高分辨率 (19) F MAS 核磁共振光谱:在化氧酸盐中存在结构障碍和不寻常的 J 合
John M Griffin1, Jonathan R Yates, Andrew J Berry
1School of Chemistry and EaStCHEM, University of St. Andrews, North Haugh, St. Andrews KY16 9ST, UK.
Journal of the American Chemical Society
|October 21, 2010
概括
高分辨率的-19神奇角度旋转NMR显示了克利诺米特的显著结构障碍. 观察到意想不到的-联结,挑战了关于这种酸中的离子键的假设.
科学领域:
- 固态NMR光谱学 固态NMR光谱学
- 材料科学 材料科学 材料科学
- 晶体学 晶体学是指结晶学.
背景情况:
- 魔术角度旋转 (MAS) NMR是一种强大的技术,用于研究晶体固体中的原子环境.
- 克利诺米特是一种含水酸,由于OH的F(-) 等替代物,可以表现出结构障碍.
- 了解结合特征对于描述矿物质的特性和行为至关重要.
研究的目的:
- 通过使用高分辨率的 (19) F MAS NMR 来调查化物替代的化石中的结构障碍和结合.
- 通过将实验数据与密度函数理论 (DFT) 计算相关联来分配观察到的 (19) F NMR 信号.
- 探索观测到的 (19) F-(19) F标量 (J) 合的性质和影响.
主要方法:
- 高分辨率的 (19) F 魔力角旋转 (MAS) 核磁共振光谱.
- 密度函数理论 (DFT) 计算用于NMR参数预测.
- 二维 (19) F 双量子 MAS 核磁共振实验.
- (19) F J 分辨率的MAS 核磁共振光谱.
主要成果:
- 在50%的替代克利诺米特中确定了四个不同的 (19) F NMR 位点,表明了广泛的结构障碍.
- 通过模拟各种本地F环境,DFT计算成功地分配了19F峰值.
- 观察到意想不到的 (19) F-(19) F标量 (J) 合,并通过 DFT 和 J 解析的 NMR 实验得到证实.
- 在合成和天然的克利诺米特样本中发现了类似的障碍和旋转-旋转相互作用.
结论:
- 高分辨率的 (19) F MAS 核磁共振是有效的特征结构障碍在复杂的固体,如klinohumite.
- 存在的 (19) F-(19) F J 合表明,Mg-F 相互作用的共价性比以前假设的更强.
- 这些发现提供了关于固态材料的结合性质和透过空间J合的机制的见解.
相关概念视频
¹H NMR: Interpreting Distorted and Overlapping Signals
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
2D NMR: Homonuclear Correlation Spectroscopy (COSY)
Homonuclear correlation spectroscopy, or COSY, is a 2-dimensional NMR technique that provides information about coupled protons. Typically, the geminal and vicinal coupling are observed. For example, consider the COSY spectrum of ethyl acetate, where its 1D proton NMR spectrum is plotted along the vertical and horizontal axes with their corresponding chemical shift scale. Three spots on the diagonal corresponding to the three peaks in the 1D proton spectrum are called diagonal peaks. The COSY...
2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)
Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does...
NMR Spectroscopy: Spin–Spin Coupling
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...


