dr. wolf's chm 201 & 202 22-1 chapter 22 amines. dr. wolf's chm 201 & 202 22-2...
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Dr. Wolf's CHM 201 & 202 22-1
Chapter 22Chapter 22AminesAmines
Dr. Wolf's CHM 201 & 202 22-2
22.122.1
Amine NomenclatureAmine Nomenclature
Dr. Wolf's CHM 201 & 202 22-3
AlkylamineAlkylamine
N attached to alkyl groupN attached to alkyl group
ArylamineArylamine
N attached to aryl groupN attached to aryl group
Primary, secondary, or tertiaryPrimary, secondary, or tertiary
determined by number of carbon atoms determined by number of carbon atoms directly attached to nitrogendirectly attached to nitrogen
Classification of AminesClassification of Amines
Dr. Wolf's CHM 201 & 202 22-4
Two IUPAC stylesTwo IUPAC styles
1)1) analogous to alcohols: replace -analogous to alcohols: replace -e e ending by -ending by -amineamine
2)2) name alkyl group and attach -name alkyl group and attach -amineamineas a suffixas a suffix
Nomenclature of Primary Alkylamines (RNHNomenclature of Primary Alkylamines (RNH22))
Dr. Wolf's CHM 201 & 202 22-5
Examples: some primary alkylaminesExamples: some primary alkylamines
CHCH33CHCHCHCH22CHCH22CHCH33
NNHH22
(RNH(RNH22: one carbon directly attached to N): one carbon directly attached to N)
CHCH33CHCH22NNHH22 NNHH22
ethylamineethylamine or or ethanamineethanamine
cyclohexylaminecyclohexylamine or orcyclohexanaminecyclohexanamine
1-methylbutylamine 1-methylbutylamine oror2-pentanamine2-pentanamine
Dr. Wolf's CHM 201 & 202 22-6
Name as derivatives of aniline.Name as derivatives of aniline.
Nomenclature of Primary Arylamines (ArNHNomenclature of Primary Arylamines (ArNH22))
pp-fluoroaniline-fluoroaniline 5-bromo-2-ethylaniline5-bromo-2-ethylaniline
NNHH22FF
NNHH22
BrBr CHCH22CHCH33
Dr. Wolf's CHM 201 & 202 22-7
Amino groups as substituentsAmino groups as substituents
pp-aminobenzaldehyde-aminobenzaldehyde
amino groups rank below OH groups and higher amino groups rank below OH groups and higher
oxidation states of carbonoxidation states of carbon
in such cases name the amino group as a in such cases name the amino group as a
substituentsubstituent NNHH22HHCC
OO
HHOOCHCH22CHCH22NNHH22
2-aminoethanol2-aminoethanol
Dr. Wolf's CHM 201 & 202 22-8
Name as Name as NN-substituted derivatives of parent -substituted derivatives of parent primary amine.primary amine.
(N is a locant-it is not alphabetized, but(N is a locant-it is not alphabetized, butis treated the same way as a numericalis treated the same way as a numericallocant)locant)
Parent amine is one with longest carbonParent amine is one with longest carbonchain.chain.
Secondary and Tertiary AminesSecondary and Tertiary Amines
Dr. Wolf's CHM 201 & 202 22-9
ExamplesExamples
CHCH33NNHCHHCH22CHCH33 NN-methylethylamine-methylethylamine NNHCHHCH22CHCH33
NONO22
ClCl
4-chloro-4-chloro-NN-ethyl-3-nitroaniline-ethyl-3-nitroaniline
CHCH33
NN
CHCH33
NN,,NN-dimethylcycloheptylamine-dimethylcycloheptylamine
Dr. Wolf's CHM 201 & 202 22-10
A nitrogen with four substituents is positivelyA nitrogen with four substituents is positivelycharged and is named as a derivative of charged and is named as a derivative of ammonium ammonium ion (NHion (NH44
++).).
Ammonium SaltsAmmonium Salts
CHCH33NHNH33
++ClCl
––
methylammoniummethylammonium
chloridechloride
NN
CHCH33
HH
CHCH22CHCH33
++CFCF33COCO22
––
NN-ethyl--ethyl-NN-methylcyclopentylammonium-methylcyclopentylammonium
trifluoroacetatetrifluoroacetate
Dr. Wolf's CHM 201 & 202 22-11
When all four atoms attached to N are carbon,When all four atoms attached to N are carbon,the ion is called a the ion is called a quaternary ammonium quaternary ammonium ion andion andsalts that contain it are called salts that contain it are called quaternaryquaternary ammoniumammonium salts. salts.
