1 derivatives of carboxylic acids and nucleophilic acyl substitution
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1
Derivatives of Derivatives of Carboxylic Acids Carboxylic Acids and Nucleophilic and Nucleophilic Acyl SubstitutionAcyl Substitution
2
Carboxylic Carboxylic AcidsAcids• A class of organic compounds
containing at least one carboxyl group
C
O
OH
3
R C
O
OH
R = alkyl group or H alkanoic acid(sat’d)R = aryl group aromatic carboxylic acid
4
R C
O
OH
Aliphatic carboxylic acid = fatty acids (sat’d or unsat’d)∵ obtained from fat/oil
E.g.stearic acid, CH3(CH2)16COOHoleic acid,
CH3(CH2)7CH=CH(CH2)7COOH
5
Carboxylic Carboxylic AcidsAcids• Carboxyl group
combination of the carbonyl group and the hydroxyl group
6
Nomenclature
Suffix : carboxylic acid or oic acidPrefix : carboxy
7
Q.62
C C
COOH
HH
H3C
C C
O
OHHO
O
COOH
butanoic acid
(2Z)-but-2-enoic acid
ethanedioic acid
8
Q.62
HOOC
COOH
OH
COOH COOHHOOC
butanedioic acid 2-hydroxypropane-
1,2,3-tricarboxylic acid(citric acid)
3-carboxy-3-hydroxypentainedicarboxylic
acid
9
Q.62
COOH HOOC
COOHbenzoic acid
Benzene-1,3-dicarboxylic acid
10
Q.62
HO
COOH
COOH
phenylethanoic acid
4-hydroxybenzoic
acid
11
Derivatives of carboxylic acids (pp.9-10)
Name Structure
Acyl(Acid) chlorides
Acid anhydride
s
Esters
Acid Amides
12
Acyl (Acid) ChloridesAcyl (Acid) Chlorides
Suffix : -oic acid replaced by –oyl chloride
Prefix : chlorocarbonyl
R C
O
Cl
13
Acyl (Acid) ChloridesAcyl (Acid) Chlorides
H2C C
O
ClCO
OH
3-chloro-3-oxopropanoic acid
Priority : --COOH > anhydride > ester > acid chloride > acid amideThe carbonyl C is counted as part of the carbon skeleton
14
CHH2C C
Cl
OHOOC
H3C
4-chloro-2-methyl-4-oxobutanoic acid
C
C
Cl
O
Cl
O
hexanedioyl dichloride
HOOC
COOH
C
ClO
3-(chlorocarbonyl)hexanedioic
acid
Q.63
15
Acid anhydrideAcid anhydride
Suffix : -acid replaced by –anhydride
R C
O
O
CR'
O
16
C
O
O
CR
O
Acid anhydrideAcid anhydride
Prefix : n-(alkanoyloxy)-n-oxo (if *C is counted as part of the main chain) n indicates the position of the *C in the main chain
*
17
C
O
O
CR
O
Acid anhydrideAcid anhydride
Prefix : (alkanoyloxy)carbonyl (if *C is not counted as part of the main chain)
*
18
Acid anhydrideAcid anhydride
H3C C
O
O
CH3C
O
H3C C
O
O
CC2H5
O
ethanoic anhydride
ethanoic propanoic anhydride
19
Acid anhydrideAcid anhydride
H3C C
O
O
C
O
C
O
C
O
O
benzoic ethanoic
anhydride
butanedioic anhydride
20
Q.64
C
O
C
O
O
Benzene-1,2-dioic anhydride
21
EsterEster
Suffix : -oic acid replaced by –oate preceded by the name of R’
R C
O
O
R'
22
R
O
C
O
Prefix : n-alkoxy-n-oxo(if *C is counted as part of the main chain) n indicates the position of the *C in the main chain
*
EsterEster
23
Prefix : alkoxycarbonyl (if *C is not counted as part of the main chain)
EsterEster R
O
C
O
*
24
EsterEster
H3C C
O
O
CH3
H3C C
O
O
CH
CH2
C
O
O
CH3
Br
methyl ethanoate
ethenyl ethanoate
methyl 4-bromobenzoat
e
25
Q.65
COOH
C
O
CH3
O COOH
O
C
CH3
O
2-(methoxycarbonyl)benzoic
acid
2-(ethanoyloxy)benzoic acid2-(acetyloxy)benzoic acid
26
Acid amideAcid amide
Suffix : -oic acid replaced by -amide
R C
NH2
O
27
NH2
C
O
Prefix : n-amino-n-oxo (if *C is counted as part of the main chain) n indicates the position of the *C in the main chain
*
EsterEster
28
NH2
C
O
Prefix : aminocarbonyl (if *C is not counted as part of the main chain)
EsterEster
*
29
C
NH2
O
H3C C
HN
O
H3C
CH3
C
N
O
H3C
CH3
H3C
ethanamide(1)
N-methylethanamide(2)
N,N-dimethylethanamide(3)
EsterEster
30
Q.66
C
NH2
O
(CH2)2 HOOC COOH
C
O NH2
C
NH2
O
HOOC
benzamide
4-amino-4-oxobutanoic
acid
3-(aminocarbonyl)heptanedioic
acid
31
Physical Physical Properties of Properties of
Alkanoic AcidsAlkanoic Acids
32
33
OdourOdour
Methanoic / ethanoic acid
sharp, irritating odours
Propanoic to heptanoic acid
strong, unpleasant odours
Butanoic acid body odour
Higher members low volatility little odour
34
Alkanoic acidMelting point /oC
Boiling point/oC
Density/g cm-3
Solubility in water/g per H2O
Methanoic acid 8.4 101 1.220 Ethanoic acid 16.6 118 1.047 Propanoic acid 20.8 141 0.992 Butanoic acid 6.5 164 0.964 Pentanoic acid 34.5 186 0.939 3.7Hexanoic acid 1.5 205 0.927 1.0Heptanoic acid 10 224 0.913 0.25Octanoic acid 16 239 0.910 0.7Nonanoic acid 12.5 253 0.907 0.07Decanoic acid 31 269 0.886 0.2
b.p. steadily as the number of C atoms ∵ London dispersion forces become stronger as the size of electron cloud
35
Alkanoic acidMelting point /oC
Boiling point/oC
Density/g cm-3
Solubility in water/g per H2O
Methanoic acid 8.4 101 1.220 Ethanoic acid 16.6 118 1.047 Propanoic acid 20.8 141 0.992 Butanoic acid 6.5 164 0.964 Pentanoic acid 34.5 186 0.939 3.7Hexanoic acid 1.5 205 0.927 1.0Heptanoic acid 10 224 0.913 0.25Octanoic acid 16 239 0.910 0.7Nonanoic acid 12.5 253 0.907 0.07Decanoic acid 31 269 0.886 0.2
HCOOH/CH3COOH have exceptionally high m.p.∵ smaller size 1.closer packing 2.forming H-bonds more extensitively
36
Alkanoic acidMelting point /oC
Boiling point/oC
Density/g cm-3
Solubility in water/g per H2O
Methanoic acid 8.4 101 1.220 Ethanoic acid 16.6 118 1.047 Propanoic acid 20.8 141 0.992 Butanoic acid 6.5 164 0.964 Pentanoic acid 34.5 186 0.939 3.7Hexanoic acid 1.5 205 0.927 1.0Heptanoic acid 10 224 0.913 0.25Octanoic acid 16 239 0.910 0.7Nonanoic acid 12.5 253 0.907 0.07Decanoic acid 31 269 0.886 0.2
Members with EVEN no. of C atoms aremore symmetrical Higher packing efficiency Higher m.p.
