World Journal of Chemical Education
ISSN (Print): 2375-1665 ISSN (Online): 2375-1657 Website: Editor-in-chief: Prof. V. Jagannadham
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World Journal of Chemical Education. 2019, 7(2), 102-108
DOI: 10.12691/wjce-7-2-10
Open AccessSpecial Issue

Learning to Think in Mechanistic Alternatives: SN1 vs. E1 and the Gibbs-Helmholtz Equation

Catharina Schmitt1, Lukas Kaiser1 and Michael Schween1,

1Faculty of Chemistry, Philipps-Universität Marburg, Marburg, 35032, Germany

Pub. Date: April 11, 2019

Cite this paper:
Catharina Schmitt, Lukas Kaiser and Michael Schween. Learning to Think in Mechanistic Alternatives: SN1 vs. E1 and the Gibbs-Helmholtz Equation. World Journal of Chemical Education. 2019; 7(2):102-108. doi: 10.12691/wjce-7-2-10


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 (ΔH>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.

high school first-year undergraduate laboratory instruction mechanistic reasoning in organic chemistry substitution vs. elimination thinking in mechanistic alternatives Gibbs-Helmholtz equation

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