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首页> 外文期刊>Journal of magnetic resonance >Direct Assignment of ~(13)C NMR Spectra of Rigid Solids by Two-Dimensional Magic-Angle-Spinning Separated-Local-Field Spectroscopy
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Direct Assignment of ~(13)C NMR Spectra of Rigid Solids by Two-Dimensional Magic-Angle-Spinning Separated-Local-Field Spectroscopy

机译：二维魔术角旋转分离局部场光谱法直接分配刚性固体的〜（13）C NMR光谱

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摘要

An alternative two-dimensional magic-angle-spinning separated-local-field (MASSLF) approach for directly assigning the13C spectra of rigid solids is proposed. This procedure does not employ homonuclear1H decoupling during the evolution period. The unique patterns of the dipolar spectra of CH, CH2, CH3, and C groups in theF1dimension are clearly distinguishable even under the influence of the homonuclear1H dipolar interaction. In theF1dimension, the CH group shows a Pake doublet pattern, the CH2group shows a "broad triplet-like" pattern, the CH3group shows a much narrower peak with high intensity due to its fast rotation at room temperature, and the C groups show a much narrower peak with low intensity (compared to the intensity of CH3groups) corresponding to the remote heteronuclear dipolar couplings. The CH3groups can be distinguished from the nontetrahedrally bound quaternary C groups by the significant intensity difference of the heteronuclear dipolar spectra in addition to the large chemical-shift difference. The13C heteronuclear dipolar spectra of CH and CH2groups suffer severe broadening due to remote couplings and spin exchange among protons. The MASSLF spectra are sensitive to the local environment of the carbons. The tetrahedrally bound quaternary carbons are not clearly distinguished from CH3groups in this approach, due to their similar chemical shifts, comparable intensities, and linewidths of the dipolar spectra.
机译：提出了另一种直接分配刚性固体的13 C光谱的二维魔术角旋转分离局部场（MASSLF）方法。此过程在进化期间未采用同核1H解耦。即使在同核1H偶极相互作用的影响下，F1维中CH，CH2，CH3和C基团的偶极谱的独特模式也可以清楚地区分。在F1维中，CH组显示为Pake doublet模式，CH2组显示为“宽三重态”模式，CH3组由于在室温下快速旋转而显示出窄得多的峰，且强度很高。较窄的峰，具有较低的强度（与CH3基团的强度相比），对应于远程异核偶极耦合。除了较大的化学位移差异外，CH3基团还可以通过异核偶极光谱的显着强度差异与非四面体结合的季C基团区分开。由于质子之间的远程耦合和自旋交换，CH和CH2基团的13 C异核偶极光谱遭受严重展宽。 MASSLF光谱对碳的局部环境敏感。由于四氯键结合的四级碳具有相似的化学位移，可比较的强度和偶极谱的线宽，因此在这种方法中无法与CH3基团清楚地区分开。

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