Hydride Abstraction from 1,2-Diols by the Pentaaqua(oxo)chromium(IV) Ion
摘要:
Kinetic studies of the oxidation of 1,2-diols by the pentaaqua(oxo)chromium(IV) ion, (H2O)5Cr(IV)=O2+, were carried out in dilute aqueous solutions of perchloric acid. These reactions yield the superoxochromium(III) ion CrOO2+, providing evidence that the two-electron reduction of Cr(IV)O2+ to Cr2+ occurred in a single step. The rate constants for the primary and secondary diols are comparable to each other and approximately 10 times larger than that for pinacol (k = 3.7 L mol-1 s-1). The kinetic isotope effect of the O-H hydrogens is negligible, k(H)/k(D) = 0.95-1.3, whereas that for the C-H hydrogens is substantial, k(H)/k(D) = 3.7-4.8. A 2-equiv mechanism is proposed, in which CrO2+ abstracts a hydride ion from an a-position in the primary and secondary diols and from alpha,beta-position in pinacol.
频哪醇的结构和振动光谱。第 2 部分。频哪醇的新晶型:红外光谱鉴定凝聚相中 G 和 T 构象异构体的关键
摘要:
摘要 在这项研究中,频哪醇(2,3-二甲基丁烷-2,3-二醇)的 G 和 T(关于 OC-CO 键的 gauche 和反式)构象异构体在分子通过分子间氢缔合的条件下被鉴定出来。债券。例如,通过升华获得的频哪醇的已知晶型(A 型)包含 G 和 T 构象异构体。我们发现频哪醇可以从非极性溶剂中结晶出一种新的晶型,即 B 型。这种 B 型也可在液体频哪醇快速冷却后在红外 (IR) 低温恒温器中获得。根据单晶分子结构测定,B 型仅包含 G 构象异构体。通过比较 A 和 B 形式的光谱,可以明确指定 T 构象异构体的红外波段,从而能够识别所有相中存在的构象异构体。通过分析出现在 835-815 cm-1 区域的谱带,我们观察到在固态(B 型除外)和液态以及极性溶液中频哪醇同时采用 G 和 T 构象异构体。然而,在每种情况下,G 构象异构体的种群都优于 T 构象异构体的种群。在极性溶剂中,T 构象异构体的数量与最近使用