A New Look at the Classical Beckmann Rearrangement: A Strong Case of Active Solvent Effect
| Autor: | Luc G. Vanquickenborne, Minh Tho Nguyen, Greet Raspoet |
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| Rok vydání: | 1997 |
| Předmět: | |
| Zdroj: | Journal of the American Chemical Society. 119:2552-2562 |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/ja962364q |
| Popis: | Substituent and solvent effects on the reaction pathway of the Beckmann rearrangement were studied. Energy surfaces of the isolated gas phase systems were mapped out using ab initio MO calculations at the MPn and QCISD(T) levels with basis sets ranging from 6-31G(d,p) to 6-311++G(2df,2p). In the simplest gas phase system, the most favored path is as follows: protonation of formaldehyde oxime → N-protonated species → O-protonated species → fragmentation products, in which the 1,2-H-shift connecting both protonated isomers is rate-determining. While both methyl and formyl substituents on C and O of the oxime have only a small effect on the rate-controlling energy barrier, they significantly modify the barrier to fragmentation. The bulk solvent effect which is treated by a polarizable continuum model does affect only marginally the activation parameters with respect to the gas phase values. A combination of both quantum and statistical mechanics was also used to probe the solvent effect. In order to investi... |
| Databáze: | OpenAIRE |
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