1. Carbonyl Compounds and Nucleophilic Addition

2. Carbonyl compounds Contain at least one carbonyl group.
R = R’ or R  R’

3. Aldehydes  terminal carbonyl groups
propanal
butanal
pentanal
No need to specify the position of the carbonyl group

4. pentan-2-one
pentan-3-one

5. cyclohexanone
cyclohexanecarbaldehyde
cyclohexylmethanal
cyclohexylethanal

6. benzaldehyde
1-phenylethanone
diphenylmethanone
benzophenone

7. 4-oxopentanoic acid
5-oxopentanoic acid
4-oxopentanal

8. Physical Properties
1. Most simple aliphatic ketones and aldehydes are liquids at room temperature except methanal (b.p. = 21C) and ethanal (b.p. = 20.8C)
Aliphatic aldehydes have an unpleasant and pungent smell
Ketones and aromatic aldehydes have a pleasant and sweet odour

9. Aldehydes: Methanal HCHO -21 -92  Ethanal CH3CHO 20.8 -124 0.783
Physical properties of some aldehydes and ketones
Name
Molecular formula
Boiling point (oC)
Melting point (oC)
Density at 20oC (g cm-3)
Aldehydes:
Methanal
HCHO
-21
-92 
Ethanal
CH3CHO
20.8
-124
0.783
Propanal
CH3CH2CHO
48.8
-81
0.807
Butanal
CH3(CH2)2CHO
75.7
-99
0.817
Methylpropanal
(CH3)2CHCHO
64.2
-65.9
0.790
Benzaldehyde
C6H5CHO
179
-26
1.046

10. 2. Less dense than water except aromatic members
Name
Molecular formula
Boiling point (oC)
Melting point (oC)
Density at 20oC (g cm-3)
Ketones:
Propanone
CH3COCH3
56.2
-95.4
0.791
Butanone
CH3COCH2CH3
79.6
-86.9
0.806
Pentan-2-one
CH3CO(CH2)2CH3
102
-77.8
0.811
Pentan-3-one
CH3CH2COCH2CH3
-39.9
0.814
3-Methylbutan-2-one
CH3COCH(CH3)2 95
-92
0.803
Hexan-2-one
Phenylethanone
CH3CO(CH2)3CH3
C6H5COCH3
127
202
-56.9
19.6
0.812
1.028

11. Boiling point : - (similar molecular masses)
carboxylic acid > alcohol > aldehyde, ketone > CxHy
Presence of polar group
Absence of –OH group

12. Solubility
Small aldehydes and ketones show appreciable solubilities in water due to the formation of intermolecular hydrogen bonds with water

13. Solubility
Ethanal and propanone are miscible with water in all proportions.
Propanone(acetone) is volatile and miscible with water
 Once used to clean quick-fit apparatus
potentially carcinogenic

14. Solubility Methanal gas dissolves readily in water
Aqueous solutions of methanal (Formalin) are used to preserve biological specimens
Methanal(formaldehyde) is highly toxic

15. Industrial preparation
By dehydrogenation (oxidation) of alcohols
Further oxidation is prohibited
Out-dated

16. Laboratory preparation
Oxidation of alcohols
1 alcohol  aldehyde  carboxylic acid
2 alcohol  ketone
Further oxidation of aldehyde to carboxylic acid is prohibited by
(i) using a milder O.A., e.g. H+/ Cr2O72

18. Laboratory preparation
Oxidation of alcohols
1 alcohol  aldehyde  carboxylic acid
2 alcohol  ketone
Further oxidation of aldehyde to carboxylic acid is prohibited by
(i) using a milder O.A., e.g. H+/ Cr2O72
(ii) distilling off the product as it is formed

19. 70C > T > 21C

20. Heating under reflux
Ethanol  ethanoic acid

21. carboxylic acid
2 alcohol  ketone
Further oxidation of ketone to carboxylic acid has not synthetic application since
1. it requires more drastic reaction conditions
2. it results in a mixture of organic products
High T

22. 2. Reduction of acid chlorides
The catalyst Pd or BaSO4 is poisoned with S to prevent further reduction to alcohol

23. oxidation reduction Aldehydes  Intermediate oxidation state
Carboxylic acid or acyl chloride
Aldehyde
Alcohol
reduction
Aldehydes
 Intermediate oxidation state
 Preparation must be well controlled.

