RING SIZE LIMITS FOR THE DIRECT OBSERVATION OF HYDRIDO-BRIDGED SECONDARY CYCLOALKYL CATIONS - CORRESPONDENCE WITH CHEMICAL-REACTIVITY STUDIES
RING SIZE LIMITS FOR THE DIRECT OBSERVATION OF HYDRIDO-BRIDGED SECONDARY CYCLOALKYL CATIONS - CORRESPONDENCE WITH CHEMICAL-REACTIVITY STUDIES
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DOI：
10.1021/ja00506a018
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发表时间：
1979-01-01
影响因子：
15
通讯作者：
SORENSEN, TS
中科院分区：
文献类型：
--
作者：
KIRCHEN, RP;SORENSEN, TS
在含有8-11个碳原子的环中直接观察到稳定的双氧桥环烷基阳离子，这与在涉及假定的碳阳离子中间体的反应中观察到直接跨环氢位移的环烷基环完全对应。在这个可观察到的离子系列中，离子反应性和核磁共振性质都存在有趣的变化。对于8、9和11个碳原子的环，形成相应的1-甲基7-、8-和10-碳叔离子，而10元桥连离子消除氢并形成十烷基阳离子。核磁共振结果表明，两个末端氢的化学位移的减少与桥氢的化学位移的相应增加相匹配。这种行为与理论模型是一致的，该模型粗略地将键合描绘为两个阳离子中心之间的氢化物离子。桥连氢上的负电荷随着两个桥连碳的分离增加而增加。Prelog和科普以及他们各自的同事1从1952年开始的经典研究已经确定，在涉及碳正离子中间体的反应中，从Cg到Cp的环烷基环发生直接的跨环氢化物位移。在Cp系统中未观察到这种反应性，在Cj情况下仅以较小的方式观察到。我们最近制备了可观察到的C10环癸基阳离子2· 3，并根据非常不寻常的NMR光谱提出，该离子具有μ-双氧桥连结构1。
The direct observation of stable hydrido-bridged cycloalkyl cations, in rings containing 8-11 carbon atoms, corre-sponds exactly with those cycloalkyl rings where direct transannular hydrogen shifts have been observed in reactions involving a presumed carbocation intermediate. Within this observable ion series, there are interesting variations in both the ion reactivity and in the NMR properties. For rings of 8, 9, and 11 carbons, the corresponding 1-methyl 7-, 8-, and 10-carbon tertiary ion is formed, whereas the 10-membered hydrido-bridged ion eliminates hydrogen and forms the decalyl cation. The NMR results show that decreases in thechemical shiftof the two terminal hydrogens are matched by a corresponding increase in the chemical shifts of the bridging hydrogen. This behavior is consistent with theoretical models which crudely picture the bonding as a hydride ion centered between two cationic centers. The negative charge on the bridging hydrogen increases as the separation of the two bridged carbons is increased. Correspondingly, the terminal protonsexperience an increased positive charge.The classic studies by Prelog and Cope and their respec-tive co-workers1 beginning in 1952 have established that cy-cloalkyl rings from Cg to Cp undergo direct transannular hydride shifts in reactions involving a carbocation intermediate. This reactivity was not observed for Cp systems and only in a minor way for the Cj case. We have recently prepared the observable Cio cyclodecyl cation2· 3 and have suggested, based on the very unusual NMR spectrum, that this ion possesses a µ-hydrido-bridged structure 1.