9-9-11
Organic Organic ChemistryChemistry
William H. BrownWilliam H. Brown
Christopher S. FooteChristopher S. Foote
Brent L. IversonBrent L. Iverson
William H. BrownWilliam H. Brown
Christopher S. FooteChristopher S. Foote
Brent L. IversonBrent L. Iverson
9-9-22
Nucleophilic Nucleophilic Substitution and Substitution and -Elimination-Elimination
Chapter 8
Chapter 9Chapter 9
9-9-33
Nucleophilic SubstitutionNucleophilic Substitution
Nucleophilic substitution:Nucleophilic substitution: any reaction in which one nucleophile substitutes for another at a tetravalent carbon
Nucleophile:Nucleophile: a molecule or ion that donates a pair of electrons to another molecule or ion to form a new covalent bond; a Lewis base
nucleophilicsubstitution
Nucleophile
++ C NuC LvNu:- Lv
Leavinggroup
9-9-44
Nucleophilic SubstitutionNucleophilic Substitution
Some nucleophilic substitution reactions
I -
HS -
RO -
HO -
- C N
HC C -
Nu
NH3
HOH
CH3I
CH3SH
CH3OH
CH3OR
CH3O-HH
CH3C N
CH3Br
CH3NH3+
CH3C CH
CH3Nu Br
+an alcohol (after proton transfer)
an alkylammonium ion
an alkyl iodide
a nitrile
an alkyne
::
:
:
:::
:
a thiol (a mercaptan)
an ether
an alcohol
Reaction: + +: :
:
:
:
: :
9-9-55
SolventsSolvents
Protic solvent:Protic solvent: a solvent that is a hydrogen bond donor • the most common protic solvents contain -OH groups
Aprotic solvent:Aprotic solvent: a solvent that cannot serve as a hydrogen bond donor• nowhere in the molecule is there a hydrogen bonded
to an atom of high electronegativity
9-9-66
Dielectric ConstantDielectric Constant
Solvents are classified as polar and nonpolar• the most common measure of solvent polarity is
dielectric constant
Dielectric constant:Dielectric constant: a measure of a solvent’s ability to insulate opposite charges from one another• the greater the value of the dielectric constant of a
solvent, the smaller the interaction between ions of opposite charge dissolved in that solvent
• polar solvent: dielectric constant > 15• nonpolar solvent: dielectric constant < 15
9-9-77
Protic SolventsProtic Solvents
H2OHCOOH
CH3OH
CH3CH2OH
CH3COOH
Solvent Structure
DielectricConstant(25°C)
WaterFormic acid
Methanol
Ethanol
7959
33
24
Acetic acid 6
9-9-88
Aprotic SolventsAprotic Solvents
CH2Cl2CH3CH2OCH2CH3
CH3C N
CH3(CH2)4CH3
(CH3)2S=O
(CH3)2NCHO
(CH3)2C=O
C6H5CH3 2.3Toluene
4.3Diethyl ether
9.1Dichloromethane
SolventDielectricConstantStructure
Dimethyl sulfoxide (DMSO)
Acetonitrile
Acetone
N,N-Dimethylformamide (DMF)
48.9
37.5
36.7
20.7
Polar
Nonpolar
Hexane 1.9
9-9-99
MechanismsMechanisms
Chemists propose two limiting mechanisms for nucleophilic substitution• a fundamental difference between them is the timing of
bond-breaking and bond-forming steps
At one extreme, the two processes take place simultaneously; designated SN2• S = substitution• N = nucleophilic• 2 = bimolecular (two species are involved in the rate-
determining step)
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Mechanism - SMechanism - SNN22
• both reactants are involved in the transition state of the rate-determining step
C Br
H
HH
HO:- + C
H
H H
HO Brδ- δ-
Transition state with simultaneous bond breaking and bond forming
C
H
HH
HO + Br::
: :::
::
::
::: : ::
9-9-1111
Mechanism - SMechanism - SNN22
9-9-1212
Mechanism - SMechanism - SNN11
Bond breaking between carbon and the leaving group is entirely completed before bond forming with the nucleophile begins
This mechanism is designated SN1 where• S = substitution• N = nucleophilic• 1 = unimolecular (only one species is involved in the
rate-determining step)
9-9-1313
Mechanism - SMechanism - SNN11
• Step 1: ionization of the C-X bond gives a carbocation intermediate
C
CH3
CH3H3C
+C
H3C
H3CBr
H3C
slow, ratedetermining
A carbocation intermediate; its shape is trigonal planar
+ Br
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Mechanism - SMechanism - SNN11
• Step 2: reaction of the carbocation (an electrophile) with methanol (a nucleophile) gives an oxonium ion
• Step 3: proton transfer completes the reaction
C
CH3
CH3H3C
OCH3
H
C
CH3
CH3
O
H3C
H CH3
C
H3C
H3C
O
H3CH
CH3
+
Electrophile Nucleophile
fast
Oxonium ions
+ + ::
: :
:+
+++ fastC
H3CH3C
OH3C
OCH3
HOHO
CH3CH3
H
H
CH3
H3C
CH3C
H3C
:: : ::
9-9-1515
Mechanism - SMechanism - SNN11
9-9-1616
Evidence of SEvidence of SNN reactions reactions
1. What is relationship between the rate of an SN reaction and: • the structure of Nu?• the structure of RLv?• the structure of the leaving group?• the solvent?
