Alkenes, Reactions

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Alkenes, Reactions
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R-H R-X R-OH R-O-R
Alkenes
NR NR ? ? ?
NR ? ? some NR NR
NR ? ? NR NR
NR NR ? NR ?
NR ? NR NR ?
NR NR NR NR ?
Acids Bases Metals Oxidation Reduction Halogens
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Alkenes, reactions. Addition ionic free
radical Reduction Oxidation Substitution
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• Reactions, alkenes
• Addition of hydrogen (reduction).
• Addition of halogens.
• Addition of hydrogen halides.
• Addition of sulfuric acid.
• Addition of water (hydration).
• Addition of aqueous halogens (halohydrin
  formation).
• 7. Oxymercuration-demercuration.

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8. Hydroboration-oxidation. 9. Addition of free
radicals. 10. Addition of carbenes. 11. Epoxidatio
n. 12. Hydroxylation. 13. Allylic
halogenation 14. Ozonolysis. 15. Vigorous
oxidation.
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• Addition of hydrogen (reduction).
• C C H2 Ni, Pt, or Pd ?
  C C
• 
  H H
• a) Requires catalyst.
• 1 synthesis of alkanes
• CH3CHCHCH3 H2, Ni ? CH3CH2CH2CH3
• 2-butene n-butane

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Alkanes Nomenclature Syntheses 1. addition
of hydrogen to an alkene 2. reduction of an
alkyl halide a) hydrolysis of a Grignard
reagent b) with an active metal and acid 3.
Corey-House Synthesis Reactions 1.
halogenation 2. combustion (oxidation) 3.
pyrolysis (cracking)
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heat of hydrogenation CH3CHCH2 H2, Pt ?
CH3CH2CH3 30 Kcal/mole ethylene 32.8 prop
ylene 30.1 cis-2-butene 28.6 trans-2-butene 27.
6 isobutylene 28.4
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fats oils triglycerides
O CH2OCCH2CH2CH2CH2CH2CH2CH2CH2CH3
O CHOCCH2CH2CH2CH2CH2CH2CH2CH2CH3
O CH2OCCH2CH2CH2CH2CH2CH2CH3
saturated fat
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O CH2OCCH2CH2CH2CH2CHCH2CH2
CH2CH3 O CHOCCH2CH2CH2CH2CHC
H2CH2CH2CH3 O CH2OCCH2CH2CHCH
CH2CH2CH3 O - 3 unsaturated
oil
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Saturated triglycerides are solids at room
temperature and are called fats. butter fat,
lard, vegetable shortening, beef tallow,
etc. Unsaturated triglycerides have lower mps
than saturated triglycerides. Those that are
liquids at room temperature are called oils.
(All double bonds are cis-.) corn oil, peanut
oil, Canola oil, cottonseed oil, etc.
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polyunsaturated oils H2, Ni ? saturated
fats liquid at RT solid at RT

oleomargarine
butter substitute
(dyed yellow) Trans-fatty acids formed
in the synthesis of margarine have been
implicated in the formation of bad cholesterol,
hardening of the arteries and heart disease. ?
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• 2. Addition of halogens.
• C C X2 ? C C
• 
  X X
• X2 Br2 or Cl2
• test for unsaturation with Br2
• CH3CH2CHCH2 Br2/CCl4 ? CH3CH2CHCH2
• 
  Br Br
• 1-butene 1,2-dibromobutane

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• Addition of hydrogen halides.
• C C HX ? C C
• 
  H X
• HX HI, HBr, HCl
• Markovnikov orientation
• CH3CHCH2 HI ? CH3CHCH3
• 
  I
• CH3 CH3
• CH2CCH2 HBr ? CH3CCH3
• 
  Br

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Markovnikovs Rule In the addition of an acid
to an alkene the hydrogen will go to the vinyl
carbon that already has the greater number of
hydrogens.
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CH3CH2CHCH2 HCl ?
CH3CH2CHCH3 Cl
CH3 CH3 CH3CHCCH3 HBr ?
CH3CH2CCH3
Br CH3CHCHCH3
HI ? CH3CH2CHCH3
I
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An exception to Markovikovs Rule CH3CHCH2
HBr, peroxides ? CH3CH2CH2Br
CH3
CH3 CH3CCH2 HBr, peroxides
? CH3CHCH2Br anti-Markovnikov
orientation note this is only for HBr.
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Markovnikov doesnt always correctly predict the
product! CH3
CH3 CH2CHCHCH3 HI ? CH3CH2CCH3
?
I Rearrangement!
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why Markovinkov? CH3CHCH2 HBr ?
CH3CHCH2 1o carbocation
?
?
H
or? CH3CHCH2 2o carbocation
?
more stable
H
Br- ? CH3CHCH3

