Dynamic NMR study of the electronic state of heteroaromatics. IX—π-Electron deficiency of various substituted thiazinethiones, thiazinium salts and analogous pyrimidines by means of barriers to rotation about exocyclic partial C,N double bonds
✍ Scribed by E. Kleinpeter; W. Schroth; K. Pihlaja
- Publisher
- John Wiley and Sons
- Year
- 1991
- Tongue
- English
- Weight
- 503 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
The ^1^H NMR spectra and the barriers to rotation about exocyclic partial C,N double bonds of various series of thiazinethiones 1, the corresponding thiazinium salts 5–9 and some pyrimidinethiones 10–13 are reported and discussed with respect to the π‐electron deficiency of these heteroaromatic compounds. Substituent influences are critically considered; in particular, the C,N barrier differences of C,NMe~2~ and C, pyrrolidino were used to estimate the type of dynamic process, which is different in pyrimidinethiones 10–13 and thiazinethiones/thiazinium salts 1–9. The compounds studied corroborate the pseudo‐chalcogeno analogy principle. Previously studied compounds are included to display the π‐electron deficiency influence of the heterocyclic system on the ^1^H chemical shifts of NR~2~, phenyl, the H‐5 protons and the exocyclic barriers to C,N rotation; adequate quantitative estimations are reported.