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Electron-withdrawing Substituents (electron-withdrawing + substituent)
Selected AbstractsSuperelectrophilic Activation of N -Substituted Isatins: Implications for Polymer Synthesis, a Theoretical StudyMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2009Daniel Romero Nieto Abstract The stability and reactivity of mono- and multi-protonatred N -substituted isatin derivatives were studied at PBE0/aug-cc-pvtz//PBE0/6-31+G** level of theory in triflic acid (TFSA) solution. Calculations showed that the monocationic intermediates are the principal reactive species in the reaction of hydroxyalkylation of isatin derivatives in TFSA media. Electron-withdrawing substituents on the nitrogen atom increase the reactivity of isatin-containing electrophiles towards aromatic hydrocarbons, in accordance with their expected electronic influence. Steric factors also play an important role in the reactivity of isatin-containing electrophiles, especially in the second reaction step, due to their more sterically hindered reactive center. [source] Synthesis and Characterization of Radical Cations Derived from Mono- and Biferrocenyl-Substituted 2-Aza-1,3-butadienes: A Study of the Influence of an Asymmetric and Oxidizable Bridge on Intramolecular Electron TransferEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005Vega Lloveras Abstract The synthesis and study of structural and electronic properties of mono-ferrocenyl ,-conjugated complexes 5a,d, whose electronic characteristics have been systematically varied by introducing an electron-donating or electron-withdrawing substituent either at the 1-position or at the 4-position of the 2-aza-1,3-butadiene moiety linked to the ferrocenyl unit, are presented. The structural and electronic properties of the homobimetallic complex 5f, with two ferrocene units linked through the asymmetric and oxidizable 2-aza-1,3-butadiene bridge, is also reported. The crystal structures of complexes 5b, 5d, and 5f show a large degree of conjugation in this family of compounds. Complexes 5 show a rich electrochemical behavior due both to the oxidation of ferrocenyl units and the 2-aza-1,3-butadiene bridge, as revealed by cyclic voltammetry. Radical cations 5+· were prepared from 5 by coulometric oxidations following their generation by absorption spectroscopy. The electronic properties of all reported neutral and oxidized ,-conjugated complexes have been investigated by means of UV/Vis,near-IR, EPR and 57Fe Mössbauer spectroscopy. The detailed study of mono-oxidized species 5a+·,5f+· has permitted the determination of the influence of an asymmetric bridge with an electroactive character on the intramolecular electron transfer (IET) phenomenon, thus demonstrating that the 2-aza-1,3-butadiene bridge promotes the IET between the two metallic units of 5f+· through two different pathways. The experimental data and conclusions are supported by DFT computations (B3LYP/3-21G*) and time-dependent DFT methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Syntheses and structures of sulfilimine, sulfone diimine, and sulfoximine derivatives of a monocyclic thiophene, 3,4-di- tert -butylthiopheneHETEROATOM CHEMISTRY, Issue 5 2001Juzo Nakayama The reaction of 3,4-di-tert-butylthiophene (6a) with N-[(p-tolylsulfonyl)imino]-phenyliodinane (TsN=IPh) in the presence of Cu(MeCN)4PF6 in MeCN at room temperature provided 3,4-di-tert-butyl-1-[(p-tolylsulfonyl)imino]-1,1-dihydrothiophene (3b),3,4-di-tert-butyl-1,1-bis[(p-tolylsulfonyl)imino]-1,1-dihydrothiophene (5a), and 1-(p-tolylsulfonyl)-3,4-di-tert-butylpyrrole (7a) as the principal products. The use of 20 molar amounts of 6a gave 3b in an increased yield of 61%. Treatment of 3,4-di-tert-butylthiophene 1-oxide (1a) with (CF3CO)2O or (CF3SO2)2O, followed by reactions with RSO2NH2, ROC(=O)NH2, or RCONH2, furnished a series of S-imino derivatives (3b,c,e,h) of 6a, which carry an electron-withdrawing substituent on the imino nitrogen atom. Treatment of the S-imino derivative 3f (substituent on the nitrogen atom = COBu) with CF3CO2H gave an aminosulfonium salt (13), whose deprotonation led to the parent N-unsubstituted 1-imide derivative (3n). Treatment of 2,4-di-tert-butylthiophene 1-oxide (1b) with TsN=IPh in the presence of Cu(MeCN)4PF6 in MeCN at room temperature provided 2,4-di-tert-butyl-1-[(p-toluenesulfonyl)imino]-1,1-dihydrothiophene 1-oxide (4e) in 81% yield. Hydrolysis of 4e by concentrated H2SO4 at room temperature furnished 2,4-di-tert-butyl-1-imino-1,1-dihydrothiophene 1-oxide (4f) in 89% yield. A pair of enantiomers of 4f were separated by high-performance liquid chromatography (HPLC) on a chiral column, and their absolute configurations were determined by an X-ray crystallographic analysis. Structures of sulfilimine, sulfone diimine, and sulfoximine derivatives of monocyclic thiophenes, obtained in these ways, are discussed based on spectroscopies (IR and 1H and 13C NMR) and X-ray crystallographic analyses. