Stable Vinyl Cations. Direct Spectroscopic Observation of Vinyl-Substituted Vinyl Cations
Stable Vinyl Cations. Direct Spectroscopic Observation of Vinyl-Substituted Vinyl Cations
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稳定的乙烯基阳离子。
DOI：
10.1021/ja00367a069
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发表时间：
1982
影响因子：
15
通讯作者：
H. Mayr
中科院分区：
文献类型：
--
作者：
H. Siehl;H. Mayr
909 似乎比其他共振要宽得多。因此，低温光谱（图 1）没有给出“经典”降冰片阳离子冻结的证据。这仅意味着，如果以快速平衡经典离子的方式观察光谱，则该平衡势垒必须低于约 3 kcal mol-I。在这个限制内，人们可以采取不同的观点。 Saunders 最近对适当氘标记的降冰片基阳离子的研究表明，由于对称性的扰动，同位素分裂非常小。这一结果为“非经典”对称降冰片基阳离子提供了更强有力的支持，尽管不太直接。我们预计将来能够在 30 K 范围内进行 MAS 13C NMR 光谱，并期待在这个扩展的温度范围内对该阳离子和其他阳离子进行更多研究。
909 appear to be significantly broader than the other resonances. Thus, the low-temperature spectra (Figure 1) give no evidence of freezing out of a "classical" norbornyl cation. This means only that if one views the spectra in terms of rapidly equilibrating classical ions, the barrier of that equilibration must be lower than about 3 kcal mol-I. Within this limitation, one can adopt a different view. The recent studies of the appropriately deuterium labeled norbornyl cation by Saunders show very small isotopic splittings owing to perturbation of ~ymmetry.'~ This result is stronger support, albeit less direct, for the "nonclassical" symmetrical norbornyl cation. We anticipate that we shall be able to conduct MAS 13C NMR spectroscopy in the 30 K range in the future and look forward to additional studies of this and other cations over this extended temperature range.