CROSS POLARIZATION AND MAGIC ANGLE SAMPLE SPINNING NMR-SPECTRA OF MODEL ORGANIC-COMPOUNDS .3. EFFECT OF THE C-13-H-1 DIPOLAR INTERACTION ON CROSS POLARIZATION AND CARBON-PROTON DEPHASING
CROSS POLARIZATION AND MAGIC ANGLE SAMPLE SPINNING NMR-SPECTRA OF MODEL ORGANIC-COMPOUNDS .3. EFFECT OF THE C-13-H-1 DIPOLAR INTERACTION ON CROSS POLARIZATION AND CARBON-PROTON DEPHASING
复制标题
DOI：
10.1021/ja00360a025
复制
发表时间：
1983-01-01
影响因子：
15
通讯作者：
PUGMIRE, RJ
中科院分区：
文献类型：
--
作者：
ALEMANY, LB;GRANT, DM;PUGMIRE, RJ
分别在不同接触和延迟时间下采用传统的交叉极化和偶极去相技术的碳-13核磁共振研究，提供了关于13C-*H偶极-偶极相互作用大小的有价值的信息。在光谱具有重叠共振的固体中，这种技术区分质子化和非质子化碳。在偶极去相谱中，亚甲基和亚甲基碳与直接键合的质子强耦合，可以发生偶极和旋转调制共振。甲基碳表现出非常广泛的有效偶极偶联，因为甲基旋转迅速，这取决于结构环境的变化。没有观察到甲基中的偶极调制。与其他甲基碳原子相比，铁-丁基甲基中的碳原子的有效偶极相互作用更弱。这些动量减弱的偶极相互作用类似于四元脂肪族碳原子所经历的。芳环上a/erf-丁基的空间拥挤(平均而言)导致其一个甲基的迁移率与另外两个不同。对叔丁基中的季碳和甲基碳的研究结果表明，在任何其他官能团中都没有明显的双指数衰减。由于质子的远离，非质子化的sp2杂化碳原子也表现出弱的偶极耦合。由于运动自由度和结构的变化，耦合的大小有很大的不同。
Carbon-13 NMR studies involving conventional cross polarization and dipolar dephasing techniques at a variety of contact and delay times, respectively, provide valuable information on the magnitude of 13C-* H dipole-dipole interactions. In solids whose spectra have overlapping resonances, such techniques discriminate between protonated and nonprotonated carbons. In dipolar dephased spectra, dipolar and rotational modulation of the resonances can occur for methineand methylene carbons, which are strongly coupled to the directly bonded protons. Methyl carbons exhibit a very wide range of effective dipolar couplings because of rapid methyl rotation that varies depending upon the structural environment. Dipolar modulation in methyl groups is not observed. Carbon atoms in ferr-butyl methyl groups experience even weaker effective dipolar interactions than other methyl carbonatoms. These motionally decreased dipolar interactions are similar to those experienced by the quaternary aliphatic carbonatom. Steric crowding of a/erf-butyl group on an aromatic ring causes (on the average) one of its methyl groups to differ in mobility from the other two. A biexponential decay not evident in any of the other functional groups studied results for both the quaternary and methyl carbons in the teri-butyl group. Nonprotonated sp2-hybridized carbon atoms also exhibit weak dipolar couplings because of the remoteness of protons. The magnitude of the coupling varies substantially as a result of variations in motional freedom and structure.