Chemistry notes aldehydes ketones and carboxylic acid

Notes provide aldehydes ketones and carboxylic acid this notes are good for teaching

1. Aldehydes and ketones
Chapter 15

2. The carbonyl group
•Aldehydes and ketones are among the first examples of compounds that
possess a C-O double bond that we’ve seen (oxidation of alcohols section,
Ch-14).
•This group is called a carbonyl group, and it has very different chemical
properties than a C-C double bond in alkenes:
•Because oxygen is more electronegative than carbon, the bond is polar.
•Bond angles are about 120
o
around the carbon atom (see VSEPR theory).

+

C O

3. The carbonyl group
•The local geometry around the carbonyl group
is trigonal planar. The rest of the molecule
doesn’t have to be planar:
H
H
H CH
3
CH
3
CH
3
CH
3
CH
3
C
C
O
C
C
Local trigonal
planar geometry

4. Compounds containing the carbonyl group
•The following classes of organic compounds involve the
carbonyl group:
–Aldehydes have a H-atom or a carbon substituent (alkyl,
cycloalkyl, aromatic) bound to a CHO group (carbonyl
group bound to a H-atom):
C H
O
R
C H
O
C H
O
CH
3C H
O
H
General formula for aldehyde:

5. Compounds containing the carbonyl group
•Ketones have two carbon substituents (akyl,
cycloalkyl, aromatic and not necessarily the same)
R'C
O
R
CH
2CH
3
CH
CH
3
CH
3
C
O
C
O
CH
3C
O
CH
3
General formula for ketones:

6. Compounds containing the carbonyl group
•Carboxylic acids have an OH (hydroxyl) group bound to the
carbonyl carbon, in addition to either a H-atom or a carbon
group (alkyl, cycloalkyl, aromatic):
C OH
O
R
C OH
O
C OH
O
H CH
CH
3
CH
3 CH
2C OH
O
C OH
O
CH
3
General formula for carboxylic acids:

7. Compounds containing the carbonyl group
•Esters have a carbonyl group singly bound to an oxygen,
which in turn is bound to a carbon group (alkyl, cycloalkyl, or
aromatic). The other bond to the carbonyl is either to a H-
atom or another carbon group:
R'OC
O
R
CH
2
CH
3
CH
CH
3
OC
O
CH
2
CH
3
OC
O
CH
3O CH
3
C
O
H
General formula for an ester:

8. Compounds containing the carbonyl group
•Amides are the first nitrogen-containing organic compounds we’ve seen.
In these compounds, the carbonyl group is bound to a nitrogen (an amino
group), in addition to either a H-atom or a carbon group (alkyl, cycloalkyl,
aromatic). The R’ and R” groups of the amino group may either be H or
carbon groups:
R"
R'
C N
O
R
C NC N
CH
2
CH
3
CH
2
C NH
2
O
CH
3
H
O
CH
3
CH
3
CH
3
O
H
General formula for an amide:

9. Aldehyde and ketone functional group
•As we saw, alcohols can be used to create aldehydes and
ketones. Oxidation of a primary alcohol yields an aldehyde:
•And oxidation of a secondary alcohol yields a ketone:
[O]
CH
2
CH
3
C H
O
CH
2
CH
3
C
H
H
OH
[O]
CH
2
CH
3
C CH
3
O
CH
2
CH
3
C
H
CH
3
OH

10. Aldehyde and ketone functional group
•Cyclic aldehydes are not possible, because in order for the carbonyl group
to be part of the ring structure, two bonds to carbon groups would be
required.
•Aldehydes may incorporate ring structures, but not be part of the ring.
•Also, note that cyclic ketones aren’t heterocyclic compounds.
a cyclic ketone
a cyclic diketone
an aldehyde incorporating
a cyclic compound
C H
O
O
O
O

11. CH
CH
3
O
H
CH
3
C H
O
CH
2CH
2
C H
O
CH
2CH
3
Nomenclature for aldehydes
•IUPAC rules:
–Select as the parent chain the longest continuous chain that includes
the carbonyl carbon
–Name the parent chain by changing the corresponding alkane name
(ending with “e”) to an ending with “al”
–Number the parent chain assuming the carbonyl carbon is C-1
–Identify substituents on the parent chain as before, at the beginning
of the compound’s name.
Propanal
4-Methylpentanal
2-Ethylpentanal

12. Nomenclature for aldehydes
•For aldehydes having short carbon chains, the following
common names are usually encountered:
•The following aromatic aldehyde is called benzaldehyde:
Formaldehyde
(Methanal)
Acetaldehyde
(Ethanal)
Propionaldehyde
(Propanal)
Butyraldehyde
(Butanal)
C H
O
CH
2
CH
3C H
O
CH
3
C H
O
CH
2
CH
2
CH
3CH H
O
C
H
O
4-Bromobenzaldehyde 4-Hydroxy-2-methylbenzaldehyde
OH
CH
3
C
H
O
Br
C
H
O
Derivatives:
IUPAC
Benzaldehyde

