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1.
A series of substituted chlorinated chalcones namely, 3‐(2,4‐dichlorophenyl)‐1‐(4′‐X‐phenyl)‐2‐propen‐1‐one, have been synthesized, X being H, NH2, OMe, Me, F, Cl, CO2Et, CN, and NO2. Dual substituent parameter (DSP) models of 13C NMR chemical shift (CS) have revealed that π‐polarization concept could be utilized to explain the reverse field effect at CO, the enhanced substituent field effect at CO, C‐2, and C‐5, and the decreased sensitivity of substituent field effect at C‐6. Chlorine atoms dipole direction at the benzylidene ring either enhances or reduces substituent effect depending on how they couple with the substituent dipole at the probe site. The correlation of 13C NMR CS of C‐2, C‐5, and C‐6 with σ and σ indicates that chlorine atoms in the benzylidine ring deplete the ring from charges. Both MSP of Hammett and DSP of Taft 13C NMR CS models give similar trends of substituent effects at C‐2, C‐5, and C‐6. However, the former fail to give a significant correlation for CO and C‐6 13C NMR CS. MSP of σq and DSP of Taft and Reynolds models significantly correlated 13C NMR CS of Cβ. MSP of σq fails to correlate C‐1′ 13C NMR CS. Investigation of 13C NMR CS of non‐chlorinated chalcones series: 3‐phenyl‐1‐(4′‐X‐phenyl)‐2‐propen‐1‐one has revealed similar trends of substituent effects as in the chlorinated chalcones series for C‐1′, CO, Cα, and Cβ. In contrast, the substituent effect of the non‐chlorinated chalcone series at C‐2, C‐5, and C‐6 did not correlate with any substituent constant. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

2.
Knowledge of the strength of the metal–ligand bond breaking and formation is fundamental for an understanding of the thermodynamics underlying many important stoichiometric and catalytic organometallic reactions. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe―C bond energies of para‐substituted benzyldicarbonyl(η5‐cyclopentadienyl)iron, p‐G‐C6H4CH2Fp [1, G = NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, NMe2; Fp = (η5‐C5H5)(CO)2Fe], and para‐substituted α‐cyanobenzyldicarbonyl(η5‐cyclopentadienyl)iron, p‐G‐PANFp [2, PAN = C6H4CH(CN)]. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔHhet(Fe―C)'s. The good linear correlations [r = 0.98 (g, 1a), 0.99 (g, 2b)] between the substituent effects of heterolytic Fe―C bond energies [ΔΔHhet(Fe―C)'s] of series 1 and 2 and the differences of acidic dissociation constants (ΔpKa) of C―H bonds of p‐G‐C6H4CH3 and p‐G‐C6H4CH2CN imply that the governing structural factors for these bond scissions are similar. And the excellent linear correlations [r = ?1.00 (g, 1c), ?0.99 (g, 2d)] between ΔΔHhet(Fe―C)'s and the substituent σp? constants show that these correlations are in accordance with Hammett linear free energy relationships. The polar effects of these substituents and the basis set effects influence the accuracy of ΔHhet(Fe―C)'s. ΔΔHhet(Fe―C)'s(1, 2) follow the Capto‐dative Principle. The detailed knowledge of the factors that determine the Fp―C bond strengths would greatly aid in understanding reactivity patterns in many processes. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

3.
Thirty‐four novel α/β‐tetrapeptides ( 1–34 ) have been prepared employing solid‐phase and in‐parallel synthetic protocols. α/β ‐Tetrapeptides 1 – 34 were prepared by a combination of three α‐amino acid residues (alanine (Ala), phenylalanine (Phe), and isoleucine (Ile)) with one β‐amino acid residue (β3‐homophenylglycine). The corresponding complexes of several selected α/β‐tetrapeptides with alkali, alkaline earth, and transition metals, [tP + M+], were evaluated using ion electrospray‐ionization mass spectrometry (ESI‐MS). According to the results from analysis of mixtures, we can conclude that the position of the β‐amino acid is determinant in the affinity toward different metal cations. Computational modeling (DFT, B3LYP 6‐311++G) provided useful information regarding the most likely coordination sites of the metal ions on the receptor α/β‐tetrapeptide 12 , HO2C‐α‐Phe‐α‐Phe‐α‐Ile‐β3‐hPhg‐NH2, as well as the conformational changes induced by the metal upon [tP + M+] complex formation. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

