通过可滴定同位素位移对分子内 OH/OH 氢键的 1H NMR 研究,The Journal of Organic Chemistry

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通过可滴定同位素位移对分子内 OH/OH 氢键的 1H NMR 研究
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2021-11-16 , DOI: 10.1021/acs.joc.1c01910
Kavoos Kolahdouzan ₁ , O Maduka Ogba ₂ , Daniel J O'Leary ₁

Affiliation

溶解在非极性溶剂如 CD ₂ Cl ₂和苯-d ₆中的部分氘化 1,4- 和 1,3-二醇的甲醇滴定提供了¹在质子溶剂浓度增加的条件下，OH/OD 同位素位移的 H NMR 测量，诊断完整的分子内氢键。1,4- 和 1,3- 二醇具有构象有利的分子内 OH/OH 氢键可以滴定到恒定的同位素位移值，尽管具有可变的符号，在过量甲醇当量的存在下，提供了在这些条件下完整的分子内氢键的证据状况。相反，当存在过量甲醇时，具有构象不稳定的分子内氢键的 1,3-二醇中的同位素位移滴定为零，这与这些条件下的分子内氢键断裂一致。此外，_in = δOH _out )，这是平衡同位素效应所必需的，为同位素效应的内在贡献提供了证据。因此，OH/OD 同位素位移滴定提供了一种了解这些同位素效应的起源和探测分子内 OH/OH 氢键响应质子溶剂提供的分子间氢键的完整或非完整性质的方法。

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1H NMR Studies of Intramolecular OH/OH Hydrogen Bonds via Titratable Isotope Shifts

Methanol titrations of partially deuterated 1,4- and 1,3-diols dissolved in nonpolar solvents such as CD₂Cl₂ and benzene-d₆ have provided ¹H NMR measurements of OH/OD isotope shifts, diagnostic for intact intramolecular hydrogen bonds, under conditions of increasing protic solvent concentration. 1,4- and 1,3-diols with conformationally favored intramolecular OH/OH hydrogen bonds can be titrated to constant isotope shift values, albeit with variable sign, in the presence of excess methanol equivalents, providing evidence for intact intramolecular hydrogen bonds under these conditions. Conversely, the isotope shift in a 1,3-diol with a conformationally labile intramolecular hydrogen bond titrated to zero when in the presence of excess equivalents methanol, consistent with intramolecular hydrogen bond rupture under these conditions. Additionally, the titration behavior of hydroxyl chemical shifts in diols and protected derivatives has revealed significant OH/OD isotope shifts in the absence of chemical shift differences (δOH_in = δOH_out) that are necessary for an equilibrium isotope effect, lending evidence for an intrinsic contribution to the isotope effect. OH/OD isotope shift titration thus provides a means for understanding the origins of these isotope effects and for probing the intact or nonintact nature of intramolecular OH/OH hydrogen bonds in response to intermolecular hydrogen bonds provided by a protic solvent.

更新日期：2021-11-16

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