37
Alkanoic acidMelting point /oC
Boiling point/oC
Density/g cm-3
Solubility in water/g per H2O
Methanoic acid 8.4 101 1.220 Ethanoic acid 16.6 118 1.047 Propanoic acid 20.8 141 0.992 Butanoic acid 6.5 164 0.964 Pentanoic acid 34.5 186 0.939 3.7Hexanoic acid 1.5 205 0.927 1.0Heptanoic acid 10 224 0.913 0.25Octanoic acid 16 239 0.910 0.7Nonanoic acid 12.5 253 0.907 0.07Decanoic acid 31 269 0.886 0.2
Pure ethanoic acid = glacial ethanoic acidIt freezes in cold weather
38
More extensive H-bonds
H-bondsDipole-dipole interaction
Dispersion forces ONLY
39
Alkanoic acidMelting point /oC
Boiling point/oC
Density/g cm-3
Solubility in water/g per H2O
Methanoic acid 8.4 101 1.220 Ethanoic acid 16.6 118 1.047 Propanoic acid 20.8 141 0.992 Butanoic acid 6.5 164 0.964 Pentanoic acid 34.5 186 0.939 3.7Hexanoic acid 1.5 205 0.927 1.0Heptanoic acid 10 224 0.913 0.25Octanoic acid 16 239 0.910 0.7Nonanoic acid 12.5 253 0.907 0.07Decanoic acid 31 269 0.886 0.2
Less dense than water exceptHCOOH/CH3COOH
40
Alkanoic acidMelting point /oC
Boiling point/oC
Density/g cm-3
Solubility in water/g per H2O
Methanoic acid 8.4 101 1.220 Ethanoic acid 16.6 118 1.047 Propanoic acid 20.8 141 0.992 Butanoic acid 6.5 164 0.964 Pentanoic acid 34.5 186 0.939 3.7Hexanoic acid 1.5 205 0.927 1.0Heptanoic acid 10 224 0.913 0.25Octanoic acid 16 239 0.910 0.7Nonanoic acid 12.5 253 0.907 0.07Decanoic acid 31 269 0.886 0.2
as R.M.M. R.M.M. extent of H-bond formation
molecules not drawn closer lower packing efficiency
41
Alkanoic acidMelting point /oC
Boiling point/oC
Density/g cm-3
Solubility in water/g per H2O
Methane GasEthane GasPropane GasButane GasPentane 0.626Hexane 0.655Heptane 0.684Octane 0.703Nonane 0.718Decane 0.730
For alkanes, as R.M.M. ∵ no intermolecular H-bondsR.M.M. Dispersion forces become stronger
closer packing
42
Alkanoic acidMelting point /oC
Boiling point/oC
Density/g cm-3
Solubility in water/g per H2O
Methanoic acid 8.4 101 1.220 Ethanoic acid 16.6 118 1.047 Propanoic acid 20.8 141 0.992 Butanoic acid 6.5 164 0.964 Pentanoic acid 34.5 186 0.939 3.7Hexanoic acid 1.5 205 0.927 1.0Heptanoic acid 10 224 0.913 0.25Octanoic acid 16 239 0.910 0.7Nonanoic acid 12.5 253 0.907 0.07Decanoic acid 31 269 0.886 0.2
First FOUR members are miscible with water in all proportions due to extensive H-bond formation between acid molecules and water molecules
43
Alkanoic acidMelting point /oC
Boiling point/oC
Density/g cm-3
Solubility in water/g per H2O
Methanoic acid 8.4 101 1.220 Ethanoic acid 16.6 118 1.047 Propanoic acid 20.8 141 0.992 Butanoic acid 6.5 164 0.964 Pentanoic acid 34.5 186 0.939 3.7Hexanoic acid 1.5 205 0.927 1.0Heptanoic acid 10 224 0.913 0.25Octanoic acid 16 239 0.910 0.7Nonanoic acid 12.5 253 0.907 0.07Decanoic acid 31 269 0.886 0.2
From pentanoic acid, solubility as R.M.M. The bulky R groups prevent formation of H-bonds between –COOH and H2O
44
COOH
H
O
H
H
O
H
H
O
H
H
O
H
45
C
O
O
Na
Emulsifying action of soap (salts of carboxylic acids) depends on the length of the hydrocarbon chain
Non-polar
ionic
46
Length of hydrocarbon chain Property
Short ( 15 C atoms)Ionic properties
predominate
Long ( 19 C atoms)Non-polar properties
predominate
Intermediate(16-18 C atoms)
e.g. palmitic acid, C15H31COOH
stearic acid, C17H35COOH
Possess both ionic/non-polar
properties
47
Preparation of Carboxylic
Acids
48
1.1. Hydrolysis of NitrilesHydrolysis of Nitriles
RCN
R C
O
OH
heat
R C
O
O
H3O+
RX(1o)
C O
'R
"R
Elimination occurs for 2 and 3 RX as CN is a relatively strong base
49
ExampleExampless
50
2.2. Oxidation of aldehydes and 1Oxidation of aldehydes and 1 alcohols (pp.83-84, 93)alcohols (pp.83-84, 93)
3.3. Oxidation of aromatic side Oxidation of aromatic side chainschains (pp.54-55)(pp.54-55)
4.4. Iodoform reactions Iodoform reactions (p.92)(p.92)
51
C
H
O
Q.67 COOH
COOH
52
Q.68
H3C C
CH3
O
H3C COOH
HOOC C
O
CH3
1… 2…
Prolonged
heating
HOOC COOH
53
5.5. Hydrolysis of EstersHydrolysis of Esters
R C
O
O
R'
NaOH(aq)
heat
R C
O
O
Na
+ R'OH
removed by distillation
E.g.