4.
Density functional theory (DFT) calculations of ring‐shaped α‐cyclo[N]thiophenes with N = 2 to N = 18 have been performed for ideal structures of high symmetry (point groups Cnv and Dnh) and for optimum energy structures of lower symmetry (D2d, Cs, C2v, Ci or C1). Whereas the first three members of the series behave exceptionally the higher members are typical cyclothiophenes consisting of weakly interacting thiophene rings. In contrast to neutral compounds, cations and dications of cyclothiophenes with N ≥5 exhibit pronounced electron delocalizations along the carbon backbone. However, if the functional B3LYP is replaced by BH cations of large ring‐size cations show polaron‐type charge defects. According to broken symmetry DFT calculations dications with N = 14 and N = 18 have biradical character. These structures correspond to two‐polaron‐type structures rather than to dipolarons. The calculated vertical ionization energies of cyclo[N]thiophene are comparable with those of oligo[N]thiophenes of the same number of thiophene rings but the calculated absolute energies are probably too low at large ring size. Cyclothiophenes absorb light of lower energies than the related oligothiophenes. Cyclothiophenes belong to the strongly absorbing organic chromophores. In case of high molecular symmetry some of the excited states of cyclothiophenes are degenerate. The degeneracy is lifted with lower symmetries but the general absorption feature remains. The theoretical results are discussed with respect to recent experimental findings. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

5.
The structures of 2‐substituted malonamides, YCH(CONR1R2)CONR3R4 (Y = Br, SO2Me, CONH2, COMe, and NO2) were investigated. When Y = Br, R1R2 = R3R4 = HEt; Y = SO2Me, R1–R4 = H and for Y = CONH2 or CONHPh, R1–R4 = Me, the structure in solution is that of the amide tautomer. X‐ray crystallography shows solid‐state amide structures for Y = SO2Me or CONH2, R1–R4 = H. Nitromalonamide displays an enol structure in the solid state with a strong hydrogen bond (OO distance = 2.3730 Å at 100 K) and d(OH) ≠ d(OH). An apparently symmetric enol was observed in solution, even in appreciable percentages in highly polar solvents such as DMSO‐d6, but Kenol values decrease on increasing the solvent polarity. The N,N′‐dimethyl derivative is less enolic. Acetylmalonamides display a mixture of enol on the acetyl group and amide in non‐polar solvents, and only the amide in DMSO‐d6. DFT calculations gave the following order of pKenol values for Y: H > CONH2 > COMe ≥ COMe (on acetyl) ≥ MeSO2 > CN > NO2 in the gas phase, CHCl3, and DMSO. The enol on the C?O group is preferred to the aci‐nitro compound, and the N? O? HO?C is less favored than the C?O? HO?C hydrogen bond. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

6.
Persistent carbocations generated by the protonation of hetero‐polycyclic aromatic compounds with oxygen atom(s) were studied by experimental NMR and density function theory calculations. Benzo[kl]xanthene ( 1 ), dibenzo[d,d′]benzo[1,2‐b:4,3‐b′]difuran ( 2 ), and dibenzo[d,d′]benzo[1,2‐b:4,5‐b′]difuran ( 3 ) were synthesized by the annulation of arenediazonium salts. Compound 1 in FSO3H‐SbF5 (4:1)/SO2ClF and 3 in FSO3H‐SbF5 (1:1)/SO2ClF ionized to 1aH+ with protonation at C(4) and to 3aH+ with protonation at C(6), and these cations were successfully observed by NMR at low temperatures. The density function theory calculations indicated that 1aH+ and 3aH+ were the most stable protonated carbocations and that 2 should ionize to 2aH+ with protonation at C(6). According to the changes in 13C chemical shifts (Δδ13C), the positive charge was delocalized into the naphthalene unit for 1aH+ , into one benzo[b,d]furan unit for 2aH+ , and into one benzo[b,d]furan unit for 3aH+ . Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

