Schleyer Paul von Ragué, Najafian Katayoun
Institut für Organische Chemie der Universität Erlangen-Nürnberg, Henkstrasse 42, D-91054 Erlangen, Germany, and Department of Chemistry, University of Georgia, Athens, Georgia 30602.
Inorg Chem. 1998 Jul 13;37(14):3454-3470. doi: 10.1021/ic980110v.
Comprehensive ab initio calculations RMP2(fc)/6-31G on the closo-monocarbaboranes, CB(n)()(-)(1)H(n)()(-) (n = 5-12), and the closo-dicarboranes, C(2)B(n)()(-)(2)H(n)() (n = 5-12), show that the relative energies of all the positional isomers agree with the qualitative connectivity considerations of Williams and with the topological charge stabilization rule of Gimarc. The reaction energies (DeltaH) of the most stable positional isomers, 1-CB(4)H(5)(-), CB(5)H(6)(-), 2-CB(6)H(7)(-), 1-CB(7)H(8)(-), 5-CB(8)H(9)(-), 1-CB(9)H(10)(-), 2-CB(10)H(11)(-), CB(11)H(12)(-), as well as 1,5-C(2)B(3)H(5), 1,6-C(2)B(4)H(6), 2,4-C(2)B(5)H(7), 1,7-C(2)B(6)H(8), 4,5-C(2)B(7)H(9), 1,10-C(2)B(8)H(10), 2,3-C(2)B(9)H(11), and 1,12-C(2)B(10)H(12) (computed using the equations, CBH(2)(-) + (n - 1)BH(increment) --> CB(n)()H(n)()(+1)(-) (n = 4-11) and C(2)H(2) + nBH(increment) --> C(2)B(n)()H(n)()(+2) (n = 3-10)), show that the stabilities of closo-CB(n)()(-)(1)H(n)()(-) and of closo-C(2)B(n)()(-)(2)H(n)() generally increase with increasing cluster size from 5 to 12 vertexes. This is a characteristic of three-dimensional aromaticity. There are variations in stabilities of individual closo-CB(n)()(-)(1)H(n)()(-) and closo-C(2)B(n)()(-)(2)H(n)() species, but these show quite similar trends. Moreover, there is rough additivity for each carbon replacement. The rather large nucleus independent chemical shifts (NICS) and the magnetic susceptibilities (chi), which correspond well with one another, also show all closo-CB(n)()(-)(1)H(n)()(-) and closo-C(2)B(n)()(-)(2)H(n)() species to exhibit "three-dimensional aromaticity". However, the aromaticity ordering based on these magnetic properties does not always agree with the relative stabilities of positional isomers of the same cluster, when other effects such as connectivity and charge considerations are important.
对闭式-单碳硼烷CB(n)()(-)(1)H(n)()(-)（n = 5 - 12）和闭式-二碳硼烷C(2)B(n)()(-)(2)H(n)()（n = 5 - 12）进行的全从头算RMP2(fc)/6 - 31G计算表明，所有位置异构体的相对能量与Williams的定性连接性考量以及Gimarc的拓扑电荷稳定规则相符。最稳定位置异构体1 - CB(4)H(5)(-)、CB(5)H(6)(-)、2 - CB(6)H(7)(-)、1 - CB(7)H(8)(-)、5 - CB(8)H(9)(-)、1 - CB(9)H(10)(-)、2 - CB(10)H(11)(-)、CB(11)H(12)(-)以及1,5 - C(2)B(3)H(5)、1,6 - C(2)B(4)H(6)、2,4 - C(2)B(5)H(7)、1,7 - C(2)B(6)H(8)、4,5 - C(2)B(7)H(9)、1,10 - C(2)B(8)H(10)、2,3 - C(2)B(9)H(11)和1,12 - C(2)B(10)H(12)的反应能（ΔH）（使用方程式CBH(2)(-) + (n - 1)BH(increment) --> CB(n)()H(n)()(+1)(-)（n = 4 - 11）和C(2)H(2) + nBH(increment) --> C(2)B(n)()H(n)()(+2)（n = 3 - 10）计算得出）表明，闭式 - CB(n)()(-)(1)H(n)()(-)和闭式 - C(2)B(n)()(-)(2)H(n)()的稳定性通常随着簇尺寸从5个顶点增加到12个顶点而增加。这是三维芳香性的一个特征。各个闭式 - CB(n)()(-)(1)H(n)()(-)和闭式 - C(2)B(n)()(-)(2)H(n)()物种的稳定性存在差异，但这些差异呈现出相当相似的趋势。此外，每次碳取代都具有大致的加和性。相当大的核独立化学位移（NICS）和彼此对应良好的磁化率（χ）也表明所有闭式 - CB(n)()(-)(1)H(n)()(-)和闭式 - C(2)B(n)()(-)(2)H(n)()物种都表现出“三维芳香性”。然而，当连接性和电荷考量等其他效应很重要时，基于这些磁性性质的芳香性排序并不总是与同一簇的位置异构体的相对稳定性一致
