Resolving the complexity of organic chemistry students' reasoning through the lens of a mechanistic framework

Abstract

Research in organic chemistry education has revealed that students often rely on rote memorization when learning mechanisms. Not much is known about student productive resources for causal reasoning. To investigate incipient stages of student causal reasoning about single mechanistic steps of organic reactions, we developed a theoretical framework for this type of mechanistic reasoning. Inspired by mechanistic approaches from philosophy of science, primarily philosophy of organic chemistry, the framework divides reasoning about mechanisms into structural and energetic accounts as well as static and dynamic approaches to change. In qualitative interviews, undergraduate organic chemistry students were asked to think aloud about the relative activation energies of contrasting cases,i.e.two different reactants undergoing a leaving group departure step. The analysis of students’ reasoning demonstrated the applicability of the framework and expanded the framework by different levels of complexity of relations that students constructed between differences of the molecules and changes that occur in a leaving group departure. We further analyzed how students’ certainty about the relevance of their reasoning for a claim about activation energy corresponded to their static and dynamic approaches to change and how students’ success corresponded to the complexity of relations that they constructed. Our findings support the necessity for clear communication of and stronger emphasis on the fundamental basis of elementary steps in organic chemistry. Implications for teaching the structure of mechanistic reasoning in organic chemistry and for the design of mechanism tasks are discussed.

Designing a scaffold for mechanistic reasoning in organic chemistry

“…4) Making a judgment about the influence of a qualitative difference of electronic effects on the activation energy can impose a high cognitive load on the leaner since it requires the consideration of implicit information, cause-effect reasoning, and reasoning about different areas of chemistry, e.g. structural vs. energetic (Caspari, Kranz, & Graulich, 2018). Scaffolding prompts can reduce this cognitive load by aiming at different portions of this complex task.…”

“…implicit property, and using this cause to derive an (electronic) effect on the change (e.g. overlap of the π-orbital of the double bond with the empty p-orbital of the forming carbocation) (Caspari et al, 2018). With this relation, a causal chain (structural claim) is established that now serves as a basis to make a claim (energetic claim) about the differences in activation energy.…”

“…With this relation, a causal chain (structural claim) is established that now serves as a basis to make a claim (energetic claim) about the differences in activation energy. Figure 4 shows a visualization of the generic reasoning structure that is common to answering all types of mechanistic contrasting cases, in organic chemistry or in other disciplines (Caspari & Graulich, 2019;Caspari, Kranz, & Graulich, 2018).…”

Haptic kinetics: A novel 3D‐model of organic reaction processes for inclusive teaching

“…Organische Chemie wird vonL ernenden in Schule undU niversitäti mmer wieder alss chwierig bisu nverständlich beschrieben [ 1,2].U mm çglicheU rsachend afürz ue rgründen, liegte sn ahe, sich mitd er Fragez ub efassen, wiei nd ieser Domäne gedachtund kommuniziert wird.Goodwinhat in na-turwissenschaftsphilosophischenA rbeitend argelegt,d assE rklärungen in derOrganischen Chemie wenigerauf mathemati-schenGesetzmäßigkeitenals vielmehr auf Diagrammen ("dia-grams")f ußen,k onkret Lewis-Formelnu nd gebogenenP feilen( im sogenannten electron pushingf ormalism)s owie Energiepotentialdiagrammen [3,4]. Korrespondierend dazu nutzt dieO rganische Chemie in ihrenE rklärungen typischerweise induktiv gewonneneq ualitative Prinzipien undK onzeptez ur Beschreibung undE rklärungd er betrachtetens trukturell-en-ergetischenE igenschaften undP rozesse, wiez .B.d as Hammond-Postulato derd as Bell-Evans-Polanyi-Theorem [3,5]. Lewis-Formelnund Energiediagramme stellenals Repräsentationen aufder Symbolebeneabernicht nurK ommunikationsmittel dar.…”

How do electronic substituent effects work? – Additional contrasting cases for a differentiated inquiry illustrated by the example of alkaline ester hydrolysis

“…DieW irkung elektronischer Substituenteneffekte aufden Verlauf vonR eaktioneni st in ders ynthetischenO rganischen Chemie vonh erausragenderB edeutung.A uf derE bene der Struktur-Reaktivitäts-Beziehungen übenS ubstituenten einen Einfluss aufR eaktionsgeschwindigkeiten, chemischeG leichgewichte undSelektivitätenaus,der spezifisch fürden jeweili-genreaktionsmechanistischenK ontext istu nd oftmalsaus der Interaktion verschiedenerEffekteund strukturellerGegebenheiten resultiert.U md iesenE influssf üru nterschiedlichste Reaktionen fachgerechtvorhersagen underklärenzukçnnen, sind einV erständnisvon OrganischerChemieauf demNiveau des strukturellenInteraktionismus 1 [1]sowie dieFähigkeitzur Entwicklungm echanistischer Begründungen [ 2,3,4] [ 6,7,8] undi nsbesondere beiv orliegendere lektronischerI nteraktion mehrerer Strukturmerkmale dend araus resultierenden Reaktionsverlauf nichtmehrfachgerechtvorhersagen konnten [9]. Entsprechend habenw ir in Orientierung am Inventing-with-Contrasting-Cases-Ansatz(ICC) [10,11]bereits eine Lerngele-genheitfürStudierende desgymnasialen Lehramts entwickelt, diee inen innovativenZ ugangz ur Wirkungsweisee lektroni-scherS ubstituenteneffektea mM odellbeispield er alkalischen Hydrolyses ubstituierterB enzoesäureethylestere rçffnet [ 12].…”