7.
The gas‐phase acidities (GA) of 2‐aryl‐2‐chloro‐1,1,1‐trifluoroethanes ( 1a ), 2‐aryl‐2‐fluoro‐1,1,1‐trifluoroethanes ( 2a ), and related compounds, XC6H4CH(Z)R where Z = Cl ( 1 ) or F ( 2 ) and R = C2F5 ( b ), t‐C4F9 ( c ), C(CF3)2C2F5 ( d ), C(CF3)2Me ( e ), Me ( f ), H ( g ), were investigated experimentally and computationally. On the basis of an excellent linear correlation (R2 > 0.99) of acidities of 1c , 1d , 1e , 1f and 2c , 2d , 2e , 2f where there is no fluorine atom at β‐position to the deprotonation site with the corrected number of fluorine atoms contained in the fluorinated alkyl group, the extent of β‐fluorine negative hyperconjugation of the CF3 and C2F5 groups (ΔGoβ‐F) was evaluated. The GAel values given by subtraction ΔGoβ‐F from the apparent GA value were considered to represent the electronic effect of the substituent X. The substituent effects on the GAel values and GA values for 1c , 1d , 1e , 1f and 2c , 2d , 2e , 2f were successfully analyzed in terms of the Yukawa–Tsuno equation. The variation of resonance demand parameter r? with the R group observed for various XC6H4CH(Z)R was linearly related to the GA (GAel) value of the respective phenyl‐substituted fluorinated alkanes. On the other hand, the corresponding correlation for the ρ values provided three lines for ArCH(Cl)R, ArCH(F)R and ArCH2R, respectively. These results supported our previous conclusion that the r? and ρ values are governed by the thermodynamic stability of the parent ion (ring substituent = H). Other factors arising from an atom bonded to the acidic center also influence the ρ value. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

8.
A series of nitrophenyl β‐cyclodextrin derivatives: mono[6‐deoxy‐6‐(4‐nitrobenzamido)]‐per‐ O‐methyl‐β‐cyclodextrin (R1? Ph? NO2), mono[6‐deoxy‐6‐(3‐nitrobenzamido)]‐per‐O‐methyl‐β‐cyclodextrin (R2? Ph? NO2) and heptakis[6‐deoxy‐6‐(4‐nitrobenzamido)‐2,3‐di‐O‐methyl]‐β‐cyclodextrin [R3? (Ph? NO2)7] were synthesized. Purity and composition of the obtained substances were checked. Electroreduction of nitro groups of the new synthesized compounds was investigated on mercury electrode using cyclic voltammetry and chronocoulometry. The parameters of the reduction processes of ? NO2 groups of the investigated compounds were found not to be comparable to the reduction of nitrobenzene under the same experimental conditions. Moreover, the electroreduction of nitro groups in these nitrophenyl derivatives was dependent on pH, the type of the studied compound, and slightly on the solvent composition. All the reactants were strongly adsorbed on mercury electrode. In the case of R3? (Ph? NO2)7, its seven nitro groups were reduced practically at the same potential, and no radical anion formation was observed. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

9.
Long‐range electronic substituent effects were targeted using the substituent dependence of δC(C═N), and specific cross‐interactions were explored extendedly. A wide set of N‐(4‐X–benzylidene)‐4‐(4‐Y–styryl) anilines, p‐X–C6H4CH═NC6H4CH═CHC6H4p‐Y (X = NMe2, OMe, Me, H, Cl, F, CN, or NO2; Y = NMe2, OMe, Me, H, Cl, or CN) were prepared for this study, and their 13C NMR chemical shifts δC(C═N) of C═N bonds were measured. The results show that both the inductive and resonance effects of the substituents Y on the δC(C═N) of p‐X–C6H4CH═NC6H4CH═CHC6H4p‐Y are less than those of the substituents Y in p‐X–C6H4CH═NC6H4p‐Y. Moreover, the sensitivity of the electronic character of the C═N function to electron donation/electron withdrawal by the substituent X or Y attenuates as the length of the conjugated chain is elongated. It was confirmed that the substituent cross‐interaction is an important factor influencing δC(C═N), not only when both X and Y are varied but also when either X or Y is fixed. The long‐range transmission of the specific cross‐interaction effects on δC(C═N) decreases with increasing conjugated distance between X and Y. The results of this study suggest that there is a long‐range transmission of the substituent effects in p‐X–C6H4CH═NC6H4CH═CHC6H4p‐Y. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

