acid-catalyzed hydration of alkenes -...
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6.106.10Acid-Catalyzed Hydration of AlkenesAcid-Catalyzed Hydration of Alkenes
HH——OOHHCC CC ++ OOHHCC CCHH
Acid-Catalyzed Hydration of AlkenesAcid-Catalyzed Hydration of Alkenes
reaction is acid catalyzed; typical hydrationreaction is acid catalyzed; typical hydrationmedium is 50% Hmedium is 50% H22SOSO44-50% H-50% H22OO
Follows Markovnikov's RuleFollows Markovnikov's Rule
(90%)(90%)
50% H50% H22SOSO44
50% H50% H22OO
HH33CC
HH33CC CHCH33
HH
CC CC
OOHH
CC CHCH22CHCH33CHCH33
CHCH33
Follows Markovnikov's RuleFollows Markovnikov's Rule
50% H50% H22SOSO44
50% H50% H22OO
Follows Markovnikov's RuleFollows Markovnikov's Rule
(80%)(80%)
OOHH
CHCH33
CHCH22
+ H+ H22OOHH++
involves a carbocation intermediateinvolves a carbocation intermediate
is the reverse of acid-catalyzed dehydrationis the reverse of acid-catalyzed dehydrationof alcohols to alkenesof alcohols to alkenes
HH33CC
HH33CC
CC CHCH22
OOHH
CC CHCH33CHCH33
CHCH33
MechanismMechanism
Addition of Water to Alkene(alcohols)
Addition of Water to Alkenes(alcohols)
QuestionQuestion
Which Which alkene alkene will undergo acid-catalyzedwill undergo acid-catalyzedhydrolysis at the fastest rate?hydrolysis at the fastest rate?
A)A) B)B)
C)C) D)D)
In an equilibrium process, the same intermediates In an equilibrium process, the same intermediates and transition states are encountered in the and transition states are encountered in the forward direction and the reverse, but in the forward direction and the reverse, but in the opposite order. opposite order.
+ H+ H22OOHH++
HH33CC
HH33CC
CC CHCH22
OOHH
CC CHCH33CHCH33
CHCH33
Principle of Microscopic ReversibilityPrinciple of Microscopic Reversibility
HH22O addition: O addition: Markovnikov's Markovnikov's RuleRule QuestionQuestion
The product isolated from the acid-catalyzedThe product isolated from the acid-catalyzedhydration of (hydration of (Z)Z)-3-methyl-2-pentene is:-3-methyl-2-pentene is:
A)A) 2-ethyl-2-butanol2-ethyl-2-butanol
B)B) 2-ethyl-1-butanol2-ethyl-1-butanol
C)C) 3-methyl-2-pentanol3-methyl-2-pentanol
D)D) 3-methyl-3-pentanol3-methyl-3-pentanol
QuestionQuestion
The product isolated from the acid-catalyzedThe product isolated from the acid-catalyzedhydration of (hydration of (E)E)-3-methyl-2-pentene is:-3-methyl-2-pentene is:
A)A) chiralchiral
B)B) achiralachiral
Addition of Alcohol to Alkenes(ethers)
RegioRegiochemistrychemistry withstanding, in order to withstanding, in order to understand the understand thestereochemistry of thestereochemistry of the product, you must consider two things:product, you must consider two things:
(1) Stereochemistry of the starting (1) Stereochemistry of the starting alkene alkene (cis or trans; (cis or trans;
Z or E)Z or E)
(2) Stereochemistry of the addition (syn or anti)(2) Stereochemistry of the addition (syn or anti)
Stereochemistry of Addition to AlkenesStereochemistry of Addition to Alkenes
CC CC ++ EE——YY CC CCEE YY
Optically inactive reactants produce optically inactive products.Optically inactive reactants produce optically inactive products.((RacemicRacemic mixtures are optically inactive) mixtures are optically inactive)
The The correlary correlary is that an optically active starting material is that an optically active starting material MAY produce an MAY produce an optically active product depending on the mechanism.optically active product depending on the mechanism.