Br
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In ionic electrophilic addition to an alkene, the
electrophile always adds to the carbon-carbon
double bond so as to form the more stable
carbocation.
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• Addition of sulfuric acid.
• C C H2SO4 ? C C
• 
  H OSO3H
• alkyl hydrogen sulfate
• Markovnikov orientation.
• CH3CHCH2 H2SO4 ? CH3CHCH3
• 
  O
• 
  O-S-O
• 
  OH

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• Addition of water.
• 
  
• C C H2O, H ? C C
  
• 
  H OH
• a) requires acid
• Markovnikov orientation
• low yield ?
• CH3CH2CHCH2 H2O, H ? CH3CH2CHCH3
• OH

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H
C C H2O ?
C C

OH
H Mechanism for addition of water to an alkene
to form an alcohol is the exact reverse of the
mechanism (E1) for the dehydration of an alcohol
to form an alkene.
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How do we know that the mechanism isnt this
way? One step, concerted, no
carbocation
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CH3CHCH2 Br2 H2O NaCl
? CH3CHCH2 CH3CHCH2
CH3CHCH2 Br Br
OH Br Cl Br
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Some evidence suggests that the intermediate is
not a normal carbocation but a halonium ion

C C
Br ? The addition of X2 to an alkene is
an anti-addition.
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• Addition of halogens water (halohydrin
  formation)
• 
  
• C C X2, H2O ? C C HX
• 
  
• 
  OH X
• X2 Br2, Cl2
• Br2 electrophile
• CH3CHCH2 Br2(aq.) ? CH3CHCH2
  HBr
• 
  OH Br

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7. Oxymercuration-demercuration.

C C H2O, Hg(OAc)2 ? C
C acetic

acid
OH HgOAc

C C NaBH4 ? C C

OH HgOAc
OH H alcohol
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• oxymercuration-demercuration
• 1 synthesis of alcohols.
• Markovnikov orientation.
• 100 yields. ?
• no rearrangements ?
• CH3CH2CHCH2 H2O, Hg(OAc)2 then NaBH4 ?
• CH3CH2CHCH3
• 
  OH

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With alcohol instead of water alkoxymercuration-
demercuration
C
C ROH, Hg(TFA)2 ? C C


OR HgTFA

C C NaBH4 ?
C C
OR HgTFA
OR H ether
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• alkoxymercuration-demercuration
• 2 synthesis of ethers.
• Markovnikov orientation.
• 100 yields. ?
• no rearrangements ?
• CH3CHCH2 CH3CHCH3, Hg(TFA)2 then NaBH4 ?
• OH
• 
  CH3 CH3
• CH3CH-O-CHCH3
• 
  diisopropyl ether
• 
  
• Avoids the elimination with 2o/3o RX in
  Williamson Synthesis.

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Ethers nomenclature syntheses 1. Williamson
Synthesis 2. alkoxymercuration-demercuration
reactions 1. acid cleavage
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8. Hydroboration-oxidation.
C C
(BH3)2 ? C C

diborane H B


C
C H2O2, NaOH ? C C

H B
H OH
alcohol
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• hydroboration-oxidation
• 2 synthesis of alcohols.
• Anti-Markovnikov orientation. ?
• 100 yields. ?
• no rearrangements ?
• CH3CH2CHCH2 (BH3)2 then H2O2, NaOH ?
• CH3CH2CH2CH2-OH
• 
  

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CH3 CH3CCH2 H2O, Hg(OAc)2 then
NaBH4 ?
CH3 Markovnikov
CH3CCH3
OH
CH3 CH3CCH2 (BH3)2 then H2O2, NaOH ?

CH3
anti-Markovnikov CH3CHCH2

OH
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Alcohols nomenclature syntheses 1.
oxymercuration-demercuration 2.
hydroboration-oxidation 3. 4. hydrolysis of
a 1o / CH3 alcohol 5. 6. 8.
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• 9. Addition of free radicals.
• 
  
• C C HBr, peroxides ? C C
• 
  
• H X
• anti-Markovnikov orientation.
• free radical addition
• HI, HCl Peroxides
• CH3CHCH2 HBr, peroxides ? CH3CH2CH2-Br

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• Mechanism for free radical addition of HBr
• Initiating steps
• 1) peroxide ? 2 radical
• 2) radical HBr ? radicalH Br
  (Br electrophile)
• Propagating steps
• 3) Br CH3CHCH2 ? CH3CHCH2-Br (2o free
  radical)
• 
  
• 4) CH3CHCH2-Br HBr ? CH3CH2CH2-Br
  Br
• 3), 4), 3), 4)
• Terminating steps
• Br Br ? Br2
• Etc.

