1,721,020 research outputs found
Ion pairing and reactivity of the alkali metal and alkaline earth metal derivatives of ethyl (5-bromopentyl)acetoacetate
No full textMetal ion effects on the rate of intramolecular O-alkylation of the anion of ethyl(3-chloropropyl)acetoacetate
No full textAlkali-metal ion catalysis and inhibition of acetyl transfer from p-nitroaryl acetates to hexanoate ion
No full textA dinuclear strontium(II) complex as substrate-selective catalyst of ester cleavage
No full text[No abstract available
A ring-fusion/ring-fission mechanism for the metathesis reaction of macrocyclic formaldehyde acetals
No full textImportant insight has been obtained into the mechanism of the reversible acid-catalysed transacetalation of cyclophane formaldehyde acetals (formals) C-i in MCI, at 25 degrees C. ne order of appearance of the lowest oligomers in the early stages of the equilibration reaction is fully consistent with ring-fusion/ring-fission processes in which oxonium ion intermediates undergo S(N)2 reactions, according to an acid-catalysed bimolecular (A2) mechanism. The alternative acid-catalysed monomolecular (A1) reaction path, based on "back-biting" processes of carbenium ions generated by S(N)1-type cleavage of oxonium ion intermediates, predicts sequences that are in marked contrast with experimental findings
The Ba(II) complex of a crown ether bearing a sulphydryl side-arm as turnover catalyst of ester cleavage
No full textWhen activated by barium(II), 18-mercaptometyl-1,4,7,10,13,16-hexaoxacyclononadecane acts as turnover catalyst in the methanolysis of p-nitrophenyl acetate (pNPOAc) under slightly basic conditions in CH3CN-CH3OH 9:1 (v/v). The function of the complexed barium ion is to enhance the nucleophilicity of the pendant SH group towards the acetyl group of the ester. and to assist as a built-in electrophile the subsequent transfer of the acetyl group from the acetylated intermediate to the solvent. Besides the above double displacement mechanism of ester cleavage, a direct metal-ion assisted methanolysis involving reaction of pNPOAc with the ternary complex (5 BaOMe)(+) has been detected. (C) 1996 Elsevier Science Lt
The bis-barium complex of a butterfly crown ether as a phototunable supramolecular catalyst
No full textReversible phototuning of the catalytic efficiency of the bis-barium complex of azobis(benzo-18-crown-6) in the basic ethanolysis of anilide derivatives has been achieved by light-induced cis reversible arrow trans interconversion of the azobenzene spacer unit of the catalyst. The geometry of the productive catalyst-substrate complex is more favorable when the concave cis form of the catalyst is involved. Continuous photoregulation of the catalytic activity at any intermediate value between the "HIGH" and "LOW" levels was achieved by proper adjustment of the excitation wavelength or the irradiation time. The complete and relatively fast interconvertibility of photostationary states allowed the activity of the catalyst to be repeatedly photoswitched "HIGH" and "LOW" in the course of the same run
Supramolecular control of reactivity and catalysis - effective molarities of recognition-mediated bimolecular reactions
No full textReactivity data relating to bimolecular reactions of compounds featuring complementary recognition sites are critically surveyed and discussed in terms of effective molarity (EM) as an absolute measure of the efficiency of the intracomplex reactions. Comparison of experimentally determined EM values with idealized values estimated for strain-free cyclizations on the basis of the number of internal rotors in the linker allowed quantification of the penalties of imperfect design in terms of entropy and strain. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Reactivity data relating to bimolecular reactions of compounds
featuring complementary recognition sites are critically
surveyed and discussed in terms of effective molarity
(EM) as an absolute measure of the efficiency of the intracomplex
reactions. Comparison of experimentally determined EM values with idealized values estimated for strain-free cyclizations
on the basis of the number of internal rotors in the
linker allowed quantification of the penalties of imperfect design
in terms of entropy and strain
Effect of Cation-Complexing Agents on the Ba(II)-Assisted Basic Ethanolysis of Phenyl Acetate: From Cation Deactivation to Cation Activation
No full text- …