Ammonium SaltsAmmonium Salts
++
CHCH22 NN
CHCH33
CHCH33
CHCH33 II––
benzyltrimethylammonium iodidebenzyltrimethylammonium iodide
Dr. Wolf's CHM 201 & 202 22-12
22.222.2
Structure and BondingStructure and Bonding
Dr. Wolf's CHM 201 & 202 22-13
147 pm147 pm
106°106°112°112°
AlkylaminesAlkylamines
Dr. Wolf's CHM 201 & 202 22-14
Most prominent feature is high electrostaticMost prominent feature is high electrostaticpotential at nitrogen. Reactivity of nitrogen lonepotential at nitrogen. Reactivity of nitrogen lonepair dominates properties of amines. pair dominates properties of amines.
AlkylaminesAlkylamines
Dr. Wolf's CHM 201 & 202 22-15
Compare geometry at N of methylamine, aniline,Compare geometry at N of methylamine, aniline,and formamide.and formamide.
spsp33 spsp22
Geometry at NGeometry at N
Pyramidal geometry at Pyramidal geometry at spsp33-hybridized N in -hybridized N in
methylamine.methylamine.
Planar geometry at Planar geometry at spsp22-hybridized N in formamide.-hybridized N in formamide.
CCOO
NNHH22
HH
CC NNHH22
HH
HH
HH
Dr. Wolf's CHM 201 & 202 22-16
Compare geometry at N of methylamine, aniline,Compare geometry at N of methylamine, aniline,and formamide.and formamide.
spsp33 spsp22
Geometry at NGeometry at N
Pyramidal geometry at Pyramidal geometry at spsp33-hybridized N in -hybridized N in
methylamine.methylamine.
Planar geometry at Planar geometry at spsp22-hybridized N in formamide.-hybridized N in formamide.
Dr. Wolf's CHM 201 & 202 22-17
Angle that the C—N bond makes with bisector ofAngle that the C—N bond makes with bisector ofH—N—H angle is a measure of geometry at N.H—N—H angle is a measure of geometry at N.
spsp33 spsp22
Geometry at NGeometry at N
~125°~125°180°180°
Note: this is not the same as the H—N—H bond angleNote: this is not the same as the H—N—H bond angle
Dr. Wolf's CHM 201 & 202 22-18
Angle that the C—N bond makes with bisector ofAngle that the C—N bond makes with bisector ofH—N—H angle is a measure of geometry at N.H—N—H angle is a measure of geometry at N.
spsp33 spsp22
Geometry at NGeometry at N
~125°~125°180°180°
142.5°142.5°
Dr. Wolf's CHM 201 & 202 22-19
Geometry at N in aniline is pyramidal; closer toGeometry at N in aniline is pyramidal; closer tomethylamine than to formamide.methylamine than to formamide.
Geometry at NGeometry at N
142.5°142.5°
Dr. Wolf's CHM 201 & 202 22-20
Geometry at NGeometry at N
142.5°142.5°
Hybridization of N in aniline lies between Hybridization of N in aniline lies between spsp33 and and spsp22..
Lone pair of N can be delocalized into ring best if N is Lone pair of N can be delocalized into ring best if N is
spsp22 and lone pair is in a and lone pair is in a pp orbital. orbital.
Lone pair bound most strongly by N if pair is in an Lone pair bound most strongly by N if pair is in an spsp33
orbital of N, rather than orbital of N, rather than pp..
Actual hybridization is a compromise that maximizesActual hybridization is a compromise that maximizes
binding of lone pair.binding of lone pair.
Dr. Wolf's CHM 201 & 202 22-21
Electrostatic Potential Maps of AnilineElectrostatic Potential Maps of Aniline
Nonplanar geometry at Nonplanar geometry at N. Region of highestN. Region of highestnegative potential is at N.negative potential is at N.
Planar geometry at N. Planar geometry at N. High negative potential High negative potential shared by N and ring.shared by N and ring.
Dr. Wolf's CHM 201 & 202 22-22
22.322.3
Physical PropertiesPhysical Properties
Dr. Wolf's CHM 201 & 202 22-23
Amines are more polar and have higher boiling Amines are more polar and have higher boiling points than alkanes; but are less polar andpoints than alkanes; but are less polar andhave lower boiling points than alcohols.have lower boiling points than alcohols.
Physical PropertiesPhysical Properties
CHCH33CHCH22CHCH33 CHCH33CHCH22NNHH22 CHCH33CHCH22OOHH
dipoledipolemoment (moment ():):
boiling point:boiling point:
0 D0 D 1.2 D1.2 D 1.7 D1.7 D
-42°C-42°C 17°C17°C 78°C78°C
Dr. Wolf's CHM 201 & 202 22-24
Boiling points of isomeric amines decrease inBoiling points of isomeric amines decrease ingoing from primary to secondary to tertiary amines.going from primary to secondary to tertiary amines.
