Example Problems HBr R-0-0-R Heat HBr R-0-0R, Heat HBr R-0-0R, Heat HBr R-0-0R, Heat 2013 Pearson Education Inc
Example Problems 16 © 2013 Pearson Education Inc. + HBr + HBr H H H + HBr H H H + HBr Heat R-O-O-R Heat R-O-O-R Heat R-O-O-R Heat R-O-O-R
Hydration of Alkenes OH C-C+H.o alkene alcohol (Markovnikov orientation) 01Paarson Eaunion,ie Addition of water to the double bond forms an alcohol. The addition follows Markovnikov's rule. This is the reverse of the dehydration of alcohol. Uses dilute solutions of H2SO or HaPOa to drive equilibrium toward hydration. 2013 Pearson Education Inc. 17
Hydration of Alkenes • Addition of water to the double bond forms an alcohol. • The addition follows Markovnikov’s rule. • This is the reverse of the dehydration of alcohol. • Uses dilute solutions of H2SO4 or H3PO4 to drive equilibrium toward hydration. 17 © 2013 Pearson Education Inc
Mechanism for Hydration Step 1:Protonation of the double bond forms a carbocation. on the more substituted carbon Step 2:Nucleophilic attack of water. Step 3:Deprotonation of the alcohol. 18 2013 Pearson Education Inc
Mechanism for Hydration Step 1: Protonation of the double bond forms a carbocation. Step 2: Nucleophilic attack of water. Step 3: Deprotonation of the alcohol. 18 © 2013 Pearson Education Inc
Orientation of Hydration CH CH CH, CH,-C-CH-CH,H--H CH-C-CH-CH, but not CH3-C-CH-CH3 H H 3°，more stable 2,lessstable e20t行Pearson Educationin The protonation follows Markovnikov's rule:The proton adds to the less substituted end of the double bond,so the positive charge appears at the more substituted end (most stable carbocation). 2013 Pearson Education Inc. 19
Orientation of Hydration The protonation follows Markovnikov’s rule: The proton adds to the less substituted end of the double bond, so the positive charge appears at the more substituted end (most stable carbocation). 19 © 2013 Pearson Education Inc
Rearrangements Possible in Electrophilic Addition Reactions CH3 CH3 CH3一C-CH=CH2 50%H2S0, CH3一C一CH一CH3 CH3 OH CH3 3.3-dimethylbut-1-ene 2.3-dimethylbutan-2-ol (major product) 年问w+生一线 Methyl Shift: CH3 CH3 CH3 CH3-C-CH-CH3 → CH3-C-CH-CH3 →CH3-C—CH-CH3 CH3 CH3 OH CH3 2°，less stable 3°，more stable 2,3-dimethyl-2-butanol (major product) A methyl shift after protonation will produce the more stable tertiary carbocation. 20 2013 Pearson Education Inc
Rearrangements Possible in Electrophilic Addition Reactions • A methyl shift after protonation will produce the more stable tertiary carbocation. 2,3-dimethyl-2-butanol (major product) CH3 C CH CH3 CH3 CH3 CH3 C CH CH3 CH3 CH3 CH3 C CH CH3 CH3 OH CH3 2 o , less stable 3 o , more stable Methyl Shift: 20 © 2013 Pearson Education Inc