Fat/oil Soap + glycerol
NaOH(aq)
heat
54
5.5. Hydrolysis of EstersHydrolysis of Esters
R C
O
O
R'
NaOH(aq)
heat
R C
O
O
Na
+ R'OH
H3O+
R C
OH
O
55
6.6. Carbonation of Grignard Carbonation of Grignard reagentsreagents
R-X R[MgBr]+Mg
Dry etherGrignard reagent
R : CH3-, 1/2/3 alkyl, benzyl, aryl
56
6.6. Carbonation of Grignard Carbonation of Grignard reagentsreagents
R-X R[MgX]+Mg
Dry etherDry ice (CO2)
R C
OMgX
O
R C
OH
O
H3O+
+ 1 C
57
R [MgX] C OO
+
6.6. Carbonation of Grignard Carbonation of Grignard reagentsreagents
R-X R[MgX]+Mg
Dry ether
CR
OMgX
O
58
7.7. Cannizzaro reactionsCannizzaro reactions
H3O+
C
OH
O
C
H
O
conc. NaOH
heat
C
ONa
O
+OH
For aldehydes
without HC
C
O
H
H
H
removed by distillation
59
Reactions of Carboxylic
Acids
60
Acidity of Carboxylic AcidsAcidity of Carboxylic Acids
• weak acids
RCOOH + H2O RCOO- + H3O+
[RCOOH]]O][H[RCOO
K 3-
a
pKa = –log Ka
The smaller the value of pKa, the stronger the acid
61
Acid
RCOOH
H2CO3 H2O
pKa 4-5 6.4 ~10 15.7
OH
Acidity as pKa
62
Formation of Formation of SaltsSalts1. 1. Reaction with Reactive Reaction with Reactive MetalsMetals
Irreversible as H2 leaves the reaction mixture
63
2. Reaction with 2. Reaction with BasesBases
RCOOH + NaOH RCOONa + H2O
Weaker acid
Stronger acid
Equilibrium positions lie on the right
2RCOOH + K2CO3 2RCOOK + H2CO3
RCOOH + KHCO3 RCOOK + H2CO3
64
OH + KHCO3 + H2CO3OK
Stronger acidWeaker
acid
Phenols react with OH, but they do not react with HCO3
OH + NaOH + H2OONa
Stronger acid
Weaker acid
No observable change
(effervescence)
65
Is there effervescence when Na is added to phenol? Explain.
OH + 2Na + H2(g)ONa22
Yes. The reaction proceeds to the completion as H2 leaves the reaction mixture.
66
Carboxylic acids and phenols can be distinguished by their different acidities
1989 AL Paper I Q.4 (modified)
67
COOH
COOH OH
A B C
COOHOH
OH
(a) Outline a chemical test to distinguish between A and B.
Add NaHCO3(aq) to A and B separately.Ony B reacts apparently to give gas bubbles of CO2
68
COOH
COOH OH
A B C
COOHOH
OH
(b) C also gives a +ve result in (a). Show how you would determine whether the sample is C or a mixture of A and B.Determine the melting point of the sample.
If the sample is pure C, it will give a sharp m.p..
The identity of C can be confirmed by carrying out mixted melting point test.
69
(c) Outline a scheme to extract A from a mixture containing A, B and C.
Mixture of A, B and C
ether
Ether solution of A, B and C
Ether layer, A
Aqueous layer, sodium salts of B and C
Shaken with NaHCO3(aq)
Evaporation of ether
Pure A
Sodium salts of B and C dissolve in water
b.p. = 34.6C
O C2H5
C2H5
70
Q.69
COOH OH OH
A B C
Outline a scheme to separate completely A, B and C from a mixture of them in ether.
Acidity : A > H2CO3 > B > H2O > CA, B are sparingly soluble solids in water
71
Ether solution of A, B ands C
Ether layer, B + C
Aqueous layer, sodium salt of A
shaken with NaHCO3(aq)
H3O+
Ppt of A
filtration
Impure A
Pure A
recrystallization
(m.p. = 122.4C)
COOH OH
A B
OH
C
COO + H+ COOH
p.120
72
Ether layer, B + C Shaken with
NaOH(aq)
Aqueous layer, sodium salt of B
Ether layer, C
Evaporation of ether
Pure C
H3O+
Ppt of B
filtration
Impure B
Pure B
recrystallization
(m.p. = 40.5C)
OH
B
OH
C
O + H+ OH
73
CH3COONaNaOH(s) from soda lime
fusion
NaOH(s) from soda lime
fusionCOONa
CH4 + Na2CO3
+ Na2CO3
Applied ONLY to synthesis of methane and benzene
DecarboxylationDecarboxylation
74
DecarboxylationDecarboxylation
On the contrary,
2HCOO-Na+heat
COO-Na+
COO-Na+
H2 +
RCH2COO-Na+ + NaOHmore
difficultNa2CO3 + RCH3 + other by-products
decarboxylation is widely applied to synthesis of carbonyl compounds (refer to p.85)
75
RCOOH RCH2OH (1o)
R C
O
O
R'
1. LiAlH4 / dry ether
2. H3O+
(Ester is more easily reduced)
ReductionReduction
H2/Pt
No reaction
or, NaBH4/H2O
76
OxidationOxidation
Not easily oxidized except : -
HCOOH CO 2 + H2OKMnO4 / H+
heat
COOH
COOH
KMnO4 / H+
heat2CO2 + H2O
77
DehydrationDehydration
Not easily dehydrated except : -
HCOOH CO + H 2O
COOH
COOH
CO2 + CO + H 2Oconc. H2SO4
conc. H2SO4
78
Q.70
Conc. H2SO4
C
C
O OH
HO O
CO2 + CO + H2O
+3
+3
+4
+2
79
Formation of acid derivativesFormation of acid derivatives
Refer to preparation of acid derivatives (pp.115-120)
80
Acidity of Organic Acidity of Organic CompoundsCompounds(Bronsted/Lowry Concept)
[HA(aq)](aq)](aq)][AO[H
K-
3a
smaller pKa higher acidity
larger pKa lower acidity
HA(aq) + H2O(l) H3O+(aq) + A(aq)
81
Two factors affecting the acidity of H–A : -(1) Strength of H–A bond (minor effect)
(2) Stability of the conjugate base, A (major effect)
82
Two factors affecting the acidity of H–A : -(1) Strength of H–A bond (minor effect)
Stronger H–A bond lower acidity
Acidity : H-I > H-Br > H-Cl >> H-FCan be ignored for organic cpds ∵(i) H is always bonded to C, N or