2. What is the stereochemical outcome if the leaving group is displaced from a chiral center?
3. Under what conditions are skeletal rearrangements observed?
9-9-1717
KineticsKinetics
For an SN1 reaction• reaction occurs in two steps• the reaction leading to formation transition state for
the carbocation intermediate involves only the haloalkane and not the nucleophile
• the result is a first-order reaction
CH3CBrCH3
CH3
CH3OH
d[(CH3)3CBr]dt
Rate = - = k[(CH3)3CBr]
CH3COCH3
CH3
CH3
HBr+ +
2-Bromo-2-methylpropane
Methanol 2-Methoxy-2-methylpropane
9-9-1818
KineticsKinetics
For an SN2 reaction, • reaction occurs in one step• the reaction leading to the transition state involves the
haloalkane and the nucleophile• the result is a second-order reaction; first order in
haloalkane and first order in nucleophile
d[CH3Br]
dtrate = = k[CH3Br][OH-]
CH3Br + Na+OH- CH3OH + Na+Br-
Bromomethane Methanol
9-9-1919
NucleophilicityNucleophilicity
Nucleophilicity:Nucleophilicity: a kinetic property measured by the rate at which a Nu causes a nucleophilic substitution under a standardized set of experimental conditions
Basicity:Basicity: a equilibrium property measured by the position of equilibrium in an acid-base reaction
Because all nucleophiles are also bases, we study correlations between nucleophilicity and basicity
9-9-2020
NucleophilicityNucleophilicity
Good
Poor
Br-, I-
HO-, CH3O-, RO-CH3S
-, RS-
CH3COO-, RCOO-
H2OCH3OH, ROHCH3COOH, RCOOH
NH3, RNH2, R2NH, R3NCH3SH, RSH, R2S
Nucleophile
Moderate
CN-, N3-
Effectiveness
Cl-, F-
9-9-2121
NucleophilicityNucleophilicity
Relative nucleophilicities of halide ions in polar aprotic solvents are quite different from those in polar protic solvents
How do we account for these differences?
Increasing Nucleophilicity
Solvent
Polar aprotic
Polar protic F- < Cl- < Br- < I-
I- < Br- < Cl- < F-
9-9-2222
NucleophilicityNucleophilicity
A guiding principle is the freer the nucleophile, the greater its nucleophilicity
Polar aprotic solvents (e.g., DMSO, acetone, acetonitrile, DMF) • are very effective in solvating cations, but not nearly
so effective in solvating anions. • because anions are only poorly solvated, they
participate readily in SN reactions, and
• nucleophilicity parallels basicity: F- > Cl- > Br- > I-
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NucleophilicityNucleophilicity
Polar protic solvents (e.g., water, methanol)• anions are highly solvated by hydrogen bonding with
the solvent• the more concentrated the negative charge of the
anion, the more tightly it is held in a solvent shell• the nucleophile must be at least partially removed
from its solvent shell to participate in SN reactions
• because F- is most tightly solvated and I- the least, nucleophilicity is I- > Br- > Cl- > F-
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NucleophilicityNucleophilicity
Generalization• within a row of the Periodic Table, nucleophilicity
increases from left to right; that is, it increases with basicity
Increasing NucleophilicityPeriod
Period 2
Period 3
F- < OH- < NH2- < CH3
-
Cl- < SH- < PH2-
9-9-2525
NucleophilicityNucleophilicity
Generalization• in a series of reagents with the same nucleophilic
atom, anionic reagents are stronger nucleophiles than neutral reagents; this trend parallels the basicity of the nucleophile
Increasing Nucleophilicity
ROH < RO-H2O < OH-
NH3 < NH2-
RSH < RS-
9-9-2626
NucleophilicityNucleophilicity
Generalization• when comparing groups of reagents in which the
nucleophilic atom is the same, the stronger the base, the greater the nucleophilicity
Nucleophile RCOO-
HO-
RO-
