NMR chemical shifts of common laboratory solvents as trace impurities
NMR chemical shifts of common laboratory solvents as trace impurities
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DOI：
10.1021/jo971176v
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发表时间：
1997-10-17
影响因子：
3.6
通讯作者：
Nudelman, A
中科院分区：
文献类型：
--
作者：
Gottlieb, HE;Kotlyar, V;Nudelman, A
结果质子谱(表1)。样品0.6mL，含有1μL的三甲氧胺，1自己运行。根据这一光谱，我们确定了溶剂残留峰2和水峰的化学位移。应该注意的是，后者与温度有很大关系(见下文)。此外，任何潜在的氢键受体都会倾向于将水信号向下移动；对于非极性溶剂尤其如此。相反，在DMSO中，水已经与溶剂形成了强烈的氢键，溶质对其化学位移的影响微乎其微。D2O也是如此；残留HDO的化学位移非常依赖于温度(见下文)，但可能与直觉相反，与溶质(和pH)显著无关。然后，我们向核磁共振管中加入3μL。化学位移已在表1中读出并列出。除有说明外，偶合常数和峰形基本上与溶剂无关，并且只出现一次。对于D20溶剂，可接受的参照峰(δ)0)是3-(三甲基硅基)丙磺酸钠盐的甲基信号；在每个核磁共振管中加入一个晶体。然而，这种材料有几个缺点：它不挥发，所以如果必须回收样品，它不能很容易地消除。此外，除非人们以相对昂贵的氚形式购买它，否则它会为光谱增加三个更多的信号(亚甲基1、2和3分别出现在2.91、1.76和0.63ppm)。我们建议使用剩余的HDO峰作为辅助参考；我们发现，如果考虑温度的影响(见下文)，这是非常可重复性的。对于D2O，我们使用了一套不同的库存溶液，因为许多极性较低的底物不是明显可溶于水的(见表1)。我们还检测了乙酸钠和甲酸钠(化学位移分别为1.90和8.44ppm)。
ResultsProton Spectra (Table 1). A sample of 0.6 mL of the solvent, containing 1 μL of TMS, 1 was first run on its own. From this spectrum we determined the chemical shifts of the solvent residual peak2 and the water peak. It should be noted that the latter is quite temperaturedependent (vide infra). Also, any potential hydrogenbond acceptor will tend to shift the water signal downfield; this is particularly true for nonpolar solvents. In contrast, in eg DMSO the water is already strongly hydrogen-bonded to the solvent, and solutes have only a negligible effect on its chemical shift. This is also true for D2O; the chemical shift of the residual HDO is very temperature-dependent (vide infra) but, maybe counterintuitively, remarkably solute (and pH) independent. We then added 3 μL of one of our stock solutions to the NMR tube. The chemical shifts were read and are presented in Table 1. Except where indicated, the coupling constants, and therefore the peak shapes, are essentially solvent-independent and are presented only once.For D2Oasasolvent, the accepted reference peak (δ) 0) is the methyl signal of the sodium salt of 3-(trimethylsilyl) propanesulfonic acid; one crystal of this was added to each NMR tube. This material has several disadvantages, however: it is not volatile, so it cannot be readily eliminated if the sample has to be recovered. In addition, unless one purchases it in the relatively expensive deuterated form, it adds three more signals to the spectrum (methylenes 1, 2, and 3 appear at 2.91, 1.76, and 0.63 ppm, respectively). We suggest that the residual HDO peak be used as a secondary reference; we find that if the effects of temperature are taken into account (vide infra), this is very reproducible. For D2O, we used a different set of stock solutions, since many of the less polar substrates are not significantly watersoluble (see Table 1). We also ran sodium acetate and sodium formate (chemical shifts: 1.90 and 8.44 ppm, respectively).