O;(ii) C-H, N-H and O-H bonds have
similar bond strengths
83
(2) Stability of the conjugate base, A (major effect)
higher stability of A weaker basicity of A
higher acidity of H-A
Stability of A depends on(i) Electronegativity of A
Higher EN better accomodation of –ve charge by A higher stability of A
84
Stability of A depends on(ii) Electronic effect
- Inductive effect (+ve or –ve)- resonance effect (more important)
85
Organic Compound pKa Organic Compound pKa
CH3CH2–H 50 CH3CH2CH2O–H ~17
H–H 50 HO – H 15.7
CH2=CH–H 44 C6H5O–H (phenol) ~10
NH2–H 36 4.87
CHC–H 25 CH3COO–H 4.76
CH3COCH2–H 20 4.20
C
O
O H
C
O
O H
86
Interpretation of the Relative Stability of Typical Organic Compounds
HO-H H2N-H H3C-H
pKa 15.7 36 50
Electronegativity : - - O > N > CStability of conjugate base : -HO > H2N > H3C
The more electronegative atom can accommodate the negative charge more easily
87
CH3COCH2-H H3C-H
pKa 20 50
C
O
CH2H3CC
O
CH2H3C
The -ve charge on C becomes less available for attracting a proton CH3COCH2
becomes a weaker base CH3COCH2-H becomes a stronger conjugate acid
Resonance effect
88
CHC-H CH2=CH-HCH3CH2-
H
pKa 25 44 50
Stability of conjugate base : -CHC > CH2=CH > CH3CH2
sp sp2 sp3
Ease of accommodation of the –ve charge : -sp C > sp2 C > sp3 C
89
CH3COO-HCH3CH2CH2O-
H
pKa 4.74 ~10 ~17
O H
CH3CH2CH2 OH3C C
O
O
O
> >
Stability of conjugate base : -
Destabilized by +ve inductive effect
Stabilized by resonance effect
90
Q.71
H3C C
O
O
H3C C
O
O
The two structures are equally stableThe –ve charge is shared by two electronegative O atoms Delocalization of –ve charge is more favoured
91
Q.71O O O O
The –ve charge is accommodated by the less electronegative C atoms less stable delocalization is less favoured
92
Q.72
pKa 4.20 4.87
C
O
O
H
C
O
O
H
C
OO
C
OOThe –ve charge is not shared by the ring less extensive
delocalization
93
C
OO
C
OO
C
OOC
OO
C
OO
The –ve charge is shared by the ring slightly more extensive delocalizationThe effect is small since the three structures are less stable due to separation of opposite charges
94
Effects of substituents on acidity of carboxylic acids1. Aliphatic carboxylic acids
RCOOH + H2O RCOO- + H3O+
Electron-donating R groups destabilize the RCOO
RCOOH is less acidicElectron-withdrawing R groups stabilize the RCOO
RCOOH is more acidic
95
Carboxylic acid pKa Conjugate base
CF3COO–H 0 CF3COO
CCl3COO–H 0.65 CCl3COO
CH2FCOO–H 2.66 CHCOO
CH2ClCOO–H 2.81 CH2ClCOO
CH2BrCOO–H 2.87 CH2BrCOO
CH2ICOO–H 3.13 CH2ICOO
HCOO–H 3.77 HCOO
CH3COO–H 4.76 CH3 COO
96
Inductive effect on acidity rapidly when the substituents are placed farther away from the carboxyl group
pKa 2.85 4.05 4.52 4.82
COOH COOH COOHCOOH
Cl
Cl
Cl
> > >
97
2. Aromatic carboxylic acids CH3
COOHCOOHCOOH
CF3
> >
Acidity :-
Electron-donating group on the ring reduces the acidity by destabilizing the conjugate base.Electron-donating group on the ring increases the –ve charge on the conjugate base, making it more available for attracting a proton Stronger conjugate base Weaker acid
98
2. Aromatic carboxylic acids CH3
COOHCOOHCOOH
CF3
> >
Acidity :-
Electron-withdrawing group on the ring increases the acidity by stabilizing the conjugate base.Electron-withdrawing group on the ring disperses the –ve charge on the conjugate base, making it less available for attracting a proton Weaker conjugate base Stronger acid
99
Q.73
pKa 2.98 4.20 4.58
COOHCOOH
OH
> >
COOH
HO
100
Q.73COOH COOH
OHpKa = 4.20
pKa = 4.58
OH withdraws electrons by –ve inductive effect
-OH donates electrons by resonance effect
Resonance effect > inductive effectThe net effect is electron-donating
101
COOH COOH
OH
pKa = 4.20
pKa = 2.98
C
O
O O
HThe conjugate base is stabilized by intramolecular hydrogen bond
102
(1) Acidity : dioic acids > monocarboxylic acidThe conjugate bases are stabilized by intramolecular H-bonds
C
C
O O
OO
H
Acid pKa1 pKa2
pKa2 – pKa1
HOOCCOOH 1.2 4.2 3.0HOOCCH2COOH 2.9 5.7 2.8
HOOC (CH2)2COOH 4.2 5.6 1.4HOOC (CH2)3COOH 4.3 5.5 1.2HOOC (CH2)4COOH 4.4 5.6 1.2
CH3COOH 4.76 - -
103
Acid pKa1 pKa2
pKa2 – pKa1
HOOCCOOH 1.2 4.2 3.0HOOCCH2COOH 2.9 5.7 2.8
HOOC (CH2)2COOH 4.2 5.6 1.4HOOC (CH2)3COOH 4.3 5.5 1.2HOOC (CH2)4COOH 4.4 5.6 1.2
CH3COOH 4.76 - -
(i) The repulsion between two –COO groups does not favour the 2nd dissociation
(2) pKa2 > pKa1
C
C
O O
OO
H
C
C
O O
OO
104
Acid pKa1 pKa2
pKa2 – pKa1
HOOCCOOH 1.2 4.2 3.0HOOCCH2COOH 2.9 5.7 2.8
HOOC (CH2)2COOH 4.2 5.6 1.4HOOC (CH2)3COOH 4.3 5.5 1.2HOOC (CH2)4COOH 4.4 5.6 1.2
CH3COOH 4.76 - -
(ii) The doubly charged anion attracts the proton more strongly
(2) pKa2 > pKa1
C
C
O O
OO
H
C
C
O O
OO
H+
105
Acid pKa1 pKa2
pKa2 – pKa1
HOOCCOOH 1.2 4.2 3.0HOOCCH2COOH 2.9 5.7 2.8
HOOC (CH2)2COOH 4.2 5.6 1.4HOOC (CH2)3COOH 4.3 5.5 1.2HOOC (CH2)4COOH 4.4 5.6 1.2
CH3COOH 4.76 - -
∵ intramolecular H-bonds are less easily formed
