Chemistry 20
Chapter 9
Aldehydes and Ketones
Carbonyl group
O
C
Aldehydes
Ketones
Carboxylic acids
Esters
O
CH3 COCH2 CH3+ N aOH
Ethyl acetate
Sodium
hydroxide
H
h
Aldehydes and Ketones
O
• In an aldehyde, at
least one H atom is
attached to a
carbonyl group.
• In a ketone, two
carbon groups are
attached to a
carbonyl group.
C
Naming Aldehydes
Step 1
Select the longest carbon chain
that contains the carbonyl group (C=O).
Step 2
Number from the end nearest C=O group.
Step 3
Change the ending of parent alkane from -e to -al.
No number for carbonyl group C=O (it always comes first).
Step 4
Give the location and name of each substituent
(alphabetical order) as a prefix to the name of the
main chain.
Naming Aldehydes
• Common names for the first two aldehydes use the prefixes “form” (1C)
and “acet” (2C) followed by “aldehyde”.
O
H─C─H
methanal
(formaldehyde)
O
CH3─ C ─H
ethanal
(acetaldehyde)
O
CH3─CH2─ C ─H
propanal
CH3
O
CH3─CH─CH2─ C─H
4
3
2
3-Methylbutanal
1
O
Cl─CH2─CH2─ C─H
3
2
1
3-Chloropropanal
Naming Ketones
Step 1
Select the longest carbon chain
that contains the carbonyl group (C=O).
Step 2
Number from the end nearest C=O group.
Step 3
Change the ending of parent alkane from -e to -one.
Use the number to show the location of C=O.
Step 4
Give the location and name of each substituent
(alphabetical order) as a prefix to the name of the
main chain.
Naming Ketones
• In the common name, name the “alkyl groups” alphabetically attached
to the carbonyl group and add the word “ketone”.
O
CH3 ─ C ─CH3
O
CH3─C─CH2─CH3
1
Propanone
(dimethyl ketone)
2
3
4
2-Butanone
(ethyl methyl ketone)
e
e
O O
O C
H
1
2 O1 2
2
1
5
3
2
4
+ O2
6
Cl
2
4
5
Acetone
5-Meth yl-3-h exanone
Acetone
1
2
3
4
+ O2
2
6
1
2
5-Meth
yl-3-h exanone
2-Methylcycloh exanone
O
O
O
H
OH
3-Chloro Benzaldehyde
O
2-Methylcycloh
exanone
O
O1 23 45
6
O
2
Benzoic acid
O
3
O
1
Benzaldehyde
2-Methylcycloh
exanone
2-Methylcycloh exanone
5-Meth yl-3-h exanone
1
2
O
C
O
C
5
1
6
2
1
2
5-Meth
yl-3-h exanone
2-Methylcycloh exanone
2-Methylcycloh exanone
2-Meth
O
5
6
O
2
1
H
lbutan al
al
3
O
O
3
1
O2
H
3
1
2
Hexanal
H
2-Prop enal
(Acrolein)
4
4
2
3
1
2
H
2-Prop enal
(Acrolein)
H
3-Methylbutan al
OH O
4
5
4
3
1
3
1
H
3-Hydroxy-4-meth ylp entanal
NH2
3-Amino-4-ethyl-2-h exanone
O
OH O
5
4
3
H
O
3-Hydroxy-4-meth
1ylp entanal
6
4 3 2
OH O
5
1
1
H
O
1 ylp entanal
3-Hydroxy-4-meth
6
4 3 2
NH2
3-Amino-4-ethyl-2-h exanone
6
4
3
2
1
NH2
3-Amino-4-ethyl-2-h exanone
3-A
Physical properties of Aldehydes and Ketones
1. They have strong odors (ketones have pleasant odors).
δ-
2. They are polar compounds.
C-O
δ+
3.5-2.5 = 1
3. Only dipole-dipole interactions (no hydrogen bonding).
4. Low boiling points compare to amines and alcohols.
Higher than hydrocarbons.
H
5. Soluble in water (no soluble in nonpolar compounds).
δ-
Hydrogen bond with water.
δ+
δ+
H
O
Chemical properties of Aldehydes and Ketones
1. Oxidation: only for aldehydes (not for ketones).
O
O
CH3─CH2─CH2─CH2─C─H
=
=
K2Cr2O7
CH3─CH2─CH2─CH2─C─OH
H2SO4
Pentanal
Pentanoic acid
K2Cr2O7: Oxidizing agent
Liquid aldehydes
are sensetive to oxidation.
O
C
2
H
O
C
+ O2
2
OH
No oxidizing agent
Benzaldehyde
Benzoic acid
Tollen’s Test (Silver-mirror test)
Tollens’ reagent is specific for the oxidation of aldehydes (not for ketones).
O
+
R-C-H + 2 Ag( NH3 ) 2 + 3 OH
A ldehyde Tollens'
reagen t
O
R-C-O + 2 Ag + 4 NH3 + 2 H2 O
Carboxylic Silver
an ion
mirror
Chemical properties of Aldehydes and Ketones
2. Reduction:
Like reducing the alkene (C = C) to alkane (C – C):
– Reduction of an aldehyde gives a primary alcohol (-CH2OH).
– Reduction of a ketone gives a secondary alcohol (-CHOH-).
=
O
+ H2
Pentanal
1-Pen tan ol
=
O
CH3─C─CH2─CH3
2-butanone
CH3─CH2─CH2─CH2─CH2─ OH
+ H
2
tran si ti o n
m etal catal y st
OH
-
CH3─CH2─CH2─CH2─C─ H
tran si ti on
metal cataly st
CH3─CH─CH2─CH3
2-butanol
Chemical properties of Aldehydes and Ketones
Sodium borohydride: produces hydride ion: H-
NaBH4
Reducing agent
Reduction mechanism:
H :-
+
C O
H
C O
-
H3 O +
H
C O-H
Hydride
ion
O
NaBH4
OH
+
H3 O
O-H
H
Chemical properties of Aldehydes and Ketones
Advantage of NaBH4:
Reduction by NaBH4 does not affect a carbon-carbon double bond
or an aromatic ring.
O
C
H
1 . NaBH4
CH2 OH
2 . H23O
O+
Cin namaldehyde
Cinnamyl alcoh ol
Chemical properties of Aldehydes and Ketones
3. Addition of alcohols (hemiacetals):
H of the alcohol adds to the carbonyl oxygen and
OR adds to the carbonyl carbon.
O
H
C + O-CH2 CH3
H
Benzald ehyde Eth anol
O-H
C OCH2 CH3
H
A hemiacetal
unstable
Chemical properties of Aldehydes and Ketones
3. Addition of alcohols (Acetals):
O-H
Acid
C OCH2 CH3 + H O-CH 2 CH 3
H
A hemiacetal
Ethanol
O CH2CH3
C OCH2 CH3 + H2O
H
An Acetal
Chemical properties of Aldehydes and Ketones
3. Addition of alcohols (hemiacetals):
If –OH is part of the same molecule that contains C=O.
O
5
4
3
2
1
H
O-H
4-Hyd roxypentanal
redraw to
show the -OH
an d -CHO clos e
to each oth er
3
2
1
4
5
O
H
C
H
O
H
O-H
O
A cyclic hemiacetal