核磁共振仪是近代科研工作的一种重要工具,也是一种重要分析手段。实验证明,顺磁性原子核(如氢核 H~1)具有核自旋作用,这种自旋在一定的外加磁场作用下,变为具有一定频率的旋进。当用与此频率相当的电磁波照射时,就发生共振和吸收。所得的吸收图谱就是核磁共振波谱。同样是氢核 H~1,由于所处分子中环境的不同,在一定的外加磁场作用下,所吸收照射波的频率也不同。这是由于氢核外围电子在外磁场作用下,产生反抗磁场,抵消了一部分外磁场的结果,这就是所谓的“屏蔽效应”,其大小决定于分子结构。如果以某一标准物质(一般用四甲基硅烷 TMS)的 H~1吸收峰位置为原 Nuclear magnetic resonance is an important tool in modern scientific research, but also an important analytical tool. Experiments show that the paramagnetic nuclei (such as hydrogen nuclei H ~ 1) have a nuclear spin effect, this spin in a certain external magnetic field into a certain frequency precession. Resonance and absorption occur when irradiated with an electromagnetic wave of this frequency. The resulting absorption spectrum is the nuclear magnetic resonance spectrum. The same is hydrogen H ~ 1, due to the different molecules in the environment, the role of a certain magnetic field, the frequency of radiation absorbed by the waves are also different. This is due to the external proton in the outer nuclear magnetic field, resulting in resistance to magnetic field, offset part of the external magnetic field results, which is the so-called “shielding effect”, its size depends on the molecular structure. If a standard substance (usually tetramethylsilane TMS) H ~ 1 absorption peak position of the original