(3) pKa1 as the two –COOH groups are further apart
106
Acid pKa1 pKa2
pKa2 – pKa1
HOOCCOOH 1.2 4.2 3.0HOOCCH2COOH 2.9 5.7 2.8
HOOC (CH2)2COOH 4.2 5.6 1.4HOOC (CH2)3COOH 4.3 5.5 1.2HOOC (CH2)4COOH 4.4 5.6 1.2
CH3COOH 4.76 - -
The repulsion between the two –COO groups down the series pKa2 remains relatively constantSince, pKa1 down the series(pKa2-pKa1) down the series
(4) (pKa2-pKa1) down the series
107
[B(aq)](aq)](aq)][OH[HB
K-
b
smaller pKb higher basicity
larger pKb lower basicity
B(aq) + H2O(l) HB+(aq) + OH(aq)
Basicity of Organic Basicity of Organic CompoundsCompounds
108
Two factors affecting the basicity: -
(1) Ability to donate a lone pair to a proton
Basicity : -
More electron-donating alkyl group attached to NMore available to donate a lone pair to a proton
N
R
R'
R''
N
R
R'
H
N
R
H
H
N
H
H
H
> > >
3 2 1
109
(2) The extent of solvation of the conjugate acid
Extent of solvation : -
N
R
R'
R''
N
R
R'
H
N
R
H
H
N
H
H
H
HHHH > > >
1 2 3More H attached to NMore available to form H-bond with water(solvent)Extent of solvation Stability of conjugate acid Basicity of amine
110
N
H
H
H
H
O
HH
H
O
H
H
O
HH
O
H
Good solvationExtensive formation of H-bonds with water
111
Overall Basicity (from experiments) : -2 amines > 1 amines > 3 amines > NH3
pKb 3.27 3.36 4.22 4.74
N H
H3C
H3C
N H
H
H3C
N CH3
H3C
H3C
N H
H
H
>> > >
112
NH2
H3C NH2
pKb 9.38 3.36
(a)Q.74(a)
CH3NH2
-CH3 is electron-donating
The lone pair on N is more available to abstract a proton
113
NH2
The lone pair on N is shared by the benzene ring due to resonance effect
Less available to abtract a proton
NH2 NH2 NH2
114
Both –OH and –CH3 groups are electron-donating
Lone pair on N is more available to abstract a proton
Stronger base than phenylamine
NH2
OH
NH2
CH3
NH2
>&
Q.74(b)
115
NH2
OH
NH2
CH3
>
Q.74(b)
Resonance effect is more electron-donating than positive inductive effect
116
NH2
NO2
NH2Q.74(b)
>
-NO2 group is electron-withdrawing
Lone pair on N is less available to abstract a proton
Weaker base than phenylamine
117
NH2
H3C C
NH2
O
>
Q.74(c)
H3C C
NH2
O
H3C C
NH2
O
Oxygen is more electronegative than N and C
Lone pair on N is withdrawn more
Less basic than phenylamine
118
Basicity of organic compounds : -
Aliphatic > NH3 > Aromatic > Amidesamine
s
amines
(2 > 1 > 3)
119
Amines form water-soluble salts with mineral acids
CH3NH2 + HCl(aq) CH3NH3
+Cl(CH3)2NH + HCl(aq) (CH3)2NH2
+Cl
(CH3)3N + HCl(aq) (CH3)3NH+Cl1. Used in drug formulation for easier
absorption2. Used in purification of amines from other organic compounds
120
Ether solution of A, B, C and D
Ether layer, A,B,DAqueous layer, sodium salt of C
shaken with NaHCO3(aq)
H3O+
Ppt of C
filtration
Impure C
Pure C
recrystallization
COO + H+ COOH
Q.75
OH NH2 COOH CH3
121
Ether solution of A, B and D
Ether layer, B,DAqueous layer, sodium salt of A
shaken with NaOH(aq)
H3O+
Ppt of A
filtration
Impure A
Pure A
recrystallization
Q.75
OH NH2 COOH CH3
O + H+ OH
122
Ether layer, B + D Shaken with HCl(aq)
Aqueous layer, sodium salt of B
Ether layer, D
Evaporation of ether
Pure C
OH-
B + Aq. solutionShaken with ether
B in ether layer
Pure B
Evaporation of ether
(liquid)
(liquid)
OH NH2 COOH CH3
123
Reactivity of carboxylic acids and their derivatives towards nucleophilic reactions
1. Aldehydes/ketones undergo AdN rather than SNCarboxylic acids/derivatives undergo SN rather than AdN
124
O C
H
R
Nu
C
R
Nu
O
H O C
Nu
R
+ H
O C
R'
R
Nu
C
R
Nu
O
R' O C
Nu
R
+ R'
Strong bases, unstable
A discussion on the reactivity of carboxylic acids and their derivatives towards nucleophilic rxs1. Aldehydes/ketones undergo AdN rather than SN
125
Reactivity of carboxylic acids and their derivatives towards nucleophilic reactions
1. Carboxylic acids/derivatives undergo SN rather than AdN
O C
L
R
Nu
C
R
Nu
O
L O C
Nu
R
+ L
Weak base,stable
126
Strength of acids : - HCl > RCOOH > HOH > ROH > H2NH > RH > HH
Strength of bases : -Cl < RCOO < HO < RO < H2N < R < H
O C
L
R
Nu
C
R
Nu
O
L O C
Nu
R
+ L
O C
H
R
Nu
C
R
Nu
O
H O C
Nu
R
+ H
O C
R'
R
Nu
C
R
Nu
O
R' O C
Nu
R
+ R'
127
O C
L
R
Nu
C
R
Nu
O
L O C
Nu
R
+ L
Reactivity : -
R C
Cl
O R C
O
O
C
O
'R
R C
OH
O
R C
O
O
R'
R C
NH2
O
>> > >
(2)
128
Reactivity : -
R C
Cl
O R C
O
O
C
O
'R
R C
OH
O
R C
O
O
R'
R C
NH2
O
>> > >
(2)
(i) Ease of leaving(Stability of bases) : -Cl > RCOO > HO > RO > H2N > R > H
∵ Strength of bases : -Cl < RCOO < HO < RO < H2N < R <
H
Reasons : -
129
Reasons : -
R C
Cl
O
R C
Cl
O
R C
O/N
O
R C
O/N
O
Incre
asin
g
reso
nan
ce e
ffect
(2p)
(2p)
(3p)
(2p)
(2p)
(2p)
(ii) Resonance effect : -
Efficiency of orbital overlap : 2p/2p > 3p/2p
Less stableMore reactive
More stableLess reactive
130
Reactivity : -
The less reactive derivatives can be prepared from the more reactive derivative via nucleophilic substitution reactions.
