Chem 164/261 Oct 25, 2011 Addition reactions of alkenes - Follows ...

Chem 164/261 Oct 25, 2011Addition reactions of alkenesC CA!! !BcarbocationintermediateC CABC CA BA- Follows Markovnikov ruleH 3 C ! HC CH HOH O SOOHCH 3 HH C CHH3 CO HHCH 3 HCH 3 HH C C HH C C HO HO HH CH 3 CH3methylethyl ether- The reverse reaction is called an eliminationHydroborationGeneralProtonation (alkane)Oxidation (alcohol)SynHHB! !HC CC CconcertedR 2 B H(all bonds breakand form at same time)NaOHH O O HH 2 O 2C CHO HHC CH H

Formally Anti-MarkovnikovAddition of H-OH in opposite sense.B 2 H 6 – diborane behaves like BH 3HHBHHBHH2 xHHBHEg 1.!HH! !B!HH BH 22BNaOHH 2 O 2HEg. HCl33OHEg 2.1) B 2 H 62) H 2 O 2NaOHHOHSyn addition of H 2 OOverall anti-Markovnikov addition of waterHH 3 CHNaOHH 3 CHBHH BH 22 HHBH 2H 2 O 2HOH

Reduction: process that adds electronsEg.H 2PtC CH HOxidation: process that removes electronsOzonolysis: cleavage of alkenes by ozone (O 3 )General reaction:resonance formsOOO O O3 O OOOOspontaneousOO OreductionZnOO+ ZnOOOOOzonideExplosiveOzonideMore stableKetone and/or aldehydesEg.1. O 32. ZnOacetone+H H 2 OOHformaldehydegasFormalin SolutionC OCOC(H)COHcarbonylketonealdehydeformaldehyde name comes from formic acid, which comes from formica (ant):OH HformaldehydeHOOHformic acid is an ant defense substance(formica means ant)

Mechanism:HHO 3OOOHHO OHOHHOHO OreductionZnOOHHO OOZnOSample question for practice: What is a possible structure for the starting material below(C 10 H 16 )?Are there other isomers that will give the same products for ozonolysis followed by Zntreatment?HH1. O?3C 10 H2. Zn16OOH3 degrees of unsaturationOOOHOHOOHOOHO1) O 32) ZnH 2PtOHHH 3 C CH 3MyrceneEpoxidation – Oxirane formation1) Epoxide formation (epoxidation) – Oxirane formationex)

C COR CO OHperacetic acidOC CO+ R COHan etherepoxideor oxiranecarboxylic acid• Syn Addition• Concerted reaction: all bonds break and form at the same timeH 3 C CH 3C CH HOH 3 C CperacidO OHCH 3CH 3H OHOStereospecific ReactionH 3 C HC CH CH 3OH 3 C CperacidO OHCH 3OH H 3COConcerted reaction is always stereospecificMechanism:H3 CH HH C C HadO O b HC c OHHC COHHO+ H 3 C COHacetic acid