Stereochemistry of Addition to AlkenesStereochemistry of Addition to Alkenes
CC CC ++ EE——YY CC CCEE YY
QuestionQuestion
The product isolated from the acid-catalyzedThe product isolated from the acid-catalyzedhydration of (hydration of (E)- or (Z)E)- or (Z)-3-methyl-2-pentene is:-3-methyl-2-pentene is:
A)A) optically activeoptically active
B)B) an optically inactivean optically inactive racemic racemic mixture mixture
C) an optically inactive C) an optically inactive enantiomer enantiomer
6.126.12Hydroboration-Oxidation of AlkenesHydroboration-Oxidation of Alkenes
Needed: a method for hydration of Needed: a method for hydration of alkenes with a regioselectivity opposite to alkenes with a regioselectivity opposite to Markovnikov's rule.Markovnikov's rule.
Suppose you wanted to prepare 1-decanol Suppose you wanted to prepare 1-decanol from 1-decene?from 1-decene?
SynthesisSynthesis
OHOH
Two-step reaction sequence called Two-step reaction sequence called hydroborationhydroboration--oxidation converts alkenes to alcohols with a oxidation converts alkenes to alcohols with a regiochemistry regiochemistry opposite to opposite to Markovnikov's Markovnikov's rule.rule.
1. 1. hydroborationhydroboration
2. oxidation2. oxidation
SynthesisSynthesis
OHOH
++ H H——BHBH22CC CC HH BHBH22CC CC
Hydroboration Hydroboration can be viewed as the addition ofcan be viewed as the addition ofborane borane (BH(BH33) to the double bond. But BH) to the double bond. But BH33 is is not the reagent actually used.not the reagent actually used.
Hydroboration StepHydroboration Step
++ H H——BHBH22CC CC HH BHBH22CC CC
Hydroboration reagents:Hydroboration reagents:
HH22BB
HH
HH
BHBH22
Diborane (BDiborane (B22HH66))normally used in an normally used in an ether-like solventether-like solventcalled "diglyme"called "diglyme"
Hydroboration StepHydroboration Step
++ H H——BHBH22CC CC HH BHBH22CC CC
Hydroboration Hydroboration reagents:reagents:
BoraneBorane--tetrahydrofurantetrahydrofurancomplex (Hcomplex (H33B-THF)B-THF)
Hydroboration StepHydroboration Step
+ OO
BHBH33–
••••
HH22OO22, HO, HO––
HH BHBH22CC CC HH OOHHCC CC
Organoborane formed in the hydroborationOrganoborane formed in the hydroborationstep is oxidized with hydrogen peroxide.step is oxidized with hydrogen peroxide.
Oxidation StepOxidation Step
1. B1. B22HH66, , diglymediglyme
2. H2. H22OO22, HO, HO––
(93%)(93%)
ExampleExample
OOHH (98%)(98%)
HH33CC
HH33CC
CHCH33
HH
CC CC1. 1. HH33B-THFB-THF
2. H2. H22OO22, HO, HO––
HH
CC CCCHCH33
CHCH33
CHCH33
HH OOHH
ExampleExample
hydration of alkeneshydration of alkenes
regioselectivity opposite to Markovnikov's rule regioselectivity opposite to Markovnikov's rule
no rearrangementno rearrangement
stereospecific stereospecific synsyn addition addition
Features of Hydroboration-OxidationFeatures of Hydroboration-Oxidation
1. B1. B22HH66, , diglymediglyme
2. H2. H22OO22, HO, HO––
(82%)(82%)
ExampleExample
OOHH
6.136.13Stereochemistry of Hydroboration-OxidationStereochemistry of Hydroboration-Oxidation
hydration of alkeneshydration of alkenes
regioselectivity opposite to Markovnikov's rule regioselectivity opposite to Markovnikov's rule
no rearrangementno rearrangement
stereospecific stereospecific synsyn addition addition
Features of Hydroboration-OxidationFeatures of Hydroboration-Oxidation
H and OH become attached to same H and OH become attached to same face of double bondface of double bond
1. B1. B22HH66
2. H2. H22OO22, NaOH, NaOH
only product is only product is transtrans-2-methylcyclopentanol-2-methylcyclopentanol(86%) yield(86%) yield
syn Additionsyn Addition
CHCH33
HH
HH
CHCH33
HH
HHOO
QuestionQuestion
HydroborationHydroboration-oxidation of which one of the-oxidation of which one of thefollowing yields a primary alcohol as the majorfollowing yields a primary alcohol as the majorproduct?product?