13. Nomenclature for ketones
•IUPAC:
–Select as the parent chain the longest continuous chain that involves
the carbonyl carbon
–Name the parent chain by removing the “e” from the corresponding
alkane name and adding “one”
–Number the chain to give the carbonyl group the lowest numbering.
The number goes before the parent chain name
–Determine the number and location of substituents and number them
accordingly
–For cyclic ketones, the carbonyl carbon is C-1 and the name begins
with “cyclo”
3-Hexanone
4-Methyl-2-hexanone
3-Bromo-2-butanone
2-Methylcyclopentanone
CH
3 O
CH
CH
3
Br
C
O
CH
3
CH
2CH
3
CH C CH
3
O
CH
2CH
3
CH
2CH
3C
O
CH
2CH
2CH
3

14. Nomenclature for ketones
•The common system of naming ketones is
similar to what we saw for ethers:
Ethyl propyl ketone
Isobutyl methyl ketone1-Bromoethyl methyl ketone
CH
CH
3
C CH
3
O
CH
2CH
3CH
2CH
3C
O
CH
2CH
2CH
3 CH
CH
3
Br
C
O
CH
3

15. Isomerism for aldehydes and ketones
•Aldehydes and ketones that have a given number of carbon
atoms are functional group isomers. (This is the third group of
compounds we have seen that have this relationship; others
were alcohols/ethers and thiols/thioethers)
Propanone
Propanal
C3H6O
CH
2
CH
3C
O
H
C
CH
3
O
CH
3
a ketone an aldehyde

16. Isomerism for aldehydes and ketones
•Positional isomers are possible for ketones (but not
aldehydes)
•And skeletal isomers are possible for both
3-Pentanone
C5H10O
2-Pentanone
CH
2
CH
3CH
2
C
O
CH
3
CH
2
CH
3
CH
2
CH
3 C
O
C5H10O
2-Pentanone
3-Methyl-2-butanone
CH
CH
3
CH
3C
O
CH
3
CH
2
CH
3CH
2
C
O
CH
3

17. Common aldehydes and ketones
•Aldehydes are often recognizable by their
“sweet” smells:
Vanillin
(vanilla flavoring)
Benzaldehyde
(almond flavoring)
Cinnamaldehyde
(cinnamon flavoring)
C
O
HCH
CHC
H
O
O
CH
3
OH
C
H
O

18. Common aldehydes and ketones
•Some ketones (e.g. acetone) have a “sweet”
smell also). Other examples are:
2-Heptanone
(clove flavoring)
Butanedione
(butter flavoring)
Carvone
(spearmint flavoring)
CH
3
O
CH
3 CH
2
C
CH
3
O
C
CH
3
O
CH
3
C
O
C
CH
3
(CH
2)
4

19. Naturally occurring aldehydes and
ketones
•A wide variety of
biologically relevant
molecules possess
aldehyde and/or ketone
functional groups:
Testosterone
Progesterone
Cortisone
OH
O
CH
3
CH
3
O
O
CH
3
O
CH
3
CH
3
O
OH
CH
3
CH
3
O
CH
2OH
D-Glucose
CH
2OHC
H
C
H
C
H
C
H
OHOH
OH
OH
C
H
O

20. Physical properties of aldehydes and
ketones
•Neither aldehydes nor ketones possess the ability to H-bond
with other molecules like themselves. Consequently, boiling
points for aldehydes and ketones are lower than for alcohols
of similar molar mass.
•The C-O double bond in these molecules is polar, so dipole-
dipole forces do exist. As a result, their boiling points tend to
be higher than for alkanes of similar molar mass.

+

C O

21. Physical properties of aldehydes and
ketones

22. Physical properties of aldehydes and
ketones
•Water molecules can interact (H-bond) with the non-bonding
pairs of the carbonyl group oxygen atom, enabling aldehydes
and ketones that have small carbon chain components to be
water-soluble.
•As we saw for alcohols, the greater the carbon chain length,
the lower the water-solubility (makes the molecule less polar)

H-bond
..



.
.
..
..
H
OH
OC

23. Physical properties of aldehydes and
ketones

24. Physical properties of aldehydes and
ketones
Comparing an aldehyde and a ketone of a given number of C-atoms, the ketone
is generally more soluble. Why?

25. Preparation of aldehydes and ketones
•We saw already (in Ch-
14) how alcohols can be
oxidized to form
aldehydes and ketones.
•Primary (1
o
) alcohols are
oxidized to aldehydes
(and subsequently to
carboxylic acids)
•Secondary (2
o
) alcohols
are oxidized to ketones
1
o
alcohol
[O]
[O]
2
o
alcohol
aldehyde
ketone
H
O
CR
H
H
OH
CR
O
CR
H
OH
CR R'R'
[O] = KMnO
4
or K
2
Cr
2
O
7

26. Oxidation and reduction of aldehydes
and ketones
•Aldehydes can be oxidized easily to carboxylic
acids
•Ketones are resistant to oxidation.
Oxidation reactions
aldehyde
[O]
[O]
ketone
no reaction
carboxylic acid
O
CR
OH
O
CRH
O
CR
R'

