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S N 2 Mechanism

Slides 2 through 9 lead the students to the molecular orbital argument for backside displacement in S N 2 reactions. S N 2 Mechanism. backside attack  2 explanations less hindrance to approach of nucleophile from behind C-L bond than from front MO theory. S N 2 Mechanism. S N 2 Mechanism.

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S N 2 Mechanism

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  1. Slides 2 through 9 lead the students to the molecular orbital argument for backside displacement in SN2 reactions.

  2. SN2 Mechanism • backside attack •  2 explanations • less hindrance to approach of nucleophile from behind C-L bond than from front • MO theory

  3. SN2 Mechanism

  4. SN2 Mechanism -         Is there good overlap? a. Yes b. No c. This interaction is orthogonal.

  5. SN2 Mechanism - Is this a stabilizing interaction?  a. Yes b. No c. Neither

  6. SN2 Mechanism - Is this a stabilizing interaction? • Yes b. No c. Neither

  7. SN2 Mechanism • Front side attack

  8. SN2 Mechanism -         Is there good overlap? • Yes • No c. This interaction is orthogonal.

  9. SN2 Mechanism Is this a stabilizing interaction? • Yes • No

  10. SN2 Mechanism partial bond, charge is dispersed   - 2 partial bonds are weaker than 1 full bond - nonbonded interactions are greater Would you expect the intermediate structure to be higher or lower in energy than iodoethane and bromoethane?  a. higher b. lower c. approximately equal

  11. Potential Energy Diagram of Reaction • The height of the TS above reactants is the amount of energy that is required for a molecule of starting material to be transformed into product. What is this specifically known as? a. Kinetic energy b. Free energy c. Reaction energy • Reactant energy • Activation Energy

  12. The following question addresses the effect of contact ion pairs and solvent separated ion pairs on the stereochemistry of SN1 reactions.

  13. Which enantiomer is more likely to form? • Path a b. Path b. c. No preference

  14. Slides 15 through 18 review the effect of substrate structure on nucleophilic reactions.

  15. 1. Effect of Substrate Rate of SN2 reaction (from left to right) a. increasing b. decreasing c. ~ same

  16. Why? a. electron donating ability of alkyl groups b. electron withdrawing ability of alkyl groups c. steric hindrance blocking approach of nucleophiles • leaving group ability increasing

  17. In the same series … Ease of carbocation formation from left to right ? • increasing b. decreasing c. ~ same

  18. Rate of SN1 reaction from left to right? • increasing b. decreasing c. ~ same

  19. Slides 20 through 23 ensure that students understand potential energy diagrams in relation to solvent effects.

  20. Solvents affect the energy difference between reactants and TS. It affects the height of the energy barrier. • The dashed line represents how solvent affected the reaction. Would the reaction proceed faster or slower in this solvent?

  21. Would the reaction proceed faster or slower in this solvent? • faster b. slower c. ~ same The activation energy is smaller. When that is true, the reaction rate is faster.

  22. Now the dashed line represents how another solvent affected the reaction.

  23. Would the reaction proceed faster or slower in this solvent? • faster b. slower c. ~ same

  24. What is the approximate hybridization of the central C atom of the transition state? a. s b. sp c. sp2 d. sp3 e. p

  25. What is the approximate electronic geometry around the central C atom? a. Linear b. trigonalplanar c. pyramidal d. tetrahedral e. trigonalbipyramidal

  26. What are the partial charges on the I and Br atoms respectively? a. d+ and d+ b. d- and d+ c. d+ and d- d. d- and d- e. There should be no partial charges.

  27. What type of substrate is 2-bromooctane? a. primary b. secondary c. tertiary d. quaternary e. methyl

  28. Predict the product(s) of the following SN2 reaction.

  29. Predict the product(s) of the following SN1 reaction.

  30. What atom will bond to the indicated C atom in the final isolated product? a. S b. N c. Cl d. O e. H

  31. Enter the #’s of the reagents in the proper sequence that will synthesize the D labeled compound from 3-methyl-1-butanol.

  32. Enter the #’s of the reagents in the proper sequence that will synthesize the D labelled compound from 3-methyl-1butanol.

  33. Predict the major product(s) of the following reaction.

  34. Predict the major product of the following reaction.

  35. Enter the #’s of the reagents in the proper sequence that will synthesize hex-3-yne from but-1-yne

  36. Which of the anions would be the strongest nucleophile in ethanol? • F- • Cl- • Br- • I- • They are equally reactive.

  37. Which of the following would be predicted to be the most stable carbocation?

  38. Which of the following substrates would be predicted to react fastest by the SN2 reaction?

  39. Which of the following substrates would be predicted to react fastest by the SN1 reaction?

  40. Based on inductive effects, which of the following anilines would be the least basic?

  41. Which of the following anilines would be the most nucleophiic?

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