1e Aldehyde & Ketone

8/12/2019 1e Aldehyde & Ketone

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CHAPTER 4: ORGANIC CHEMISTRY

PART ECARBONYL

COMPOUNDS


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Carbonyl compounds have functional group called

carbonyl (C=O)

Carbon and oxygen are joined together by double

bond which consist of sigma () and a pi () bond

The carbon and oxygen in the carbonyl group are

sp2-hybridized, trigonal planar with bond angles of

120

OC

12

0o


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The carbonyl group.


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Class

General

formula Class

General

formula

Aldehydes Ketones

Carboxylic

acidsEsters

AmidesAcid

chlorides

Some common classes of carbonyl compounds

C

O

R H

C

O

R OH

C

O

R NH2

C

O

R R 1

C

O

R OR1

C

O

R Cl


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ALDEHYDES & KETONES

Aldehyde

Ketone

C

O

R H

C

O

R R 1

R: H, alkyl, aryl (eg: benzene)

R and R1: alkyl or aryl

R and R1cannot be

hydrogen


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ALDEHYDES & KETONES

Contain the carbonylgroup

Aldehydes = at least 1 side H

Ketones = both sides R groups

Many aldehydes and ketones have pleasant tastesand aromas

Formaldehyde : H2C=O

pungent gas

formalin = a preservative

wood smoke, carcinogenic

Acetone : CH3C(=O)CH3

nail-polish remover


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Aldehyde Odors and Flavors

butanal = butter

vanillin = vanilla

benzaldehyde = almonds

cinnamaldehyde = cinnamon

7


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Physical properties

At room temperature, Formaldehyde (simplestaldehyde) is a gas but heavier aldehydes are and

ketones are liquid

The carbonyl compounds are POLARdue to the

presence of carbonyl functional group; with

oxygen being more electronegative

C O

R

R

Electrophilic carbon

(electron acceptor)


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C=O bond are shorter and stronger than C=C

bond

Since there is no hydrogen on the carbonyl oxygen,

aldehydes and ketones do not form hydrogen

bonds with themselves but they can hydrogen-

bond to water through the carbonyl oxygen.

Low-molecular weight aldehydes and ketones are

water-soluble;water solubility decreases as the size

of the molecule increases.


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Nomenclature of Aldehydes

Choose the longest carbon chain that containstheCHO

TheCHO is always numbered as carbon 1

because it always at end chain

Aldehyde ending is al

If the CHO group is bonded to a ring, name the

ring and add the suffix carbaldehyde.The carbon

to which the aldehyde group is attached is C1


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Examples: Simple aldehyde

C

O

H HC

O

H CH3

C

O

H CH2-CH3

methanal ethanal

propanal


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Examples: Substituted aldehyde

O

H H

O

Cl

H

OOH

4,4-dimethylpentanal 4-chloro-4-methylpentanal

3-hydroxybutanal


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Examples: Dial

HH

O

O

H

O

H

O

butanedial

pentanedial


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CH

O

CH

O

Cl

cyclohexanecarbaldehyde

2-chlorocyclobutanecarbaldehyde

Examples: Cyclic aldehyde


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Common Names of the Aldehydes

O

CH H

O

CCH3 H

O

CCH2 HCH3

OC

CH2 HCH2CH3

OC

CH2 HCH2CH2CH3

O

CCH2 HCH2CH2CH2CH3

Formaldehyde Acetaldehyde Propionaldehyde

Butyraldehyde Valeraldehyde

Caproaldehyde

1 2 3

4 5

6

C

O

H

Benzaldehyde


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Nomenclature of Ketones

Choose the longest continuous carbon chain thatcontains the carbonyl carbon

Number the chain starting with the end closest to

the ketone group

Ketone ending isone

Molecules with more than one ketone group arenamed by preceding the suffix with a counting

prefix (dione, trione, etc.); position numbers mustbe used for each ketone group


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Examples: Simple ketones

C

O

H3C CH3C

O

H3CH2C CH3

propanone(acetone)

butanone

C

O

H3C-H2C CH2CH3

3-pentanone

Pentan-3-one


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Examples: Substituted ketones

C

O

H3CHC CH3

CH3 O

CCH2 CH

CH3 CH2

CH2

CH3

CH3

3-methyl-2-butanone

4-ethyl-3-hexanone


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Examples: multiple ketones

O O

O

O

Cl

O

2,4-pentadione

4-chloro-2,5,7-octanetrione


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Examples: cyclic ketones

O

C

O

CH2-CH3

cyclopentanone

3-chloro-2-methylcyclopentanone

O

CH3Cl

1-cyclobutyl-1-propanone


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Common Names of the Ketones

alkyl alkyl ketone

CH 3

C

CH 2

CH 2

CH 3

O

Methyl propyl ketone

O

C

CH2 CH2

CH3 CH3

Diethyl ketone


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In 5 minutes answer these questions:-

1. Name the following aldehydes and ketone:

CH

O

Cl

H

O O

H

H

OBr

H

O

(a) (b)

(c) (d)

2-chloro-3-methylbenzaldehyde

propanedial

2-butenal 3-bromobutanal


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2. Draw structures corresponding to the following

IUPAC names:

a) 3-methylbutanal

b) 2,2-dimethylcyclohexanecarbaldehyde

c) 5-hexen-3-one

d) 1-cyclobutyl-1-propanone

e) 1,3-cyclohexanedione

H

Oa)

O

H

b)

Oc)

Od)

e)

O

O


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Reaction of Aldehydes & Ketones

1. Nucleophilic addition

2. Reduction to Alcohol

3. Oxidation

4. Iodoform test


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Nucleophilic addition

The carbonyl group in aldehydes and ketones has

a constant polarity.