24. Friedel-Crafts acylation
(Preparation of aromatic ketones)

25. 4. Decarboxylation of calcium salts
Symmetrical ketones can be obtained by heating a single calcium carboxylate

26. Cross decarboxylation is preferred
4. Decarboxylation of calcium salts
Aldehydes can be obtained by heating a mixture of two calcium carboxylates
Cross decarboxylation is preferred

27. Decarboxylation of sodium salts gives methane or benzene. (p. 30 and p
NaOH(s) from soda lime
fusion
CH3COONa(s) CH Na2CO3
NaOH(s) from soda lime
fusion
+ Na2CO3

28. Keto-enol tautomerism
5. Catalytic hydration of alkynes
enol
ketone
Keto-enol tautomerism

29. Keto-enol tautomerism
5. Catalytic hydration of alkynes
enol
Keto-enol tautomerism
aldehyde

30. 6. Ozonolysis of symmetrical alkenes

31. Unsymmetrical alkenes give a mixture of two carbonyl compounds making subsequent purification more difficult.
1. O3
2. Zn dust / H2O

32. Reactions of Aldehydes and Ketones
Nucleophilic Addition Reactions (AdN)
Condensation Reactions (Addition-Elimination)
Iodoform Reactions (Oxidation)
Oxidation Reactions
Reduction Reactions

33. Bonding in the Carbonyl Group
The carbonyl carbon atom is sp2-hybridized
sp2 – 2p head-on overlap   bond
2p – 2p side-way overlap   bond
The  and  bonds in the C = O bond

34. The carbonyl group is planar(sp2-hybridized) and highly polarized due to
(i) Polarization of  bond (inductive effect)
(ii) Polarization of  bond (mesomeric effect) + 

35. Susceptible to nucleophilic attack+ 
50%

36. Bond Enthalpy (kJ/mol) :
C=C (611) < 2 C–C (346) ( bond <  bond)
C=O (749) > 2 C–O (358) ( bond >  bond)
Due to polarization of the C-O  bond

37. Nucleophilic Addition Reactions (AdN)
Acid-catalyzed
More susceptible to nucleophilic attack

38. Nucleophilic Addition Reactions (AdN)
Base-catalyzed
Stronger nucleophile

39. AdN vs AdE
(Non-polar) + 

40. Reaction mechanism Slow (r.d.s.) H+ and Nu added across the C=O bond
Fast

41. Q.52
50% H+
50%
A racemic mixture

42. Reactivity depends on two factors : -
(i) Electronic effect
(ii) Steric effect

43. (i) Electronic effect Electron-deficiency of carbonyl C 
Ease of nucleophilic attack 
Reactivity 

44. > Decreasing reactivity
Decreasing positive charge on carbonyl carbon

45. Carbonyl C is less positive due to delocalization of positive charge to the benzene ring.
Or,
The C-O bond has less  character
 less mesomeric effect

46. Reactivity : -
>

47. (ii) Steric effect No. /bulkiness of R groups at carbonyl C 
Steric hindrance 
Reactivity 

48. Increasing steric hindrance
Decreasing reactivity
>
Increasing steric hindrance

49. pentan-3-one

50. Reactivity of AdN : -
Aldehydes > ketones
Aliphatic > aromatic

51. Q.53
Reactivity : -

52. Examples of AdN
1. Addition of Hydrogen Cyanide

53. 1. Addition of Hydrogen Cyanide

54. Mechanism : - HCN is very toxic  in situ preparation
NaCN + H2SO4  NaHSO4 + HCN

55. Mechanism : - HCN is a weaker nucleophile than CN
NaCN + H2SO4  NaHSO4 + HCN
excess

56. Mechanism : - A mixture of CN/HCN is a buffer of pH  9
NaCN + H2SO4  NaHSO4 + HCN
excess
pKa of HCN = 9.4

57. The reaction mixture is buffered at pH 9 to ensure highest yield at greatest rate.
If pH < 9,
H+ + CN HCN
The equilibrium position shifts to the right
 [CN] 
 Reactivity 

