Structural investigations of C-nitrosobenzenes. Part 2. NMR studies of monomer-dimer equilibria including restricted nitroso group rotation in monomers
Structural investigations of C-nitrosobenzenes. Part 2. NMR studies of monomer-dimer equilibria including restricted nitroso group rotation in monomers
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DOI：
10.1039/a708653i
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发表时间：
1998-04-01
期刊：
影响因子：
--
通讯作者：
Orrell, KG
中科院分区：
文献类型：
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作者：
Fletcher, DA;Gowenlock, BG;Orrell, KG
本文用全H-1 NMR谱带形状分析法测定了单体亚硝基苯和十一种取代亚硝基苯在溶液中的亚硝基转动能垒。旋转的Delta G双匕首（298.15 K）值在31-41 kJ mol（-1）范围内。4-取代的化合物的值与取代基的Hamburg sigma（p）（+）参数很好地相关。对亚硝基苯的实验能垒与理论计算进行了比较。研究了这些化合物在溶液中的单体-二聚体平衡，计算了Z-和E-偶氮二聚体解离成单体的Δ H-、Δ S-和Δ C-数据。本文用含时和二维交换谱（2D-EXSY）的NMR测量方法，获得了3-甲基亚硝基苯和3，5-二甲基亚硝基苯二聚体的解离动力学数据，讨论了二聚体和单体的基态和过渡态（包括它们的旋转异构体之间的交换）的能量分布。
Energy barriers associated with rotation of nitroso groups in monomeric nitrosobenzene and eleven monomeric substituted nitrosobenzenes in solution have been measured by total H-1 NMR bandshape analysis. Delta G double dagger (298.15 K) values for the rotations are in the range 31-41 kJ mol(-1). The values for 4-substituted compounds correlate well with the Hammete sigma(p)(+) parameter for the substituent. The experimental energy barrier for nitrosobenzene is compared with theoretical calculations. Monomer-dimer equilibria of these compounds in solution have been investigated, with Delta H-, Delta S- and Delta C- data calculated for the dissociation of both Z-and E-azodioxy dimers to monomers. Kinetic data, based on time-dependent and two-dimensional exchange spectroscopy (2D-EXSY) NMR measurements, have been obtained for the dissociation of 3-methylnitrosobenzene and 3,5-dimethylnitrosobenzene dimers, Energy profiles for the ground and transition states of both dimers and monomers (including exchange between both their rotameric forms) are discussed.