Transcript Organic Chemistry - Home | Rutgers

Organic
Chemistry
William H. Brown
Christopher S. Foote
Brent L. Iverson
9-1
Nucleophilic
Substitution and
-Elimination
Chapter 9
9-2
Nucleophilic Substitution
-
Nu:
+
Nucleophile
C
Lv
nucleophilic
substitution
C
Nu +
Lv
Leaving
group
 Nucleophilic
substitution: any reaction in which
one nucleophile substitutes for another at a
tetravalent carbon
 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
9-3
Nucleophilic Substitution
 Some
nucleophilic substitution reactions
-
: :
:
:
: :
Reaction: Nu : + CH3 Br :
CH3 Nu + : Br :
CH3 OH
an alcohol
RO :
CH3 OR
an ether
CH3 SH
a thiol (a mercaptan)
CH3 C CH
an alkyne
CH3 C N:
a nitrile
: :
: :
HO :
: :
: :
-
:
:
HS :
-
HC C:
-:
C N:
an alkyl iodide
CH3 NH3 +
an alkylammonium ion
+
:
: :
HOH
CH3 I :
:
:
: NH3
:
:
: I :-
CH3 O-H
H
an alcohol (after
proton transfer)
9-4
Solvents
 Protic
solvent: a solvent that is a hydrogen bond
donor
• the most common protic solvents contain -OH groups
 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
9-5
Dielectric Constant
 Solvents
are classified as polar and nonpolar
• the most common measure of solvent polarity is
dielectric constant
constant: a measure of a solvent’s
ability to insulate opposite charges from one
another
 Dielectric
• 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
9-6
Protic Solvents
Structure
H2 O
HCOOH
Dielectric
Constant
(25°C)
79
59
Methanol
CH3 OH
33
Ethanol
CH3 CH2 OH
24
Acetic acid
CH3 COOH
6
Solvent
Water
Formic acid
9-7
Aprotic Solvents
Dielectric
Constant
Solvent
Polar
Dimethyl sulfoxide (DMSO)
Structure
( CH3 ) 2 S=O
48.9
Acetonitrile
CH3 C N
37.5
N,N-Dimethylformamide (DMF) ( CH3 ) 2 NCHO
36.7
Acetone
( CH3 ) 2 C=O
20.7
Nonpolar
Dichloromethane
Diethyl ether
CH2 Cl2
CH3 CH2 OCH2 CH3
9.1
4.3
Toluene
C6 H5 CH3
2.3
Hexane
CH3 ( CH2 ) 4 CH3
1.9
9-8
Mechanisms
 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 ratedetermining step)
9-9
Mechanism - SN2
• both reactants are involved in the transition state of
the rate-determining step
H
H
Br :
HO
+ : Br :
: :
C
:
HO
: :
:
Br :
:
C
:
:
+
:
:
:
-
HO:
H
-
-
C
H
H
H H
H
H
Transition state with simultaneous
bond breaking and bond forming
9-10
Mechanism - SN2
9-11
Mechanism - SN1
 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)
9-12
Mechanism - SN1
• Step 1: ionization of the C-X bond gives a carbocation
intermediate
H3 C
C
H3 C
H3 C
Br
slow, rate
determining
CH3
C+
+
Br
H3 C CH3
A carbocation intermediate;
its shape is trigonal planar
9-13
Mechanism - SN1
• Step 2: reaction of the carbocation (an electrophile)
with methanol (a nucleophile) gives an oxonium ion
CH3
+
:
C+
: OCH3
fast
H
H3 C CH3
CH 3
H3 C
:O
H
Electrophile Nucleophile
+
C
CH3
H3 C
CH 3
CH 3
C
O:
H 3C
H 3C
H
Oxonium ions
• Step 3: proton transfer completes the reaction
H
+ CH 3
O:
+ :O :
CH3
H
fast
H3 C
C
H3 C
H3 C
H
CH3
+
:
+
O
H O:
CH3
:
H3 C
C
H3 C
H3 C
9-14
Mechanism - SN1
9-15
Evidence of SN 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?
