Application of NMR spectroscopy of chiral association complexes 11—Rotation about the C(sp2)—C(aryl) Bond in 2,6-Difluorobenzamides Studied by 19F NMR
✍ Scribed by Miroslav Holǐk; Milena Turečková; Albrecht Mannschreck; Georgine Stühler
- Publisher
- John Wiley and Sons
- Year
- 1982
- Tongue
- English
- Weight
- 446 KB
- Volume
- 19
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
The energy barrier to rotation about the C(sp^2^)C(aryl) single bond in non‐planar N,N‐dimethyl‐, N,N‐tetramethylene‐, N,N‐diisopropyl‐2,6‐difluorobenzamides and in N,N‐dimethyl‐2‐chloro‐6‐fluorobenzamide was investigated by ^19^F{^1^H} NMR in the presence of an optically active shift reagent. The free energy of activation was calculated from the coalescence temperature of the fluorine signals; the calculation was accomplished using the simple, approximative equation and, also, by the graphical procedure including the (eigen) line width, i.e. without the broadening caused by two‐site exchange. A distinct effect of the size of the N‐substituents on the Δ__G__~c~‡values was observed, in accordance with expectation.