1. OF ALDEHYDES AND KETONES
THE CHEMISTRY
OF ALDEHYDES AND KETONES

2. ALDEHYDES & KETONES CONTENTS Prior knowledge Structural differences
Nomenclature
Preparation
Identification
Oxidation
Nucleophilic addition
Reduction

3. CARBONYL COMPOUNDS - STRUCTURE
Structure carbonyl groups consists of
a carbon-oxygen double bond
the bond is polar due to the
difference in electronegativity
Difference ALDEHYDES - at least one H attached to the carbonyl group
C = O H
C = O H
CH3

4. CARBONYL COMPOUNDS - STRUCTURE
Structure carbonyl groups consists of
a carbon-oxygen double bond
the bond is polar due to the
difference in electronegativity
Difference ALDEHYDES - at least one H attached to the carbonyl group
KETONES - two carbons attached to the carbonyl group
C = O H
C = O H
CH3
C = O
CH3
C = O
C2H5
CH3

5. CARBONYL COMPOUNDS - FORMULAE
Molecular C3H6O
Structural C2H5CHO CH3COCH3
Displayed
C = O H
C2H5
C = O
CH3
H C C C H
H O H
H H
H C C C O
H H H
H H

6. CARBONYL COMPOUNDS - NOMENCLATURE
Aldehydes C2H5CHO propanal
Ketones CH3COCH3 propanone
CH3CH2COCH3 butanone
CH3COCH2CH2CH3 pentan-2-one
CH3CH2COCH2CH3 pentan-3-one

7. CARBONYL COMPOUNDS - FORMATION
ALDEHYDES
Oxidation of
primary (1°) alcohols RCH2OH [O] ——> RCHO H2O
beware of further oxidation RCHO [O] ——> RCOOH
Reduction of
carboxylic acids RCOOH [H] ——> RCHO + H2O
KETONES
secondary (2°) alcohols RCHOHR [O] ——> RCOR H2O

8. CARBONYL COMPOUNDS - IDENTIFICATION
Differentiation to distinguish aldehydes from ketones, use a mild oxidising agent
Tollen’s
Reagent ammoniacal silver nitrate
mild oxidising agent which will oxidise aldehydes but not ketones
contains the diammine silver(I) ion - [Ag(NH3)2 ]+
the silver(I) ion is reduced to silver Ag+(aq) + e¯ ——> Ag(s)
the test is known as THE SILVER MIRROR TEST

9. CARBONYL COMPOUNDS - IDENTIFICATION
Differentiation to distinguish aldehydes from ketones, use a mild oxidising agent
Tollen’s
Reagent ammoniacal silver nitrate
mild oxidising agent which will oxidise aldehydes but not ketones
contains the diammine silver(I) ion - [Ag(NH3)2 ]+
the silver(I) ion is reduced to silver Ag+(aq) + e¯ ——> Ag(s)
the test is known as THE SILVER MIRROR TEST
Fehling’s
Solution contains a copper(II) complex ion giving a blue solution
on warming, it will oxidise aliphatic (but not aromatic) aldehydes
the copper(II) is reduced to copper(I)
a red precipitate of copper(I) oxide, Cu2O, is formed
The silver mirror test is the better alternative as it works with all aldehydes
Ketones do not react with Tollen’s Reagent or Fehling’s Solution

10. CARBONYL COMPOUNDS - CHEMICAL PROPERTIES
OXIDATION
• provides a way of differentiating between aldehydes and ketones
• mild oxidising agents are best
• aldehydes are easier to oxidise
ALDEHYDES easily oxidised to acids
RCHO(l) [O] ——> RCOOH(l)
CH3CHO(l) [O] ——> CH3COOH(l)
KETONES are not readily oxidised

11. CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Nucleophilic addition: occurs with both aldehydes and ketones
involves addition to the C=O double bond
unlike alkenes, they are attacked by nucleophiles
attack is at the positive carbon centre due to the
difference in electronegativities
alkenes are non-polar and are attacked by electrophiles undergoing electrophilic addition
Group
Bond
Polarity
Attacking species
Result
ALKENES
C=C
NON-POLAR
ELECTROPHILES
ADDITION
CARBONYLS
C=O
POLAR
NUCLEOPHILES
ADDITION

12. CARBONYL COMPOUNDS - REDUCTION WITH NaBH4
Reagent sodium borohydride , NaBH4
Conditions aqueous or alcoholic solution
Mechanism Nucleophilic addition (also reduction as it is addition of H¯)
Nucleophile H¯ (hydride ion)
Product(s) Alcohols Aldehydes are REDUCED to primary (1°) alcohols.
Ketones are REDUCED to secondary (2°) alcohols.
Equation(s) CH3CHO [H] ——> CH3CH2OH
CH3COCH [H] ——> CH3CHOHCH3
Notes The water provides a proton
Question NaBH4 doesn’t reduce C=C bonds. WHY?
CH2 = CHCHO [H] ———> CH2 = CHCH2OH

13. What should you be able to do?
REVISION CHECK
What should you be able to do?
Recall the structure of and bonding in the carbonyl group
Explain the difference in structure between aldehydes and ketones
Recall the different response to oxidation of aldehydes and ketones
Recall the products from the reduction of carbonyl compounds
CAN YOU DO ALL OF THESE? YES NO

14. OF ALDEHYDES AND KETONES
THE CHEMISTRY
OF ALDEHYDES AND KETONES
THE END