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The barriers to interconversion of the stereomers of a number of N-cyano-O-phenylisoureas and related systems have been examined by variable temperature 1H NMR spectroscope. Rate constants were determined from the coalescence temperature using the Gutowsky-Holm equation, and free energies of activation then derived using the Eyring equation. The effect of structure on the rate process is discussed in relation to the bond-rotation and nitrogen-inversion mechanisms and it is concluded that the observations are best explained by a mixture of mechanisms. |
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