- 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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- Preparation and reactions of samarium diiodide in nitriles
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Samarium diiodide can be prepared from samarium metal in various nitriles. Because of its chemical inertness pivalonitrile is the most suitable solvent. Organic reactions mediated by SmI2 are slower than in THF, but selectivities are often improved. Reactions are greatly accelerated by addition of catalytic amounts of some transition metal salts.
- Hamann, Beatrice,Namy, Jean-Louis,Kagan, Henri B.
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p. 14225 - 14234
(2007/10/03)
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