SUBTOPIC: ALDEHYDES AND KETONES

Functional group

R-CHO1) Name of functional group:2) Name of family:

Functional group

OR-C-R

1) Name of Functional group:2) Name of family:

UsesCitral Jasmone

Vanilin Muscone

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NomenclatureAldehydes

1) Identify parent chain, which is the longest continuous carbon chain containing aldehyde fg2) No need to designate the position of aldehyde fg bc aldehyde always assume position no 1.3) Replace the suffix ‘ane’ with ‘anal’

a. Eg:

Ketones1) Locate parent chain containing ketone fg2) Give ketone lowest no3) Change suffix ‘ane’ in alkane into ‘one’

Eg:

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Physical properties

Melting points and boiling points

1) Aldehydes and ketones have polar carbonyl groups however they have lower mps and bps than alcohols with similar molar mass.

2) Aldehydes and ketones can only form weak DDI among themselves respectively.3) A little heat is needed to break the secondary interactions between molecules. Hence lower mp

and bp

Diagram:

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Solubility in water1) Lower aldehydes and ketones are soluble in water because they can form hydrogen bonds with

very polar water molecules.2) Diagram:

Aldehyde

Ketone

3) Higher aldehydes and ketones are less soluble in water. This is because even though they have polar carbonyl groups, the long non-polar hydrocarbons outweigh the polarity of their functional groups, making the whole molecule less polar. They cannot form strong hydrogen bonds with very polar water molecules; hence aldehydes and ketones are less soluble in water.

Solubility in organic solventsSoluble in non-polar organic solvents because they can form DF with the solvent molecules.

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Chemical propertiesFormation of aldehydes

1) aldehydes can be formed from the controlled oxidation reaction of primary alcohols using limited amount of acidified potassium dichromate solution as oxidizing agent.

2) Other oxidizing agent such as acidified sodium dichromate solution can also be used. Eg:

HR-C-O-H R-CHO H

3) Procedure:a) Primary alcohol is placed into round bottom flask with a bit of anti-bumping granules or

boiling chips.b) Acidified potassium dichromate solution is placed in dropping funnelc) The round bottom flask is then connected to the dropping funnel and distillation

apparatusd) Then add acidified potassium dichromate solution from the dropping funnel drop wise

into primary alcohole) Distill off aldehyde at its boiling point as it is being formed

Diagram:

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Ketones

Formation of ketonea. Oxidize secondary alcohol into ketone using acidified potassium/sodium dichromateb. Procedure:

i. Place secondary ketone in round bottom flask and add boiling chipsii. Heat under reflux

1. The purposes of heating under reflux are to increase rate of reaction and to prevent the volatile cpds from escaping the rxn mixture.

c. Eg:

Chemical reactionsAldehydes

1) Tollen’s testa. Oxidizing agent Tollen’s reagent/ Ammoniacal silver Nitrate solution can be used to

oxidize Aldehyde into carboxylate anion

b. Procedure:i. Place I ml of Tollen’s reagent into a test tube

ii. Then add few drops of aldehyde sample into the test tubeiii. Observation: Formation of silver mirror due to reduction of silver ion into

metallic silver

c. Eqn: R-CHO (l) R-COO- (aq) Ag(NH3)2

+ (aq) Ag (s)

Eg:

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2) Oxidation into carboxylic acida. Aldehyde can be oxidized into carboxylic acid using excess acidified potassium/sodium

dichromate or acidified potassium permanganate solutionb. Procedure:

i. Place 1 ml of aldehyde sample into a test tubeii. Add 1 ml of acidified potassium dichromate

iii. Observation: Colour change from orange to green due to reduction of Cr 6+ (orange) to Cr 3+ (green)

iv. Eq: R-CHO (l) R-COOH (l)

Cr2O72- (aq) Cr3+ (aq)

vi. Eg:

Ketones No reaction with acidified potassium dichromate or permanganate

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CARBOHYDRATES

1. Definition of carbohydrate

a. Polyhydroxy aldehyde or polyhydroxy ketone

b. General formula of carbohydrate, CxH2yOy

Eg: MF C6H12O6 conforms to the gen formula CxH2yOy where x=6, y=6 MF C12H22O11 conforms to the gen formula CxH2yOy where x=12, y=11

MF (C6H10O5)n conforms to the gen formula CxH2yOy where x=6, y=5

2. Types of carbohydrate

a. Monosaccharides i. Simplest sugar

ii. General formula CxH2xOx where 3<x<8iii. Most common form in nature is based on 6C eg C6H12O6

iv. Fructose, glucose & galactose are structural isomers because they have same MF but different SF

v. 5C & 6C monosaccharides can form cyclic structure.vi. Establish equilibrium between straight chain & cyclic form in water.

b. Disaccharides (C12H22O11 )i. Form when 2 monosaccharides join together in a condensation reaction.

ii. Sucrose, maltose, lactose are structural isomers.

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c. Polysaccharides (C6H10O5 )n

i. Starch, glycogen, cellulose(cotton)

3. Physical propertiesa. Monosaccharides

i. Very soluble in water because relatively small compared to polysaccharides and have many very polar hydroxyl groups spread around the molecules (has low C: OH ratio) which can form many/extensive strong hydrogen bonds with water molecules.

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ii. Insoluble in non-polar organic solvent because the monosaccharide molecules tend to form hydrogen bonds between them.

b. Disaccharidesi. Many very polar hydroxyl groups spread around molecules.

ii. Soluble in water due to extensive strong hydrogen bonds formed between disaccharide molecules and very polar water molecules.

c. Polysaccharidesi. Absorb water but do not dissolve in water.

ii. Polysaccharides can absorb water due to many very polar hydroxyl groups but cannot dissolve in water due to their large molar mass. Polysaccharide molecules tend to form hydrogen bond between polysaccharide chains.

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4. Chemical reactionsa. Monosaccharides

i. Acidified Dichromate solution, Cr2O7 2- /H+

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Limited Cr2O7

2- /H+

ExcessCr2O7

2- /H+

Limited Cr2O7

2- /H+

Excess Cr2O7

2- /H+

ii. Tollen’s reagent, Ag(NH3)2 +

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Ag(NH3)2 +

Ag(NH3)2 +

b. Disaccharides

i. Formation: 2 C6H12O6 C12H22O11 + H2O

ii. Hydrolysis: C12H22O11 + H2O :2 C6H12O6

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c. Polysaccharides

i. Formation:

ii. Partial hydrolysis:

iii. Complete hydrolysis:

:

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