Chemistry Institute, University of Campinas, Campinas, SP, Brazil.
Magn Reson Chem. 2011 Dec;49(12):763-7. doi: 10.1002/mrc.2838. Epub 2011 Nov 17.
The present study shows that a hydrogen bond between the OH group and the fluorine atom is not involved in the (1h)J(FH) spin-spin coupling transmission either for 4-bromo-2-fluorophenol or 2-fluorophenol. In fact, according to a quantum theory of atoms in molecules analysis, no bond critical point is found between O-H and F moieties. The nature of the transmission mechanism of the Fermi contact term of the (1h)J(FH) spin-spin coupling is studied by analyzing canonical molecular orbitals (see J. Phys. Chem. A 2010, 114, 1044), and it is observed that virtual orbitals play only a quite minor role in its transmission. This is typical of a Fermi contact term transmitted mainly through exchange interactions owing to the overlap of proximate electronic clouds; therefore, it is suggested to identify them as (nTS)J(FH) coupling where n stands for the number of formal bonds separating the coupling nuclei. In the cases studied in this work is n = 4. Results presented in this work could provide an interesting rationalization for different experimental signs known in the current literature for proximate J(FH) couplings.
本研究表明，在 4-溴-2-氟苯酚或 2-氟苯酚中，(1h)J(FH) 自旋-自旋偶合传递过程并不涉及 OH 基团与氟原子之间的氢键。事实上，根据分子中原子的量子理论分析，在 O-H 和 F 部分之间未发现键临界点。通过分析正则分子轨道（参见 J. Phys. Chem. A 2010, 114, 1044），研究了 (1h)J(FH) 自旋-自旋偶合的费米接触项的传递机制的性质，观察到虚拟轨道在其传递中仅起很小的作用。这是典型的费米接触项，主要通过由于相邻电子云的重叠而产生的交换相互作用来传递；因此，建议将它们识别为 (nTS)J(FH) 偶合，其中 n 代表将偶合核分开的形式键的数量。在本工作中研究的情况下，n = 4。本工作中提出的结果可为当前文献中已知的相邻 J(FH) 偶合的不同实验符号提供有趣的合理化解释。