58. The reaction mixture is buffered at pH 9 to ensure highest yield at greatest rate.
If pH > 9,
[H+] 
 The equilibrium position shifts to the left
 Yield 

59. Used for lengthening the carbon chain
1. LiAlH4/dry ether
2. H2O
Dry ether is used as LiAlH4 reacts violently with water
H2O(l) + H(aq)  H2(g) + OH(aq)
from AlH4

60. HCN adds preferentially to C=O leaving C=C and benzene ring unaffected.
At pH 9, H+ is not concentrated enough to trigger electrophilic attack

61. HCN adds preferentially to C=O leaving C=C and benzene ring unaffected.
No reaction
Or, H in HCN is not positive enough to trigger electrophilic attack

62. HCN adds preferentially to C=O leaving C=C and benzene ring unaffected.+

63. Q.57
Cl and HSO4 are much weaker bases and nucleophiles than CN to trigger nucleophilic attacks.

64. Q.54 CH3CH2CHO  CH3CH2CH2COOH excess NaCN H2SO4 H2 Ni 70% H2SO4
reflux

65. 2. Addition of Sodium Hydrogensulphate(IV)
excess & saturated
Excess NaHSO3 should be used to shift the equilibrium position to the right (yield )

66. 2. Addition of Sodium Hydrogensulphate(IV)
excess & saturated
Q.55
Since the equilibrium position lies on the right
Acidity : -OH < -SO3H

67. More stable
Less stable

68. Very sensitive to steric hindrance
 limited to aliphatic aldehyde and sterically unhindered ketones

69. The aldehydes and ketones can be regenerated by treating the bisulphite addition product with H+(aq) or OH(aq)
Used for the purification of carbonyl compounds

70. Q.56
Outline how you can separate a mixture of butanone (b.p. = 79.6°C) and 1-chlorobutane (b.p. = 78.5°C) in ether.
The mixture of butanone and 1-chlorobutane cannot be separated by distillation as
(1) their boiling points are too close
(2) butanone tends to decompose below its b.p.
(p.91, 1st paragraph)

71. Ionic
 water soluble

72. organic layer (with 1-chlorobutane)
aqueous layer (with adduct)

73. CH3COC2H5 + NaCl + H2O + SO2

74. organic layer (with butanone)
aqueous layer (with NaCl)

75. Diethyl ether has a much lower b.p. (34.6C)
 can be removed easily without decomposition of butanone

76. toxic
Not recommended
NaHSO3
NaCN SN

77. Condensation (Addition-Elimination) Reactions
H2O +
Addition

78. Overall reaction : -
phenylhydrazine
HO–NH2
hydroxylamine
NH2–NH2
hydrazine
2,4-dinitrophenylhydrazine
Brady’s reagent
2,4-DNP

79. Reaction with hydroxylamine
cis or trans oxime

80. Reaction with hydrazine

81. Reaction with hydrazine
Examples : -

82. Reaction with phenylhydrazine
phenylhydrazone

83. Reaction with 2,4-dinitrophenylhydrazine
coloured ppt

84. Examples : -

85. Identification of carbonyl compounds
Derivatives (e.g. oximes) of carbonyl compounds are insoluble solids with have sharp m.p.
The carbonyl compounds can be identified by
preparing their solid derivatives followed by
recrystallization and
metling point determination (checked against data books)

86. 2. Reaction with 2,4-Dinitrophenylhydrazine
Brady’s reagent is especially important in this respect since the products (2,4-dinitrophenylhydrazones) are coloured ppt with sharp melting points.