R C
Cl
O R C
O
O
C
O
'R
R C
OH
O
R C
O
O
R'
R C
NH2
O
>> > >
(2)
131
R C
OH
O
R C
Cl
O
R C
O
O
C
O
'R
R C
O
O
R"
R C
NH2
O
NH3
Preparation of Acid Derivatives
132
R C
OH
O
R C
Cl
O
R C
O
O
C
O
'R
R C
O
O
R"
R C
NH2
O
NH3
Preparation of Acid Derivatives
133
R C
OH
O
R C
Cl
O
R C
O
O
C
O
'R
R C
O
O
R"
R C
NH2
O
NH3
Preparation of Acid Derivatives
134
R C
OH
O
R C
Cl
O
R C
O
O
C
O
'R
R C
O
O
R"
R C
NH2
O
NH3
Preparation of Acid Derivatives
135
R C
OH
O
R C
Cl
O
R C
O
O
C
O
'R
R C
O
O
R"
R C
NH2
O
NH3
Preparation of Acid Derivatives Non-SN reactions
136
R C
Cl
O
C
Cl
O
>(3)
C
O
Cl
C – O bond of benzoyl chloride has less mesomeric effect
Carbonyl C of benzoyl chloride is less positive
Less susceptible to nucleophilic attack
137
(4) R C
Cl
O
ClC>+ +
The carbonyl C is attached to TWO electron-withdrawing atoms
more positive
more susceptible to electrophilic attacks
138
(4) R C
Cl
O
ClC>+ +
Also, the nucleophile experiences less steric hindrance with acyl chloride because the reaction site is planar
139
A. Preparation of Acid Chlorides
R C
O
OH
PCl5/SOCl2/PCl5
heatR C
O
Cl
SOCl2 : thionyl chloride or sulphur oxychloride
140
R C
OH
O
+ PCl 5 R C
Cl
O
+ POCl3 + HCl(g)(l)(s)
b.p. = 106℃
sublimes at 160℃
(1) Acid chloride with high b.p.
Higher b.p. than acid chloride due to intermolecular H-bonds
removed first byfractional distillation
Phosphorus oxychloride
(>170C)
141
(2) Acid chloride with high/intermediate/low b.p.
R C
OH
O
+ SOCl2 R C
Cl
O
+ SO2(g) + HCl(g)
can be removed
easily
b.p. = 74.6℃
(l)
(85C < b.p. < 170C)
Most useful
or b.p. < 65C
142
(3) Acid chloride with low b.p.
R C
OH
O
+ PCl3 R C
Cl
O
33 + H3PO3(s)
decomposes at 200℃
b.p. = 79℃
(l)
(3) Acid chloride with low b.p.
(< 69C)
Removed first by fractional distillation
143
Q.76
COOH + PCl5(s)heat
COCl + POCl3(l) + HCl(g)
b.p.=197.2C
b.p.=106C
b.p.=249C
s.t.=160C
COOH + SOCl2(l)heat
COCl + SO2(g) + HCl(g)
b.p.=74.6C
144
Q.76
b.p.51C
b.p.=118C
heatH3C C
OH
O
+ PCl3(l) H3C C
Cl
O
+ H3PO3(l)
d.c.200C
b.p.=76C
Removed first by fractional distillation
145
B. Preparation of Acid Anhydrides
R C
Cl
O
'R C
OH
O
pyridine
R C
O
O
C'R
O
+ HCl+
(1)
Acyl chlorides must be stored in anhydrous conditions
they hydrolyze rapidly in the presence of even a trace amount of water(p.122)
RCOCl + H2O RCOOH + HCl
146
B. Preparation of Acid Anhydrides
R C
Cl
O
'R C
OH
O
pyridine
R C
O
O
C'R
O
+ HCl+
(1)
R R’ unsymmetrical anhydride
R = R’ symmetrical anhydride
147
B. Preparation of Acid Anhydrides
R C
Cl
O
'R C
OH
O
pyridine
R C
O
O
C'R
O
+ HCl+
(1)
+ HClN NH Cl
pyridineEquilibrium position shifts to the right
Yield
148
B. Preparation of Acid Anhydrides
R C
Cl
O
'R C
O Na
O
pyridine
R C
O
O
C'R
O
+
(2)
+ NaCl(s)
R R’ unsymmetrical anhydride
R = R’ symmetrical anhydride
149
B. Preparation of Acid Anhydrides
R C
Cl
O
'R C
O Na
O
pyridine
R C
O
O
C'R
O
+
(2)
+ NaCl(s)
NaCl(s) produced is removed by precipitation
Equilibrium position shifts to the right
Yield
150
B. Preparation of Acid Anhydrides
R C
OH
O R C
O
O
CR
O
(3)
+ H2OP2O5
heat2
Only suitable for preparing symmetrical anhydrides
dehydrating agent
P4O10 = P2O5
Non-SN reaction
151
Q.77
It gives a mixture of three acid anhydrides.
RCOOH + R’COOH
P4O10heat
CR
O
O
C'R
O
CR
O
O
CR
O
C'R
O
O
C'R
O
+ +
152
R C
OH
O
R C
Cl
O
R C
O
O
C
O
'R
R C
O
O
R"
R C
NH2
O
NH3
Preparation of Acid AmidesAmmonolysis
NH
3
NH3
NH3
NH3
153
C. Preparation of Acid Amides
The overall reaction is : -
R C
OH
O
R C
NH2
O
+ H2OH2N H+heat
(excess)
(1) Ammonolysis of Carboxylic Acids
breaking of ammonia= ammonolysis
154
heatR C
NH2
O
+ H2O
C. Preparation of Acid Amides
R C
OH
O
+ NH3(aq) R C
O NH4
O
(1) Ammonolysis of Carboxylic Acids
neutralization
dehydration
155
heatR C
NH2
O
+ H2O
C. Preparation of Acid Amides
R C
OH
O
+ NH3(aq) R C
O NH4
O
(1) Ammonolysis of Carboxylic Acids
prevent hydrolysis of the ammonium carboxylate
R C
OH
O
+ H2O(l)R C
O NH4
O
+ NH3(aq)
excess
excess RCOOH
excess
156
(2) Ammonolysis of Acid Chlorides(better method)(Acylation of NH3/amines)
R C
Cl
O
+ NH3(aq) R C
NH2
O
+ HCl
(1o)
R C
Cl
O
R C
NHR'
O
+ HCl
(2o)
+ R'NH2
(1o)
R C
Cl
O
R C
N
O
+ HCl
(3o)(2o)
N H
"R
'R
+
R'
"R
(excess)NH3(aq) excess
(2) excess
R’NH2(aq) (1)
excess
(1)
(2)
(3)
Acyl group
Aminolysis
157
(2) Ammonolysis of Acid Chlorides
(benzoylation of NH3/amines)
C
O
Cl
+ NH3C
O
NH2
+ HCl
C
O
Cl
+ RNH2 C
O
NH
+ HCl
R
C
O
Cl
+ C
O
N
+ HClN
R
R' H
R
R'
benzoyl group
158
R C
Cl
O
+ NH3(aq) R C
NH2
O
+ HCl
(1o)
R C
Cl
O
R C
NHR'
O
+ HCl
(2o)
+ R'NH2
(1o)
R C
Cl
O
R C
N
O
+ HCl
(3o)(2o)
N H
"R
'R
+
R'
"R
(excess)NH3(aq) excess
(2) excess
R’NH2(aq) (1)
excess
Removed by excess NH3/amines Yield
159
NOT applicable to 3 amine due to absence of H
R C
Cl
O
+ N R'''
''R
'R
no reaction
160
H3C C
NH2
O
Further acylation is inhibited because amides are weaker nucleophiles than amines
H3C C
NH2
O
161
The acyl and benzoyl derivatives of amines are usually crystalline solids with sharp m.p..