Conjugate acid
pKa
RCOOH4-5
ROHHOH
16-1815.7
Hydroxide ion
Alkoxide ion
Carboxylate ion
Increasing Acidity
Increasing Nucleophilicity
9-9-2727
StereochemistryStereochemistry
For an SN1 reaction at a chiral center, the R and S enantiomers are formed in equal amounts, and the product is a racemic mixture
C
H
Cl
Cl
-Cl-
C+
H
Cl
CH3OH
-H+ CH3O C
H
Cl Cl
C OCH3
H
R EnantiomerS Enantiomer
+
R EnantiomerA racemic mixture
Planar carbocation (achiral)
9-9-2828
StereochemistryStereochemistry
For SN1 reactions at a chiral center• examples of complete racemization have been
observed, but• partial racemization with a slight excess of inversion is
more common
Approach of the nucleophile from this side is less hindered
+
R1
C
HR2
Cl-
Approach of the nucleophile fromthis side is partially blocked by leaving group, which remains associated with the carbocation as anion pair
9-9-2929
StereochemistryStereochemistry
For SN2 reactions at a chiral center, there is inversion of configuration at the chiral center
Experiment of Hughes and Ingold
Iacetone
SN2-131+
I I131
I-+
2-Iodooctane
9-9-3030
Hughes-Ingold ExptHughes-Ingold Expt
• the reaction is 2nd order, therefore, SN2
• the rate of racemization of enantiomerically pure 2-iodooctane is twice the rate of incorporation of I-131
I:- CH
I
C6H13
H3CH
CH3
C6H13
I C ISN2
acetone+131 131
+
(S)-2-I odooctane (R)-2-Iodooctane
9-9-3131
Structure of RXStructure of RX
SN1 reactions: governed by electronic factors • the relative stabilities of carbocation intermediates
SN2 reactions: governed by steric factors • the relative ease of approach of a nucleophile to the
reaction siteGoverned byelectronic factors
Governed bysteric factors
SN1
SN2
R3CX R2CHX RCH2X CH3X
Access to the site of reaction
(3°) (methyl)(2°) (1°)
Carbocation stability
9-9-3232
Effect of Effect of -Branching-Branching
1.2 x 10-51.2 x 10-3Relative Rate
Alkyl Bromide
-Branches 0 1 2 3
1.0 4.1 x 10-1
Br Br Br Br
9-9-3333
Effect of Effect of -Branching-Branching
CH3CH2Br
freeaccess
Bromoethane(Ethyl bromide)
CH3CCH2Br
CH3
CH3
1-Bromo-2,2-dimethylpropane(Neopentyl bromide)
blockedaccess
9-9-3434
Allylic HalidesAllylic Halides
Allylic cations are stabilized by resonance delocalization of the positive charge• a 1° allylic cation is about as stable as a 2° alkyl cation
+ +
Allyl cation(a hybrid of two equivalent contributing
structures)
CH2=CH-CH2 CH2-CH=CH2
9-9-3535
Allylic CationsAllylic Cations
• 2° & 3° allylic cations are even more stable
• as also are benzylic cations
• adding these carbocations to those from Section 6.3
C6H5-CH2+CH2
+
Benzyl cation(a benzylic carbocation)
The benzyl cation is also writtenin this abbreviated form
CH2=CH-CH-CH3
CH3
CH2=CH-C-CH3
++
A 2° allylic carbocation A 3° allylic carbocation
Increasing stability of carbocations
2° alkyl1° allylic1° benzylic
methyl < 1° alkyl < < 3° alkyl2° allylic2° benzylic
<3° allylic3° benzylic
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The Leaving GroupThe Leaving Group
The more stable the anion, the better the leaving ability• the most stable anions are the conjugate bases of
strong acids
I- > Br- > Cl- > H2O >> F- > CH3CO- > HO- > CH3O- > NH2-
Reactivity as a leaving group
Stability of anion; strength of conjugate acid
rarely function as leaving groups
O
9-9-3737
The Solvent - SThe Solvent - SNN22
The most common type of SN2 reaction involves a negative Nu and a negative leaving group
• the weaker the solvation of Nu, the less the energy required to remove it from its solvation shell and the greater the rate of SN2
+ +
Transition state
negatively chargednucleophile
negatively chargedleaving group