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:333,348, 2001 [source] Kinetic and mechanistic investigation into the influence of chelate substituents on the substitution reactions of platinum(II) terpyridine complexesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2008Deogratius Jaganyi The substitution kinetics of the complexes [Pt{4,-(o -CH3 -Ph)-terpy} Cl]SbF6 (CH3PhPtCl(Sb)), [Pt{4,-(o -CH3 -Ph)-terpy}Cl]CF3SO3 (CH3PhPtCl(CF)), [Pt(4,-Ph-terpy)Cl]SbF6 (PhPtCl), [Pt(terpy)Cl]Cl·2H2O (PtCl), [Pt{4,-(o -Cl-Ph)-terpy}Cl]SbF6 (ClPhPtCl), and [Pt{4,-(o -CF3 -Ph)-terpy}Cl]SbF6 (CF3PhPtCl), where terpy is 2,2,:6,,2,-terpyridine, with the nucleophiles thiourea (TU), N,N,-dimethylthiourea (DMTU), and N,N,N,,N,-tetramethylthiourea (TMTU) were investigated in methanol as a solvent. The substitution reactions of the chloride displacement from the metal complexes by the nucleophiles were investigated as a function of nucleophile concentration and temperature under pseudo-first-order conditions using the stopped-flow technique. The reactions followed the simple rate law kobs = k2[Nu]. The results indicate that the introduction of substituents in the ortho position of the phenyl group on the ancillary ring of the terpy unit does influence the extent of ,-backbonding in the terpy ring. This controls the electrophilicity of the platinum center, which in turn controls the lability of the chloro-leaving group. The strength of the electron-donating or -withdrawing ability of the substituents correlates with the reactivity of the complexes. Electron-donating substituents decrease the rate of substitution, whereas electron-withdrawing substituents increase the rate of substitution. This was supported by DFT calculations at the B3LYP/LACVP+** level of theory, which showed that most of the electron density of the HOMO is concentrated on the phenyl ligand rather than on the metal center in the case of the strongest electron-withdrawing substituent in CF3PhPtCl. The opposite was found to be true with the strongest electron-donating substituent in CH3PhPtCl. Thiourea was found to be the best nucleophile with N,N,N,,N,-tetramethylthiourea being the weakest due to steric effects. The temperature dependence studies support an associative mode of activation. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 808,818, 2008 [source] Substituent effect on electron affinity, gas-phase basicity, and structure of monosubstituted propargyl radicals and their anions: a theoretical studyJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2010Gab-Yong Lee Abstract The substituent effect of electron-withdrawing groups on electron affinity and gas-phase basicity has been investigated for substituted propargyl radicals and their corresponding anions. It is shown that when a hydrogen of the , -CH2 group or acetylenic CH in the propargyl system is substituted by an electron-withdrawing substituent, electron affinity increases, whereas gas-phase basicity decreases. The calculated electron affinities are 0.95,eV (CHCCH2,), 1.15,eV (CHCCHF,), 1.38,eV (CHCCHCl,), 1.48,eV (CHCCHBr,) for the isomers with terminal CH and 1.66,eV (CFCCH2,), 1.70,eV (CClCCH2,), 1.86,eV (CBrCCH2,) for the isomers with terminal CX at B3LYP level. The calculated gas-phase basicities for their anions are 378.4,kcal/mol (CHCCH2:,), 371.6,kcal/mol (CHCCHF:,), 365.1,kcal/mol (CHCCHCl:,), 363.5,kcal/mol (CHCCHBr:,) for the isomers with terminal CH and 362.6,kcal/mol (CFCCH2:,), 360.4,kcal/mol (CClCCH2:,), 356.3,kcal/mol (CBrCCH2:,) for the isomers with terminal CX at B3LYP level. It is concluded that the larger the magnitude of electron-withdrawing, the greater is the electron affinity of radical and the smaller is the gas-phase basicity of its anion. This tendency of the electron affinities and gas-phase bacisities is greater in isomers with the terminal CX than isomers with the terminal CH. Copyright © 2009 John Wiley & Sons, Ltd. [source] Luminescent chiral organoboron 8-aminoquinolate-coordination polymersAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2010Yuichiro Tokoro Abstract We have successfully synthesized optically active organoboron aminoquinolate-based coordination polymers bearing the chiral side chain derived from L -alanine, and studied their optical behavior by UV,vis and photoluminescence spectroscopies. Higher absolute quantum yields (,F) of the obtained polymers, measured by integrating sphere method, were observed with electron-withdrawing substituent (,F = 0.80) than with electron-donating substituent (,F = 0.52). The circular dichroism (CD) study in the mixed solvents of CHCl3 and DMF showed that the secondary structures of the obtained polymers were stabilized by hydrogen-bonding interaction in the side chain. From concentration dependence on the CD spectra, the chirality of the obtained polymers originated from the nature of one molecule. Copyright © 2009 John Wiley & Sons, Ltd. [source] Metal-Controlled Anion-Binding Tendencies of the Thiourea Unit of ThiosemicarbazonesCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2008Valeria Amendola Dr. Abstract The terdentate ligand 3 (LH, 2-formylpyridine 4-thiosemicarbazone) forms with FeII and NiII 2:1 complexes of octahedral geometry of formula [MII(LH)2]2+. X-ray diffraction studies have shown that in both complexes the thiourea moieties of the coordinated thiosemicarbazones are exposed to the outside and are prone to establish hydrogen-bonding bifurcate interactions with oxoanions. However, spectrophotometric studies in CHCl3 solution have shown that only the poorly basic NO3, ion is able to form authentic hydrogen-bond complexes with thiourea subunits, whereas all the other investigated anions (CH3COO,, NO2,, F,) induce deprotonation of the N-H fragment. The extreme enhancement of the thiourea acidity is based on the coordinative interaction of the sulphur atom with the metal, which stabilises the thiolate form, and it is much higher than that exerted by any other covalently linked electron-withdrawing substituent, for example, NO2. [source] Fine-Tuning Ligands for Catalysis Using Supramolecular StrategiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2007Vincent F. Slagt Abstract Coordinative bonds have been used to prepare supramolecular ligands leading to well-defined catalysts formed by assembly. The construction of these ligands is based on selective metal,ligand interactions between nitrogen donor atoms of phosphorus-nitrogen building blocks and various zinc(II) porphyrins. The major advantage of this supramolecular approach of catalyst preparation is the simplification of ligand variation enabling straightforward modification of steric, electronic and chiral properties of the supramolecular ligand. A large number of new ligands becomes accessible by this modular variation of the building blocks. The ligand assembly based on pyridyl phosphites and zinc(II) porphyrin with electron-withdrawing substituents led to a twelve-fold increase in activity and an increase in enantioselectivity from 17 to 50,% in the rhodium-catalyzed hydrogenation of dimethyl itaconate. The first examples of assemblies based on non-chiral ligands and chiral zinc(II) porphyrin template molecules show, as proof of principle, an enantiomeric excess up to 18,% in the asymmetric palladium-catalyzed allylic alkylation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Effect of Substitution on the Change of Refractive Index in Dithienylethenes: An Ellipsometric Study,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2004C. Bertarelli Abstract An ellipsometric study was carried out in order to investigate the photoinduced change of the refractive index (,n) of a series of diarylethenes across the entire spectral range 260,1700,nm. This technique allowed examination of the influence of the resonance conditions on the refractive index. Changing the chemical design of diarylethenes by introducing electron-donating or electron-withdrawing substituents in 5,5,-positions of thiophyene allowed derivation of some correlations between chemical structure and ,n. A strong donor substituent directly linked to the 5,5,-position of the diarylethene moiety gave rise to an increase in the change of the refractive index. 