Summary University of California, IrvineCHEM 51scaffold 4.LAB

Chem 51LB Experiment 4 Report Scaffold Dehydration and Dehydrobromination of Butanol and Bromobutane compounds Analysis of Products by Gas Chromatography Purpose/Introduction A. What was the purpo se of using different butanols/bromobutanes? The position of the hydroxy and bromo groups on the carbon chain yields different products and mechanisms of eliminations. B. What was the purpose of taking a gas chromatography analysis of the products? The GC analysis allowed for the ratio of products to be seen from the given reaction, confirm the mechanism the reactants underwent, and see which mechanism was most successful. Theory C. What are the environments need for E1 and E2 reactions? An E1 mechanism requires a weak base, and a 2°, or 3° leaving group (LG). An E2 mechanism requires a strong base, and a 1°, 2°, or 3° LG. Both mechanisms require β hydrogens to donate their electrons to a double bond and protonate the base, however E2 mechanisms require the hydrogen to be antiperiplanar. D. What is the difference between an E1/E2 reactions? An E1 reaction undergoes first order kinetics. There is an intermediate carbocation that forms after the LG departs, which is stabilized by the formation of a double bond and protonation of the base. An E2 reaction undergoes second order kinetics. The LG and β hydrogen leave simultaneously, and a double bond forms. E. Which mechanism do each of the experimental reactions prefer? The HCl reaction prefers E1 with the 1-butanol and 2-butanol, since there is a weak base and a protonated H2O LG. The Ktert-butoxide (KtBuO) reaction prefers E2 with the 1-bromobutane and 2-bromobutane, since there is a strong base and a primary or secondary LG. The detailed mechanisms are attached below. Results