1

2

Structures of Aldehydes & Ketones

3

• Both aldehydes and ketones contain a carbonyl ( C=O) group.

RC

H

O

ArC

H

O

aldehydes

RC

R

O

ArC

R

O

ketones

ArC

Ar

O

4

•In a linear expression, the aldehyde group is often written as:

CHO

H3CC

H

O

is equivalent to CH3CHO

5

•In the linear expression of a ketone, the carbonyl group is written as:

CO

H3CC

CH3

O

is equivalent to CH3COCH3

6

Naming Aldehydes & Ketones

7

IUPAC Rules for Naming Aldehydes1. To establish the parent name, select the

longest continuous chain of carbon atoms that contains the aldehyde group.

2. The carbons of the parent chain are numbered starting with the aldehyde group. Since the aldehyde group is at the beginning (or end) of a chain, it is understood to be number 1.

8

IUPAC Rules for Naming Aldehydes

3. Form the parent aldehyde name by dropping the –e from the corresponding alkane name and adding the suffix –al.

4. Other groups attached to the parent chain are named and numbered as we have done before.

9

H3CC

H

O

ethanal

HC

CH2CH2CHCH2CH3

O

CH34-methyhexanal

2 3 4 5 61

Naming Aldehydes

4-methylhexanal

ethanal

10

11

Common Names for Aldehydes

HC

H

O

formaldehydeH

CCH3

O

acetaldehyde

CH

O

benzaldehyde

12

IUPAC Rules for Naming Ketones

1. To establish the parent name, select the longest continuous chain of carbon atoms that contain the ketone group.

2. Form the parent name by dropping the –e from the corresponding alkane name and add the suffix –one.

13

IUPAC Rules for Naming Ketones

3. If the chain is longer than four carbons, it is numbered so that the carbonyl group has the smallest number possible; this number is prefixed to the parent name of the ketone.

4. Other groups attached to the parent chain are named and numbered as we have done before.

14

Naming Ketones

H3CC

CH3

O

propanone

H3CH2CC

CH2CH2CHCH2CH3

O

CH36-methyl-3-octanone

2 3 4 51H3C

CCH2CH2CH3

O

2-petanone

4 51 23 6 7 8

2-pentanone

15

Common Names for Ketones

H3CC

CH3

O

propanoneacetone

H3CC

CH2CH3

O

butanonemethyl ethyl ketone, MEK

16

Bonding and Physical Properties

17

Bonding• The carbon atom of the carbonyl group

is sp2-hybridized and is joined to three other atoms by sigma bonds.

• The fourth bond is made by overlapping p electrons of carbon and oxygen to form a pi bond between the carbon and oxygen atoms.

18

Bonding• Because the oxygen atom is considerably

more electronegative than carbon, the C=O group is polar.

• Many of the chemical reactions of aldehydes and ketones are due to this polarity.

C O + -

19

Properties• Unlike alcohols, aldehydes and ketones

cannot hydrogen-bond to themselves, because no hydrogen atom is attached to the oxygen atom of the carbonyl group.

• Aldehydes and ketones, therefore, have lower boiling points than alcohols of comparable molar mass.

2020

Effect of Hydrogen Bonding on Physical Properties

Alcohols can undergohydrogen bonding resulting in higher boiling points andhigher solubility.

Aldehydes and ketones cannot undergo hydrogen bonding resulting in lower boiling points and lower solubility.

21

Mole Weight Boiling point oC

22

Chemical Properties of Aldehydes &

Ketones

23

Reactions of Aldehydes & Ketones

• Oxidation– aldehydes only

• Reduction– aldehydes and ketones

• Addition– aldehydes and ketones

24

Oxidation of Aldehydes• Aldehydes are easily oxidized to carboxylic

acids by a variety of oxidizing agents, including (under some conditions) oxygen of the air.

RC

H

O

+ Cr2O72- + 8 H+

3

RC

OH

O3

+ 3 Cr3+ + 4H2O

25

Tollens’ Silver Mirror Test

• Tollens’ reagent,which contains Ag+, oxidizes aldehydes, but not ketones.