negative charge dispersed in the transition state
LvC LvCNu CNuNu:-δ−δ−
Lv
9-9-3838
The Solvent - SThe Solvent - SNN22
Br N3-
CH3C N
CH3OHH2O
(CH3 )2S=O
(CH3 )2NCHO
N3 Br-
SolventType
polar aprotic
polar protic
5000
2800
1300
71
k(methanol)
k(solvent)
Solvent
+solvent
SN2+
9-9-3939
The Solvent - SThe Solvent - SNN11
SN1 reactions involve creation and separation of unlike charge in the transition state of the rate-determining step
Rate depends on the ability of the solvent to keep these charges separated and to solvate both the anion and the cation
Polar protic solvents (formic acid, water, methanol) are the most effective solvents for SN1 reactions
9-9-4040
The Solvent - SThe Solvent - SNN11
water
80% water: 20% ethanol
40% water: 60% ethanolethanol
Solvent
solvolysis++
k(solvent)
k(ethanol)
1
100
14,000
100,000
CH3
CH3 CH3
CH3
CH3CCl ROH CH3COR HCl
9-9-4141
Rearrangements in SRearrangements in SNN11
Rearrangements are common in SN1 reactions if the initial carbocation can rearrange to a more stable one
2-Methoxy-2-phenylbutane2-Chloro-3-phenylbutane
++ CH3OH + Cl -
CH3OHCH3OH
HCl
OCH3
+
9-9-4242
Rearrangements in SRearrangements in SNN11
Mechanism of a carbocation rearrangement
Cl
H
O-CH3
H
H
O
H
CH3
Cl+
+
A 2° carbocation
++
A 3° benzylic carbocation
+++
An oxonium ion
:
:
(1)
(2)
(3)
9-9-4343
Summary of SSummary of SNN1 & S1 & SNN22
CH3X
RCH2X
R2CHX
R3CX
Type of Alkyl Halide
Methyl
Primary
Secondary
Tertiary
SN2 SN1
Substitution at a stereocenter
SN2 is favored. SN1 does not occur. The methyl cationis so unstable, it is never observedin solution.
SN1 rarely occurs. Primary cations are so unstable, that they are never observed in solution.
SN1 is favored in protic solvents withpoor nucleophiles. Carbocation rearrangements may occur.
SN2 is favored in aproticsolvents with goodnucleophiles.
SN2 does not occur becauseof steric hindrance aroundthe reaction center.
SN1 is favored because of the ease of formation of tertiary carbocations.
Inversion of configuration.The nucleophile attacksthe stereocenter from theside opposite the leavinggroup.
Racemization is favored. The carbocationintermediate is planar, and attack of thenucleophile occurs with equalprobability from either side. There is often some net inversion of configuration.
SN2 is favored.
9-9-4444
SSNN1/S1/SNN2 Problems2 Problems
• Problem 1:Problem 1: predict the mechanism for this reaction, and the stereochemistry of each product
• Problem 2:Problem 2: predict the mechanism of this reaction
+ +Na+CN- Na+Br -DMSOBr CN
Cl
CH3OH/ H2O
OH OCH3
HCl+(R)-2-Chlorobutane
+ +
9-9-4545
SSNN1/S1/SNN2 Problems2 Problems
• Problem 3:Problem 3: predict the mechanism of this reaction and the configuration of product
• Problem 4:Problem 4: predict the mechanism of this reaction and the configuration of the product
Br
CH3S-Na+
SCH3
Na+Br-+ +acetone(R)-2- Bromobutane
Br CH3COH
O
OCCH3
O
HBr+ acetic acid +
(R)-3-Bromo-cyclohexene
9-9-4646
SSNN1/S1/SNN2 Problems2 Problems
• Problem 5:Problem 5: predict the mechanism of this reaction
++
toluene(CH3 )3P P(CH3)3 Br-Br
9-9-4747
-Elimination-Elimination
-Elimination:-Elimination: a reaction in which a molecule, such as HCl, HBr, HI, or HOH, is split out or eliminated from adjacent carbons
C C
X
H
CH3CH2O-Na+
C C
CH3CH2OH
CH3CH2OH Na+X -
α+
+ +
A haloalkane Base
An alkene
9-9-4848
-Elimination-Elimination
Zaitsev rule:Zaitsev rule: the major product of a -elimination is the more stable (the more highly substituted) alkene
2-Methyl-2-butene (major product)
CH3CH2O-Na+
CH3CH2OH 2-Bromo-2-methylbutane
2-Methyl-1-butene
Br+
+
1-Methyl-cyclopentene
