Solvolysis and Isomerization of cis- and trans-1-Bromo-1-(p-anisyl)-propene (α-Bromoanethole) Mesomeric Vinyl Cations, Part V
✍ Scribed by C. A. Grob; R. Nussbaumer
- Publisher
- John Wiley and Sons
- Year
- 1971
- Tongue
- German
- Weight
- 507 KB
- Volume
- 54
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
The influence of a β‐methyl group on the reactivity of two stereoisomeric vinyl bromides has been studied. In 80% ethanol cis‐(8) and trans‐α‐bromoanethole (9) undergo first order reactions leading to p‐methoxypropiophenone (15), 1‐ethoxy‐1‐(p‐anisyl)‐propene (16) and p‐anisylpropyne (12). Solvolysis of the cis isomer 8 is accompanied by isomerization to the more stable trans isomer 9 which is approx. eight times less reactive than 8. Cis‐trans isomerization is also observed in nitrobenzene at 150°.
These results are in agreement with the unimolecular substitution‐elimination (S~N~1−__E__1) mechanism which competes with cis‐trans isomerization at the ion pair stage.
The solvolysis rate of 9 is slightly lower and that of 8 somewhat higher than the rate of α‐bromo‐p‐methoxystyrene (3c). In the absence of other effects a β‐methyl group therefore slightly depresses the ionization rate, presumably by steric hindrance of solvation. These results confirm the negligible polar influence of a β‐methyl substituent on the stability of vinyl cations.