87. Melting point of 2,4-dinitrophenyl-hydrazine (oC)
M.p. of 2,4-DNP derivatives of some aldehydes and ketones
Name
Molecular formula
Melting point of 2,4-dinitrophenyl-hydrazine (oC)
Aldehydes:
Methanal
HCHO
167
Ethanal
CH3CHO
168
Propanal
CH3CH2CHO
156
Butanal
CH3CH2CH2CHO
123
Benzaldehyde
C6H5CHO
237

88. Melting point of 2,4-dinitrophenyl-hydrazine (oC)
M.p. of 2,4-DNP derivatives of some aldehydes and ketones
Name
Molecular formula
Melting point of 2,4-dinitrophenyl-hydrazine (oC)
Ketones:
Propanone
CH3COCH3
128
Butanone
CH3CH2COCH3
115
Pentan-2-one
CH3CH2CH2COCH3
141
Pentan-3-one
CH3CH2COCH2CH3
156
Hexan-2-one
CH3CH2CH2CH2COCH3
107
Phenylethanone
C6H5COCH3
250

89. Q.58 (a) For cyclopentanone,
1. Prepare BOTH oxime and 2,4-DNP derivatives.
Oxime
2,4-DNP
Methyl propyl ketone
58C
144C
cyclopentanone
50C
142C
2. Purify the products by recrystallization.
3. Determine the melting points of the derivatives and compare the results with those in the above table.

90. 4-methylcyclohexanone
Q.58
(a) For 4-methylcyclohexanone,
1. Prepare BOTH oxime and 2,4-DNP derivatives.
Oxime
2,4-DNP
propanone
59C
126C
4-methylcyclohexanone
37C
130C
2. Purify the products by recrystallization.
3. Determine the melting points of the derivatives and compare the results with those in the above table.

91. C. Iodoform Reactions NaOH/I2 + CHI3(s) warm CHI3(iodoform) : -
a yellow crystal with a characteristic smell

92. C. Iodoform Reactions NaOH/I2 + CHI3(s) warm
Used as a test for carbonyl compounds with at least one methyl group attached to the carbonyl C.

93. C. Iodoform Reactions ethanal NaOH/I2 + CHI3(s) warm
The only aldehyde that gives +ve result is
ethanal

94. C. Iodoform Reactions NaOH/I2 + CHI3(s) warm
Give two ketones that give +ve results

95. O.A.
NaOH/I2
+ CHI3(s)
warm
NaOH/I2
warm

96. Iodoform test CH3OH -ve 1 alcohol CH3CH(H)OH only 2 alcohol
CH3CH(CH3)OH,
CH3CH(C2H5)OH, ……
3 alcohol
All give –ve results

97. +ve, turns cloudy immediately
Lucas test : ZnCl2/conc.HCl
CH3OH
-ve
1 alcohol
-ve
2 alcohol
+ve within 5 mins
3 alcohol
+ve, turns cloudy immediately

98. Reaction with Na CH3OH 1 alcohol 2 alcohol 3 alcohol
Colourless gas burns with a pop sound
1 alcohol
Colourless gas burns with a pop sound
2 alcohol
Colourless gas burns with a pop sound
3 alcohol
Colourless gas burns with a pop sound

99. Reaction with KMnO4/H+ CH3OH +ve, gas bubbles(of CO2) 1 alcohol +ve
CH3OH  HCOOH  CO2(g) + H2O
CH3OH
+ve, gas bubbles(of CO2)
1 alcohol
+ve
2 alcohol
3 alcohol
-ve

100. NaOH/I2
+ CHI3(s)
warm H+
Preparation of carboxylic acid with one less C atom than the starting compound

101. Solid removed by filtration
Q.59
heat
KMnO4/OH +
Purification is difficult

102. Only ONE organic product is formed (refer to p.93)
Oxidation reactions of ketones have no synthetic use except
Only ONE organic product is formed (refer to p.93)