A) A) B)B)
C)C) D)D)
HH33CC
HH33CC
CHCH33
HH
CC CC1. 1. HH33B-THFB-THF
2. H2. H22OO22, HO, HO––
HH
CC CCCHCH33
CHCH33
CHCH33
HH OOHH
QuestionQuestion
A)A) The product isThe product is achiral achiralB)B) The product is optically activeThe product is optically activeC)C) The product is aThe product is a racemic racemic mixture mixtureD)D) The product is a The product is a single enantiomersingle enantiomer
6.156.15
Addition of HalogensAddition of Halogens
to Alkenesto Alkenes
++ XX22 XX XX
electrophilic electrophilic addition to double bondaddition to double bondforms a vicinalforms a vicinal dihalide dihalide
CC CCCC CC
General featuresGeneral features
CHCH33CHCHCHCHCH(CHCH(CH33))22
(100%)(100%)
CHClCHCl3300°°CC
CHCHCH(CHCH(CH33))22CHCH33CHCHBrBr22
ExampleExample
BrBr BrBr
FF22 addition proceeds with explosive violence addition proceeds with explosive violence
II22 addition is endothermic: vicinal addition is endothermic: vicinal diiodides diiodides
dissociate to andissociate to an alkene alkene and Iand I22
limited to Cllimited to Cl22 and Br and Br22
ScopeScope HalogenationHalogenation
anti additionanti additionanti addition
6.166.16Stereochemistry of Halogen AdditionStereochemistry of Halogen Addition
BrBr22
transtrans-1,2--1,2-DibromocyclopentaneDibromocyclopentane80% yield; only product80% yield; only product
ExampleExample
HH
HH
BrBr
BrBr
HH
HH
ClCl22
transtrans-1,2--1,2-DichlorocyclooctaneDichlorocyclooctane73% yield; only product73% yield; only product
ExampleExample
HH
HH
HH
HH
ClCl
ClCl
6.176.17Mechanism of Halogen Addition toMechanism of Halogen Addition to
Alkenes:Alkenes: Halonium Halonium IonsIons
BrBr22 is not polar, but it is is not polar, but it is polarizable polarizable
two stepstwo steps(1) (1) formation offormation of bromonium bromonium ionion(2)(2) nucleophilic nucleophilic attack onattack on bromonium bromonium
ion by bromideion by bromide
Mechanism isMechanism is electrophilic electrophilic additionadditionAddition of Halogens to Alkenes
ethyleneethylene HH22C=CHC=CH22 11
propenepropene CHCH33CH=CHCH=CH22 6161
2-2-methylpropene methylpropene (CH(CH33))22C=CHC=CH22 54005400
2,3-2,3-dimethyldimethyl-2--2-butene butene (CH(CH33))22C=C(CHC=C(CH33))22 920,000920,000
More highly substituted double bonds react faster.More highly substituted double bonds react faster.
Alkyl groups on the double bond make itAlkyl groups on the double bond make it
more more ““electron rich.electron rich.””
