At the same time or one after the other? – Exploring reaction paths of nucleophilic substitution reactions using historic insights and experiments

Abstract

Zusammenfassung: VieleLernendenehmendie organische Chemie (OC) alsunstrukturiertesund unübersichtliches Fachgebiet wahr.R eaktionsmechanismen werden dabeih äufig nichta ls Orientierungshilfen, sondern vielmehr alszusätzlicheHerausforderungen betrachtet.ZuBeginndes 20.J ahrhundertshatte dieOCals Fachwissenschaft mitvergleichbarenProblemen zu kämpfen.Einen Wendepunkt stelltehierdie systematischeAnwendungp hysikalischerP rinzipien aufo rganische Reaktionen durchd ie Forschenden um Ingold dar. Kinetische Untersuchungen legten beispielsweise nahe,dassinnukleophilenSubstitutionsreaktionendie Abspaltung derA bgangsgruppe undd er Angriffd es Nukleophiles entweder gleichzeitig oder nacheinanders tattfinden kçnnen. In dervorliegendenArbeitwerdendiese historischen Erkenntnisse durcheinfache, schulgeeignete Experimentefürden Unterricht zugänglich gemacht. EinfiktivesA udiotagebuch vonHilda Ingold wird als history lift vorgeschlagen, um denSchüler:innendie grundlegende Erkenntnis zu ermçglichen, dass füre inen Reaktionstyp prinzipiellverschiedene Reaktionswegedenkbarsind. Stichworte: Historisch-problemorientierter Unterricht •R eaktionsmechanismend er organischenC hemie• NukleophileSubstitution•Reaktionskinetik •SchülerexperimentAt thes amet ime or onea fter theo ther?-Exploringr eactionp aths of nucleophilics ubstitutionr eactions usinghistoricinsightsand experiments Abstract: Organicchemistry (OC) appearstobeanunstructuredand confusingsubject to many learners.Reaction mechanisms oftens eemt ob ea na dditionalc hallenge rather than ah elpful guideline. Comparable problemswerealsofound forOCasascienceatthe beginningofthe 20 th century. Oneturning pointwas thesystematica pplication of physical principles on organicr eactionst hrough Ingold andc oworkers.K inetic measurementsimpliedfor examplet hatinn ucleophilicsubstitutionreactions theelimination of theleaving groupand theattack of thenucleophilecould either occuratthe same timeo rstepwise. In this work theh istoricinsights aremade accessible forschoollessons by easy experimentssuitablefor school students.Afictionalaudio diary of HildaI ngoldi sp roposeda sahistory lift to make learners realizet hati np rincipled ifferent reaction pathways arepossiblefor onereaction type.

Using Stop Motion Animations to Activate and Analyze High School Students’ Intuitive Resources about Reaction Mechanisms

“…In the other reaction path (later called SN2, Figure 1 bottom), the attack of the nucleophile and the abstraction of the leaving group happen at the same time [8,11]. The prominent role of nucleophilic substitution reactions in the history of science [6] highlights their potential to introduce fundamental ideas on processes in chemical reactions in high school or undergraduate chemistry [12][13][14].…”

“…The prominent role of nucleophilic substitution reactions in the history of science [6] highlights their potential to introduce fundamental ideas on processes in chemical reactions in high school or undergraduate chemistry [12][13][14].…”

“…The following is a brief description of the intervention to help situate the study. The out-of-school laboratory "A Look Behind the Reaction Arrow" was designed based on experiments developed in our group [12,58,59] for high school students in grades 11 to 13. The out-of-school laboratory is installed at a large university in the German state of Baden-Württemberg and is visited by school classes together with their teachers during school hours.…”

“…Precipitation reactions of bromide were used to allow conclusions on the kinetics of the different reactions. Further details and experimental procedures are described in the literature [12].…”