C=O

+

The O atom attracts electrophiles; the C atom attracts

nucleophiles


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Carbonyl compounds have oxygen atom whichis more electronegative than carbon atom

The carbonyl carbon is electron deficient and

susceptible to be attacked by nucleophile

Examples of nucleophile arei. Hydrogen cyanide, HCN

ii. Water, H2O

iii. Alcohol

iv. Grignard Reagent


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i. Nucleophilic addition of HCN

mechanism

C

O 1 . CN- (nucleophilic attack)

2 . H+ (protonantion)

C

CN

O H

cyanohydrin


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ii. Nucleophilic addition of H2O

Hydration reaction which produce carbonyl

hydrate

Hydrate is a molecule with twoOH group

bonded to same carbon atomgem-diols

R

C

R

O + H2O R C OH

R

OH

cat. H+

or OH-


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Acid catalyzed addition of H2O


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iii. Nucleophilic addition of Alcohol

C

O+ ROH, H+

C

OR

OR

C

OH

OR

catalyst(dry HCl)

acetal/ketal

hemiacetal/hemiketal


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Mechanism


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iv. Nucleophilic addition of Grignard reagents

C

O

+ RMgX C

O

R

MgBr

C

O

R

MgBr

+ H2O C

OH

R+ Mg(OH)Br

larger alcohol

(a)

(b)


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Reduction to alcohols

Reducing agents commonly used are:-

i. Lithium aluminium hydride, LiAlH4in

ether, H3O+

ii. Sodium boronhydride, NaBH4

iii. Nickel with hydrogen gas at 180C(catalytic hydrogenation)

LiAlH4 and NaBH4 provides nucleophile, H-

(hydride ion) which attack the electrondeficients carbonyl carbon.


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Oxidation

Aldehydes are oxidized to carboxylic acids.

Oxidation reactions:

i. KMnO4, K2Cr2O7

ii. Tollensreagents (silver mirror test)

iii. Fehlings solutions Color changes

Ketones cannot undergo

oxidation!!!


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i. Oxidation of aldehydes with KMnO4and K2Cr2O7


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ii. Tollens reagents (silver mirror test)

Contains the complex diamine silver ion

complex, Ag(NH3)2+

Aldehyde is oxidised to form carboxylate,

RCOO-

Colourless Ag(NH3

)2

+ion is reduced to

silver which appear as silver mirror on the

wall of the test tube

C

O

R H + -

C

O

R O-

+ 2Ag + 2H2O

C

O

CH3CH2 H

2Ag(NH3)2+

+ 3OH + 4NH3

+ -

2Ag(NH3)2+

+ 3OH CO

CH3CH2 O-

2Ag + 2H2O+ 4NH3+


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C

O

R H + 2Cu2+

+ 5OH-

C

O

R O- + Cu2O + 3H2O

C

O

CH3 H + 2Cu2+

+ 5OH-

C

O

CH3 O + Cu2O + 3H2O

-

brick redprecipitate

C

O

CH3 CH3+ 2Cu2+

+ 5OH-

no reaction (no change of colour)

Can be use to distinguish between;

Aldehydes (+ve) & ketones (-ve)

Aliphatic aldehydes (+ve) & benzaldehyde (-ve)


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Iodoform test

Similar to alcohol, carbonyl compounds can also

react with iodine in alkaline solution, NaOH,warm to form yellow precipitate or

triiodomethane, CH3I

Useful test for methyl ketone group (CH3C=O)

Carbonyl compounds which give positive result

have the following structure

CH3

O

C R R can be H/ / any C chain

R

O

C CH3 + 3I2 + 4NaOH CHI 3(s) + CR OO

Na+

+ 3NaI + 3H2OTriiodomethane

(yellow precipitate)


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V

The time that we are waiting for!!!!


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Questions:-

1. Draw the structure of the products formed when

the following compounds undergo reduction under

suitable condition:-

a) HCHO CH CH2CH2-C

O O

CH3c)

b)C

O

CH3 d) HOCH2

CH2

C-H

O

a) HCHO CH CH CH C CHc)


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OHa) C

H

HH CH3

b) C

OH

HH CH2CH2

OH

C H

a) HCHO CH CH2CH2-C

O O

CH3c)

b) C

O

CH3 d) HOCH2CH2C-H

O

CH3c) C

OH

HH

d) C

OH

HH CH2

OH

CH


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2. Suggest how you would differentiate between the

following pairs of compounds.

a) Propanal and propanone

b) 3-pentanone and 2-pentanone

c) Butanal and benzaldehyde

Oxidation with KMnO4;propanal will be oxidized

(purplecolour decolorised) while propanone will not.

Iodoform test;2-pentanone will give positive result (yellow

precipitate) while 3-pentanone will give negative result.

Fehling test; butanal will give positive result (brick red

precipitate) while benzaldehyde will give negative result.


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summary

Define and determine the carbonyl

compound

Differentiate between aldehyde and ketone

compound Naming and draw aldehydes and ketones

compound

Determine the reactions of aldehyde and

ketones

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