Thus, amines can be identified by
1. preparing their acyl/benzoyl derivatives
2. recrystallization
3. melting point determination
Similar to identification of carbonyl compounds (pp.91-92)
162
Q. 78
Why is the impure solid dissolved in the minimum quantity of hot solvent?
A hot solvent is used to ensure
maximum dissolution of target product
163
Q. 78
Why is the impure solid dissolved in the minimum quantity of hot solvent?
If minimum quantity of solvent is used to ensure
(a) minimum dissolution of insoluble impurities during hot filtration(step 3)
(b) minimum loss of target product during suction filtration (step 5).
164
Why is hot filtration done in ways as described by step 3 ?
(a) Hot filtration is to minimize thecrystallization of filtrate on the funnel.
Q. 79
(b) A shot-stem funnel fitted with a piece of fluted filter paper is to speed up the filtration so as to minimize the crystallization of filtrate on the funnel.
165
Q. 80
Why are the crystals washed in ways as described by step 6 ?
(a) Washing the crystals with the mother liquor (a saturated solution) can dissolve no more target product.
the yield is not reduced
(b) Washing the crystals with solvent can remove the mother liquor (containing dissolved impurities) from the crystals
Only a little cold solvent is used to minimize the loss of target product.
166
(3) Ammonolysis of Acid Anhydrides
R C
O
O
C
O
R
R C
NH2
O
R C
NHR'
O
+
+
R C
OH
O
R C
OH
O
The yield is increased by removing the products with excess NH3 or amine
(1)
(2)
167
(4) Partial Hydrolysis of Nitriles
RCNH2O
H+or OH-, reflux
R C
NH2
O
Non-SN reaction
168
Further hydrolysis gives carboxylic acids (in acidic medium) orcarboxylate in (basic medium).
R C
NH2
OH2O
R C
O NH4
O
R C
OH
O
R C
O
O
169
R C
OH
O
R C
O NH4
O
+ H2OR C
NH2
Ohydrolysishydrolysis
Hydrolysis of amide = The reverse of ammonolysis of RCOOH
H2O+ NH3
heatammonolysis
170
R C
OH
O
R C
Cl
O
R C
O
O
C
O
'R
R C
O
O
R"
R C
NH2
O
NH3
Preparation of Esters
R’’O
HR’
’OH
R’’O
H
Alcoholysis
171
R C
OH
O
+ R'OHH+
refluxR C
O
O
R'
+ H2OR’O – H
C. Preparation of Esters
(1) Alcoholysis of Carboxylic Acids
Esterification
172
(2) Alcoholysis of Acid Chlorides
R C
Cl
O
+ R'OH R C
O
O
R'
+ HClOH-
R C
Cl
O
R C
O
O
+ HClOH-
OH+
Faster and irreversibleOH ions serve to
(i) the yield by removing HCl
phenolysis
173
(2) Alcoholysis of Acid Chlorides
R C
Cl
O
+ R'OH R C
O
O
R'
+ HClOH-
R C
Cl
O
R C
O
O
+ HClOH-
OH+
OH ions serve to
(ii) Speed up the nucleophilic attack by generating the more powerful nucleophile.
OH + OH- O + H2O
174
(3) Alcoholysis of Acid Anhydrides
R C
O
O
+ R'OH R C
O
O
R'C
O
R
heatR C
OH
O
+
Heating is required as acid anhydrides are less reactive than acid chlorides
175
Reactions of Reactions of the the
Derivatives of Derivatives of Carboxylic Carboxylic
AcidsAcids
176
Z
C
RL
O
H
Nucleophilic Acyl Substitution
C O
L
R
HZ C O
R
Z
H
L+
C O
R
Z
+ HL
HZ: nucleophile
L leaving group
slow
fast
fast
177
Z
C
RL
O
H
Nucleophilic Acyl Substitution
C O
L
R
HZ
HZ: nucleophile
L leaving group
slow
fast
+C O
R
Z
H2Z
fast
C O
R
Z
H
L+
HZ
178
Z
C
RL
O
H
Nucleophilic Acyl Substitution
C O
L
R
HZ
More stable intermediate
slow
fast
+C O
R
Z
H2Z
fast
C O
R
Z
H
L+
HZ
Less steric hindrance than the 5-coordinated transition state of RX(SN2)Obeying octet rule while the 3-coordinated carbocation of RX(SN1) is not
179
Z
C
RL
O
H
Nucleophilic Acyl Substitution
C O
L
R
HZ
HZ: = H-OH, H-OR, H-NH2, H-NHR, H-NRR’
slow
fast
+C O
R
Z
H2Z
fast
C O
R
Z
H
L+
HZ
180
A. Hydrolysis (Reactions with water)HZ = H-
OHDecre
asin
g re
activ
ity
H3C CCl
O+ H2O
coldH3C C
OH
O + HCl
H3C CO
O
CO
H3C
+ H2O H3C COH
OH3C C
OH
O
+
H3C CO
O
CH3
+ H2OH+ or OH-
heatH3C C
OH
OCH3OH+
H3C CNH2
O
+ H2OH+ or OH-
heatH3C C
OH
O
+ H2N H
catalysts
catalysts
181
C O
L
R
+ H+ C OH
L
R
Acid-catalyzed
Carbonyl C becomes more susceptible to nucleophilic attacks
182
Base-catalyzed
C O
L
R
+ OH-
OH ion is a stronger nucleophile than H2O
183
A. Hydrolysis (Reactions with water)HZ = H-
OHH3C C
Cl
O+ H2O
coldH3C C
OH
O + HCl
H3C CO
O
CO
H3C
+ H2O H3C COH
OH3C C
OH
O
+
H3C CO
O
CH3
+ H2OH+ or OH-
heatH3C C
OH
OCH3OH+
H3C CNH2
O
+ H2OH+ or OH-
heatH3C C
OH
O
+ H2N H
Decre
asin
g re
activ
ity
Or, CH3COO
184
B. Alcoholysis (Reactions with alcohols)HZ = H-OR
Phenolysis (Reactions with phenols)HZ = H-OAr
Refer to the preparation of ester (p.121) Esters and amides do not undergo alcoholysis/phenolysis
185
C. Ammonolysis (Reactions with NH3)HZ = H-NH2
Aminolysis (Reactions with amines)HZ = H-NHR, H-NRR’ Refer to the preparation of amides (pp.119-121)
Amides do not undergo
ammonolysis/aminolysis Acid derivatives do not react with
3 amines
186
2. Reduction
R CCl
O
R CO
O
CO
R
R CO
O
R'
R CNH2
O