10.
The nature and strength of metal–ligand bonds in organotransition‐metal complexes are crucial to the understanding of organometallic reactions and catalysis. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe–N bond energies of para‐substituted anilinyldicarbonyl(η5‐cyclopentadienyl)iron [p‐G‐C6H4NH(η5‐C5H5)Fe(CO)2, abbreviated as p‐G‐C6H4NHFp (1), where G = NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, and NMe2] and para‐substituted α‐acetylanilinyldicarbonyl(η5‐cyclopentadienyl)iron [p‐G‐C6H4N(COMe)(η5‐C5H5)Fe(CO)2, abbreviated as p‐G‐C6H4N(COMe)Fp (2)] complexes. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔHhet(Fe–N)'s. The linear correlations [r = 0.98 (g, 1a), 0.93 (g, 2b)] between the substituent effects of heterolytic Fe–N bond energies [ΔΔHhet(Fe–N)'s] of series 1 and 2 and the differences of acidic dissociation constants (ΔpKa) of N–H bonds of p‐G‐C6H4NH2 and p‐G‐C6H4NH(COMe) imply that the governing structural factors for these bond scissions are similar. And the linear correlations [r = ?0.99 (g, 1c), ?0.92 (g, 2d)] between ΔΔHhet(Fe–N)'s and the substituent σp? constants show that these correlations are in accordance with Hammett linear free energy relationships. The polar effects of these substituents and the basis set effects influence the accuracy of ΔHhet(Fe–N)'s. ΔΔHhet(Fe–N)'s(1, 2) follow the captodative principle. MEα‐COMe, para‐Gs include the influences of the whole molecules. The correlation of MEα‐COMe, para‐Gs with σp? is excellent. MEα‐COMe, para‐Gs rather than ΔΔHhet(Fe–N)'s in series 2 are more suitable indexes for the overall substituent effects on ΔHhet(Fe–N)'s(2). Insight from this work may help the design of more effective catalytic processes. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

11.
The knowledge of accurate bond strengths is a fundamental basis for a proper analysis of chemical reaction mechanisms. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe–O and Fe–S bond energies of (meta‐substituted phenoxy)dicarbonyl(η5‐cyclopentadienyl) iron [m‐G‐C6H4OFp ( 1 )] and (meta‐substituted benzenethiolato)dicarbonyl(η5‐cyclopentadienyl) iron [m‐G‐C6H4SFp ( 2 )] complexes. In this study, Fp is (η5‐C5H5)Fe(CO)2, and G is NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, and NMe2. The results show that Tao–Perdew–Staroverov–Scuseria and Becke's power‐series ansatz from 1997 with dispersion corrections functionals can provide the best price/performance ratio and accurate predictions of ΔHhet(Fe–O)'s and ΔHhet(Fe–S)'s. The excellent linear free energy relations [r = 1.00 (g, 1e), 1.00 (g, 2b)] among the ΔΔHhet (Fe–O)'s and δΔG0 of O?H bonds of m‐G‐C6H4OH or ΔΔHhet(Fe–S)'s and ΔpKa's of S?H bonds of m‐G‐C6H4SH imply that the governing structural factors for these bond scissions are similar. And, the linear correlations [r = ?0.97 (g, 1 g), ?0.97 (g, 2 h)] among the ΔΔHhet (Fe–O)'s or ΔΔHhet(Fe–S)'s and the substituent σm constants show that these correlations are in accordance with Hammett linear free energy relationships. The inductive effects of these substituents and the basis set effects influence the accuracy of ΔHhet(Fe–O)'s or ΔHhet(Fe–S)'s. The ΔΔHhet(Fe–O)'s(g) (1) and ΔΔHhet(Fe–S)'s(g)(2) follow the capto‐dative Principle. The substituent effects on the Fe–O bonds are much stronger than those on the less polar Fe–S bonds. Insight from this work may help the design of more effective catalytic processes. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

