- Electron-withdrawing substituents decrease the electrophilicity of the carbonyl carbon. An investigation with the aid of 13C NMR chemical shifts, v(C=O) frequency values, charge densities, and isodesmic reactions to interprete substituent effects on reactivity
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13C NMR chemical shifts and v(C=O) frequencies have been measured for several series of phenyl-or acyl-substituted phenyl acetates and for acyl-substituted methyl acetates to investigate the substituent-induced changes in the electrophilic character of the carbonyl carbon. Charge density, bond order, and energy calculations have also been performed. The spectroscopic and charge density results indicate that opposite to the conventional thinking, electron-withdrawing substituents do not increase the electrophilicity of the carbonyl carbon but instead decrease it. On the other hand, reaction energies of the isodesmic reactions designed show that electron-withdrawing substituents destabilize the carbonyl derivatives investigated. So, a significant ground-state destabilization of carboxylic acid esters, and carbonyl compounds in general, due to the decreased resonance stabilization, is proposed as a novel concept to explain both the increase in their reactivity and the changes in the chemical shifts and carbonyl frequencies induced by electron-withdrawing substituents.
- Neuvonen, Helmi,Neuvonen, Kari,Koch, Andreas,Kleinpeter, Erich,Pasanen, Paavo
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p. 6995 - 7003
(2007/10/03)
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- Investigations on substituent and solvent effects on solvolysis reactions Part IX. The influence of polar substituents on the imidazole catalyzed hydrolysis of 2,4-dinitrophenyl acetates in water
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The imidazole catalyzed hydrolysis of polar substituted 2,4-dinitrophenyl acetates in water has been investigated at different temperatures. The observed rates correspond to the bimolecular nucleophilic addition of the imidazole at the carboxylic carbon atom followed by a very fast hydrolysis of the N-acetylimidazole in water. The influence of polar substituents in the acid moiety of the ester molecule on the hydrolysis reaction can be described by an electrostatic dipole-dipole interaction in the same way as the neutral hydrolysis of polar substituted ethyl acetates.
- Bittner,Schmeer
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p. 2593 - 2596
(2007/10/03)
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