Conformational equilibria and torsional barriers of the isopropyl groups in N,N-diiso-propylbenzamide and its thio and seleno analogues
✍ Scribed by Ulf Berg; Ingrid Pettersson
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- English
- Weight
- 537 KB
- Volume
- 23
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
The conformations of the isopropyl groups and the barriers to conformational interconversion in N,N-diisopropylbenzamide (l), and its thio (2) and seleno (3) analogues have been studied by dynamic '€I NMR spectroscopy. In 1 only one conformation is observed, whereas 2 and 3 exist as mixtorc?s of three conformations. The use of the strongly deshielding C=X (X = 0, S, Se) group and comparison with earlier results on similar systems allows total assignment, in the case of 2, redying an earlier proposal. The temperature dependence of the NMR spectra of 2 and 3 clearly shows that the Eand 2-isopropyl groups rotate with very diiferent rates, thns providing experimental evidence for the stepwise nature of the conformational interchange. i V , ~-D ~o p r o p y l [ ~-( m e t h y l t h i o ) b e n ~l i d e n e ] ~o n i ~ ioqde (4). This compound C,H,(CH,S)C= N[CH(CH3)2]21-was prepared from 2 and methyl