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Nucleophilic Reactivities (nucleophilic + reactivity)
Selected AbstractsNucleophilic Reactivities of Azulene and Fulvenes,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2009Mariusz K, dziorek Abstract The kinetics of the reactions of azulene (1), 6,6-dimethylfulvene (2), 6-[4-(dimethylamino)phenyl]fulvene (3) and 6-(julolidin-9-yl)fulvene (4) with a set of benzhydrylium ions (reference electrophiles) have been investigated in MeCN. The second-order rate constants for these reactions correlate linearly with the electrophilicity parameters (E) of the benzhydrylium ions. According to the linear free-enthalpy relationship log,k2(20 °C) = s(N + E), the nucleophilicity parameters N and s of the ,-nucleophiles 1,4 were determined and compared with those of other types of nucleophiles. Azulene (1, N = 6.66) is about 10 times more nucleophilic than N -methylpyrrole and comparable to 2-methylindole. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Nucleophilic Reactivities of Pyrroles,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2008Tobias A. Nigst Abstract The second-order rate constants of the reactions of alkyl-substituted pyrroles with a series of benzhydrylium ions were determined in acetonitrile, and the reaction products were fully characterized by NMR spectroscopy and mass spectrometry. The formation of the , adducts is the rate-limiting step of these reactions. Because the second-order rate constants correlate linearly with the electrophilicity parameters of the benzhydrylium ions, the determination of the nucleophilicity parameters N and s according to the linear free energy relationship log k2 (20 °C) = s(N + E) was achieved. With these findings, a direct comparison of the nucleophilic reactivities of these ,-excessive heterocycles with other nucleophiles became possible, and the pyrroles were integrated into the comprehensive scale of nucleophilicity, covering a range of 8,9 orders of magnitude from N -(triisopropylsilyl)pyrrole (N = 3.12), the weakest nucleophile of this series, to kryptopyrrole (3-ethyl-2,4-dimethylpyrrole, N = 11.63). Thus, highly reactive pyrroles show similar nucleophilic reactivities as enamines, whereas those of less-reactive pyrroles are comparable to allylsilanes or indoles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] ChemInform Abstract: Nucleophilic Reactivities of Tributylstannyl-Substituted Furans and Thiophenes.CHEMINFORM, Issue 38 2001Mirjam Herrlich Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Functionalized surfactant mediated reactions of carboxylate, phosphate and sulphonate estersJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2010Shuchi Tiwari Abstract Nucleophilic reactivity of some functionalized surfactants, i.e. quaternary pyridinium aldoximes towards the hydrolysis of p -nitrophenyl acetate (PNPA), p -nitrophenyl benzoate (PNPB), p -nitrophenyldiphenyl phosphate (PNPDPP) and p -nitrophenyl p -toluene sulphonate (PNPTS) has been studied at pH 7.1 and 27,°C. Addition of functionalized surfactant to reaction medium causes progressive increase in the rate of hydrolysis and reaches a maximum and then decreases due to further addition of surfactant. An increase in the alkyl chain length of functionalized surfactants resulted in an increase in the first-order rate constant. The apparent pKa and CMC of functionalized surfactants have also been determined by spectrophotometric and conductometric methods, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Nucleophilic Reactivities of Pyrroles,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2008Tobias A. Nigst Abstract The second-order rate constants of the reactions of alkyl-substituted pyrroles with a series of benzhydrylium ions were determined in acetonitrile, and the reaction products were fully characterized by NMR spectroscopy and mass spectrometry. The formation of the , adducts is the rate-limiting step of these reactions. Because the second-order rate constants correlate linearly with the electrophilicity parameters of the benzhydrylium ions, the determination of the nucleophilicity parameters N and s according to the linear free energy relationship log k2 (20 °C) = s(N + E) was achieved. With these findings, a direct comparison of the nucleophilic reactivities of these ,-excessive heterocycles with other nucleophiles became possible, and the pyrroles were integrated into the comprehensive scale of nucleophilicity, covering a range of 8,9 orders of magnitude from N -(triisopropylsilyl)pyrrole (N = 3.12), the weakest nucleophile of this series, to kryptopyrrole (3-ethyl-2,4-dimethylpyrrole, N = 11.63). Thus, highly reactive pyrroles show similar nucleophilic reactivities as enamines, whereas those of less-reactive pyrroles are comparable to allylsilanes or indoles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Broadly distributed nucleophilic reactivity of proteins coordinated with specific ligand binding activityJOURNAL OF MOLECULAR RECOGNITION, Issue 4 2005Yasuhiro Nishiyama Abstract Covalent nucleophile,electrophile interactions have been established to be important for recognition of substrates by several enzymes. Here, we employed an electrophilic amidino phosphonate ester (EP1) to study the nucleophilic reactivity of the following proteins: albumin, soluble epidermal growth factor receptor (sEGFR), soluble CD4 (sCD4), calmodulin, casein, ,-lactalbumin, ovalbumin, soybean trypsin inhibitor and HIV-1 gp120. Except for soybean trypsin inhibitor and ,-lactalbumin, these proteins formed adducts with EP1 that were not dissociated by denaturing treatments. Despite their negligible proteolytic activity, gp120, sEGFR and albumin reacted irreversibly with EP1 at rates comparable to the serine protease trypsin. The neutral counterpart of EP1 reacted marginally with the proteins, indicating the requirement for a positive charge close to the electrophilic group. Prior heating resulted in altered rates of formation of the EP1,protein adducts accompanied by discrete changes in the fluorescence emission spectra of the proteins, suggesting that the three-dimensional protein structure governs the nucleophilic reactivity. sCD4 and vasoactive intestinal peptide (VIP) containing phosphonate groups (EP3 and EP4, respectively) reacted with their cognate high-affinity binding proteins gp120 and calmodulin, respectively, at rates exceeding the corresponding reactions with EP1. Reduced formation of EP3,gp120 adducts and EP4,calmodulin adducts in the presence of sCD4 and VIP devoid of the phosphonate groups was evident, suggesting that the nucleophilic reactivity is expressed in coordination with non-covalent recognition of peptide determinants. These observations suggest the potential of EPs for specific and covalent targeting of proteins, and raise the possibility of nucleophile,electrophile pairing as a novel mechanism stabilizing protein,protein complexes. Copyright © 2005 John Wiley & Sons, Ltd. [source] Reactivity parameters for rationalizing iminium-catalyzed reactions,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010Sami Lakhdar Abstract The correlation equation (1), lg k(20,°C),=,s(E,+,N), where electrophiles are characterized by one (E) and nucleophiles are characterized by two parameters (N, s) was used to rationalize the scope of iminium-catalyzed reactions. Kinetics of the reactions of iminium triflates, pregenerated from cinnamaldehyde and secondary amines, with cyclic ketene acetals were studied by UV,Vis spectroscopy. From the second-order rate constants, electrophilicity parameters ,10,<,E,<,,7 have been derived for these iminium ions. Eqn (1) was found to correctly predict the rate constants for the reactions of the cinnamaldehyde-derived iminium ions with pyrroles, indoles, and sulfur ylides. The zwitterion obtained from cinnamaldehyde and indoline-2-carboxylic acid reacts more than 105 times faster with a sulfur ylide than predicted by Eqn (1), which is explained by MacMillan's ,electrostatic activation'. The failure of imidazolidinones to catalyze cyclopropanations of ,,,-unsaturated carbonyl compounds by sulfur ylides is not due to the low nucleophilic reactivity of sulfur ylides but due to their high Brønsted basicity which inhibits the formation of the iminium ions. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||