(major product)
CH3O-Na+
CH3OH
1-Bromo-1-methyl-cyclopentane
Br
Methylene-cyclopentane
9-9-4949
-Elimination-Elimination
There are two limiting mechanisms for -elimination reactions
E1 mechanism:E1 mechanism: at one extreme, breaking of the R-Lv bond to give a carbocation is complete before reaction with base to break the C-H bond• only R-Lv is involved in the rate-determining step
E2 mechanism:E2 mechanism: at the other extreme, breaking of the R-Lv and C-H bonds is concerted• both R-Lv and base are involved in the rate-determining step
9-9-5050
E1 MechanismE1 Mechanism
• ionization of C-Lv gives a carbocation intermediate
• proton transfer from the carbocation intermediate to the base (in this case, the solvent) gives the alkene
CH3-C-CH3
Br
CH3
CH3-C-CH3
CH3
Br
slow, ratedetermining
+(A carbocation intermediate)
+
O:
H
H3CH-CH2-C-CH3
CH3
O
H
H3CH CH2=C-CH3
CH3fast
+
++ +
9-9-5151
E1 MechanismE1 Mechanism
9-9-5252
E2 MechanismE2 Mechanism
9-9-5353
Kinetics of E1 and E2Kinetics of E1 and E2
E1 mechanism • reaction occurs in two steps• the rate-determining step is carbocation formation• the reaction is 1st order in RLv and zero order is base
E2 mechanism• reaction occurs in one step• reaction is 2nd order; first order in RLv and 1st order
in based[RLv]
dtRate = = k[RLv][Base]
d[RLv]
dtRate = = k[RLv]
9-9-5454
Regioselectivity of E1/E2Regioselectivity of E1/E2
E1: major product is the more stable alkene E2: with strong base, the major product is the
more stable (more substituted) alkene• double bond character is highly developed in the
transition state• thus, the transition state of lowest energy is that
leading to the most stable (the most highly substituted) alkene
E2: with a strong, sterically hindered base such as tert-butoxide, the major product is often the less stable (less substituted) alkene
9-9-5555
Stereoselectivity of E2Stereoselectivity of E2
E2 is most favorable (lowest activation energy) when H and Lv are oriented anti and coplanar
CH3O:-
C C
H
Lv
CH3OH
C C
Lv-H and -Lv are anti and coplanar
(dihedral angle 180°)
9-9-5656
Stereochemistry of E2Stereochemistry of E2
Consider E2 of these stereoisomers
Cl
CH3O-Na+
CH3OH
CH3O-Na+
CH3OHCl
+
(R)-3-Isopropyl-cyclohexene
1-Isopropyl-cyclohexene
(major product)
cis-1-Chloro-2-isopropyl-
cyclohexane
trans-1-Chloro-2-isopropyl-
cyclohexane
(R)-3-Isopropyl-cyclohexene
9-9-5757
Stereochemistry of E2Stereochemistry of E2
• in the more stable chair of the cis isomer, the larger isopropyl is equatorial and chlorine is axial
CH3O:-
H
H
H
H
Cl
CH3OH :Cl
1-Isopropyl-cyclohexene
2
1
6 + +E2
9-9-5858
Stereochemistry of E2Stereochemistry of E2
• in the more stable chair of the trans isomer, there is no H anti and coplanar with Lv, but there is one in the less stable chair
More stable chair (no H is anti and coplanar to Cl)
Less stable chair(H on carbon 6 is
anti and coplanar to Cl)
2
2
11
6 6Cl
H
H
H
H
Cl
HH
HH
9-9-5959
Stereochemistry of E2Stereochemistry of E2
• it is only the less stable chair conformation of this isomer that can undergo an E2 reaction
H
Cl
HH
HCH3O:
-
CH3OH Cl
(R)-3-Isopropyl-cyclohexene
21
6E2
+ +
9-9-6060
Stereochemistry of E2Stereochemistry of E2
Problem:Problem: account for the fact that E2 reaction of the meso-dibromide gives only the E alkene
C6H5CH-CHC6H5
Br BrCH3O- Na+
CH3OH
C C
Br H
C6H5C6H5
meso-1,2-Dibromo-1,2-diphenylethane
(E)-1-Bromo-1,2-diphenylethylene
9-9-6161
Summary of E2 vs E1Summary of E2 vs E1
RCH2X
R2CHX
R3CX
Alkyl halide E1 E2
Primary
Secondary
Tertiary
E1 does not occur.Primary carbocations areso unstable, they are neverobserved in solution.
