文章基本信息

标题：Learning to Think in Mechanistic Alternatives: S_N1 vs. E1 and the Gibbs-Helmholtz Equation
本地全文：下载
作者：Catharina Schmitt ; Lukas Kaiser ; Michael Schween 等
期刊名称：World Journal of Chemical Education
印刷版ISSN：2375-1665
电子版ISSN：2375-1657
出版年度：2019
卷号：7
期号：2
页码：102-108
DOI：10.12691/wjce-7-2-10
出版社：Science and Education Publishing
摘要：One of the biggest challenges for learners of organic chemistry is learning to think in competing mechanistic alternatives and using cross-linked chemical knowledge. An outstanding subject for this is the competition between SN1 and E1 reactions. In this case, it is special that the competing reactions have an identical first step and separate into different paths only from the intermediate, the second step, of the reaction. Learners who are familiar with the SN1 mechanism have the opportunity to work out the fact that in addition to the SN1 reaction, the E1 reaction is also proceeding, which more or less dominates, depending on the substrate, nucleophile or solvent and the temperature. This differentiation is undertaken with a set of experimental learning opportunities we have developed using simple qualitative analytics. Our learning opportunities are designed as contrasting cases, one of them with a variation of temperature in one setup. These allow the question why a chemical reaction can occur even though it is enthalpically unfavorable, i.e. has a positive reaction enthalpy (H>0), to be answered. The latter helps the learners to realize that in addition to the enthalpy of reaction, there must be another energetic quantity that determines the thermodynamics of chemical reactions: Entropy. In the end, this leads to the discussion of the Gibbs-Helmholtz equation and, thus, to basic insights into chemical thermodynamics.
关键词：high school; first-year undergraduate; laboratory instruction; mechanistic reasoning in organic chemistry; substitution vs;elimination; thinking in mechanistic alternatives; Gibbs-Helmholtz equation