1,2-bis(2-methyl-5-formyl-3-thienyl)perfluorocyclopentene phenyl hydrazone showed a large and stable ,n of 0.005 at 1.5,,m and appeared to be a good candidate for the development of telecommunication devices. [source] Kinetic and mechanistic investigation into the influence of chelate substituents on the substitution reactions of platinum(II) terpyridine complexesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2008Deogratius Jaganyi The substitution kinetics of the complexes [Pt{4,-(o -CH3 -Ph)-terpy} Cl]SbF6 (CH3PhPtCl(Sb)), [Pt{4,-(o -CH3 -Ph)-terpy}Cl]CF3SO3 (CH3PhPtCl(CF)), [Pt(4,-Ph-terpy)Cl]SbF6 (PhPtCl), [Pt(terpy)Cl]Cl·2H2O (PtCl), [Pt{4,-(o -Cl-Ph)-terpy}Cl]SbF6 (ClPhPtCl), and [Pt{4,-(o -CF3 -Ph)-terpy}Cl]SbF6 (CF3PhPtCl), where terpy is 2,2,:6,,2,-terpyridine, with the nucleophiles thiourea (TU), N,N,-dimethylthiourea (DMTU), and N,N,N,,N,-tetramethylthiourea (TMTU) were investigated in methanol as a solvent. The substitution reactions of the chloride displacement from the metal complexes by the nucleophiles were investigated as a function of nucleophile concentration and temperature under pseudo-first-order conditions using the stopped-flow technique. The reactions followed the simple rate law kobs = k2[Nu]. The results indicate that the introduction of substituents in the ortho position of the phenyl group on the ancillary ring of the terpy unit does influence the extent of ,-backbonding in the terpy ring. This controls the electrophilicity of the platinum center, which in turn controls the lability of the chloro-leaving group. The strength of the electron-donating or -withdrawing ability of the substituents correlates with the reactivity of the complexes. Electron-donating substituents decrease the rate of substitution, whereas electron-withdrawing substituents increase the rate of substitution. This was supported by DFT calculations at the B3LYP/LACVP+** level of theory, which showed that most of the electron density of the HOMO is concentrated on the phenyl ligand rather than on the metal center in the case of the strongest electron-withdrawing substituent in CF3PhPtCl. The opposite was found to be true with the strongest electron-donating substituent in CH3PhPtCl. Thiourea was found to be the best nucleophile with N,N,N,,N,-tetramethylthiourea being the weakest due to steric effects. The temperature dependence studies support an associative mode of activation. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 808,818, 2008 [source] Oxidation of substituted benzaldehydes by quinolinium chlorochromate: A structure and solvent dependent kinetic studyINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2003G. Fatima Jeyanthi The kinetics of oxidation of several para-substituted benzaldehydes by quinolinium chlorochromate was studied under pseudo-first-order conditions in different (hydrogen bond donor and hydrogen bond acceptor) neat organic solvents. The operation of nonspecific and specific solvent,solvent,solute interactions was explored by correlating the rate data with solvent parameters through correlation analysis. Both electron-releasing and electron-withdrawing substituents enhanced the rate and the Hammett plot showed a break in the reactivity order indicating applicability of dual mechanism. An explanation in conformity with structure and solvent effects on reactivity has been proposed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 154,158, 2003 [source] Density functional study of the relative reactivity in the concerted 1,3-dipolar cycloaddition of nitrile ylide to disubstituted ethylenesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2001Hsin-Yi Liao Abstract Density functional theory was used to perform a theoretical evaluation of (E)-1,2-disubstituted ethylenes as dipolarophiles for the 1,3-dipolar cycloaddition reaction. The reactivities of electron-withdrawing and -donating substituted ethylenes were examined by estimating their activation energies. The calculated activation energies predicted that the most reactive species is (E)-1,2-C2H2(NO)2, whereas the least reactive is (E)-2-butene. Namely, it was demonstrated that 16-electron 1,3-dipole reactants with more electropositive substituents in terminal positions and ethylenes that possess more strongly electron-withdrawing substituents facilitate 1,3-dipolar cycloaddition reactions. All of the theoretical results can be rationalized using the configuration mixing model. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 318,323, 2001 [source] NMR and DFT investigations of the substituent and solvent effect on amino,imino tautomerism in acridin-9-amines substituted at the exocyclic nitrogen atom,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2005Youssif Ebead Abstract The 1H and 13C NMR spectra of 9-(methoxyamino)acridine (1) and 9-hydrazinoacridine (2) show that these compounds exist principally in the imino tautomeric form in CDCl3, acetone- d6, CD3CN, DMSO- d6 and Py- d5, all solvents with different polarities and abilities to participate in specific interactions. The spectra of the other two compounds investigated,N -(2-chloroethyl)acridin-9-amine (3) and N -(5-methylpyridin-2-yl)acridin-9-amine (4),indicate that they coexist in the amino and imino forms. The