103. D. Oxidation 1. Oxidized to carboxylic acids by strong O.A.
O.A. : - KMnO4/H+ or OH
K2Cr2O7/H+
conc. HNO3

104. D. Oxidation 1. Oxidized to carboxylic acids by strong O.A.
Ease of oxidation : -
Aldehyde > ketone
Aliphatic > aromatic

105. 2. Oxidized to salts of carboxylic acids by mild O.A.
O.A. : - Tollen’s reagent
Fehling’s reagent
Benedict’s solution

106. Unstable  freshly prepared
Reactions with Tollen’s reagent (silver mirror test)
Preparation of Tollen’s reagent, [Ag(NH3)2]+
Adding aqueous ammonia solution to silver nitrate solution until the precipitate of silver(I) oxide just redissolves.
2Ag+(aq) + 2OH(aq)  Ag2O(s) + H2O(l)
Ag2O(s) + 4NH3(aq) + H2O(l)
 2[Ag(NH3)2]+(aq) + 2OH(aq)
Unstable  freshly prepared

107.  RCOONH4+ + 2Ag(s) + H2O + 3NH3
Reactions with Tollen’s reagent (silver mirror test) +1 +3 +1
2[Ag(NH3)2]OH + RCHO
 RCOONH Ag(s) + H2O + 3NH3
Forming a silver coating (mirror) on the surface of glassware.

108.  RCOONH4+ + 2Ag(s) + H2O + 3NH3
Reactions with Tollen’s reagent (silver mirror test) +1 +3 +1
2[Ag(NH3)2]OH + RCHO
 RCOONH Ag(s) + H2O + 3NH3
Black solid deposit is formed instead of the silver mirror if the surface of the glassware (e.g. test tube) is not clean.

109.  RCOONH4+ + 2Ag(s) + H2O + 3NH3
Reactions with Tollen’s reagent (silver mirror test) +1 +3 +1
2[Ag(NH3)2]OH + RCHO
 RCOONH Ag(s) + H2O + 3NH3
No reaction with ketones
Aliphatic aldehyde > aromatic aldehyde

110.  RCOONH4+ + 2Ag(s) + H2O + 3NH3
Reactions with Tollen’s reagent (silver mirror test) +1 +3 +1
2[Ag(NH3)2]OH + RCHO
 RCOONH Ag(s) + H2O + 3NH3
Forming highly explosive silver nitride when the resulting mixture is heated to dryness
2Ag3N(s)  6Ag(s) + N2(g) + energy

111. Preparation of Fehling’s reagent
Reactions with Fehling’s reagent/Benedict’s solution
Preparation of Fehling’s reagent
Mixing solution A (CuSO4(aq)) with solution B (tartrate / excess NaOH)
Deep blue solution due to complex formation of Cu2+ with tartrate

112. Preparation of Benedict’s solution
Reactions with Fehling’s reagent/Benedict’s solution
Preparation of Benedict’s solution
Mixing solution A (CuSO4(aq)) with solution B (citrate / excess NaOH)
Deep blue solution due to complex formation of Cu2+ with citrate

113. Forming a reddish brown ppt of Cu2O
Reactions with Fehling’s reagent/Benedict’s solution
from Cu(II) complex +1 +3 +2 +1
RCHO + 2Cu NaOH + H2O
 RCOONa+ + Cu2O(s) + 4H+
Forming a reddish brown ppt of Cu2O

114. Only aliphatic aldehydes give +ve results
Reactions with Fehling’s reagent/Benedict’s solution +1 +3 +2 +1
RCHO + 2Cu NaOH + H2O
 RCOONa+ + Cu2O(s) + 4H+
Only aliphatic aldehydes give +ve results
No reaction with aromatic aldehydes and ketones.