27. Oxidation and reduction of aldehydes
and ketones
•There are several tests that have been
developed to determine the presence of
aldehydes, based on their oxidation to
carboxylic acids:
–Tollen’s test
–Benedict’s test
Oxidation reactions
Ag
+
NH3, H2O
heat
Ag
silver metalcarboxylic acidaldehyde
H
O
CR OH
O
CR+ +
Cu
2+
Cu2O
reddish solidcarboxylic acidaldehyde
H
O
CR OH
O
CR ++

28. Oxidation and reduction of aldehydes
and ketones
•Both aldehydes and
ketones are easily
reduced to alcohols
with H
2
in the
presence of a
catalyst (Ni, Pt, Cu).
Reduction reactions

29. Reactions of aldehydes and ketones
with alcohols
•When aldehydes and ketones react with alcohols
in the presence of an acid, the resulting product
is called a hemiacetal. Hemiacetals can further
react with alcohols to form acetals:
aldehyde or ketone + alcoholhemiacetal
hemiacetal + alcohol  acetal
acid
catalyst
acid
catalyst
Hemiacetals

30. Reactions of aldehydes and ketones
with alcohols
hemiacetal
aldehyde alcohol



hemiacetal

ketone alcohol
 


R
O
C
H
O
OR
HO
C
R O
HO
C
O
H
R
HO
C
R
H
O
HO
C
H
O
R H
O
C
R'
R"
R'
R"
R"
R'
R'
R'
R'
+
+
A hemiacetal is an organic compound that possesses a carbon atom that is bound to
an OH (hydroxy) group and an OR (alkoxy) group

31. Reactions of aldehydes and ketones
with alcohols
•Hemiacetal formation can also involve a carbonyl group and
OH group on the same molecule. Here is an important
process which involves this reaction:
See this again in Ch-18
Hemiacetals
Cyclic hemiacetals are stable,
unlike non-cyclic hemiacetals

32. Reactions of aldehydes and
ketones with alcohols
•Hemiacetals can be converted to acetals in the presence of an
alcohol and a catalytic amount of acid:
Acetals


H2O
acetal

H2O
acetalhemiacetal
(derived from
a ketone)
hemiacetal
(derived from
an aldehyde)
HO
R C O
O
R C O
O
R
H
C OR
H
OC
HO
HO
O
H
R
HO
C
R'
R" R"' OH
R'
R"'
R"
R'
R"
R" OH
R"
R'R'+
++
+

33. Reactions of aldehydes and
ketones with alcohols
•Indicate whether each of the following structures is a
hemiacetal, acetal, or neither:
OH
CH
2CH
3
OH
CH
2
CH
3
C
OH
O
CH
3
C CH
3CH
3
C
CH
3
CH
3O
CH
3
CHCH
3
CH
3
O

34. Reactions of aldehydes and
ketones with alcohols
•Acetals can be isolated and used in subsequent chemical reactions.
(Hemiacetals are less stable and generally can’t be isolated.)
•If an acetal is treated with acid in the presence of water, a hydrolysis
reaction occurs
Acetals
Hydrolysis reaction: a reaction of a compound with water in which the compound splits into
two or more fragments.
H2O
acid
catalyst
acetal (derived
from an aldehyde)
acetal (derived
from a ketone)
ketone
aldehyde alcohol 1 alcohol 2
H2O
acid
catalyst
alcohol 2alcohol 1
H
O
R C O OHOH
OHOH
O
CR
O
R C O
H
O
CR
R"'
R" R"R'
R"'R"R'
R"'
R'
R"+ +
+
+
++

35. Reactions of aldehydes and
ketones with alcohols
•Draw the aldehyde/ketone and alcohols that will result when the acetals
below are treated with acid/H
2O:
aldehyde/ketone alcohols
CH
CH
3
CH
2CH
3
CCH
3
CH
2CH
3 O
O
CH
3
CH
2CH
3
OCH
3
C
CHCH
3
CH
3
O
H
O CH
3
C
CH
2CH
3O
CH
3CH
2CH
3

36. Sulfur-containing carbonyl groups
•Sulfur analogues of aldehydes and ketones are known. The sulfur
atom can either replace the carbon or the oxygen of the carbonyl
group.
•In the first case, the resulting compounds are called thioaldehydes
or thioketones, and these are generally unstable:
•In the second case, sulfoxides result:
a thioaldehyde a thioketone
R'C
S
RC H
S
R
a sulfoxide
R'S
O
R

37. Sulfur-containing carbonyl groups
•The best known example of a sulfoxide is Dimethyl sulfoxide
(DMSO), which is a sulfur analogue of acetone:
•DMSO is an excellent solvent; it can dissolve a wide variety of
polar and non-polar substances.
DMSO acetone
C CH
3
O
CH
3
S CH
3
O
CH
3
-
.
.
.
....
.
.
.
.
...
CH
3
O
SCH
3 CH
3
O
SCH
3
+