12.
Four L ‐valine (L ‐Val) phosphonate dipeptides that are potent inhibitors of zinc metalloproteases, namely, L ‐Val‐C(Me)2‐PO3H2 (V1), L ‐Val‐CH(iP)‐PO3H2 (V2), L ‐Val‐CH(iB)‐PO3H2 (V3), and L ‐Val‐C(Me)(iP)‐PO3H2 (V4), are studied by Fourier‐transform infrared (FT‐IR) spectroscopy, Fourier‐transform Raman spectroscopy (FT‐RS), and surface‐enhanced Raman scattering (SERS). The band assignment (wavenumbers and intensities) is made based on (B3LYP/6‐311 + + G**) calculations. Comparison of theoretical FT‐IR and FT‐RS spectra with those of SERS allows to obtain information on the orientation of these dipeptides as well as specific‐competitive interactions of their functionalities with the silver substrate. More specifically, V1 and V4 appear to interact with the silver substrate mainly via a  CsgCH3 moiety localized at the  NamideCsg(CH3)P molecular fragment. In addition, the  POH and isopropyl units of V4 assist in the adsorption process of this molecule. In contrast, the  CαNH2 and  PO3H groups of V2 and V3 interact with the silver nanoparticles, whereas their isopropyl and isobutyl fragments seem to be repelled by the silver substrate (except for the  CH2  of V3), similar to the  Cβ(CH3)2 fragment of L ‐Val for all L ‐Val phosphonate dipeptides investigated in this work. The adsorption mechanism of these molecules onto the colloidal silver surface is also affected by amide bond behavior. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
By the B3P86/6‐311G(3d,2p) method, remote substituent effects on trans‐YCH?CHCH2F were investigated by examining their conformational stabilities, molecular geometries, and stereoelectronic interactions in this paper. The cis conformer is favored for Y?H, Cl, Me, Vinyl, CF3, CN, CHO, and NO2, whereas the gauche is favored for Y?OMe, OH. A correlation of ΔH with the substituent constants σ+(Y) shows that the increasing electron‐withdrawing ability of the substituent Y increases the relative stability of the cis conformer. It was found that the substituent effect on the molecule stabilization energies (relative to CH2?CHCH2F) is more significant in the gauche conformers than in the cis conformers. In agreement, molecular structures of the gauche conformers were also observed to vary more significantly with the substitution than those of the cis conformers. By the second‐order perturbation energy (E(2)) in NBO analysis, it was found that the total C2–C3 vicinal hyperconjugation is determinant in the enthalpy difference and consequently controls the conformational stability. Further analysis shows that the substituent effect on the C2–C3 vicinal hyperconjugations is much higher in the gauche conformers than in the cis conformers. The highly sensitive πC?C→σ*C? F interaction to the substitution in the gauche conformers, is the leading factor in variation of molecular stability and geometry. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

14.
The nature and strength of metal–ligand bonds in organotransition–metal complexes is crucial to the understanding of organometallic reactions and catalysis. The Fe‐N homolytic bond dissociation energies [ΔHhomo(Fe‐N)′s] of two series of para‐substituted Fp anilines p‐G‐C6H4NHFp [1] and p‐G‐C6H4N(COMe)Fp [2] were studied using the Hartree–Fock (HF) and the density functional theory methods with large basis sets. In this study, Fp is (η5‐C5H5)Fe(CO)2 and G are NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO and NMe2. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and accurate predictions of ΔHhomo(Fe‐N)′s. B3LYP can also satisfactorily predict the α and remote substituent effects on ΔHhomo(Fe‐N)′s [ΔΔHhomo(Fe‐N)′s]. The good correlations [r = 0.96 (g, 1), 0.99(g, 2)] of ΔΔHhomo(Fe‐N)′s in series 1 and 2 with the substituent σp+ constants imply that the para‐substituent effects on ΔHhomo(Fe‐N)′s originate mainly from polar effects, but those on radical stability originate from both spin delocalization and polar effects. ΔΔHhomo(Fe‐N)′s(1,2) conform to the captodative principle. Insight from this work may help the design of more effective catalytic processes. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