9-16
Kinetics
 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
CH3
+ CH3 OH
CH3 CBr
CH3
2-Bromo-2Methanol
methylpropane
Rate = - d[ (CH3 ) 3 CBr]
dt
CH3
CH3 COCH3 + HBr
CH3
2-Methoxy-2methylpropane
= k[( CH3 ) 3 CBr]
9-17
Kinetics
 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
CH3 Br + N a+ OHBr om omethane
rate =
d[ CH 3 Br]
dt
CH3 OH + N a+ BrMethanol
=
-
k[ CH3 Br] [ OH ]
9-18
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: 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
9-19
Nucleophilicity
Effectiveness
Nucleophile
-
Good
Moderate
Poor
-
Br , I
CH 3 S , RS
HO- , CH3 O- , ROCN , N3
Cl- , FCH 3 COO , RCOO
CH 3 SH, RSH, R2 S
NH3 , RNH2 , R2 NH, R3 N
H2 O
CH 3 OH, ROH
CH 3 COOH, RCOOH
9-20
Nucleophilicity
 Relative
nucleophilicities of halide ions in polar
aprotic solvents are quite different from those in
polar protic solvents
Solvent
 How
Increasing Nucleophilicity
Polar aprotic
I - < Br - < Cl- < F-
Polar protic
F - < Cl - < Br - < I -
do we account for these differences?
9-21
Nucleophilicity
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-
9-22
Nucleophilicity
 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-
9-23
Nucleophilicity
 Generalization
• within a row of the Periodic Table, nucleophilicity
increases from left to right; that is, it increases with
basicity
Period
Increasing Nucleophilicity
Period 2
F- <
Period 3
Cl -
OH- <
<
SH- <
NH 2 - <
CH3 -
PH2 -
9-24
Nucleophilicity
 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
-
H2 O
<
OH
ROH
<
RO
NH 3
<
NH 2
RSH
<
RS
-
-
9-25
Nucleophilicity
 Generalization
• when comparing groups of reagents in which the
nucleophilic atom is the same, the stronger the base,
the greater the nucleophilicity
Nucleophile
-
RCOO
Carboxylate
ion
-
HO
Hydroxide
ion
-
RO
Alkoxide
ion
Increasing Nucleophilicity
Conjugate acid
pKa
RCOOH
4-5
HOH
15.7
Increasing Acidity
ROH
16-18
9-26
Stereochemistry
 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
Cl
H
Cl
R Enantiomer
- Cl
-
C+
CH 3 OH
-H
+
H
Cl
Planar carbocation
(achiral)
+
CH 3 O C
C OCH 3
H
H
Cl
Cl
S Enantiomer R Enantiomer
A racemic mixture
9-27
Stereochemistry
 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+
H
R2
Cl-
Approach of the
nucleophile from
this side is partially
blocked by leaving
group, which remains
associated with the
carbocation as an
ion pair
9-28
Stereochemistry
 For
SN2 reactions at a chiral center, there is
inversion of configuration at the chiral center
 Experiment of Hughes and Ingold
131
I
+ 131 I -
2-Iodooctane
SN 2
acetone
I
+
I
-
9-29
Hughes-Ingold Expt
• the reaction is 2nd order, therefore, SN2
• the rate of racemization of enantiomerically pure 2iodooctane is twice the rate of incorporation of I-131
C6 H1 3
131
-
I:
+
C
H
H3 C
I
S N2
acetone
(S)-2-Iodooctane
C6 H1 3
131
I
+
C
I
H
CH3
(R)-2-Iodooctane
9-30
Structure 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 site
Governed by
electronic factors
SN 1
Carbocation stability
R3 CX
(3°)
R2 CHX
(2°)
RCH2 X CH3 X
(1°)
(methyl)
Access to the site of reaction
SN 2
Governed by
steric factors
9-31
Effect of -Branching
Br
Br
Br
Br
Alkyl Bromide


-Branches
0
1
2
3
1.0
4.1x 10-1
-3
1.2 x 10
1.2x 10-5
Relative Rate


9-32
Effect of -Branching
CH3
