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首页> 外文会议>Symposium on Structures and Mechanisms: from Ashes to Enzymes, May 12-14, 2000 >Does the Magnitude of NMR Coupling Constants Specify Bond Polarity?
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Does the Magnitude of NMR Coupling Constants Specify Bond Polarity?

机译：NMR耦合常数的大小是否指定键极性？

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In this study we have addressed the question of whether the existence of a spin-spin coupling constant between a pair of atoms can be related to bond polarity. We have applied external electric fields along the H-F, C-F, C-C1, and C-Li bonds in the molecules HF, CH_3F, CH_3C1, and CH_3Li, respectively, to reverse the dipole moment, and have computed one-bond EOM-CCSD spin-spin coupling constants ~1J_(H-F), ~1J_(C-F), ~1J_(C-Cl), and ~1J_(C-Li) as a function of field strength. The results of this investigation demonstrate that the coupling constant is not a maximum when the bonding between the atoms is very nonpolar (covalent) as the dipole moment approaches zero. In fact, we find no correlation between the polarity of a bond and its coupling. Hence, the experimental measurement of a coupling constant cannot be interpreted as proof of the existence of a covalent bond. We have also computed EOM-CCSD two-bond coupling constants in hydrogen-bonded complexes, and addressed the question of the relationship between ~(2h)J_(X-Y) and the nature of the X-H-Y hydrogen bond. For this study we have examined the equilibrium structures of C1H:NH_3 and the value of ~(2h)J_(Cl-N) as a function of field strength and hydrogen bond type. In addition, we have computed the O-O spin-spin coupling constant ~(2h)J_(O-O) for O_2H_5~+, and for two H_2O molecules in the same orientation as in the O_2H_5~+ complex, but with the hydrogen-bonded proton removed. Our results again suggest that the experimental measurement of a coupling constant across a hydrogen bond does not prove that the hydrogen bond is covalent.
机译：在这项研究中，我们解决了一个问题：一对原子之间自旋-自旋耦合常数的存在是否与键的极性有关。我们分别沿着分子HF，CH_3F，CH_3C1和CH_3Li中的HF，CF，C-C1和C-Li键施加了外部电场来逆转偶极矩，并计算了单键EOM-CCSD自旋自旋耦合常数〜1J_（HF），〜1J_（CF），〜1J_（C-Cl）和〜1J_（C-Li）作为场强的函数。研究结果表明，当偶极矩接近零时，原子之间的键合非常非极性（共价）时，耦合常数不是最大。实际上，我们发现键的极性与其耦合之间没有关联。因此，偶合常数的实验测量不能解释为存在共价键的证据。我们还计算了氢键配合物中的EOM-CCSD两键耦合常数，并解决了〜（2h）J_（X-Y）与X-H-Y氢键性质之间的关系问题。在本研究中，我们研究了C1H：NH_3的平衡结构和〜（2h）J_（Cl-N）的值与场强和氢键类型的关系。此外，我们已经计算出O_2H_5〜+以及与H_2O_5〜+络合物方向相同但带有氢键质子的两个H_2O分子的OO自旋-自旋偶合常数〜（2h）J_（OO）删除。我们的结果再次表明，跨氢键的偶合常数的实验测量不能证明氢键是共价的。

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