15.
Comparison of 13C NMR of C = N bond chemical shifts δC(C = N) in substituted N‐(phenyl‐ethylene)‐anilines XArC(Me) = NArY (XPEAYs) with that in substituted N‐(benzylidene)‐anilines XArCH = NArY (XBAYs) was carried out. The δC(C = N) of 61 samples of XPEAYs were measured, and the substituent effect on their δC(C = N) were investigated. The results show the factors affecting the δC(C = N) of XPEAYs are quite different from that of XBAYs. A penta‐parameter correlation equation was obtained for the 61 compounds, which has correlation coefficient 0.9922 and standard error 0.12 ppm. The result indicates that, in XPEAYs, the inductive effects of substituents X and Y are major factors affecting the δC(C = N), while the conjugative effect of them have very little effect on the δC(C = N) and can be ignored. The substituent‐specific cross‐interaction effects between X and Y and between Me of C = N bond and substituent Y are important factors affecting the δC(C = N). Also, the excited‐state substituent parameter of substitute Y has certain contribution to the δC(C = N). Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

16.
The knowledge of accurate bond strengths is a fundamental basis for a proper analysis of chemical reaction mechanisms. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe–O and Fe–S bond energies of para‐substituted phenoxydicarbonyl(η5‐cyclopentadienyl) iron [p‐G‐C6H4O(η5‐C5H5)Fe(CO)2, abbreviated as p‐G‐C6H4OFp ( 1 ), where G = NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, and NMe2] and para‐substituted benzenethiolatodicarbonyl(η5‐cyclopentadienyl) iron [p‐G‐C6H4S(η5‐C5H5)Fe(CO)2, abbreviated as p‐G‐C6H4SFp ( 2 )] complexes. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔHhet(Fe–O)'s and ΔHhet(Fe–S)'s. The excellent linear free‐energy relations [r = 0.99 (g, 1a), 1.00 (g, 2b)] among the ΔΔHhet (Fe–O)'s and Δpka's of O–H bonds of p‐G‐C6H4OH or ΔΔHhet(Fe‐S)'s and Δpka's of S–H bonds of p‐G‐C6H4SH imply that the governing structural factors for these bond scissions are similar. And the linear correlations [r = ?0.99 (g, 1g), ?0.98 (g, 2h)] among the ΔΔHhet (Fe‐O)'s or ΔΔHhet(Fe‐S)'s and the substituent σp? constants show that these correlations are in accordance with Hammett linear free‐energy relationships. The polar effects of these substituents and the basis set effects influence the accuracy of ΔHhet(Fe–O)'s or ΔHhet(Fe–S)'s. ΔΔHhet(Fe–O)'s(g) ( 1 ) and ΔΔHhet(Fe–S)'s(g)( 2 ) follow the Capto‐dative principle. The substituent effects on the Fe–O bonds are much stronger than those on the less polar Fe–S bonds. Insight from this work may help the design of more effective catalytic processes. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

17.
Solvolysis rates of 2‐(aryldimethylsilyl)‐1‐methylethyl and 2‐(aryldimethylsilyl)‐1‐tert‐butylethyl trifluoroacetates were determined conductimetrically in 60% (v/v) aqueous ethanol. The effects of aryl substituents at the silicon atom on the solvolysis rates at 50 °C were correlated with parameters of r+ = 0.15 with the Yukawa–Tsuno equation, giving ρ values of ?1.5 for both secondary α‐Me and αtert‐Bu systems. The ρ values for those secondary systems are less negative than ?1.75 for the 2‐(aryldimethylsilyl)ethyl system that proceeds by the Eaborn (non‐vertical) mechanism, while they are distinctly more negative than ?0.99 for 2‐(aryldimethylsilyl)‐1‐phenylethyl system that should proceed by the Lambert (vertical) mechanism. There was a fairly linear relationship between the reaction constants (ρ) for the β‐silyl substituent effects and the solvolysis reactivities for a series of β‐silyl substrates. The solvolyses of the α‐Me and tert‐Bu substrates proceed through the transition state (TS) with an appreciable degree of the β‐silyl participation, close to the Eaborn (non‐vertical) TS rather than to the Lambert (vertical) TS. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

