13C-19F Dipolar Dephasing in Monofluorinated Organic Substances. Characterization by 1H-13C-19F Triple-Resonance 13C CP/MAS and 19F MAS NMR
13C-19F Dipolar Dephasing in Monofluorinated Organic Substances. Characterization by 1H-13C-19F Triple-Resonance 13C CP/MAS and 19F MAS NMR
复制标题
单氟化有机物质中的 13C-19F 偶极失相。
DOI：
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
E. Hagaman
中科院分区：
文献类型：
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作者：
E. Hagaman
摘要 非聚合单氟化有机物质的传统固态 CP/MAS 13C NMR 谱显示，这些碳原子的共振在空间上非常接近 19F 核的磁偶极矩，具有显着的均匀展宽。直接与 19F 键合的碳的共振可以扩大到无法识别的程度。 13C-19F 偶极相移是 13CT2 弛豫途径，并由有效的 19F 磁化扩散促进。已直接测量 19F 和 13CT2 值来描绘这些过程。主要展宽通过 13C-19F 偶极相互作用发生，并且具有 r−3 碳-氟核间距离依赖性。 13C-19F偶极相移13C光谱编辑完整的1H、19F双偶极解耦光谱，使用13C-19F偶极相互作用的强度作为编辑标准。 13C-19F偶极相移实验构成了一种在高分辨率条件下测定氟官能团的高选择性方法。共振 19F 和 1H 偶极去耦的同时应用减少了 13C 谱中的弛豫展宽。 10-15 kHz 的 19F 去耦偏移可导致 13C 线宽比最佳去耦测得的线宽大一个数量级。这种依赖性和有机氟共振的大 19F 化学位移范围阻止了含有多个、广泛分离的 19F 共振的物质中均匀抑制或消除展宽。并行 1H 和 19F 解耦必须是在常规条件下对氟化有机材料进行高分辨率 CP/MAS 13C 实验的一个不可或缺的特征（
Abstract The conventional solid-state CP/MAS 13C NMR spectra of nonpolymeric monofluorinated organic substances exhibit dramatic homogeneous broadening of resonances of those carbons in close spatial proximity to the magnetic dipole moment of the 19F nucleus. Resonances of carbons directly bonded to 19F can broaden beyond recognition. 13C-19F dipolar dephasing is the 13CT2 relaxation pathway and is promoted by efficient 19F magnetization diffusion. 19F and 13CT2 values have been measured directly to delineate these processes. The principal broadening occurs through the 13C-19F dipolar interaction and has an r−3 carbon-fluorine internuclear distance dependence. The 13C-19F dipolar-dephased 13C spectrum edits the full 1H, 19F doubly di-polar-decoupled spectrum, using the strength of the 13C-19F di-polar interaction as the editing criteria. The 13C-19F dipolar-dephasing experiment constitutes a highly selective method for fluoride functional group determination under high-resolution conditions. The coincident application of resonant 19F and 1H dipolar decoupling diminishes relaxation broadening in the 13C spectrum. 19F decoupling offsets of 10-15 kHz can result in 13C linewidths that are an order of magnitude larger than those measured with optimum decoupling. This dependence and the large 19F chemical-shift range of organofluorine resonances prevent the uniform suppression or elimination of broadening in substances containing multiple, widely separated 19F resonances. Concurrent 1H and 19F decoupling must be an integral feature of high-resolution CP/MAS 13C experiments on fluorinated organic materials performed at routine (