Aix Marseille Université , CNRS, ICR, UMR 7273, case 551, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20, France.
Laboratoire de Substances Naturelles et des Syntheses Organometalliques, Universite des Sciences et Technique de Masuku , B.P. 493, Franceville, Gabon.
J Org Chem. 2017 Jun 2;82(11):5702-5709. doi: 10.1021/acs.joc.7b00541. Epub 2017 May 16.
The design of new RRNOR alkoxyamines for various applications relies on the accurate prediction of two kinetic parameters, the C-ON bond homolysis rate constant (k) and its re-formation rate constant (k). Relationships to describe the steric and polar effects of the RRNO fragment ruling k have been developed. For all cyclic nitroxyl fragments, the steric effect is described as the sum of the bulkiness of the R and R groups (i.e., normal steric effect), while for the noncyclic nitroxyl fragment (except for one case), a leveled steric effect is assumed. In this work, we show that the normal steric effect also applies to noncyclic nitroxyl fragments and that for one case an enhanced steric effect is also observed, i.e., experimental k >5-fold larger than the predicted value.
新型 RRNOR 烷氧基胺的设计适用于各种应用，这依赖于对两个动力学参数的准确预测，即 C-O 键均裂速率常数 (k) 和其重组速率常数 (k)。现已开发出描述 RRNO 片段决定 k 的立体和极性效应的关系。对于所有环状氮氧自由基片段，立体效应被描述为 R 和 R 基团的体积之和（即，正常立体效应），而非环状氮氧自由基片段（仅有一种情况除外）则假设为平面立体效应。在这项工作中，我们表明正常立体效应也适用于非环状氮氧自由基片段，并且对于一种情况，还观察到增强的立体效应，即实验 k 值比预测值大 5 倍以上。
