Transcript ChemDraw
Teaching Guided-Inquiry Organic Chemistry Labs Jerry Mohrig Carleton College Northfield, MN Workshop Objectives Summer 2005 • Provide the participants hands-on experience with question-driven, guided-inquiry organic chemistry projects and experiments. • Allow the participants to evaluate what works well for guided-inquiry experiments and what are the practical constraints. • Help the participants learn how to invigorate their laboratory courses by using question-driven experiments. • Explore whether graduate-student teaching assistants can provide competent supervision in the use of guided-inquiry organic chemistry labs and what training will be necessary to do this successfully. • Encourage sharing of positive and negative experiences by participants regarding their teaching of organic chemistry labs. Two Important Questions Why Do We Teach Labs? What Are Our Goals In Teaching Organic Chemistry Labs? The Traditional Teaching Goals • Help students to experience the material taught in our lectures and deepen their understanding of it • Allow students to verify what the lab manual says • Teach students how to follow experimental directions Higher-Order Traditional Goals • Teach modern laboratory techniques to students • Teach students to synthesize organic compounds The Important “Non-Traditional Goals” of Laboratory Teaching • Teach students how to interpret experimental results and draw reasonable conclusions • Teach students how to design and carry out experimental procedures • Encourage students to ask questions and find answers • Allow students to explore the process of science Styles of Lab Teaching Traditional or Verification Experiments Cookbook Confirmation of knowledge students already have Cosmic futility – make a white powder, prove it’s what you expect, and donate it to chemical waste, again, and again, and again Guided-Inquiry or Discovery Experiments/Projects Question or purpose driven Outcome not known but the chemistry builds on what the students know A procedure is given The experimental results must be evaluated and conclusions drawn Open-ended Inquiry Experiments/Projects Undetermined outcome Students generate their own procedure Research-like Projects The Advantages of Multi-Week Projects • • • • Promote student engagement Allow flexible use of lab time Promote guided-inquiry instruction Use organic synthesis in the context of asking questions • Provide good teamwork opportunities • Effective at every level • Allow lower lab costs Traditional Grignard Synthesis Project NaBr H2SO4/H2O OH H3C reflux SN 2 H3C Br H3C Br Mg Br H3C ether O H3C H2O, H+ OH C4H9 H3C CH2CH3 CH2CH3 Guided-Inquiry Grignard Project Purpose: To design and carry out the Grignard synthesis of a secondary or tertiary alcohol from a simpler primary alcohol NaBr H2SO4/H2O R Mg OH R = C3H7, C4H9, C5H11, (CH3)2CHCH2CH2 reflux SN2 R Br R MgBr extraction, distillation ether NMR or IR O OH R' R R" MgBr R' = CH3, CH2CH3 R'' = H, CH3, CH2CH3 H2O, H+ R R' R'' characterization by boiling point, GC and IR Traditional Acetylation of Ferrocene O C CH3CO2COCH3 Fe Fe H3PO4 ferrocene acetylferrocene Guided-Inquiry Diacetylation of Ferrocene Question: Which diacetylferrocene isomers form? O C CH3COCl Fe Fe AlCl3, CH2Cl2 ferrocene acetylferrocene O O O C Fe O O O C C C C or Fe or Fe C 1,1'-diacetylferrocene mp 127 1,3-diacetylferrocene mp 188 1,2-diacetylferrocene mp 97 Keys to Success in Using Guided-Inquiry Labs Teaching the Art of Data Interpretation • Communication of the lab goals by the teacher • A clear well-defined question or purpose, stated up front • The right background material so that students can successfully interpret their experimental data • The availability of some modern instrumentation • A well-written techniques book, which contains modern spectroscopy as well as traditional lab techniques • Clear, student-friendly experimental directions or models for developing them • A range of question- and purpose-driven experiments and projects, from the straightforward to the more sophisticated • Teamwork opportunities Summary Guided-inquiry experiments and projects are effective • For teaching students how to evaluate their experimental data and draw conclusions from them • For helping students to learn how to design and carry out experimental procedures • For allowing students to experience first-hand the science of organic chemistry