- Heterolytic cleavage of H2 by frustrated B/N Lewis pairs
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Treatment of the Lewis acid B(C6F5)3 with the Lewis base 2,6-dimethylpiperidine (DMP) resulted in the formation of the classical Lewis acid?base adduct DMP-B(C6F5) 3, 1a, which was anticipa
- Jiang, Chunfang,Blacque, Olivier,Fox, Thomas,Berke, Heinz
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experimental part
p. 2117 - 2124
(2011/06/22)
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- Conformational schemes: An available tool for the assignment of NMR- measured barriers, demonstrated with the example of crowded piperidines
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MM3-derived full conformational schemes are proposed as a powerful and convenient tool for the currently problematic assignment of NMR-measured barriers for flexible systems that possess more than one type of independent intramolecular motion. Hindered piperidines were chosen as a molecular model with seven possible intramolecular dynamic processes. The free energies of activation for methyl group topomerization in 1,2,2,5,5-pentamethyl-, 1- ethyl-2,2,6,6-tetramethyl-, and 1-butyl-2,2,6,6-tetramethylpiperidines were determined at different temperatures by means of line-shape analysis of 13C NMR spectra. Schemes of conformational transformations for the N-Me and N-Et compounds were created with MM3-based methodology. These schemes permit the assignment of the measured barriers to ring inversion for the N-Me compound and to ring inversion-nitrogen inversion, ring inversion, and C-N rotation for the N-Alk(primary) piperidines (for the N-Et and N-Pr derivatives the experimental barriers had previously been attributed to isolated C-N rotation only). A unique dynamic process for tertiary amines, isolated nitrogen inversion, is described for the N-alkylpiperidines with an N-substituent bulkier than Me.
- Belostotskii, Anatoly M.,Gottlieb, Hugo E.,Aped, Pinchas,Hassner, Alfred
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p. 449 - 455
(2007/10/03)
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