Mapping transition state structures for thiophosphinoyl group transfer between oxyanionic nucleophiles in water and aqueous ethanol solvents
作者:Georgina I. Kalu、Collins I. Ubochi、Ikenna Onyido
DOI:10.1039/d2nj02008d
日期:——
with the More O’Ferrall–Jencks reaction map reveals two contending factors: (i) increased nucleophile/leaving group basicity moves the concerted TS towards tighter structures via vector g, while (ii) lowered solvent polarity moves the TS towards dissociative structures via vector z. The inequality z > g in water-rich solvent mixtures leads to more dissociative structures, whilst a parity of these vectors
在 50% 水–50% 乙醇和 30% 水–70% 乙醇混合物中测量硫代膦酰基从底物3a-g转移到氧亲核试剂的二级速率常数,以获得与溶剂无关的布朗斯台德系数β nuc = 0.35, β lg = -0.64;和β nuc = 0.34, β lg= -0.61,分别。与早期结果相结合,绘制出水中的协调过渡态 (TS),该过渡态在 70% 水-30% 乙醇和 50% 水-50% 乙醇中逐渐松散,但此后在富含乙醇的混合物中保持不变。使用更多 O'Ferrall-Jencks 反应图的分析揭示了两个相互竞争的因素:(i)增加的亲核试剂/离去基团碱度使协同的 TS通过矢量g向更紧密的结构移动,而(ii)降低的溶剂极性使 TS 通过矢量向离解结构移动向量z。富含水的溶剂混合物中的不等式z > g导致更多的解离结构,而这些向量的奇偶性 ( z ~g)在富含乙醇的混合物中导致不变的协同(解离)TS结构