Tsukamoto Masaki, Gopalaiah Kovuru, Kagan Henri B
Institut de Chimie Moleculaire et des Materiaux d'Orsay (UMR 8182, CNRS), Laboratoire de Catalyse Moleculaire, Universite Paris-Sud, 91405 Orsay, France.
J Phys Chem B. 2008 Dec 4;112(48):15361-8. doi: 10.1021/jp8058917.
The origin of nonlinear effects (no proportionality between enantiomeric excess (ee) of chiral auxiliary and ee of product) is first summarized in general terms, underlining the importance of the presence of molecular species bearing several moieties deriving from the chiral auxiliary. The presence of a heterochiral species, produced from enantioimpure chiral auxiliaries, usually explains well the deviation to linearity, especially asymmetric amplification. In this article it is shown that the absence of a heterochiral species is not incompatible with an asymmetric amplification. The demonstration has been done on a simple model, the equilibrium of homochiral dimerization. The monomers R and S being in equilibrium with the dimers R(2) and S(2), it was possible to calculate ee(monomer) and ee(dimer) as a function of the initial concentration and the initial ee of the monomer. The asymmetric amplification can be quite substantial for the dimer, while asymmetric depletion characterizes the residual monomers. Similar conclusions apply to homochiral tri- and tetramerizations. The extension to irreversible reactions was briefly analyzed as well as the use of these results.
首先从总体上总结了非线性效应的起源（手性助剂的对映体过量（ee）与产物的ee之间不成比例），强调了存在带有源自手性助剂的多个部分的分子物种的重要性。由对映体不纯的手性助剂产生的杂手性物种的存在通常很好地解释了线性偏差，尤其是不对称放大。本文表明，不存在杂手性物种与不对称放大并不矛盾。这一证明是在一个简单模型——同手性二聚化平衡上完成的。单体R和S与二聚体R(2)和S(2)处于平衡状态，可以根据单体的初始浓度和初始ee计算ee(单体)和ee(二聚体)。二聚体的不对称放大可能相当显著，而残留单体则表现出不对称消耗。类似的结论适用于同手性三聚化和四聚化。还简要分析了向不可逆反应的扩展以及这些结果的应用。