E2 is favored.
Main reaction with strong bases such as OH- and OR-.
Main reaction with weak bases such as H2O, ROH.
Main reaction with strong bases such as OH- and OR-.
Main reaction with weak bases such as H2O, ROH.
9-9-6262
SSNN vs E vs E
Many nucleophiles are also strong bases (OH- and RO-) and SN and E reactions often compete
The ratio of SN/E products depends on the relative rates of the two reactions
nucleophilicsubstitution
-elimination
C CH Lv + Nu-
C CH Nu +
C C H-Nu+ +
Lv
Lv
9-9-6363
SSNN vs E vs E
CH3X
RCH2X bases such as I- and CH3COO-.
SN2 SN1 reactions of methyl halides are never observed.The methyl cation is so unstable that it is never formed in solution.
SN2
E2 The main reaction with strong, bulky bases such as potassium tert-butoxide.
Primary cations are never observeded in solution and,therefore, SN1 and E1 reactions of primary halides are never observed.
Halide Reaction Comments
Methyl
Primary The main reaction with good nucleophiles/weak
9-9-6464
SSNN vs E (cont’d) vs E (cont’d)
The main reaction with bases/nucleophiles where the
R3CX
pKa of the conjugate acid is 11 or less, as for exampleI- and CH3COO-.
R2CHX
Main reaction with strong bases such as HO- and RO-.
Main reactions with poor nucleophiles/weak bases.
The main reaction with bases/nucleophiles where
E2
SN2
E2
SN2 reactions of tertiary halides are never observed
SN1/E1
Secondary
Tertiary
because of the extreme crowding around the 3° carbon.
SN1/E1Common in reactions with weak nucleophiles in polarprotic solvents, such as water, methanol, and ethanol.
pKa of the conjugate acid is 11 or greater, as for exampleOH- and CH3CH2O
-.
9-9-6565
Neighboring GroupsNeighboring Groups
In an SN2 reaction, departure of the leaving group is assisted by Nu; in an SN1 reaction, it is not
These two types of reactions are distinguished by their order of reaction; SN2 reactions are 2nd order, and SN1 reactions are 1st order
But some substitution reactions are 1st order and yet involve two successive SN2 reactions
9-9-6666
Mustard GasesMustard Gases
Mustard gases • contain either S-C-C-X or N-C-C-X
• what is unusual about the mustard gases is that they undergo hydrolysis so rapidly in water, a very poor nucleophile
ClS
Cl 2H2O HOS
OH 2HCl+ +
Bis(2-chloroethyl)sulfide(a sulfur mustard gas)
Bis(2-chloroethyl)methylamine(a nitrogen mustard gas)
ClS
Cl ClN
Cl
9-9-6767
Mustard GasesMustard Gases
• the reason is neighboring group participation by the adjacent heteroatom
• proton transfer to solvent completes the reaction
ClS
Cl
ClS O-H
H
ClS
ClS
O
H
H
Cl+
+
A cyclic sulfonium ion
an internal SN2 reaction
slow, ratedetermining
++
a secondSN2 reaction
fast+
:
:
:
9-9-6868
Phase-Transfer CatalysisPhase-Transfer Catalysis
A substance that transfers ions from an aqueous phase to an organic phase
An effective phase-transfer catalyst must have sufficient• hydrophilic character to dissolve in water and form an
ion pair with the ion to be transported• hydrophobic character to dissolve in the organic
phase and transport the ion into it
The following salt is an effective phase-transfer catalysts for the transport of anions
(CH3CH2CH2CH2)4N+Cl-
Tetrabutylammonium chloride(Bu4N
+Cl- )
9-9-6969
Phase-Transfer CatalysisPhase-Transfer Catalysis
9-9-7070
Nucleophilic Substitution Nucleophilic Substitution and and
-Elimination-Elimination
End Chapter 9End Chapter 9