115. Tollen’s /Fehling’s reagents are used to distinguish between aldehydes and other organic compounds

116. Reagents commonly used to distinguish between aldehydes and ketones
Result
Reagent
Aldehyde
Ketone
KMnO4/H+
Give acids with the same number of C atoms readily (Purple to colourless or brwon)
More difficult, gives acids of fewer C atoms
(Purple to colourless or brown)

117. Give acids with the same number of C atoms readily (Orange to green)
Reagents commonly used to distinguish between aldehydes and ketones
Result
Reagent
Aldehyde
Ketone
K2Cr2O7/H+
Give acids with the same number of C atoms readily (Orange to green)
No observable change

118. Silver mirror is formed
Reagents commonly used to distinguish between aldehydes and ketones
Result
Reagent
Aldehyde
Ketone
Tollen’s reagent
Silver mirror is formed
No observable change

119. Reddish brown ppt is formed with aliphatic aldehydes only
Reagents commonly used to distinguish between aldehydes and ketones
Result
Reagent
Aldehyde
Ketone
Fehling’s reagent
Reddish brown ppt is formed with aliphatic aldehydes only
No observable change

120. Reagents commonly used to distinguish between aldehydes and ketones
Result
Reagent
Aldehyde
Ketone
I2/NaOH (Iodoform test)
Yellow ppt is formed for ethanal only
Yellow ppt is formed for ketones with -CH3 attached to carbonyl group

121. No observable except with propanone
Reagents commonly used to distinguish between aldehydes and ketones
Result
Reagent
Aldehyde
Ketone
Schiff’s reagent
Pink colour appears
No observable except with propanone

122. Schiff’s reagent
Preparation : - Passing SO2 to magenta (a red dye) solution until it becomes colourless

123. Schiff’s reagent
Principle : - SO2 bleaches the dye leaving a colourless solution
SO2 + H2O H2SO3
H2SO3 + H2O HSO3 + H3O+
HSO3 + H2O SO32 + H3O+
SO32 + magenta SO42 + colourless solution

124. SO2 + H2O H2SO (1)
H2SO3 + H2O HSO3 + H3O (2)
HSO3 + H2O SO32 + H3O (3)
SO32 + magenta SO42 + colourless solution (4)
Sterically unhindered aldehydes or propanone react with HSO3 to give bisulphite adduct

125. SO2 + H2O H2SO (1)
H2SO3 + H2O HSO3 + H3O (2)
HSO3 + H2O SO32 + H3O (3)
SO32 + magenta SO42 + colourless solution (4)
[HSO3] 
 Shifting (1) & (2) to the right (3) & (4) to the left
 SO32/SO2 is removed
 The red colour of magenta is restored

126. Q.60
Step 1 : Qualitative tests
Iodoform test  +ve result
Schiff’s reagent  +ve result
The liquid is either ethanal or propanone

127. Q.60
Step 2 : Confirmatory tests
Preparation of 2,4-DNP derivatives
Purification of products
Melting point determination
Comparison against values in data book

128. E. Reduction (to alcohols)
1. Reactions with H2/Ni, Pt or Pd
High T & P Ni

129. 2. Reactions with LiAlH4 or NaBH4
Both LiAlH4 and NaBH4 have no reaction with C=C double bond.

130. 2. Reactions with LiAlH4 or NaBH4
NaBH4 is less reactive than LiAlH4
 can be used in protic solvent
 cannot reduce carboxylic acids and their derivatives to alcohols

131. Q.61(a) CH3COOH CH3CH2COOH CH3CH2CN PBr3 CH3CH2OH CH3CH2Br heat
1. LiAlH4/dry ether
2. H3O+
reflux
H3O+
CH3CH2CN
C2H5OH
CN
PBr3
heat
CH3CH2Br

132. Q.61(b) CH3COOH HCOOH CH3CH2OH 1. LiAlH4/dry ether 1. I2/NaOH 2. H3O+

133. Q.61(c)
conc. H2SO4
heat
K2Cr2O7/H+
reflux
H3O+(aq)

134. Q.61(d)
H3O+(aq)
NH2OH
K2Cr2O7/H+
reflux

135. Explain why there is no such a compound called “ethanone”.
31.2 Nomenclature of Carbonyl Compounds (SB p.4)
Let's Think 1
Explain why there is no such a compound called “ethanone”.
Answer
Ketones are compounds with the carbonyl group situated between two carbon chains or carbon rings. Therefore, the simplest ketone is the one with three carbon atoms. “Ethanone”, however, suggests that there are two carbon atoms in it and it does not exist.
Back