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In a free radical addition to an alkene, the
electrophilic free radical adds to the vinyl
carbon with the greater number of hydrogens to
form the more stable free radical. In the case
of HBr/peroxides, the electrophile is the bromine
free radical (Br). CH3CHCH2 HBr,
peroxides ? CH3CH2CH2-Br
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10. Addition of carbenes.

C C CH2CO or CH2N2 ,
h? ? C C
?
CH2 CH2
carbene adds across the
double bond
C C ? ? CH2
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C C
CHCl3, t-BuOK ? C C

CCl2 ?
-HCl CCl2
dichlorocarbene C C
? ? CCl2
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11. Epoxidation.
C6H5CO3H
C C (peroxybenzoic acid) ?
C C
O

epoxide Free radical addition of
oxygen diradical.
C C ?
? O
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12. Hydroxylation. (mild oxidation)

C C KMnO4 ? C C
syn

OH OH

OH
C C HCO3H
? C C anti
peroxyformic acid
OH
glycol
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CH3CHCHCH3 KMnO4 ? CH3CH-CHCH3

OH OH
2,3-butanediol test for
unsaturation purple KMnO4 ? brown
MnO2 CH2CH2 KMnO4 ? CH2CH2
OH
OH ethylene glycol anti-freeze
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13. Allylic halogenation.

C C C X2, heat ? C
C C HX
H
? allyl
X CH2CHCH3 Br2, 350oC ? CH2CHCH2Br
HBr a) X2 Cl2 or Br2 b) or
N-bromosuccinimide (NBS)
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CH2CHCH3 Br2 ? CH2CHCH3
Br
Br addition CH2CHCH3 Br2, heat ?
CH2CHCH2-Br HBr allylic substitution
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14. Ozonolysis.

C C O3 then Zn, H2O ?
C O O C used for identification of
alkenes CH3 CH3CH2CHCCH3
O3 then Zn, H2O ?

CH3
CH3CH2CHO OCCH3
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15. Vigorous oxidation. CH2 KMnO4, heat
? CO2 CHR KMnO4, heat ? RCOOH
carboxylic acid CR2 KMnO4, heat ?
OCR2 ketone
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CH3CH2CH2CHCH2 KMnO4, heat ?
CH3CH2CH2COOH
CO2 CH3
CH3 CH3CCHCH3 KMnO4, heat
? CH3CO HOOCCH3
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CH3CHCHCH3 KMnO4 ? CH3CHCHCH3

OHOH mild oxidation ? glycol CH3CHCHC
H3 hot KMnO4 ? 2 CH3COOH vigorous
oxidation
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• Reactions, alkenes
• Addition of hydrogen
• Addition of halogens
• Addition of hydrogen halides
• Addition of sulfuric acid
• Addition of water/acid
• Addition of halogens water (halohydrin
  formation)
• 7. Oxymercuration-demercuration

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8. Hydroboration-oxidation 9. Addition of free
radicals 10. Addition of carbenes 11. Epoxidation
12. Hydroxylation 13. Allylic halogenation 14. Ozo
nolysis 15. Vigorous oxidation
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CH3
CH3 CH3CCH2 H2, Pt ?
CH3CHCH3 isobutylene
CH3
Br2/CCl4 ? CH3C-CH2

Br Br
CH3
HBr ? CH3CCH3
Br

CH3
H2SO4 ? CH3CCH3
O

SO3H
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CH3
CH3 CH3CCH2 H2O, H ?
CH3CCH3 isobutylene
OH
CH3
Br2(aq.) ? CH3C-CH2Br

OH CH3

CH3 CH3CCH2 H2O,Hg(OAc)2 then NaBH4 ?
CH3CCH3 OH

CH3
(BH3)2 then H2O2, OH- ? CH3CHCH2


OH
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CH3
CH3 CH3CCH2 HBr,
peroxides ? CH3CHCH2 isobutylene

Br
CH3
CH2CO, hv ? CH3CCH2

CH2
CH3
PBA ? CH3CCH2

O

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CH3
CH3 CH3CCH2 KMnO4 ?
CH3CCH2 isobutylene
OH OH
CH3
Br2, heat ? CH2CCH2
HBr
Br
CH3
O3 then Zn/H2O ? CH3CO
OCH2

CH3
KMnO4, heat ? CH3CO
CO2