C-13 NUCLEAR MAGNETIC-RESONANCE STUDIES OF BENZOCYCLOALKENES AND FLUOROBENZOCYCLOALKENES
C-13 NUCLEAR MAGNETIC-RESONANCE STUDIES OF BENZOCYCLOALKENES AND FLUOROBENZOCYCLOALKENES
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DOI：
10.1021/jo00867a002
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发表时间：
1976-01-01
影响因子：
3.6
通讯作者：
KITCHING, W
中科院分区：
文献类型：
--
作者：
ADCOCK, W;GUPTA, BD;KITCHING, W
J 1, 3 (4Jh, h) 下降，J14 (5Jh, h) 大幅增加，并讨论了键长、角度和电负性变化的影响。使用 CNDO/2 最小化几何形状，在各种 Jh、h 的趋势中获得了 9 个令人印象深刻的一致性，并向作者表明 CNDO/2 计算的几何形状和电荷密度很可能接近事实。在对苯并环烯烃的某些硅类似物 10 的 13C NMR 光谱进行研究时，出现了“环应变”对芳基碳化学位移的影响问题，因此我们开始对苯并环烯烃本身的光谱进行检查。这项研究似乎具有潜在的启发性，因为预计芳基 13C 位移会出现相当大的变化，并且可以解释为直接在环中的原子核处的键序和电荷密度波动的反映。无论如何，这些数据都非常重要，因为它们需要以某种方式通过更完善的 13C 化学位移理论来适应。文献中确实以一种模糊的方式存在关于一种或两种苯并环烯烃的分散数据，但关键的光谱分配没有得到证实。据了解，同一领域的另外两项平行调查正在进行并已于 11’12 报告，但目前已知一份报告 11 中的一些任务需要修改。在我们的工作中，很明显，苯并环烯的战略性氟取代衍生物对于解决烃类分配的棘手问题有很大帮助，但此外还提供了其他有趣的数据。合成某些氘代衍生物的必要性激发了人们对 NMR 任务的先前建议35'13 的好奇心，并且我们在这个方向上的结论也被提出。随着人们对 13C 弛豫测量的洞察力的不断提高，14* 我们已经对一些苯并环烯烃进行了此类研究，并且根据特定旋转模式对弛豫的不同贡献，结果的系统性得到了合理化。
J 1, 3 (4Jh, h) decreased and J14 (5Jh, h) increased substan-tially, and the effects of bond length, angle, and electroneg-ativity changes were discussed. UsingCNDO/2 minimized geometries, 9 impressive agreement in trends in the various Jh, h was obtained, and indicated to the authors that the calculated geometries and charge densities by CNDO/2 were, in all likelihood, close to the truth. In connection with an investigation of the 13C NMR spectra of certain silicon analogues10 of the benzocycloalk-enes, the question of “ring-strain” effects on aryl-carbon chemical shifts arose, and we therefore commenced an ex-amination of the spectra of the benzocycloalkenes them-selves. This study seemed potentially illuminating since rather substantial variations in the aryl 13C shifts were ex-pected, and could be construed as a reflection of bondorder and charge density fluctuations at the nuclei directly in the ring. In any event, the data were of considerable im-portance, since they would need to be accommodated in some way by more refined theories of the 13C chemical shift. Scattered pieces of data on one or two benzocycloalk-enes did exist in an obscure fashion in the literature, but critical spectral assignments were not substantiated. It emerged that two other parallel investigations in the same area were being conducted and were reported, 11’12 but some of the assignments in one report11 are now known to re-quire modification. In our work, it became clear that strategically fluoro-substituted derivatives of the benzocycloalk-enes were of much assistance in the vexing question of as-signments in the hydrocarbons, but in addition afforded data of other interest. The necessity to synthesise certain deuterated derivatives stimulated a curiosity in previous suggestions35’13 of NMR assignments and our conclu-sions in this direction are also presented. With the increasing appreciation of the insight available from 13C relaxation measurements, 14* we have conducted such studies with some of the benzocycloalkenes, and the systematics of the results are rationalized in terms of dif-fering contributions to relaxation from specific rotational modes.