Counterintuitive Deshielding on the 13 C NMR Chemical Shift for the Trifluoromethyl Anion,Magnetic Resonance in Chemistry

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Counterintuitive Deshielding on the 13 C NMR Chemical Shift for the Trifluoromethyl Anion
Magnetic Resonance in Chemistry ( IF 1.9 ) Pub Date : 2019-12-08 , DOI: 10.1002/mrc.4958
Renan V Viesser ₁ , Cláudio F Tormena ₁

Affiliation

The trifluoromethyl anion (CF3−) displays 13C NMR chemical shift (175.0 ppm) surprisingly larger than neutral (CHF3, 122.2 ppm) and cation (CF3+, 150.7 ppm) compounds. This unexpected deshielding effect for a carbanion is investigated by density functional theory calculations and decomposition analyses of the 13C shielding tensor into localized molecular orbital contributions. The present work determines the shielding mechanisms involved in the observed behaviour of the fluorinated anion species, shedding light on the experimental NMR data and demystify the classical correlation between electron density and NMR chemical shift. The presence of fluorine atoms induces the carbon lone pair to create a paramagnetic shielding on the carbon nucleus.

中文翻译：

三氟甲基阴离子的 13 C NMR 化学位移的反直觉去屏蔽

三氟甲基阴离子 (CF3-) 的 13C NMR 化学位移 (175.0 ppm) 惊人地大于中性 (CHF3, 122.2 ppm) 和阳离子 (CF3+, 150.7 ppm) 化合物。通过密度泛函理论计算和将 13C 屏蔽张量分解分析为局部分子轨道贡献，研究了碳负离子的这种意想不到的去屏蔽效应。目前的工作确定了所观察到的氟化阴离子物种行为中涉及的屏蔽机制，揭示了实验 NMR 数据并揭开了电子密度和 NMR 化学位移之间的经典相关性的神秘面纱。氟原子的存在诱导碳孤对在碳核上产生顺磁屏蔽。

更新日期：2019-12-08

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