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41.
Vilve Nummert Mare Piirsalu Ilmar A. Koppel 《Journal of Physical Organic Chemistry》2013,26(4):352-359
The second‐order rate constants k (dm3mol?1s?1) for alkaline hydrolysis of meta‐, para‐ and ortho‐substituted phenyl esters of benzoic acid, C6H5CO2C6H4‐X, in aqueous 50.9% (v/v) acetonitrile have been measured spectrophotometrically at 25 °C. In substituted phenyl benzoates, C6H5CO2C6H4‐X, the substituent effects log kX ? log kH in aqueous 50.9% acetonitrile at 25 °C for para, meta and ortho derivatives showed good correlations with the Taft and Charton equations, respectively. Using the log k values for various media at 25 °C, the variation of the ortho substituent effect with solvent was found to be precisely described with the following equation: Δlog kortho = log kortho ? log kH = 1.57σI + 0.93σ°R + 1.08EsB ? 0.030ΔEσI ? 0.069ΔEσ°R, where ΔE is the solvent electrophilicity, ΔE = ES ? EH20, characterizing the hydrogen‐bond donating power of the solvent. We found that the experimental log k values for ortho‐, para‐ and meta‐substituted phenyl benzoates in aqueous 50.9% acetonitrile at 25 °C, determined in the present work, precisely coincided with the log k values predicted with the equation (log kX)calc = (log kHAN)exp + (Δlog kX)calc where the substituent effect (Δlog kX)calc was calculated from equation describing the variation of the substituent effect with the solvent electrophilicity parameter, using for aqueous 50.9% CH3CN the solvent electrophilicity parameter, ΔE = ?5.84. In going from water to aqueous 50.9% CH3CN, the ortho inductive term grows twice less as compared with the para polar effect. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
42.
Vilve Nummert Mare Piirsalu Vahur M?emets Signe Vahur Ilmar A. Koppel 《Journal of Physical Organic Chemistry》2009,22(12):1155-1165
13C NMR spectra of 37 ortho‐, meta‐, and para‐substituted phenyl benzoates, containing substituents in benzoyl and phenyl moiety, 4 ortho‐substituted methyl and 5 ethyl benzoates as well as 9 R‐substituted alkyl benzoates have been recorded. The influence of the ortho substituents on the carbonyl carbon 13C NMR chemical shift, δCO, was found to be described by a linear multiple regression equation containing the inductive, σI, resonance, σ°R, and steric, E, or υ substituent constants. For all the ortho‐substituted esters containing substituents in the acyl part as well as the phenyl part, the substituent‐induced reverse inductive effect (ρI < 0), the normal resonance effect (ρR > 0), and the negative steric effect (δortho < 0) with the E were observed. In the case of ortho substituents in the phenyl part, the resonance effect was negligible. Due to inductive effect, the ortho electron‐withdrawing substituents showed an upfield shift or shielding of the carbonyl carbon, while the electron‐donating substituents had an opposite effect. Because of the sterical consequences, ortho substituents revealed a deshielding effect on the 13C NMR chemical shift of the carbonyl carbon. For all the meta‐ and para‐substituted esters, the reverse substituent‐induced inductive and resonance effects (ρI < 0, ρR < 0) were found to be significant. In alkyl benzoates, the alkyl substituents showed the reverse inductive and steric effects. The log k values for the alkaline hydrolysis in water, aqueous 0.5 M Bu4NBr and 2.25 M Bu4NBr, and the IR frequencies, νCO, for the ortho‐, meta‐, and para‐substituted phenyl benzoates and alkyl benzoates were correlated nicely with the corresponding 13C NMR substituent chemical shifts, ΔδCO. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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G. Denigès H. B. Merrill V. Lenher I. Koppel J. Štěrba-Böhmund J. Vostřebal Dorothy Hall A. E. Stoppel Ch. F. Sidener P. H. M. P. Brinton E. Färber W. F. Murray Ch. H. Cramer S. Little J. R. Camp J. W. Marden C. M. Johnson E. Montignie N. N. Tananaeff G. Tkatschenko 《Analytical and bioanalytical chemistry》1931,86(9-10):382-391
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48.
IA Simpson R Bol ID Bull RP Evershed K Petzke SJ Dockrill 《Rapid communications in mass spectrometry : RCM》1999,13(13):1315-1319
Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
49.
Sooväli L Rodima T Kaljurand I Kütt A Koppel IA Leito I 《Organic & biomolecular chemistry》2006,4(11):2100-2105
The pKa values in water and in dilute surfactant solution for 15 ring-substituted phenyl P1 pyrrolidino phosphazenes PhN=P(NC4H8)3 and the phenyl P1 dimethylamino phosphazene PhN=P(NMe2)3 previously studied in acetonitrile (AN) and tetrahydrofuran (THF) are reported. The nonionic surfactant Tween 20 was used for the basicity measurements of some compounds to overcome the solubility problems. Measurements with a control group of phosphazenes in both media were used to validate the use of the obtained pKa values as estimates of aqueous values. The pK(a) values of the studied phosphazenes in aqueous medium vary from 6.82 (2,6-dinitro-) to 12.00 (4-dimethylamino-). The basicity span is 5.18 pKa units. The aqueous pKa values of the P1 phosphazenes were correlated with the respective basicity data in AN and THF and from these correlations the pK(a) values in water for the parent compounds HN=P(NC4H8)3 and HN=P(NMe2)3 were estimated as 13.9 and 13.3. Also a comparison of the basicity of phosphazenes and some guanidines, amines and pyridines was made. In water the parent phosphazenes and guanidines are the strongest of all the groups of bases studied. In AN and THF the parent phosphazenes are clearly the strongest bases followed by guanidines, amines and pyridines which are bracketed between the basicities of phenyl phosphazenes. In the gas phase the phosphazenes for which data are available are clearly more basic than the other compounds referred to here. Comparison of the basicity data of P1 phosphazenes and some guanidines confirms earlier conclusions about the partly ylidic character of the N=P double bond. 相似文献
50.
Vilve Nummert Mare Piirsalu Ilmar A. Koppel 《Magnetic resonance in chemistry : MRC》2012,50(10):696-704
17O NMR spectra for 35 ortho‐, para‐, and meta‐substituted phenyl tosylates (phenyl 4‐methylbenzenesulfonates), 4‐CH3‐C6H4SO2OC6H4‐X, at natural abundance in acetonitrile at 50 °C were recorded. The 17O NMR chemical shifts, δ(17O), of the sulfonyl (SO2) and the single‐bonded phenoxy (OPh) oxygens for para and meta derivatives correlated well with dual substituent parameter treatment using the Taft inductive, σI, and resonance, σºR, constants. The influence of ortho substituents on the sulfonyl oxygen and the single‐bonded phenoxy oxygen chemical shifts, δ(17O), was found to be nicely described by the Charton equation: δ(17O)ortho = δ(17O)H + ρIσI + ρRσ°R + δEsB when the data treatment was performed separately for electron‐donating +R substituents and electron‐attracting ?R substituents. Electron‐attracting meta and para substituents in the phenyl moiety caused deshielding while the electron‐donating meta, para and ortho +R substituents produce shielding effects on the sulfonyl (SO2) and single‐bonded phenoxy (OPh) oxygens. The influence of ortho inductive and resonance effects in the case of +R substituents was found to be approximately twice higher than the corresponding influence from the para position. Due to the steric effect of ortho substituents a decrease in shielding of the oxygens at the sulfonyl group (δEsB > 0, EsB < 0) was detected. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献