Cremer Dieter, Gräfenstein Jürgen
Department of Chemistry, University of the Pacific, 3601 Pacific Avenue, Stockton, California 95211, USA.
Phys Chem Chem Phys. 2007 Jun 14;9(22):2791-816. doi: 10.1039/b700737j. Epub 2007 Mar 20.
The analysis of NMR spin-spin coupling leads to a unique insight into the electronic structure of closed-shell molecules, provided one is able to decode the different features of the spin-spin coupling mechanism. For this purpose, the physics of spin-spin coupling is described and the way how spin-spin coupling constants (SSCCs) can be quantum mechanically determined. Based on this insight, a set of requirements is derived that guide the development of a quantum mechanical analysis of spin-spin coupling. It is demonstrated that the J-OC-PSP (=J-OC-OC-PSP: Decomposition of J into orbital contributions using orbital currents and partial spin polarization) analysis method fulfills all requirements. J-OC-PSP makes it possible to partition the isotropic indirect SSCC J or its reduced analogue K as well as the four Ramsey terms (Fermi contact (FC), spin dipole (SD), diamagnetic spin orbit (DSO), paramagnetic spin orbit (PSO)) leading to J (or K) into Cartesian components (for the anisotropic Ramsey terms SD, DSO, PSO), orbital contributions or electron interaction terms. For the purpose of decoding the spin-spin coupling mechanism, FC, SD, DSO, and PSO coupling is discussed in detail and related to electronic and bonding features of the molecules in question. The myth of empirical and semiempirical relationships between SSCCs and bonding features is unveiled. It is found that most relationships are only of limited, partly dubious value, often arising from a fortuitous cancellation of terms that cannot be expected in general. These relationships are replaced by quantum chemical relations and descriptions that directly reflect the complex electronic processes leading to spin-spin coupling.
核磁共振自旋-自旋耦合分析能够深入了解闭壳层分子的电子结构，前提是能够解读自旋-自旋耦合机制的不同特征。为此，本文描述了自旋-自旋耦合的物理原理以及自旋-自旋耦合常数（SSCCs）的量子力学确定方法。基于这一认识，推导出了一组要求，以指导自旋-自旋耦合量子力学分析的发展。结果表明，J-OC-PSP（=J-OC-OC-PSP：利用轨道电流和部分自旋极化将J分解为轨道贡献）分析方法满足所有要求。J-OC-PSP能够将各向同性间接SSCC J或其简化类似物K以及导致J（或K）的四个拉姆齐项（费米接触（FC）、自旋偶极（SD）、抗磁自旋轨道（DSO）、顺磁自旋轨道（PSO））划分为笛卡尔分量（对于各向异性拉姆齐项SD、DSO、PSO）、轨道贡献或电子相互作用项。为了解读自旋-自旋耦合机制，详细讨论了FC、SD、DSO和PSO耦合，并将其与相关分子的电子和键合特征联系起来。揭示了SSCCs与键合特征之间经验和半经验关系的误区。研究发现，大多数关系的价值有限，部分关系值得怀疑，往往是由于一般情况下无法预期的项的偶然抵消所致。这些关系被直接反映导致自旋-自旋耦合的复杂电子过程的量子化学关系和描述所取代。
