ORGANIC - BROWN 8E CH ALKENES AND REACTIONS OF ALKENES

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2 CONCEPT: ALKENES and ALKYNES Alkenes/Alkynes are named by adding the suffix modifier (- /- ) to the end of the root. Alkenes/alkynes receive in numbering alkanes Location is assigned to the first double bonded carbon EXAMPLE: Name the following compound: a. Page 2

3 CONCEPT: STABILITY OF ALKENES Alkenes are also stabilized through Since this is only possible with -R groups, the more substituted the alkene, the more EXAMPLE: Rank the following alkenes in order of lowest to highest heat of combustion. Page 3

4 CONCEPT: CARBOCATION INTERMEDIATES STABILITY Carbocations are stabilized by a phenomenon called Hyperconjugation is the delocalization of charge by the interaction of an empty p-orbital with an adjacent, eclipsed σ-bond Since this is only possible with -R groups, the more substituted the carbocation, the more EXAMPLE: Which of the following alkyl halides would generate the most stable carbocation? Page 4

5 CONCEPT: CARBOCATION INTERMEDIATES REARRANGEMENTS Carbocations will rearrange to an adjacent, more stable position if possible. This is called a 1,2-Hydride Shift occurs when there is a located on an adjacent, more stable carbon. 1,2-Alkyl Shift occurs when only small groups are located on an adjacent, more stable carbon. Ring Expansion occurs when a carbocation is adjacent to a 3, 4 or 5- membered ring. Page 5

6 PRACTICE: Which of the following carbocations would be likely to rearrange? Draw each rearranged structure below. Page 6

7 CONCEPT: GENERAL MECHANISM Addition reactions are ones in which 1 bond is broken and 2 new bonds are formed. They are the inverse of reactions EXAMPLE: Provide the mechanism for the following addition reaction. Page 7

8 CONCEPT: MARKOVNIKOV S RULE When we try to perform addition on asymmetric double bonds, we now get two possible products. Markovnikov s Rule predicts that the carbocation will ALWAYS form on the carbon EXAMPLE: Provide the mechanism for the following addition reaction. Page 8

9 CONCEPT: HYDROHALOGENATION General Reaction: EXAMPLE: Provide the mechanism for the following addition reaction. Page 9

10 CONCEPT: ACID-CATALYZED HYDRATION Same reagents as acid-catalyzed dehydration, except starting with a instead of an alcohol. Same as the general mechanism hydrohalogenation, except with as the nucleophile Remember that EVERY acid-cat. mechanism begins with and ends with General Reaction: EXAMPLE: Provide the mechanism for the following addition reaction. Page 10

11 PRACTICE: Provide the mechanism and predict the product of the following reaction. Page 11

12 CONCEPT: OXYMERCURATION-REDUCTION General Reaction: Mechanism: 1. Electrophilic Addition 2. Nucleophilic Substitution (SN 2 ) 3. Reduction (demurcuration) Page 12

13 PRACTICE: Provide the mechanism and predict the product of the following reactions. a. Page 13

14 CONCEPT: HYDROBORATION-OXIDATION General Reaction: Mechanism: 1. Electrophilic Addition 2. Oxidation Page 14

15 PRACTICE: Provide the mechanism and predict the product of the following reactions. a. b. Page 15

16 CONCEPT: CATALYTIC HYDROGENATION AND WILKINSON S CATALYST General Reaction: PRACTICE: Provide the products for the following reaction. Page 16

17 CONCEPT: INTRO TO REDOX Oxidation reactions involve an increase in the content of a molecule Reduction reactions involve an increase in the content of a molecule EXAMPLE: Label the following transformations as oxidation or reduction. a. b. c. Page 17

18 CONCEPT: HALOGENATION General Reaction: Mechanism: 1. Electrophilic Addition 2. Nucleophilic Substitution (SN 2 ) Page 18

19 CONCEPT: HALOHYDRIN FORMATION General Reaction: Mechanism: 1. Electrophilic Addition 2. Nucleophilic Substitution (SN 2 ) Page 19

20 PRACTICE: Provide the mechanism and predict the product of the following reactions. a. b. Page 20

21 CONCEPT: SYN VICINAL DIHYDROXYLATION General Reaction: EXAMPLE: Predict the product for the following multi-step reaction. Page 21

22 CONCEPT: WEAK OXIDATIVE CLEAVAGE Ozonolysis: Ketones + Aldehydes + Formaldehyde PRACTICE: Predict the products of the following reaction Page 22

23 CONCEPT: OZONOLYSIS FULL MECHANISM The mechanism for ozonolysis proceeds through multiple intermediates. Ozonolysis is combined with either a reductive, or an oxidative workup Reductive workup: S(CH3)2 or Zn/HOAc Oxidative Workup: H2O2 Ozonolysis Mechanism: Reductive Workup Mechanism: Oxidative Workup Mechanism: Page 23

24 PRACTICE: Predict the products and show the full mechanism for the following reaction Page 24

25 CONCEPT: OXIDATIVE CLEAVAGE Strong Oxidative Cleavage: Ketones + Carboxylic Acid + Carbon Dioxide PRACTICE: Predict the product of the following reaction. Page 25

26 CONCEPT: OXIDATIVE CLEAVAGE Cleavage of Alkynes: Carboxylic Acid + Carbon Dioxide EXAMPLE: Predict the product of the following reaction. Page 26