CH3 CH2 Br
CH3 CCH2 Br
CH3
free
access
blocked
access
Bromoethane
(Ethyl bromide)
1-Bromo-2,2-dimethylpropane
(Neopentyl bromide)
9-33
Allylic 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
+
CH2 = CH- CH 2
+
CH2 -CH = CH 2
Allyl cation
(a hybrid of two equivalent contributing
structures)
9-34
Allylic Cations
• 2° & 3° allylic cations are even more stable
+
+
CH2 =CH-CH-CH3
A 2° allylic carbocation
CH2 =CH-C-CH3
CH3
A 3° allylic carbocation
• as also are benzylic cations
CH2 +
C6 H5 -CH2 +
Benzyl cation
The benzyl cation is also written
(a benzylic car bocation)
in this abbr eviated form
• adding these carbocations to those from Section 6.3
methyl < 1° alkyl <
2° alkyl
1° allylic
<
1° benzylic
3° alkyl
2° allylic
<
2° benzylic
3° allylic
3° benzylic
Increasing stability of carbocations
9-35
The Leaving Group
 The
more stable the anion, the better the leaving
ability
• the most stable anions are the conjugate bases of
strong acids
rarely function as
leaving groups
Reactivity as a leaving group
O
I- > Br- > Cl- > H2 O >> F- > CH3 CO- > HO- > CH3 O- > NH2 Stability of anion; strength of conjugate acid
9-36
The Solvent - SN2
 The
most common type of SN2 reaction involves
a negative Nu and a negative leaving group
negatively charged
nucleophile
Nu:
-
+
C
Lv
negative charge dispersed
in the transition state

Nu
negatively charged
leaving group

C
Lv
Nu
C
+ Lv
Transition state
• 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
9-37
The Solvent - SN2
Br
+ N3
Solvent
Type
-
SN 2
solvent
Solvent
CH3 C N
polar aprotic ( CH ) NCHO
3 2
( CH3 ) 2 S= O
polar protic H2 O
CH3 OH
N3 +
Br
-
k(solvent)
k(methanol)
5000
2800
1300
7
1
9-38
The Solvent - SN1
 SN1
reactions involve creation and separation of
unlike charge in the transition state of the ratedetermining 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
9-39
The Solvent - SN1
CH3
CH3 CCl + ROH
sol vol ysis
CH3
CH3 COR + HCl
CH3
CH3
k(s ol vent)
Solvent
water
k(ethanol)
100,000
80% water: 20% ethanol
14,000
40% water: 60% ethanol
ethanol
100
1
9-40
Rearrangements in SN1
 Rearrangements
are common in SN1 reactions if
the initial carbocation can rearrange to a more
stable one
+ CH3 OH
CH3 OH
Cl
2-Chloro-3phenylbutane
OCH3
+
+ CH3 OH + Cl
H
2-Methoxy-2-phenylbutane
9-41
Rearrangements in SN1
 Mechanism
of a carbocation rearrangement
(1)
+
Cl
+ : Cl
A 2° carbocation
(2)
+
H
H
+
A 3° benzylic carbocation
H
(3)
+
+ : O-CH3
+
H
O
CH3
An oxonium ion
9-42
Summary of SN1 & SN2
Type of
Alkyl Halide
Methyl
SN 2
SN 2 is favored.
SN 1 does not occur. The methyl cation
is so unstable, it is never observed
in solution.
SN 2 is favored.
SN 1 rarely occurs. Primary
cations are so unstable, that they are
never observed in solution.
SN 2 is favored in aprotic
solvents with good
nucleophiles.
SN 1 is favored in protic solvents with
poor nucleophiles. Carbocation
rearrangements may occur.
CH3 X
Primary
RCH2 X
Secondary
R2 CHX
Tertiary
R3 CX
SN 1
SN 2 does not occur because SN 1 is favored because of the ease of
of steric hindrance around formation of tertiary carbocations.
the reaction center.
Substitution Inversion of configuration.
at a
The nucleophile attacks
stereocenter the stereocenter from the
side opposite the leaving
group.
