THE QUESTION OF REVERSIBLE FORMATION OF BROMONIUM IONS DURING THE COURSE OF ELECTROPHILIC BROMINATION OF OLEFINS .2. THE CRYSTAL AND MOLECULAR-STRUCTURE OF THE BROMONIUM ION OF ADAMANTYLIDENEADAMANTANE
THE QUESTION OF REVERSIBLE FORMATION OF BROMONIUM IONS DURING THE COURSE OF ELECTROPHILIC BROMINATION OF OLEFINS .2. THE CRYSTAL AND MOLECULAR-STRUCTURE OF THE BROMONIUM ION OF ADAMANTYLIDENEADAMANTANE
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DOI：
10.1021/ja00301a021
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发表时间：
1985-01-01
影响因子：
15
通讯作者：
BROWN, RS
中科院分区：
文献类型：
--
作者：
SLEBOCKATILK, H;BALL, RG;BROWN, RS
对adamantylideneadamantane(1)在CH2C12 （C20H28Br4）中溴化所产生的物质进行单晶x射线分析，发现它是一个稳定的三元环溴化溴离子(2)。结构显示出一个稍微不对称的三元环，Br-C键的长度为2.116(6)和2.194 (6)Á， CC键的长度为1.497 (8)Á。环的内角在溴原子处为40.6(2)，在C原子处为72.5(3)和66.9(3)。连接金刚烷环的碳的取代面之间的二面角为32.9。伴生的Br3~反离子与Br+形成了密切的接触，暗示了一个亲密的离子对，这可能是导致三元环不对称的原因。整体结构表明，在Br原子对面有严重的拥挤，这阻止了亲核试剂接近离子。这种不寻常的特征很可能是离子对稳定性的来源。还证明了2是由1以完全可逆的方式生成的。
Single-crystal X-ray analysis of the material produced when adamantylideneadamantane (1) is brominated in CH2C12 (C20H28Br4) reveals it to be a stable three-membered cyclic bromonium ion tribromide (2). Thestructure shows a slightly asymmetric three-membered ring with lengths of 2.116 (6) and 2.194 (6) Á for the Br-C bonds and 1.497 (8) Á for the CC bond. The internal angles of the ring are 40.6 (2) at Br and 72.5 (3) and 66.9 (3) at the C atoms. The dihedral angle between the substituent planes of the carbons connecting the adamantyl rings is 32.9. The associated Br3~ counterion forms a close contact with the Br+ suggestive of an intimate ion pair which may be the cause of the asymmetry in the three-membered ring. The overall structure reveals that there is severe crowding at the side opposite to the Br atom which prevents access of a nucleophile to the ion. This unusual feature is the likely source of the stabilityof the ion pair. It is also shown that 2 is formed in a completely reversible manner from 1.