Primary amines have two hydrogens on N capable Primary amines have two hydrogens on N capable of being involved in intermolecular hydrogen of being involved in intermolecular hydrogen bonding. Secondary amines have one. Tertiary bonding. Secondary amines have one. Tertiary amines cannot be involved in intermolecular amines cannot be involved in intermolecular hydrogen bonds.hydrogen bonds.
Physical PropertiesPhysical Properties
CHCH33CHCH22NNHCHHCH33CHCH33CHCH22CHCH22NNHH22 (CH(CH33))33NN
boilingboilingpoint:point:
50°C50°C 34°C34°C 3°C3°C
Dr. Wolf's CHM 201 & 202 22-25
22.422.4
Basicity of AminesBasicity of Amines
Dr. Wolf's CHM 201 & 202 22-26
Effect of Structure on BasicityEffect of Structure on Basicity
1. Alkylamines are slightly stronger bases than 1. Alkylamines are slightly stronger bases than ammonia.ammonia.
Dr. Wolf's CHM 201 & 202 22-27
AmineAmine Conj. AcidConj. Acid pKpKaa
NHNH33 NHNH44++ 9.39.3
CHCH33CHCH22NHNH22 CHCH33CHCH22NHNH33++ 10.810.8
Table 22.1 (page 920)Table 22.1 (page 920)Basicity of Amines in Aqueous SolutionBasicity of Amines in Aqueous Solution
CHCH33CHCH22NHNH33++ is a weaker acid than NH is a weaker acid than NH44
++;;therefore, CHtherefore, CH33CHCH22NHNH22 is a stronger base is a stronger base than NHthan NH33..
Dr. Wolf's CHM 201 & 202 22-28
Effect of Structure on BasicityEffect of Structure on Basicity
1. Alkylamines are slightly stronger bases than 1. Alkylamines are slightly stronger bases than ammonia.ammonia.
2. Alkylamines differ very little in basicity.2. Alkylamines differ very little in basicity.
Dr. Wolf's CHM 201 & 202 22-29
AmineAmine Conj. AcidConj. Acid pKpKaa
NHNH33 NHNH44++ 9.39.3
CHCH33CHCH22NHNH22 CHCH33CHCH22NHNH33++ 10.810.8
(CH(CH33CHCH22))22NHNH (CH(CH33CHCH22))22NHNH22++ 11.111.1
(CH(CH33CHCH22))33NN (CH(CH33CHCH22))33NHNH++ 10.810.8
Table 22.1 (page 920)Table 22.1 (page 920)Basicity of Amines in Aqueous SolutionBasicity of Amines in Aqueous Solution
Notice that the difference separating a primary,Notice that the difference separating a primary,secondary, and tertiary amine is only 0.3 pK units.secondary, and tertiary amine is only 0.3 pK units.
Dr. Wolf's CHM 201 & 202 22-30
Effect of Structure on BasicityEffect of Structure on Basicity
1. Alkylamines are slightly stronger bases than 1. Alkylamines are slightly stronger bases than ammonia.ammonia.
2. Alkylamines differ very little in basicity.2. Alkylamines differ very little in basicity.
3. Arylamines are much weaker bases than3. Arylamines are much weaker bases thanammonia.ammonia.
Dr. Wolf's CHM 201 & 202 22-31
AmineAmine Conj. AcidConj. Acid pKpKaa
NHNH33 NHNH44++ 9.39.3
CHCH33CHCH22NHNH22 CHCH33CHCH22NHNH33++ 10.810.8
(CH(CH33CHCH22))22NHNH (CH(CH33CHCH22))22NHNH22++ 11.111.1
(CH(CH33CHCH22))33NN (CH(CH33CHCH22))33NHNH++ 10.810.8
CC66HH55NHNH22 CC66HH55NHNH33++ 4.64.6
Table 22.1 (page 920)Table 22.1 (page 920)Basicity of Amines in Aqueous SolutionBasicity of Amines in Aqueous Solution
Dr. Wolf's CHM 201 & 202 22-32
HH22NN•••• Decreased basicity of arylaminesDecreased basicity of arylamines
++HH
NN
HH
HH
++ NNHH22 ++•••• ++
HH33NN
ppKKaa = 4.6 = 4.6
ppKKaa =10.6 =10.6
StrongerStrongeracidacid
WeakerWeakeracidacid
StrongerStrongerbasebase
WeakerWeakerbasebase
Dr. Wolf's CHM 201 & 202 22-33
HH22NN•••• Decreased basicity of arylaminesDecreased basicity of arylamines
++HH
NN
HH
HH
++ NNHH22 ++•••• ++
HH33NN
StrongerStrongeracidacid
WeakerWeakeracidacid
When anilinium ion loses a proton, theWhen anilinium ion loses a proton, theresulting lone pair is delocalized into the ring.resulting lone pair is delocalized into the ring.