136. 31.2 Nomenclature of Carbonyl Compounds (SB p.4)
Check Point 31-2
(a) Draw the structural formulae of all carbonyl compounds having the molecular formula C4H8O. Give their IUPAC names.
Answer
(a)

137. Check Point 31-2 Answer Back
31.2 Nomenclature of Carbonyl Compounds (SB p.4)
Back
Check Point 31-2
(b) Draw the structural formulae of all straight-chain carbonyl compounds having the molecular formula C5H10O. Give their IUPAC names.
Answer
(b)

138. 31.3 Physical Properties of Carbonyl Compounds (SB p.7)
Example 31-3
(a) In each pair of compounds below, select the one you would expect to have a higher boiling point.
(i) A: CH3CH2CHO B: CH3CH2CH2OH
(ii) C: D:
(iii) E: CH3CH2CH2CHO F: CH3CH2CH2CH3
(iv) G: H: HOCH2CH2CH2OH
(a) (i) B (ii) D (iii) E (iv) H
Answer

139. 31.3 Physical Properties of Carbonyl Compounds (SB p.7)
Example 31-3
(b) Propanone, CH3COCH3, is completely soluble in water, but octan-4-one, CH3CH2CH2COCH2CH2CH2CH3, is almost insoluble in water. Explain their difference in solubility.
Answer
(b) The solubility of ketones in water decreases as the hydrophobic hydrocarbon portion lengthens.
Back

140. Is dehydrogenation of alcohols an oxidation or a reduction process?
31.4 Preparation of Carbonyl Compounds (SB p.8)
Let's Think 2
Is dehydrogenation of alcohols an oxidation or a reduction process?
Answer
Dehydrogenation of alcohols is an oxidation process.
Back

141. 31.4 Preparation of Carbonyl Compounds (SB p.9)
Let's Think 3
What are “primary alcohols” and “secondary alcohols”?
Answer
Primary alcohols have no or only one alkyl or aryl group directly bonded to the carbon atom bearing the hydroxyl group.
Secondary alcohols have two alkyl or aryl groups directly bonded to the carbon atom bearing the hydroxyl group.
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142. 31.5 Reactions of Carbonyl Compounds (SB p.14)
Let's Think 4
Both alkenes and carbonyl compounds are unsaturated
compounds. Their principal reactions are addition reactions. What is the major difference between the addition reactions of the two groups of compounds?
Answer
Alkenes are nucleophiles. They undergo electrophilic addition reactions readily.
Carbonyl compounds are electrophiles. They undergo nucleophilic addition reactions readily.
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143. Check Point 31-5
(a) Describe briefly how you can distinguish between two carbonyl compounds having similar boiling points.
The two compounds can be distinguished by determining the melting points of their 2,4-dinitrophenylhydrazone derivatives.

144. 31.5 Reactions of Carbonyl Compounds (SB p.18)
Check Point 31-5
Draw the structural formulae of the major organic products A to C in the following reactions:
(i) CH3CH2CHO  A  B
(ii) CH3CH2CHO  C
KCN / H2SO4
conc. HCl
20 oC
2,4-dinitrophenylhydrazine
Answer

145. Check Point 31-5 Back 31.5 Reactions of Carbonyl Compounds (SB p.18)
(i) A: B:
(ii) C:

146. 2. Reaction with 2,4-Dinitrophenylhydrazine
Purified by recrystallization from ethanol
After recrystallization,
 the products are filtered under suction
 washed with a few drops of ethanol

147. 2. Reaction with 2,4-Dinitrophenylhydrazine
The set-up of suction filtration

148. 2. Reaction with 2,4-Dinitrophenylhydrazine
Their m.p. can be determined
Compare the values with those from data books
 identify the original aldehyde or ketone