Relative Rates ofRelative Rates of Bromination Bromination QuestionQuestion
Arrange the alkenes in order of decreasing rateArrange the alkenes in order of decreasing rateof reaction toward bromine addition:of reaction toward bromine addition:2-methyl-1-butene, 2-methyl-2-butene, and 3-2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butenemethyl-1-buteneA)A) 2-methyl-1-butene > 3-methyl-1-butene >2-methyl-1-butene > 3-methyl-1-butene >
2-methyl-2-butene2-methyl-2-buteneB)B) 3-methyl-1-butene > 2-methyl-1-butene >3-methyl-1-butene > 2-methyl-1-butene >
2-methyl-2-butene2-methyl-2-buteneC)C) 2-methyl-2-butene > 2-methyl-1-butene >2-methyl-2-butene > 2-methyl-1-butene >
3-methyl-1-butene3-methyl-1-buteneD)D) 2-methyl-2-butene > 3-methyl-1-butene >2-methyl-2-butene > 3-methyl-1-butene >
2-methyl-1-butene2-methyl-1-butene
BrBr22
transtrans-1,2--1,2-dibromocyclopentanedibromocyclopentane80% yield; 2 asymmetric carbon atoms,80% yield; 2 asymmetric carbon atoms,
Chiral Chiral product,Optically inactive,product,Optically inactive,
RacemicRacemic mixture, only products formed mixture, only products formed
ExampleExample
HH
HH
BrBr
BrBr
HH
HH
DiastereomersDiastereomers
In general, In general, diastereomers diastereomers fall into two categories:fall into two categories:
geometric isomersgeometric isomers
cis-transcis-trans
stereoisomers stereoisomers containing two or morecontaining two or moreasymmetric atoms; (that are not asymmetric atoms; (that are not enantiomersenantiomers))
C
C
CH
CH3
CH3
H
CH
CH3
H
CH3
C
C
CH
CH3
CH3
H
CH
CH3
H
CH3
CH3HH
BrCl
CH3
CH3BrH Cl
H
CH3
CH3HH
BrCl
CH3
CH3BrH Cl
H
CH3
diastereomers
(S)
(R)
(R)
(R)
DiastereomersDiastereomers
Diastereomers Diastereomers have different physicalhave different physicalproperties:properties:
BP, MP, density, refractive index, solubilityBP, MP, density, refractive index, solubility
Can be separated through conventionalCan be separated through conventionalmeans (distillation, means (distillation, recrystallizationrecrystallization,,chromatography)chromatography)
H BrCO2H
CO2HBr H
CO2H
Co2H
HH
BrBr
H BrCO2H
CO2HBr H
CO2H
CO2H
HH
BrBr
MP = 158oC MP = 256oC
DiastereomersDiastereomers
A compound with A compound with ““nn”” asymmetric carbon atoms asymmetric carbon atomscan have a maximum of 2can have a maximum of 2nn stereoisomersstereoisomers.. CH3
CH3
BrBrH
HBr
BrH
H
CH3
CH3CH3
CH3
HH
BrBr
CH3
BrBr
HH
CH3
CC
CC
CC
CC
CH3
CH3
BrBrH
HBr
BrH
H
CH3
CH3CH3
CH3
HH
BrBr
CH3
BrBr
HH
CH3
CC
CC
CC
CC
CH3
CH3
BrBrH
HBr
BrH
H
CH3
CH3CH3
CH3
HH
BrBr
CH3BrBr
HH
CH3
CC
CC
CC
CC
CH3
CH3
BrBrH
HBr
BrH
H
CH3
CH3CH3
CH3
HH
BrBr
CH3BrBr
HH
CH3
CC
CC
CC
CC
2,3-dibromobutane
Enantiomers Same compound(meso)diastereomers
σ
(S)
(S) (R)
(R)
(R)
(S)
(S)
(R)
Only 3 stereoisomers for 2,3-dibromobutane.