Dr. Wolf's CHM 201 & 202 22-34
HH22NN•••• Decreased basicity of arylaminesDecreased basicity of arylamines
++HH
NN
HH
HH
++ NNHH22 ++•••• ++
HH33NN
Aniline is a weaker base because its Aniline is a weaker base because its lone pair is more strongly held.lone pair is more strongly held.
StrongerStrongerbasebase
WeakerWeakerbasebase
Dr. Wolf's CHM 201 & 202 22-35
Decreased basicity of arylaminesDecreased basicity of arylamines
CC66HH55NNHH22 (C(C66HH55))22NNHH (C(C66HH55))33NN
ppKKa a of conjugate acid:of conjugate acid:
4.64.6 0.80.8 ~-5~-5
Increasing delocalization makes diphenylamine a Increasing delocalization makes diphenylamine a
weaker base than aniline, and triphenylamine a weaker weaker base than aniline, and triphenylamine a weaker
base than diphenylamine.base than diphenylamine.
Dr. Wolf's CHM 201 & 202 22-36
Effect of Substituents on Basicity of ArylaminesEffect of Substituents on Basicity of Arylamines
1. Alkyl groups on the ring increase basicity, but1. Alkyl groups on the ring increase basicity, butonly slightly (less than 1 ponly slightly (less than 1 pKK unit). unit).
XX NHNH22
XX ppKKa a of conjugate acidof conjugate acid
HH 4.64.6CHCH33 5.35.3
Dr. Wolf's CHM 201 & 202 22-37
Effect of Substituents on Basicity of ArylaminesEffect of Substituents on Basicity of Arylamines
2. Electron withdrawing groups, especially ortho2. Electron withdrawing groups, especially orthoand/or para to amine group, decrease basicityand/or para to amine group, decrease basicityand can have a large effect.and can have a large effect.
XX NHNH22
XX ppKKa a of conjugate acidof conjugate acid
HH 4.64.6CFCF33 3.53.5
OO22NN 1.01.0
Dr. Wolf's CHM 201 & 202 22-38
p-Nitroanilinep-Nitroaniline NNHH22
OO
NN
OO
–– ••••••••••••
••••
++
••••
••••
OO
NN
OO
–– ••••••••••••
•••• ••••••••––
NNHH22
++ ++
Lone pair on amine nitrogen is conjugated with Lone pair on amine nitrogen is conjugated with
pp-nitro group—more delocalized than in aniline -nitro group—more delocalized than in aniline
itself. Delocalization lost on protonation.itself. Delocalization lost on protonation.
Dr. Wolf's CHM 201 & 202 22-39
Effect is CumulativeEffect is Cumulative
Aniline is 3800 times more basic thanAniline is 3800 times more basic than
pp-nitroaniline.-nitroaniline.
Aniline is ~1,000,000,000 times more basic than Aniline is ~1,000,000,000 times more basic than
2,4-dinitroaniline.2,4-dinitroaniline.
Dr. Wolf's CHM 201 & 202 22-40
Heterocyclic Amines Heterocyclic Amines NN
HH
••••
NN••••
is more basic thanis more basic than
piperidinepiperidine pyridinepyridineppKKaa of conjugate acid: of conjugate acid:
11.211.2
ppKKaa of conjugate acid: of conjugate acid:
5.25.2
(an alkylamine)(an alkylamine)(resembles an(resembles anarylamine inarylamine in
basicity)basicity)
Dr. Wolf's CHM 201 & 202 22-41
Heterocyclic Amines Heterocyclic Amines NN••••
is more basic thanis more basic than
imidazoleimidazole pyridinepyridineppKKaa of conjugate acid: of conjugate acid:
7.07.0
ppKKaa of conjugate acid: of conjugate acid:
5.25.2
NN HHNN•••• ••••
Dr. Wolf's CHM 201 & 202 22-42
ImidazoleImidazole NN HHNN•••• ••••
Which nitrogen is protonated in imidazole?Which nitrogen is protonated in imidazole?
