G(d, p) split valence basis set are in good agreement with experimental data on the regioselectivity of their reactions with electrophilic agents.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 390–399, February, 2005.  相似文献   

11.
Peculiarities of interaction of H+, Me3C+, and Me3Si+ ions with functional groups of molecules in the gas phase have been studied. Proton tends to form chelates with virtually all of the functional groups studied, whereas Me3Si+ ions exhibit no capacity for chelation. Using isomeric xylenes as examples it was shown that Me3Si+ ions (unlike Me3C+ ions) experience virtually no steric hindrance when they react with nucleophilic centers. Effects of functional groups present in molecules of nitriles on the generation of [M+Me3C]+ adducts in the gas phase and the Ritter reaction in solution were estimated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1767–1773, September, 1995.This work was carried out with financial support from the International Science Foundation (Grant MA7 000) and the Russian Foundation for Basic Research (Project No. 93-03-18033).  相似文献   

12.
5-C5Me5)(CO)2(PPh3)MoCHO (2) one of the few isolated neutral metal formyls, reacts with the electrophilic reagents (CF3COOH and CH3SO3F without disproportionation to give the secondary carbene complexes [(η5-C5Me5)(CO)2(PPh3)Mo(CHOE)]+ X (E = H, X = CF3COO (4); E = Me, X = PF6 (5)).  相似文献   

13.
N,N′‐dioxide ligands such as 2, 2′‐bipyridine‐N,N‐dioxide (BPDO‐I) and 4, 4′‐bipyridine‐N,N‐dioxide (BPDO‐II) were used to trap the hydrated dimethyltin cations under controlled hydrolysis. The use of the chelating ligand BPDO‐I leads to the isolation of the discrete monocation [Me2Sn(BPDO‐I)(OH2)(NO3)]+[NO3] ( 2 ), whereas the linear ligand BPDO‐II directs the construction of cationic polymers, [{Me2Sn(OH2)2(μ‐BPDO‐II)}2+{NO3}2 · 2H2O]n ( 3· 2H2O) and [{Me2Sn(μ‐OH)(BPDO‐II)}22+{NO3}2 · H2O]n ( 4· H2O) under different reaction conditions.  相似文献   

14.
The rate constants and modes of reaction of NO2+ and C2H5ONO2NO2+ with aromatic compounds and alkanes have been determined in a pulsed ion cyclotron resonance mass spectrometer. Both ions undergo competing charge transfer and substitution reactions (NO2+ + M → MO+ + NO; C2H5ONO2NO2+ + M → MNO2+ + C2H5ONO2) with aromatic molecules. In both cases, the probability that a collision results in charge transfer increases with increasing exothermicity of that process. The C2H5ONO2NO2+ ion does not undergo charge transfer with molecules having an ionization potential greater than about 212 kcal/mol (9.2 eV); this observation leads to an estimate of 13 kcal/mol for the binding energy between NO2+ and C2H5ONO2. The importance of the substitution reaction depends on the number of substituents on the aromatic ring and the molecular structure, and, in the case of C2H5ONO2NO2+ ions, on the energetics of the competing charge transfer process. Both NO2+ and C2H5ONO2NO2+ undergo hydride transfer reactions with alkanes. For both these ions, k(hydride transfer)/k (collision) increases with increasing exothermicity of reaction, but in both cases the rate constants of reaction are unusually low when compared with other hydride transfer reactions of comparable exothermicity which have been reported in the literature. This is interpreted as evidence that the attack on the alkane preferentially involves the nitrogen atom (where the charge is localized) rather than one of the oxygen atoms of NO2+.  相似文献   

15.
The mass spectra of a series of β-ketosilanes, p-Y? C6H4Me2SiCH2C(O)Me and their isomeric silyl enol ethers, p-Y? C6H4Me2SiOC(CH3)?CH2, where Y = H, Me, MeO, Cl, F and CF3, have been recorded. The fragmentation patterns for the β-ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [M? Me·]+, [M? C6H4Y·]+, [M? Me2SiO]+˙, [M? C3H4]+˙, [M? HC?CCF3]+˙, [Me2SiOH]+˙ and [C3H6O]+˙ Apparently, upon electron bombardment the β-ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [M? Me2SiO]+˙ and [Me2SiOH]+˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.  相似文献   

