Goossens Hannelore, Catak Saron, Glassner Mathias, de la Rosa Victor R, Monnery Bryn D, De Proft Frank, Van Speybroeck Veronique, Hoogenboom Richard
Center for Molecular Modeling, Ghent University, Technologiepark 903, 9052 Zwijnaarde, Belgium.
Supramolecular Chemistry Group, Department of Organic Chemistry, Ghent University, Krijgslaan 281-S4, 9000 Ghent, Belgium.
ACS Macro Lett. 2013 Aug 20;2(8):651-654. doi: 10.1021/mz400293y. Epub 2013 Jul 16.
The surprising difference in the cationic ring-opening polymerization rate of 2-cyclopropyl-2-oxazoline versus 2--propyl-2-oxazoline and 2-isopropyl-2-oxazoline was investigated both experimentally and theoretically. The polymerization kinetics of all three oxazolines were experimentally measured in acetonitrile at 140 °C, and the polymerization rate constant () was found to decrease in the order -PropOx > -PropOx > -PropOx. Theoretical free energy calculations confirmed the trend for , and a set of DFT-based reactivity descriptors, electrostatics, and frontier molecular orbitals were studied to detect the factors controlling this peculiar behavior. Our results show that the observed reactivity is dictated by electrostatic effects. More in particular, the charge on the nitrogen atom of the monomer, used to measure its nucleophilicity, was the most negative for -PropOx. Furthermore, the electrophilicity of the cations does not change substantially, and thus, the nucleophilicity of the monomers is the driving factor for .
对2-环丙基-2-恶唑啉与2-丙基-2-恶唑啉和2-异丙基-2-恶唑啉阳离子开环聚合速率的惊人差异进行了实验和理论研究。在140℃下于乙腈中对所有三种恶唑啉的聚合动力学进行了实验测定，发现聚合速率常数（）按-PropOx > -PropOx > -PropOx的顺序降低。理论自由能计算证实了的趋势，并研究了一组基于密度泛函理论（DFT）的反应性描述符、静电学和前线分子轨道，以检测控制这种特殊行为的因素。我们的结果表明，观察到的反应性由静电效应决定。更具体地说，用于测量其亲核性的单体氮原子上的电荷，对于 -PropOx是最负的。此外，阳离子的亲电性没有实质性变化，因此，单体的亲核性是 的驱动因素。