HH++ HH++ NN HHNN ••••HH
++
NN HHNN••••
HH
++
Dr. Wolf's CHM 201 & 202 22-43
ImidazoleImidazole NN HHNN•••• ••••
Protonation in the direction shown gives a Protonation in the direction shown gives a
stabilized ion.stabilized ion.
HH++ NN HHNNHH
++ ••••
NN HHNNHH
••••++
Dr. Wolf's CHM 201 & 202 22-44
22.522.5
Tetraalkylammonium SaltsTetraalkylammonium Salts
as Phase-Transfer Catalystsas Phase-Transfer Catalysts
Dr. Wolf's CHM 201 & 202 22-45
Phase-Transfer CatalysisPhase-Transfer Catalysis
Phase-transfer agents promote the solubility ofPhase-transfer agents promote the solubility ofionic substances in nonpolar solvents. Theyionic substances in nonpolar solvents. Theytransfer the ionic substance from an aqueoustransfer the ionic substance from an aqueousphase to a non-aqueous one.phase to a non-aqueous one.
Phase-transfer agents increase the rates ofPhase-transfer agents increase the rates ofreactions involving anions. The anion is relativelyreactions involving anions. The anion is relativelyunsolvated and very reactive in nonpolar mediaunsolvated and very reactive in nonpolar mediacompared to water or alcohols.compared to water or alcohols.
Dr. Wolf's CHM 201 & 202 22-46
Phase-Transfer CatalysisPhase-Transfer Catalysis
Quaternary ammonium salts are phase-transferQuaternary ammonium salts are phase-transfercatalysts. They are soluble in nonpolar solvents.catalysts. They are soluble in nonpolar solvents.
NNHH33CC
CHCH22CHCH22CHCH22CHCH22CHCH22CHCH22CHCH22CHCH33
CHCH22CHCH22CHCH22CHCH22CHCH22CHCH22CHCH22CHCH33
CHCH22CHCH22CHCH22CHCH22CHCH22CHCH22CHCH22CHCH33
++ClCl––
Methyltrioctylammonium chlorideMethyltrioctylammonium chloride
Dr. Wolf's CHM 201 & 202 22-47
Phase-Transfer CatalysisPhase-Transfer Catalysis
Quaternary ammonium salts are phase-transferQuaternary ammonium salts are phase-transfercatalysts. They are soluble in nonpolar solvents.catalysts. They are soluble in nonpolar solvents.
ClCl––
Benzyltriethylammonium chlorideBenzyltriethylammonium chloride
NN
CHCH22CHCH33
CHCH22CHCH33
CHCH22CHCH33
++
Dr. Wolf's CHM 201 & 202 22-48
ExampleExample
The SThe SNN2 reaction of sodium cyanide with butyl2 reaction of sodium cyanide with butyl
bromide occurs much faster when benzyl-bromide occurs much faster when benzyl-triethylammonium chloride is present than whentriethylammonium chloride is present than whenit is not.it is not.
CHCH33CHCH22CHCH22CHCH22BrBr ++ NaNaCNCN
CHCH33CHCH22CHCH22CHCH22CNCN ++ NaNaBrBr
benzyltriethylammonium chloridebenzyltriethylammonium chloride
Dr. Wolf's CHM 201 & 202 22-49
MechanismMechanismMechanismMechanism
ClCl––
(aqueous)(aqueous)
NN
CHCH22CHCH33
CHCH22CHCH33
CHCH22CHCH33
++
(aqueous)(aqueous)
CNCN––++
ClCl––NN
CHCH22CHCH33
CHCH22CHCH33
CHCH22CHCH33
++
++CNCN––
(aqueous)(aqueous)
(aqueous)(aqueous)
Dr. Wolf's CHM 201 & 202 22-50
NN
CHCH22CHCH33
CHCH22CHCH33
CHCH22CHCH33
++
CNCN––
(aqueous)(aqueous)
(in butyl bromide)(in butyl bromide)
NN
CHCH22CHCH33
CHCH22CHCH33
CHCH22CHCH33
++
CNCN––
MechanismMechanismMechanismMechanism
Dr. Wolf's CHM 201 & 202 22-51
(in butyl bromide)(in butyl bromide)
NN
CHCH22CHCH33
CHCH22CHCH33
CHCH22CHCH33
++
CNCN––
MechanismMechanismMechanismMechanism
CHCH33CHCH22CHCH22CHCH22BrBr++
NN
CHCH22CHCH33
CHCH22CHCH33
CHCH22CHCH33
++
BrBr––
(in butyl bromide)(in butyl bromide)
CHCH33CHCH22CHCH22CHCH22CNCN++