Alkene Halogenation OBJECTIVE: To prepare alkyl halides by reacting alkenes with hydrogen chloride and bromine. To observe the results of rearrangement mechanisms on reaction products. PROCEDURE: Enter the stockroom and click on the clipboard. Select the Hydroboration Reaction Choose the starting reagents: 4-Methyl-2-Pentene and a solvent (ether) Return to the lab and build the experimental set up. Use a heater, condenser and N2 gas. Add the reagent, HCl. You will monitor the reaction on the pull down TV and with TLC. Run a TLC sample before you start the reaction. Some reactants may not show up on TLC so make sure that you notice the contents of the reaction vessel on the TV. Note the time on the laboratory clock. Start the reaction by turning on the stir plate. Advance the laboratory clock by an interval of 1 minute and take another TLC sample and check the TV. Repeat this step until you note the appearance of product on the TLC plate or on the TV. Note the time and the size of the TLC spot. Continue to advance the clock in 20-minute intervals. Take a TLC sample and check the TV at each interval. Note the time that the reaction is complete. (The starting material will no longer be present in the reaction vessel as indicated on the TV or the TLC sample). Repeat the procedure with Buta-1,3-diene and ether and HCl. (Click on the clipboard and select the Alkene Bromation reaction.) Repeat the procedure with cyclopenta-1,3-diene and ether and Br2. (Click on the clipboard and select the Diels Alder reaction.) Click on the assessment icon at the top right corner of this page and use the data from the experiment to answer the questions in the Laboratory Report 3 Alkene Halogenation. 1. (Points: 1) What is the first step in the reaction sequence of these alkene halogenation reactions? a. Shift of the double bond of the alkene. b. Formation of a halide cation c. Homolytic cleavage of the HCl or Br2 to form the halogen free radical. d. Formation of the carbocation or bromonium ion. e. Etherification of the HCl or Br2. Save Answer 2. (Points: 1) What is the second reaction of the reaction sequence? a. Carbocation or bromonium ion rearrangement. b. Addition of the halide anion. c. Homolytic cleavage of the HCl or Br2 to form the halogen free radical d. Formation of a free halide cation e. Formation of a halide anion Save Answer 3. (Points: 1) Which of the three reactions occurs most rapidly? a. A b. B c. C Save Answer 4. (Points: 1) Why does the reaction you chose in the preceeding question occur faster than the other two? a. The reaction is run at a higher temperature. b. The carbonium ion forms faster. c. Ring alkenes react faster than linear alkenes. d. Cyclopenta-1,3-diene is aromatic. e. Cyclopenta-1,3-diene does not permit delocalization of positive charges. Save Answer 5. (Points: 1) Why was ether used as the solvent for this reaction? a. It stabilized the carbonium ion. b. It enhances the regioselectivity of the reaction. c. It is the universal solvent. d. It does not participate in the reaction. e. It is necessary for the formation of the bromonium ion. Save Answer 6. (Points: 1) What is the major product formed when 1-Pentene is reacted with Br2 in aqueous solution? a. 3-bromo-1-pentene b. 1-bromocyclopentane c. 1-bromocyclopentanol d. 1-bromo-2-pentanol e. 2-bromo-1-pentanol Save Answer 7. (Points: 1) In an alkene halogenation reaction involving a carbocation intermediate a. The formation of the carbocation is usually the fast step in the reaction sequence. b. The formation of the carbocation is usually the slow step in the reaction sequence. c. A non-polar solvent like ether is required to stabilize the carbocation. d. A polar solvent (e.g., water) is required to stabilize the carbocation. e. The opportunity for hydrogen bonding is required to stabilize the carbocation. Save Answer 8. (Points: 1) Which compound undergoes 1,4 addition with Br2? a. A b. B c. C d. D e. E Save Answer 9. (Points: 1) What is the principle product of the following reaction sequence? a. A b. B c. C d. D Save Answer,Great! This assignment goes along with a virtual lab that I performed. Please let me know if you need any of the data. Thanks!