18.
This paper reports about high reactivity of α‐silylamines in the reaction with CCl4. Unlike Et3N, α‐silylamines rapidly react with CCl4 upon irradiation with daylight to form α‐silylamine hydrochloride salts in 92–98% yields. The influence of structure of α‐silylamines and solvent on the degree of conversion was displayed. The interaction of α‐silylamines with CCl4 was studied by NMR, ESR, and IR spectroscopy. C‐centered radicals of α‐silylamines were detected by ESR spectroscopy with spin traps (MNP, ND, and PBN) in reaction mixtures in CH3CN and C6H6 and it show the radical character of this reaction. Both CH3CN and C6H6 serve as solvents as well as reagents for this reaction. A mechanism of an interaction between α‐silylamines and CCl4 is discussed. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

19.
One of the most fundamental properties in chemistry is the bond dissociation energy, the energy required to break a specific bond of a molecule. In this paper, the Fe–N homolytic bond dissociation energies [ΔHhomo(Fe–N)'s] of 2 series of (meta‐substituted anilinyl)dicarbonyl(η5‐cyclopentadienyl) iron [m‐G‐C6H4NHFp ( 1 )] and (meta‐substituted α‐acetylanilinyl)dicarbonyl(η5‐cyclopentadienyl) iron [m‐G‐C6H4N(COMe)Fp ( 2 )] were studied using density functional theory methods with large basis sets. In this study, Fp is (η5‐C5H5)Fe(CO)2, and G is NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, and NMe2. The results show that Tao‐Perdew‐Staroverov‐Scuseria, Minnesota 2006, and Becke's power‐series ansatz from 1997 with dispersion corrections functionals can provide the best price/performance ratio and accurate predictions of ΔHhomo(Fe–N)'s. The ΔΔHhomo(Fe–N)'s ( 1 and 2 ) conform to the captodative principle. The polar effects of the meta‐substituents show the dominant role to the magnitudes of ΔΔHhomo(Fe–N)'s. σα· and σc· values for meta‐substituents are all related to polar effects. Spin‐delocalization effects of the meta‐substituents in ΔΔHhomo(Fe–N)'s are small but not necessarily zero. RE plays an important role in determining the net substituent effects on ΔHhomo(Fe–N)'s. Insight from this work may help the design of more effective catalytic processes.  相似文献   

20.
The thermochemistry of organometallic complexes in solution and in the gas phase has been an area of increasing research interest. In this paper, the Fe–O and Fe–S homolytic bond dissociation energies [ΔHhomo(Fe–O)'s and ΔHhomo(Fe–S)'s] of two series of meta‐substituted phenoxydicarbonyl(η5‐cyclopentadienyl) iron [m‐G‐C6H4OFp ( 1 )] and (meta‐substituted benzenethiolato)dicarbonyl(η5‐cyclopentadienyl) iron [m‐G‐C6H4SFp ( 2 )] were studied using Hartree–Fock and density functional theory methods with large basis sets. In this study, Fp is (η5‐C5H5)Fe(CO)2, and G are NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, and NMe2. The results show that Tao–Perdew–Staroverov–Scuseria and Minnesota 2006 functionals can provide the best price/performance ratio and accurate predictions of ΔHhomo(Fe–O)'s and ΔHhomo(Fe–S)'s. The polar effects of the meta substituents show that the dominant role to the magnitudes of ΔΔHhomo(Fe–O)'s or ΔΔHhomo(Fe–S)'s. σα·, σc· values for meta substituents are all related to polar effects. Spin‐delocalization effects of the meta substituents in ΔΔHhomo(Fe–O)'s and ΔΔHhomo(Fe–S)'s are small but not necessarily zero. Molecular effects rather than ΔΔHhomo(Fe–O)'s and ΔΔHhomo(Fe–S)'s are more suitable indexes for the overall substituent effects on ΔHhomo(Fe–O)'s and ΔHhomo(Fe–S)'s. The meta substituent effects of meta‐electron‐withdrawing groups on the Fe–S bonds are much stronger than those on the Fe–O bonds. For meta‐electron‐donating groups, the meta substituent effects have the comparable magnitudes between series 1 and 2 . ΔΔHhomo(Fe–O)'s ( 1 ) and ΔΔHhomo(Fe–S)'s ( 2 ) conform to the captodative principle. Insight from this work may help the design of more effective catalytic processes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

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