An introduction to carbonyl compounds


Aldehydes and ketones: 

Aldehyde Ketone

p's to p's



Naming aldehydes and ketones:

2-Methylpentanal 2-methylpentan-3-one

Aromatic aldehydes and ketones:

Benzaldehyde Phenylethanone

Qu 1 - 4   P21

Oxidation of alcohols and aldehydes

Primary alcohols:


CH3CH2OH + [O] à CH3CHO + H2O
CH3CH2OH + 2[O] à CH3COOH + H2O

Secondary alcohols:



CH3CHO + [O] à CH3COOH + H2O

Qu 1 - 3  P23

Reactions of aldehydes and ketones

Reducing aldehydes and ketones

Reduction of aldehydes:


                         CH3CHO         +          2[H]            à               CH3CH2OH

 Reduction of ketones:

                         CH3COCH3    +          2[H]            à               CH3CH(OH)CH3

Nucleophilic addition reactions:

  • NaBH4 reacts with aldehydes and ketones by nucleophilic addition.
  • NaBH4 is a source of hydride ions, H-.
  • This is the nucleophile and is attracted to the d+ carbon in the carbonyl group.

The Mechanism:

Qu 1 - 4  P 25

Chemical tests on carbonyl compounds

1)  Detecting the presence of a carbonyl group:

                                                                                                                                Yellow / Orange crystals


Aldehyde or ketone?

2)  Tollens’ reagent

                                      Ag+(aq)        +          e-             à            Ag(s)



Summary – how to test / distinguish for aldehydes and ketones:





A yellow / orange crystalline solid is formed

A yellow / orange crystalline solid is formed

Tollen’s reagent

A silver mirror is formed as Ag+ is reduced to Ag

No reaction

Oxidation with acidified sodium dichromate (VI) (from AS)

Orange to green, as Cr6+ is reduced to Cr3+

No reaction


The orange crystals from 2,4-DNPH can be filtered, recrystallised and melting point determination.  Once you know whether it is an aldehyde or ketone from Tollen's reagent, look up the MPt of the derivative in a table to identify the crystals and hence the aldehyde / ketone.

Qu 1 - 3  P27

Carboxylic acids

Introduction to carboxylic acids


Has carbonyl group C = O                                

and hydroxyl group C – OH

                                                  Ethanoic acid – vinegar

                                                  Benzoic acid – used as flavouring in lemonade

                                                  Citric acid – Used as flavouring in citrus drinks




1)  Solubility and pH


Acid reactions of carboxylic acids:

                      RCO2H(aq)     à     H+(aq)       +       RCO2-(aq)


2.  Formation of salts:

                   Metals                            Metal hydroxides                          Metal carbonates

  • The salt is a carboxylate ion.



a)  With magnesium


             2CH3CO2H       +      Mg                 à         (CH3CO2)2Mg  +      H2

                                                                               Magnesium ethanoate


b)  With sodium hydroxide


             CH3CO2H          +      NaOH            à         CH3CO2Na       +      H2O

                                                                               Sodium ethanoate


c)  With sodium carbonate


             2CH3CO2H       +      Na2CO3         à        2CH3CO2Na     +      H2O      +      CO2

                                                                               Sodium ethanoate


In each case the carboxylic acid has donated a proton, H+

A salt is formed each time


Qu 1 - 2  P29




Esters have the general formula:

Making esters:




Esters from acid anhydrides


The reaction:






Ester hydrolysis:

Ester                         +          water                       à        Carboxylic              +             Alcohol


Carboxylic                   +           Alcohol               à        ester                      +             water




1)  Acid hydrolysis:


2)  Alkaline hydrolysis:


Esters as perfumes and flavourings:

Qu 1 - 3  P31


Fats and oils - building triglycerides

Fats and oils:

Glycerol Long chain carboxylic acid, fatty acid - hexadecanoic acid

Triglycerides - the building blocks:

A saturated fatty acid:  Hexadecanoic acid (palmitic acid)



A monounsaturated fatty acid: Octadec - 9 - enoic acid (oleic acid)


A polyunsaturated fatty acid: Octadec - 9,12 - enoic acid (linoleic acid)


Fatty acid - shorthand:

Number of carbon atoms   Number of double bonds Position of double bonds
18 : 1 (9)


18:1  (9)
18:2  (9.12)



Forming triglycerides:



Qu 1 - 4  P33


Triglycerides, diet and health


Isomerism in unsaturated fatty acids:

No free rotation around the C=C
Trans but-2-ene


  Cis but-2-ene


Fatty Acid Risk Reason Packing State Cause
Saturated Heart disease Raises blood cholesterol Close Solid Blocks arteries
Unsaturated Trans Coronary heart disease Raises blood cholesterol Close Solid Blocks arteries
Cis No Health risk   Cannot pack close together Liquid No effect


Unsaturated packing:


Non linear - inefficient packing - liquid
Linear - efficient packing - solid


Trans fats cholesterol:


High Density Lipoproteins Low Density Lipoproteins
  • These carry cholesterol out of the blood and out of the body.
  • Good
  • These carry about 65% of cholesterol around the blood
  • End up depositing lipids (fats) onto artery walls
  • This restricts blood flow
  • Bad


Fatty Acids as Biodiesel:

  • Biodiesel is in fact a methyl or ethyl ester.

  • Fats are essentially 3 methyl esters joined together.

  • This can be made by using waste cooking oil and using a procedure called:




Making Biodiesel - Transesterification:




Qu 1 - 4  P35


Qu 5 - 8  P41  /  4 - 10, 14 P42 - 45