COMPARISON OF DEUTERIUM & TRITIUM ISOTOPE EFFECTS ON CHEMICAL SHIFTS

核磁共振化学位移是非常灵敏的探针，可以检测到 被检测到的核周围的局部环境。特别是 化学位移有大量的同位素效应，这两种效应都是主要的 (在质量变化的原子上被检测到)和次级 (在质量改变的原子核附近的其他原子核上被检测到)。这个 氢的同位素提供了很大的相对质量变化，并具有 已被广泛用于研究氢键。两者都有 初级和次级移位可以是相当大的，传播 许多键是从氢键形成的位置形成的。大多数人 已经进行了比较化学位移和化合物的研究 含有质子和重氢的。氢气的谱线有些 由于四极耦合而比质子更宽，并且磁性 力矩是质子的六分之一，限制了位移的精确度 测量。我们现在已经进行了一项研究，以延长测量范围 到氚。主要的动机是比较原子核的同位素位移 和氚相对于质子，看看是否诱发了 影响的大小与质量差的大小相同，质子- 氢气移位刻度。偏离这一行为可能反映出 氢键势的不对称性，有助于理解 强氢键的作用。各种各样的有机化合物被 研究了溶解在含有分子内的有机溶剂中 氢键。捐赠者和接受者在很大程度上是不同的 一系列化学官能团，包括两个给体上的O，N和S 接受者结束了。用氚代替了质子 通过加入少量的水来完成。自转1/2 氚的性质使更准确的测定成为可能 而不是用重氢。只有很小的偏差 观察到预期的H-D/H-T比为1.4；对于大多数化合物， 价值是在预期的理论值。

NMR chemical shifts are very sensitive probes for changes in the local environment around the nuclei being detected. In particular there are substantial isotope effects on chemical shifts, both primary (being detected on the atom whose mass is changing) and secondary (being detected on other nuclei near that with altered mass). The isotopes of hydrogen provide large relative mass changes, and have been used fairly extensively to investigate hydrogen bonding. Both primary and secondary shifts can be quite substantial, propagating many bonds from the site of hydrogen bond formation. A majority of studies have been done comparing chemical shifts with compounds containing protons vs. deuterium. The deuterium lines are somewhat broader than proton due to quadrupole coupling, and the magnetic moment is 1/6th that of a proton, limiting the accuracy of the shift measurements. We have now undertaken a study to extend measurements to tritium. The main motivation is to compare the isotope shifts of deuterium and tritium relative to proton and see whether the induced effect scales with mass difference in the same way that the proton - deuterium shift scales. Deviations from this behavior could reflect asymmetry in the hydrogen bond potential, and could help understanding of strong hydrogen bonds. A wide variety of organic compounds were studied dissolved in organic solvents which contained intramolecular hydrogen bonds. The donors and acceptors were varied over a wide range of chemical functionalities, including O, N and S on both donor and acceptor ends. Substitution of tritium for protons was accomplished through addition of small amounts of water. The spin 1/2 character of tritium made possible much more accurate determinations of shifts than with deuterium. Only very small deviations from the expected H-D / H-T ratios of 1.4 were observed; for most compounds the value was at the expected theoretical value.