• Ag+ is reduced to metallic Ag, which appears as a “mirror” in the test tube.

Ag+ + e– → Ag(s)

RC

H

O

+ 2 Ag+

RC

O-NH4+

O

NH3H2O

+ 2 Ag (s)

26

28

Fehling and Benedict Tests• Benedict’s reagent,

which contains Cu2+ ions in an alkaline medium,

reacts with aldehydes that have an adjacent OH group.

• an aldehyde is oxidized to a carboxylic acid, while Cu2+ is reduced to give brick red Cu2O(s).

29

Increasing amounts of reducing sugar

green orange red brown

30

Tollens, Fehling & Benedict Tests• Because most ketones do not give a

positive with Tollens, Fehling, or Benedict solutions, these tests are used to distinguish between aldehydes and ketones.

RC

R

O

+ 2 Cu+2 NaOHH2O no reaction

RC

R

O

+ 2 Ag+ NH3H2O no reaction

31

Biochemical Oxidation of Aldehydes

• When our cells ‘burn’ carbohydrates, they take advantage of the aldehyde reactivity.

• The aldehyde is oxidized to a carboxylic acid and is eventually converted to carbon dioxide, which is then exhaled.

• This stepwise oxidation provides some of the energy necessary to sustain life.

3232

Reduction of Aldehydes & KetonesAldehydes and ketones are easily reduced to alcohols using LiAlH4,

NaBH4 , or H2/Ni .

Aldehydes yield primary alcohols (1) while ketones yield secondary alcohols ( 2) .

33

Addition Reactions of Aldehydes & Ketones

• Common addition reactions:– Addition of alcohols

• hemiacetal, hemiketal, acetal, ketal– Grignard preparations of alcohols– 2,4-dinitrophenylhydrazine (2,4-DNP)

3434

Addition of Alcohols

Aldehydes react with alcohols and a trace of acid to yield hemiacetalsas shown here.

3535

Addition of AlcoholsIn the presence of excess alcohol and a strong acid such as dry HCl,aldehydes or hemiacetals react with a second molecule of the alcohol to yield an acetal.

3636

Intramolecular Addition of Alcohols

Cyclic hemiacetals or hemiketals can form when the alcohol and the carbonyl group exist within the same molecule .

37

Addition of Alcohols to Aldehydes and Ketones

OH

OR'C

RH

OH

OR'C

RR

OR'

OR'C

RH

OR'

OR'C

RR

hemiacetal hemiketal acetal ketal

38

Grignard preparations of alcohols• A Grignard reagent is an

organic magnesium halide. It can be either an alkyl or an aryl compound (RMgX or ArMgX). Grignard (pronounced green yard) reagents were first prepared in France around 1900 by Victor Grignard (1871-1935).

39

• Grignard reagents are usually made by reacting an organic halide and magnesium metal in an ether solvent:

RX + Mg RMgXether

ArX + Mg ArMgXether

X = Cl, Br, or I

X = Br

40

• In the Grignard reagent, the bonding electrons between carbon and magnesium are shifted away from the electropositive Mg to form a strongly polar covalent bond. As a result the charge distribution in the Grignard reagent is such that the organic group (R) is partially negative and the –MgX group is partially positive. This charge distribution directs the manner in which Grignard reacts with other compounds.

41

• The Grignard reagent is one of the most versatile and widely used reagents in organic chemistry. We will consider only its reactions with aldehydes and ketones at this time. Grignards react with aldehydes and ketones to give intermediate products that form alcohols when hydrolyzed. With formaldehyde, primary alcohols are formed; with other aldehydes, secondary alcohols are formed; with ketones, tertiary alcohols are formed.

