NMR STUDIES OF AN AMINE AND AMIDES IN A NEMATIC PHASE

向列相胺和酰胺的 NMR 研究

• 批准号: 3438665
• 负责人: NARAYAN S BALAKRISHNAN
• 金额: $ 3.45万
• 依托单位: UNIVERSITY OF GUAM
• 依托单位国家: 美国
• 财政年份: 1988
• 资助国家: 美国
• 起止时间: 1988-09-30 至 1990-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/3438665
• 关键词: acetamides; amides; amines; aniline; chemical bond; chemical models; chemical structure; conformation; deuterium; dipole moment; formamide; intermolecular interaction; liquid crystal; nuclear magnetic resonance spectroscopy

The technique of NMR spectroscopy in liquid crystal solvents 1.2 will be applied to a systematic study of the stereochemistry at the nitrogen atom in substituted amides and an amine. Such model compounds (amides), containing a peptide unit, are of fundamental biochemical and spectroscopic importance for studying the structure and conformation of peptides and proteins. The determination of molecular structure by the anisotropic NMR method is based on the fact that the intramolecular dipole-dipole couplings, dominating such spectra, are inversely related to the cube of the internuclear distances of the interacting nuclei. The amide system studied in the past, with the notable exception of N-methylformamide, have been studied primarily by anisotropic 1H NMR spectroscopy. However, a study of the proton spectra in conjunction with the 13C and/or 15N NMR spectra of isotopically enriched simple amides can result in a precise determination of molecular geometrical parameters, including an estimation of dihedral angles of distortion around the nitrogen atom with minimum assumptions of bond data. This is desirable as some of the bond data are of questionable reliability. The increased number of heteronuclear dipolar couplings in isotopically enriched (13C and/or 15N) systems permits the extraction of additional pieces of precise structural information, and this has been demonstrated for 15N- (13C)methyl(13C)formamide.7 Although an analysis of the anisotropic NMR spectra containing heteronuclei usually provides only the sum of spin-spin (JAX) and dipolar (DAX) coupling constants, namely (JAX+2DAX), it is feasible to apply a recently developed technique 8 of observing the anisotropic spectra by employing a mixture of two nematic phases of opposite 8 of observing the anisotropic spectra by employing a mixture of two nematic phases of opposite diamagnetic anisotropy. Such an observation at the "co-existence point" facilitates an experimental disentanglement of JAX from DAX parameters. In this proposal, a systematic study of isotopically enriched (15N)aniline and substituted amides such as (15N)acetamide, N>N>- dimethylform(13C)-amide and (15N)dimethylacetamide is presented. The long term objectives and the specific goals of this research are: (1) to determine the details of molecular structure, including the out-of-plane angles which the N-C'H3 and N-C"H3 bonds make with the symmetry plane in dimethylformamide and dimethylacetamide; (2) to examine trends and correlations in the extent of non-planar distortions as a function of the nature and the size of groups attached to the nitrogen; (3) to test the various models for describing the dynamics of intramolecular rotations of the methyl groups in substituted amides; and (4) to determine the liquid state quadrupole coupling constants of the various deuterons in these deuterated amides.

液晶溶剂中的核磁共振波谱技术 将被应用于对立体化学的系统研究 取代酰胺和胺中的氮原子。这类模型 含有一个肽单元的化合物(酰胺)是基本的 生化和光谱对结构研究的重要性 多肽和蛋白质的构象。对…的测定 各向异性核磁共振方法的分子结构是基于 分子内偶极-偶极耦合，占主导地位 这样的光谱与核间立方体成反比 相互作用核的距离。中研究的酰胺体系 过去，除了N-甲基甲酰胺外， 主要用各向异性核磁共振氢谱进行了研究。 然而，结合~(13)C的质子谱研究 和/或同位素富集型简单酰胺的15N核磁共振波谱可以 结果精确地确定了分子的几何结构 参数，包括对二面角的估计 氮原子周围的扭曲与最小假设 债券数据。这是可取的，因为一些债券数据是 令人怀疑的可靠性。异核细胞数量的增加 富同位素(13C和/或15N)体系中的偶极耦合 允许提取额外的精密结构件 信息，这一点已经在15N- (13C)甲基(13C)甲酰胺。7尽管对 含有杂核的各向异性核磁共振谱通常提供 只有自旋-自旋(JAX)和偶极(DAX)耦合之和 常量，即(JAX+2DAX)，最近应用一个 发展了观察各向异性光谱的技术8，通过 使用两个向列相的混合物的 通过混合使用两种方法观测各向异性光谱 相反反磁各向异性的向列相。这样的一种 在“共存点”的观察有助于实验 JAX与DAX参数的解缠。 在这项提议中，对同位素富集物的系统研究 (15)苯胺和取代的酰胺，例如(15N)乙酰胺；N&gt；N&gt；- 介绍了二甲基形式(13C)-酰胺和(15N)二甲基乙酰胺。 这项研究的长期目标和具体目标 有：(1)要确定分子结构的细节， 包括N-C‘H3和N-C“H3键的离面角度 用二甲基甲酰胺中的对称面和 二甲基乙酰胺；(2)检查 非平面变形的程度作为自然和 氮上基团的大小；(3)测试 描述分子内动力学的各种模型 取代酰胺中甲基的旋转；和(4)至 测定体系的液态四极耦合常数 在这些氚化胺中有各种各样的氚。