Racemization is favored. The carbocation
intermediate is planar, and attack of the
nucleophile occurs with equal
probability from either side. There is
often some net inversion of
configuration.
9-43
SN1/SN2 Problems
• Problem 1: predict the mechanism for this reaction,
and the stereochemistry of each product
Cl
OCH3
OH
+
+ CH3 OH/ H2 O
+ HCl
(R)-2-Chlorobutane
• Problem 2: predict the mechanism of this reaction
Br
+ Na+ CN-
DMSO
CN
+ Na+ Br
-
9-44
SN1/SN2 Problems
• Problem 3: predict the mechanism of this reaction and
the configuration of product
Br
SCH3
+ CH3 S- Na+
acetone
+ Na+ Br-
(R)-2- Bromobutane
• Problem 4: predict the mechanism of this reaction and
the configuration of the product
O
Br + CH3 COH
acetic acid
O
OCCH3 + HBr
(R)-3-Bromocyclohexene
9-45
SN1/SN2 Problems
• Problem 5: predict the mechanism of this reaction
Br + ( CH3 ) 3 P
toluene
+
P( CH3 ) 3 Br -
9-46
-Elimination
 -Elimination:
a reaction in which a molecule,
such as HCl, HBr, HI, or HOH, is split out or
eliminated from adjacent carbons
H

C

C
X
A haloalkane
+ CH3 CH2 O-Na+
CH3 CH2 OH
Base
C C
+ CH3 CH2 OH + Na+ X -
An alkene
9-47
-Elimination
rule: the major product of a -elimination
is the more stable (the more highly substituted)
alkene
 Zaitsev
Br
2-Bromo-2methylbutane
Br
CH 3 CH2 O - Na +
CH3 CH2 OH
+
2-Methyl-2-butene 2-Methyl-1-butene
(major product)
CH 3 O - Na +
CH3 OH
1-Bromo-1-methylcyclopentane
+
1-MethylMethylenecyclopentene cyclopentane
(major product)
9-48
-Elimination
are two limiting mechanisms for elimination reactions
 E1 mechanism: at one extreme, breaking of the R-Lv
 There
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: 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
9-49
E1 Mechanism
• ionization of C-Lv gives a carbocation intermediate
CH3
CH3 -C-CH3
slow, rate
determining
Br
CH3
CH3 -C-CH3 +
+
Br
(A carbocation
intermediate)
• proton transfer from the carbocation intermediate to
the base (in this case, the solvent) gives the alkene
H
H3 C
CH3
O: + H-CH2 -C-CH3
+
fast
H
+
CH3
O H + CH2 =C-CH3
H3 C
9-50
E1 Mechanism
9-51
E2 Mechanism
9-52
Kinetics 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
Rate =
 E2
d[RLv]
= k[ RLv]
dt
mechanism
• reaction occurs in one step
• reaction is 2nd order; first order in RLv and 1st order
in base
Rate =
d[RLv]
= k[ RLv][ Base]
dt
9-53
Regioselectivity 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
9-54
Stereoselectivity of E2
 E2
is most favorable (lowest activation energy)
when H and Lv are oriented anti and coplanar
CH3 O:
-
CH3 O
H
H
C
C
Lv
-H and -Lv are anti and coplanar
(dihedral angle 180°)
C
C
Lv
9-55
Stereochemistry of E2
 Consider
E2 of these stereoisomers
CH3 O-Na+
Cl
cis-1-Chloro-2isopropylcyclohexane
CH3 OH
1-Isopropylcyclohexene
(major product)
-
CH3 O Na
Cl
trans-1-Chloro-2isopropylcyclohexane
+
(R)-3-Isopropylcyclohexene
+
CH3 OH
(R)-3-Isopropylcyclohexene
9-56
Stereochemistry of E2
• in the more stable chair of the cis isomer, the larger
isopropyl is equatorial and chlorine is axial
-
CH3 O:
H
2
H
6
H
E2
+ CH3 OH + :Cl
H
1
Cl
1-Isopropylcyclohexene
9-57
Stereochemistry 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
H
H
6
H
Cl
2
Cl
H
6
1
2
1
H
H
H
More stable chair
(no H is anti and
coplanar to Cl)
H
Less stable chair
(H on carbon 6 is
anti and coplanar to Cl)
9-58
Stereochemistry of E2
• it is only the less stable chair conformation of this
isomer that can undergo an E2 reaction
Cl
H
-
CH3 O:
6
H
2
1
H
E2
+ CH3 OH + Cl
H
(R)-3-Isopropylcyclohexene
9-59
Stereochemistry of E2
Problem: account for the fact that E2 reaction of the
meso-dibromide gives only the E alkene
Br Br
C6 H5 CH-CHC6 H5
meso-1,2-Dibromo1,2-diphenylethane
C6 H5
-
CH3 O Na
CH3 OH
+
C6 H5
C
C
H
Br
(E)-1-Bromo-1,2diphenylethylene
9-60
Summary of E2 vs E1
Alkyl halide
Primary
E1
E2
RCH2 X
E1 does not occur.