1. LiAlH4 / dry ether
2. H3O+
1. LiAlH4 / dry ether
2. H3O+
1. LiAlH4 / dry ether
2. H3O+
1. LiAlH4 / dry ether
2. H3O+
RCH2OH
2RCH2OH
RCH2OH + R'OH
RCH2NH2
A. LiAlH4 (p.95)
187
2. Reduction
B. H2/Pd poisoned with S (p.84)
High yield
188
3. Other reactions of acid amides
A. Hofmann Degradation
CR
O
NH2
Br2, conc. NaOHRNH2
CR
O
CH3
1. I2, conc. NaOHRCOOH
2. H3O+
Cf. Iodoform reaction One Carbon less
189
Synthetic application
H3C COH
O Br2 , conc. NaOHNH3
heatH3C C
NH2
OCH3NH2
HNO2CH3OH
[O]HCOOH
H3C CCl
O H2, Pd
sulphurH3C C
H
O
1. LiAlH4 /dry ether
2. H3 O +
CH3CH2OH
1. I 2
, con
c.
NaOH 2. H
3O
+
190
B. Dehydration
R CNH2
O P2O5
heatC NR + H2O
191
RCOOH / RCN cycle : -
R COH
O
R CNH2
O
C NR
R CNH2
O
192
Q. 81Br
C2H5ONaC2H5OH
heat
KMnO4H3O+heat
COOH
COOH
(excess)CONH2
CONH2NH3
heat
Nylon 6,6
C
CCl
O
Cl
O
1. LiAlH4, dry ether2. H3O+
NH2
H2N
Excess NH3
better
193
The END
194
Give the IUPAC names for the following compounds:
(a) (b)
(c) (d)
Answer
(a) 3-Methylbutanoic acid
(b) N-Methylethanamide
(c) Ethyl benzoate
(d) Benzoic anhydride
Back
195
An ester is formed by reacting an alcohol with a carboxylic acid. Draw the structural formulae of the following esters and in each case, give the names of the alcohol and the carboxylic acid that form the ester.
(a) Methyl ethanoate Answer(a) The structural formula of methyl ethanoate is:
It is formed from the reaction of ethanoic acid and
methanol.
196
32.2 Nomenclature of Carboxylic Acids and their Derivatives (SB p.26)
An ester is formed by reacting an alcohol with a carboxylic acid. Draw the structural formulae of the following esters and in each case, give the names of the alcohol and the carboxylic acid that form the ester.
(b) Ethyl methanoate Answer(b) The structural formula of ethyl methanoate is:
It is formed from the reaction of methanoic acid and
ethanol.
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197
Complete the following table.Answer
Molecular formula
Structural formula
IUPAC name
C3H7COOH (a) (b)
(c) (d)
(e) (f)
(g) (h) Trichloroethanoic acid
198
(a) (b) Butanoic acid
(c) CH3CH(CH3)CH2COOH (d) 3-Methylbutanoic acid
(e) C6H4ClCOOH (f) 2-Chlorobenzoic acid
(g) CCl3COOH (h)
Back
199
(a)Propanoic acid has a boiling point of 141°C which is considerably higher than that of butan-1-ol (117°C), although they have the same molecular mass. Explain why.
Answer
200
(a) Each propanoic acid molecule forms two intermolecular hydrogen
bonds with other propanoic acid molecules. However, each butan-
1-ol molecule can form only one intermolecular hydrogen bond with
other butan-1-ol molecules. Since molecules of propanoic acid
form more extensive intermolecular hydrogen bonds than those of
butan-1-ol, the boiling point of propanoic acid is higher than that of
butan-1-ol.
201
(b) Arrange the following compounds in decreasing order of solubility in water:
CH3CH2CH2COOH, CH3CH2COOCH3, CH3COOH
Answer(b) The solubility of the compounds in water decreases in
the order:
CH3COOH > CH3CH2CH2COOH > CH3CH2COOCH3
202
(c)Propanedioic acid forms intramolecular hydrogen bonds. Draw its structural formula, showing clearly the formation of intramolecular hydrogen bonds. Answer
(c)
Back
203
Write the chemical equations for the acid-catalyzed and alkali-catalyzed hydrolyses of each of the following compounds:
(a) Ethyl butanoateAnswer
(a)
204
Write the chemical equations for the acid-catalyzed and alkali-catalyzed hydrolyses of each of the following compounds:
(b) PropanamideAnswer
(b)
205
Write the chemical equations for the acid-catalyzed and alkali-catalyzed hydrolyses of each of the following compounds:
(c) Benzoyl chlorideAnswer
(c)
Back
206
Outline how a mixture of butanone and ethanoic acid can be separated in the laboratory. Answer
Back
207
(a)Complete and balance the following chemical equations:
(i)
(ii)
Answer
208
(a) (i)
(ii)
209
(b) Complete the following chemical equations:
(i)
(ii)
(iii)Answer
210
(b) (i)
(ii)
(iii)
Back
211
Explain why ethanoyl chloride must be protected from atmospheric moisture during storage. Answer
This is because ethanoyl chloride reacts
readily with water (from atmospheric
moisture) to form ethanoic acid.
Back
212
The characteristic reaction of the derivatives of carboxylic acids is nucleophilic acyl substitution.
Arrange the derivatives of carboxylic acids in decreasing order of reactivity towards nucleophilic
acyl substitution.
AnswerAcyl chlorides > acid anhydrides > esters > amides
Back
213
Draw the structural formulae of the missing compounds A to H:
(a)
(b)
(c)
Answer
214
(a)
(b)
(c)
215
Draw the structural formulae of the missing compounds A to H:
(d)
(e)
(f)
Answer
216
(d)
(e)
(f)
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