ThreeThree stereoisomers stereoisomers of 2,3-of 2,3-dibromobutanedibromobutane
22RR,3,3RR 22SS,3,3SS 22RR,3,3SS
chiralchiral chiralchiral achiralachiral
CHCH33
CHCH33
BrBrHH
HHBrBrHH BrBr
CHCH33
CHCH33
HHBrBr HH
CHCH33
CHCH33
BrBr
BrBrHH
The addition of bromine to The addition of bromine to ciscis-2-butene-2-buteneproduces:produces:
A)A) A singleA single enantiomer enantiomerB)B) A product with one asymmetric carbon atomA product with one asymmetric carbon atomC)C) An optically inactiveAn optically inactive meso meso product productD)D) A A racemicracemic mixture mixtureE)E) 4 different4 different stereoisomers stereoisomers each with 2 each with 2 chiral chiral
carbon atomscarbon atoms
QuestionQuestion
The addition of bromine to The addition of bromine to transtrans-2-butene-2-buteneproduces:produces:
A)A) A singleA single enantiomer enantiomerB)B) A product with one asymmetric carbon atomA product with one asymmetric carbon atomC)C) An optically inactiveAn optically inactive meso meso product productD)D) A A racemicracemic mixture mixtureE)E) 4 different4 different stereoisomers stereoisomers each with 2 each with 2 chiral chiral
carbon atomscarbon atoms
QuestionQuestionDiastereomersDiastereomers
When naming compounds containing multipleWhen naming compounds containing multiplechiral chiral atoms, you must give the configurationatoms, you must give the configurationaround each around each chiral chiral atom:atom:
position number and configuration of eachposition number and configuration of eachchiral chiral atom, separated by commas, all in ( )atom, separated by commas, all in ( )at the start of the compound nameat the start of the compound name
C
CH3
CH3
Cl
ClBr HH
H
C
CH3
CH3
Br
HCl
H(S)
(S)(2S, 3S)-2-bromo-3-chlorobutane
DiastereomersDiastereomers
Which ones areWhich ones are chiral chiral? Name each one. Give? Name each one. Givethethe stereochemical stereochemical relationship between them. relationship between them.
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
All of them are chiral.
DiastereomersDiastereomers
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
(2S, 3R)-2,3-dichloropentane (2R, 3S)-2,3-dichloropentane
(2S, 3S)-2,3-dichloropentane (2R, 3R)-2,3-dichloropentane
DiastereomersDiastereomers
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
CH3
CH2CH3
ClCl
HH
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
ClCl
HH
H ClCl H
Cl HH Cl
A B C D
A and B: enantiomersC and D: enantiomersA and C: diastereomersA and D: diastereomersB and C: diastereomersB and D: diastereomers
6.186.18Conversion of Alkenes to VicinalConversion of Alkenes to Vicinal
HalohydrinsHalohydrins
Addition of Halogens in the Presence of Water
(halohydrins) ++ X X22 XX XXCC CCCC CC
alkenes react with Xalkenes react with X22 to form vicinal to form vicinal dihalides dihalides
++ X X22 XX XXCC CCCC CC
++ H H22OO OHOH
+ + HH——XX
++ X X22 XX CC CCCC CC
alkenes react with Xalkenes react with X22 to form vicinal to form vicinal dihalides dihalides
alkenes react with Xalkenes react with X22 in water to give vicinal in water to give vicinal halohydrinshalohydrins
ClCl22
anti anti addition: only productaddition: only product
HH22OO
HH22CC CHCH22 BrBrCHCH22CHCH22OOHH++ BrBr22
HH22OO
(70%)(70%)
ExamplesExamples
HH
HH
OOHH
ClCl
HH
HH
ClCl22
anti anti addition: only productaddition: only product
HH22OO
HH22CC CHCH22 BrBrCHCH22CHCH22OOHH++ BrBr22
HH22OO
(70%)(70%)
ExamplesExamples
HH
HH
OOHH
ClCl
HH
HH
Perspective formula
Fischer projection
(77%)(77%)
HH33CC
CC CHCH22
HH33CC
CHCH33
OOHH
CC CHCH22BrBrCHCH33
Markovnikov's Markovnikov's rule applied torule applied to halohydrin halohydrinformation: formation: the halogen adds to the carbonthe halogen adds to the carbonhaving the greater number ofhaving the greater number of hydrogens hydrogens..
BrBr22
HH22OO
RegioselectivityRegioselectivity
CHCH22
HH33CC
CCHH33CC
transition state for attack of water ontransition state for attack of water on bromonium bromonium ion hasion has carbocation carbocationcharacter; more stable transition state (left) has positive charge oncharacter; more stable transition state (left) has positive charge on
more highly substituted carbonmore highly substituted carbon
HH33CC CHCH22
HH33CC
BrBr:: ::δ+δ+
δ+δ+
HH
OOHH δ+δ+....
BrBr:: ::
HH
OO HHδ+δ+....
CC
δ+δ+
δ+δ+
ExplanationExplanation
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