E2 is favored.
Primary carbocations are
so unstable, they are never
observed in solution.
Secondary
R2 CHX
Main reaction with weak
bases such as H2O, ROH.
Main reaction with strong
bases such as OH- and OR-.
Tertiary
R3 CX
Main reaction with weak
bases such as H2O, ROH.
Main reaction with strong
bases such as OH- and OR-.
9-61
SN vs E
nucleophiles are also strong bases (OHand RO-) and SN and E reactions often compete
 The ratio of SN/E products depends on the
relative rates of the two reactions
 Many
nucleophilic
substitution
H C
C Lv +
H C
C
Nu +
Lv
Nu-elimination
C
C
+ H-Nu +
Lv
9-62
SN vs E
Halide
Reaction
Comments
Methyl
CH3 X
SN2
SN 1 reactions of methyl halides are never observed.
The methyl cation is so unstable that it is never
formed in solution.
Primary
RCH2 X
SN 2
The main reaction with good nucleophiles/weak
bases such as I- and CH3 COO-.
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.
9-63
SN vs E (cont’d)
Secondary SN 2
R2 CHX
Tertiary
R3 CX
The main reaction with bases/nucleophiles where
pK a of the conjugate acid is 11 or less, as for example
I - and CH 3COO -.
E2
The main reaction with bases/nucleophiles where the
pK a of the conjugate acid is 11 or greater, as for example
OH - and CH3CH2O -.
SN 1/E1
Common in reactions with weak nucleophiles in polar
protic solvents, such as water, methanol, and ethanol.
E2
M ain reaction with strong bases such as HO - and RO-.
SN 1/E1
M ain reactions with poor nucleophiles/weak bases.
SN 2 reactions of tertiary halides are never observed
because of the extreme crowding around the 3° carbon.
9-64
Neighboring 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
9-65
Mustard Gases
 Mustard
gases
• contain either S-C-C-X or N-C-C-X
N
S
Cl
Cl
Bis(2-chloroethyl)sulfide
(a sulfur mustard gas)
Cl
Cl
Bis(2-chloroethyl)methylamine
(a nitrogen mustard gas)
• what is unusual about the mustard gases is that they
undergo hydrolysis so rapidly in water, a very poor
nucleophile
Cl
S
Cl
+
2 H2 O
HO
S
OH + 2 HCl
9-66
Mustard Gases
• the reason is neighboring group participation by the
adjacent heteroatom
:
slow, rate
determining
S
Cl
S
Cl
+ : O-H
H
an internal
SN 2 reaction
fast
a second
S N2 reaction
Cl
S
+
Cl
A cyclic
sulfonium ion
:
+
Cl
+
S
Cl
H
+O
H
• proton transfer to solvent completes the reaction
9-67
Phase-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
( CH3 CH2 CH2 CH2 ) 4 N + Cl Tetrabutylammonium chloride
(Bu4N + Cl- )
9-68
Phase-Transfer Catalysis
9-69
Nucleophilic Substitution
and
-Elimination
End Chapter 9
9-70