Klein, Organic Chemistry 2e 8.9 The E1 Mechanism The E1 mechanism is a 2-step process Similar to SN1 (chapter 7), the reaction rate for E1 is not affected by the concentration of the base What does the E and the 1 stand for in the E1 notation? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Klein, Organic Chemistry 2e 8.9 The E1 Mechanism Given the rate law for E1, which step in the mechanism is the rate-determining slow step? If the second step were the slow step, how would you write the rate law? Practice with conceptual checkpoint 8.26 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

8.9 The Effect of Substrate on E1 How does the substrate reactivity trend for E1 compare to the trend we discussed in chapter 7 for SN1? WHY? Just like we did for SN1 in chapter 7, to explain the reactivity trend above, we must compare the energy diagrams for each substrate Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

8.9 The Effect of Substrate on E1 To compare their energies, draw the structures for each transition state, intermediate, and product below Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

8.9 The Effect of Substrate on E1 Because E1 and SN1 proceed by the same first step, their competition will generally result in a mixture of products How might you promote one reaction over the other? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

8.9 The Effect of Substrate on E1 Alcohols can also undergo elimination or dehydration by E1, but the –OH group is not a stable leaving group In the E1 reaction below, once the water leaving group leaves the carbocation, what base should be used to complete the elimination? Practice with conceptual checkpoint 8.27 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

8.9 Regioselectivity for E1 The final step of the E1 mechanism determines the regioselectivity E1 reactions generally produce the Zaitsev product predominantly. WHY? Why can’t we control the regioselectivity in this reaction like we can in and E2 reaction? Practice with SkillBuilder 8.8 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

8.9 Stereoselectivity for E1 In the last step of the mechanism, a proton is removed from a β carbon adjacent to the sp2 hybridized carbocation Draw the appropriate carbocation that forms in the reaction below, and rationalize the product distribution Practice with conceptual checkpoint 8.31 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

8.9 Stereoselectivity for E1 Considering stereochemistry and regiochemistry, predict the products if the molecule below was treated with concentrated sulfuric acid Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Klein, Organic Chemistry 2e 8.10 Complete E1 Mechanisms Recall the similarities between SN1 and E1 After the carbocation is formed and possibly rearranged, the E1 proton transfer neutralizes the charge Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Klein, Organic Chemistry 2e 8.10 Complete E1 Mechanisms Why is the first proton transfer necessary? Practice with conceptual checkpoint 8.32 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Klein, Organic Chemistry 2e 8.10 Complete E1 Mechanisms Explain why the carbocation rearranges Practice with conceptual checkpoint 8.33 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Klein, Organic Chemistry 2e 8.10 Complete E1 Mechanisms The maximum number of steps in an E1 mechanism is generally four Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Klein, Organic Chemistry 2e 8.10 Complete E1 Mechanisms Consider the energy diagram for the mechanism on the previous slide Assess each free energy change Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e

Klein, Organic Chemistry 2e 8.10 Complete E1 Mechanisms The mechanism shows the formation of the major products Predict the minor elimination products as well Practice with SkillBuilder 8.9 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry 2e