42

Examples

Grignard reagent + formaldehyde → 1º ROHGrignard reagent + other aldehydes → 2º ROHGrignard reagent + ketones → 3º ROH

H2C O + CH3MgBr H2C OMgBr CH3CH2OH + Mg(OH)Br

CH3ether H2O

Formaldehyde

43

Examples

C O + CH3MgBr C OMgBr

H H

CH3

ether

CHOH + Mg(OH)Br

CH3

H2OBenzaldehyde

44

Examples

CH3CCH3 + CH3CH2MgBr CH3CCH3 CH3CCH3 + Mg(OH)Br

O

CH2CH3

OMgBr

ether H2OCH2CH3

OH

Acetone

45

Explanation

• The Grignard reaction with acetone may be explained in this way. In the first step of the addition of ethyl magnesium bromide, the partially positive –MgBr of the Grignard bonds to the oxygen atom, and the partially negative CH3CH2– bonds to the carbon atom of the carbonyl group of acetone.

46

CH3CCH3 + CH3CH2MgBr CH3CCH3

O

CH2CH3

O_

+MgBr

47

Explanation• In the hydrolysis step, a proton [H+]

from water bonds to the oxygen atom, leaving the hydroxyl group [–OH] to combine with the +MgBr. So, the alcohol is formed.

48

CH3CCH3

CH2CH3

O_

+MgBr

+ H OH CH3CCH3 + Mg(OH)Br

OH

CH2CH3

49

2,4-dinitrophenylhydrazine (2,4-DNP)

NNO2

NO2

N

H H

H

50

2,4-dinitrophenylhydrazine (2,4-DNP)

• The carbonyl carbon in both aldehydes and ketones reacts with 2,4-DNP to form heavy yellow to orange crystalline solids.

• These solids were used extensively for identification purposes before the use of spectrometers.

• The solid is purified by crystallization and its melting point compared to those of known structure.

51

52

Common Aldehydes & Ketones

53

Formaldehyde (Methanal)• Formaldehyde is made from methanol by

reaction with oxygen (air) in the presence of a silver or copper catalyst.

• 2 CH3OH + O2 2H2C=O + 2H2O

• Formaldehyde is widely used in the synthesis of polymers.

Ag

heat

54

Acetaldehyde (Ethanal)

• Its principal use is as an intermediate in the manufacture of other chemicals, such as acetic acid and 1-butanol.

55

Acetone and Methyl Ethyl Ketone

• Acetone is used as a solvent in the manufacture of drugs, chemicals, and explosives. It is also used as a solvent.

• Methyl ethyl ketone (MEK) is also widely used as a solvent, especially for lacquers.

56

Aldehydes & Ketones in Nature

57

C C C

C

C CO

Violet (Irone)

COH

salicylaldehyde(meadowsweet)

OHC

OOPiperonal(Heliotrope)

OH

C

CH3(CH2)4C H

O

(Eucalyptus) CH3(CH2)10C H

O

(Citrus Fruits)CH3 C C CH3

O O

Raspberries

58

C HO

Benzaldehyde(Oil of Almonds)

CHO

CH3O

HO

Vanillin

CH CH C H

O

Oil of Cinnamon

H3CCH3

OCamphor (Mothballs)

CH3

59

CH3 CCH3

CHCH2CH2C CH

CH3

C HO

Citral (Lemon Grass Oil)

C C C C C C CO

CH3

C C (C)n CO

n = 4 or 6

Alarm Pheromones in ants

60

C C

CH

C HO

Boll Weevil Sex Attractant

C

Citral(Honey Bee Recruiting Pheromone)

HO

61

C C

C

(C)12

C O

Musk Ox Sex Attractant

C

C

(C)n

(C)m

C O

Civet Cat Sex Attractant

m = 4, n = 10m = 7, n = 7m = 7, n = 9

62

Condensation Polymers

63

Leo Baekeland (1863-1944)

6464

A phenolic is a condensation polymer made from phenol as shown here.

Phenol-Formaldehyde Polymers (Bakelite)

This is a section of a phenolic( i.e. Bakelite) which is an example of a thermosetting polymer. These polymers are used in electrical equipment because of their insulating and fire-resistant properties.

65

Bakelite products

66

Bakelite products

GE Locomotive

67