16.
Methods for the synthesis of [1,2,5]oxadiazolo[3,4-c]cinnoline 5-oxides, which include the reaction of 3-nitramino-4-(R-phenyl)furazans or their O-methyl derivatives with electrophilic agents, have been developed. Unsubstituted [1,2,5]oxadiazolo[3,4-c]cinnoline 5-oxide was synthesized from 3-nitramino-4-phenylfurazan upon the action of phosphorus anhydride or oleum, as well as from O-methyl derivative of 3-nitramino-4-phenylfurazan upon the action of H2SO4, MeSO3H, CF3CO2H and BF3·Et2O, while 6-, 7-, 8-, and 9-nitro-substituted [1,2,5]oxadiazolo[3,4-c]cinnoline 5-oxides — from the corresponding 3-nitramino-4-(nitrophenyl)furazans upon the action of the H2SO4-HNO3 nitrating mixture. A suggestion has been made that an oxodiazonium ion is formed in these reactions from nitramines or their O-methyl derivatives upon the action of electrophilic agents, which is further involved into the intra-molecular reaction of electrophilic aromatic substitution (S EAr) with the aryl group. The structure of [1,2,5]oxadiazolo[3,4-c]cinnoline 5-N-oxides was confirmed by 1H, 13C, and 14N NMR spectra. Theoretical studies by the B3LYP/6-311G(d,p) method of combined molecular system (O-methylated 3-nitramino-4-phenylfurazan + [H3SO4]+) resulted in calculation of thermodynamic parameters of the sequence of cascade elementary reactions leading to the formation of [1,2,5]oxadiazolo[3,4-c]cinnoline 5-oxide.  相似文献   

17.
The reaction of NO+ with o-toluidinechromium tricarbonyl has been studied. Diazotization (attack on N) competes with NO+ attack on the metal and decarbonylation. The Cr(CO)3-complexed diazonium ion is unstable and dediazoniates even at low temperature. The dediazoniation mechanism is predominantly homolytic. Competing heterolytic dediazoniation is observed in highly ionizing, low nucleophilicity solvents such as CF3SO3H (TfOH), FSO3H and CF3CH2OH (TFE).  相似文献   

18.
Lukasz Kraszkiewicz 《Tetrahedron》2004,60(41):9113-9119
Two ‘model’ deactivated arenes, benzoic acid and nitrobenzene, were effectively monoiodinated within 1 h at 25-30 °C, with strongly electrophilic I+ reagents, prior prepared from diiodine and various oxidants (CrO3, KMnO4, active MnO2, HIO3, NaIO3, or NaIO4) in 90% (v/v) concd sulfuric acid (ca. 75 mol% H2SO4). Next, an I2/NaIO3/90% (v/v) concd H2SO4 exemplary system was used to effectively mono- or diiodinate a number of deactivated arenes. All former papers dealing with the direct iodination of deactivated arenes are briefly reviewed.  相似文献   

19.
A comprehensive thermodynamic model based on the electrolyte NRTL (eNRTL) activity coefficient equation is developed for the NaCl + H2O binary, the Na2SO4 + H2O binary and the NaCl + Na2SO4 + H2O ternary. The NRTL binary parameters for pairs H2O-(Na+, Cl) and H2O-(Na+, SO42−), and the aqueous phase infinite dilution heat capacity parameters for ions Cl and SO42− are regressed from fitting experimental data on mean ionic activity coefficient, heat capacity, liquid enthalpy and dissolution enthalpy for the NaCl + H2O binary and the Na2SO4 + H2O binary with electrolyte concentrations up to saturation and temperature up to 473.15 K. The Gibbs energy of formation, enthalpy of formation and heat capacity parameters for solids NaCl(s), NaCl·2H2O(s), Na2SO4(s) and Na2SO4·10H2O(s) are obtained by fitting experimental data on solubilities of NaCl and Na2SO4 in water. The NRTL binary parameters for the (Na+, Cl)-(Na+, SO42−) pair are regressed from fitting experimental data on dissolution enthalpies and solubilities for the NaCl + Na2SO4 + H2O ternary.  相似文献   

20.
Summary Rate constants for bimolecular reactions in the gas phase, under diffusion controlled conditions, can easily be determined by the reversed-flow gas chromatography (RF-GC) technique. The analysis of the diffusion band by means of a simple PC programme gives directly an apparent, second-order rate constant for gaseous reactions. By varying the amounts of the reactants, one can calculate the true order of the reaction and the true non-first-order rate constant of gaseous reactions. The calibration problem of the analytical techniques in non-first-order reaction kinetics is absent as are other disadvantages connected with carrier gas flow, peak shape and their instrumental spreading. The method can be used for atmospheric reactions and was applied in the gaseous reaction systems: SO2+NO2, SO2+Br2, C6H6+NO2, C6H5CH3+NO2 and C3H6+NO2 with various concentrations of reactants in nitrogen. The effect of the NO2 concentration on the apparent second-order rate constant of C2H4+NO2 at 333.2 K was also studied. Finally, the effect of sun light pre-irradiation of C2H2+NO2 in nitrogen was investigated.  相似文献   

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