amino tautomer of compound 3 predominates in CDCl3, CD3CN and Py- d5 and that of compound 4 in CDCl3 and Py- d5. On the other hand, the amino and imino forms of compound 3 coexist in acetone- d6 and probably DMSO- d6, whereas those of compound 4 coexist in acetone- d6 and DMSO- d6. The positions of the signals in the NMR spectra compare qualitatively with those predicted computationally at the GIAO/DFT level of theory. The equilibrium constants predicted by the DFT(PCM) method are in agreement with the results of NMR spectral analysis. In general, both the data predicted at the DFT level of theory and x-ray structural data show that the imino tautomers display a ,butterfly'-type geometry, whereas the amino forms are characterized by an almost flat acridine moiety. Electron-attracting substituents at the exocyclic N atom improve the stability of the imino form, and electron-withdrawing substituents do likewise for the amino form. The importance of tautomeric phenomena in the context of the ability of acridin-9-amines to participate in specific interactions is outlined in brief, as are the possible applications of these compounds as probes of environmental properties. Copyright © 2005 John Wiley & Sons, Ltd. [source] Low Bandgap Polymers by Copolymerization of Thiophene with BenzothiadiazoleMACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2009Youjun He Abstract Three low bandgap copolymers of thiophene and benzothiadiazole with electron-donating and electron-withdrawing substituents, P1, P2, and P3, have been synthesized by Pd-catalyzed Stille-coupling. Electronic energy levels of the polymers are estimated by cyclic voltammetry. The polymer films show a broad absorption band in the wavelength range from 300 to 750 nm. Among the polymers, the polymer that contains the 5,6-dinitrobenzothiadiazole unit, P3, possesses the smallest bandgap of 1.55 eV calculated from its absorption band-edge at ,800 nm. With the increase of the electron-withdrawing ability of the substituents on the benzothiadiazole unit, the energy bandgap of the polymers decreased in the order P1,>,P2,>,P3. The results indicate that stronger electron-withdrawing substituents on the acceptor unit can effectively decrease the bandgap of the polymers. [source] QSAR Analysis of 2,3-Diaryl Benzopyrans/Pyrans as Selective COX-2 Inhibitors Based on Semiempirical AM1 CalculationsMOLECULAR INFORMATICS, Issue 8 2004Sivaprakasam Prasanna Abstract Quantitative structure-activity relationship (QSAR) analysis was performed on a combined series of 2,3 diaryl benzopyrans and pyrans for their cyclooxygenase-2 (COX-2) inhibition. QSAR investigations based on semiempirical, Austin Model-1 (AM1) calculations reveal that electronic and hydophobic interactions are primarily responsible for COX-2 enzyme-ligand interaction. The derived QSAR model aided by residual analysis demonstrated that the COX-2 inhibitory activity is highly correlated with the electronic descriptors, lowest unoccupied molecular orbital (ELUMO), Dipole-Z and hydrophobicity of the molecules. The conclusion can be drawn that more hydrophobic, electron-withdrawing substituents at 3rd aromatic ring of the lead structure improves activity. The lesser the Z component the ligand has, the more correct its orientation towards the COX-2 binding site. The derived QSAR model shows good internal (exemplified through leave one out-q2=0.786) and external (r=0.5737) predictive ability for a test set and can be used in designing better selective COX-2 inhibitors among these congeners in future. [source] ChemInform Abstract: Negishi Alkyl,Aryl Cross-Coupling Catalyzed by Rh: Efficiency of Novel Tripodal 3-Diphenylphosphino-2-(diphenylphosphino)methyl-2-methylpropyl Acetate Ligand.CHEMINFORM, Issue 34 2010Syogo Ejiri Abstract The reaction is effective for the aromatic zinc derivatives bearing electron-withdrawing substituents, while poor yields are observed for the electron-donating and unsubstituted substrates [cf. [source] On the Tacticity of Polynorbornenes with 5,6- endo Pendant Groups That Contain Substituted Aryl ChromophoresCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2007Wei-Yu Lin Abstract Two dimers and a series of polymers with 5,6- endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and 13C,NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the 13C,NMR spectra when the substituents are electron-withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, ,d, was linearly related to the Hammett constant ,. Polynorbornenes with electron-withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular. [source] | ||||||||||||||||||||||