Aldehydes and ketones Flashcards
What is the functional group?
C=O carbonyl
Where is carbonyl in an aldehyde?
at the start/end of chain
Where is carbonyl in a ketone
in between carbon/ not at start/end
What is the first member of aldehydes and ketones?
ALDEHYDES
methanal
(numbers never needed as functional group is always at the start/end)
KETONES
propanone
(first member with number is pentan-2-one)
What is the general formula for aldehydes and ketones?
CnH2nO
Oxidation of alcohols (check jotter for structural formulas
Primary alcohol—>aldehyde—>carboxylic acid
Secondary alcohol—>ketone—>NO FURTHER OXIDATION
Tertiary alcohol—>THEY DONT READILY OXIDISE
Testing oxidation of alcohols
oxidation with copper oxide
-lose plug of ceramic wool
-alcohol and ceramic wool
-heat
-copper (II) oxide
-wet pH paper held in the vapour
hot copper (II) oxide is an oxidising agent
What happens to pH paper if the alcohol is primary
turns red (due to formation)
What can be used to oxidise
-primary alcohols—>aldehydes—>carboxylic acids
-secondary alcohols—>ketones
?
-copper (II) oxide or acidified -potassium dichromate (VI)
(acified to supply the H+ (to balance equation))
These cannot be used to oxidise tertiary alcohols
colour changes for testing oxidation of alcohols
black copper (II) oxide forms a brown solid
orange dichromate solution turns blue/green
in organic chemistry, What is oxidation?
An increase in the oxygen:hydrogen ratio
gain of oxygen or loss of hydrogen
In organic chemistry, What is reduction?
A decrease in the oxygen:hydrogen ratio
loss of oxygen or gain of hydrogen
How can you distinguish between aldehydes and ketones?
Several oxidising. agents can be used
-acidified potassium dichromate Cr2O7^2- (aq) + H+ (aq)
-orange->blue/green
Cr2O7^2- (aq) reduced to Cr^3+
-Fehling’s solution Cu^2+ in alkaline solution
-blue->orange/brick red
Cu^2+ (aq) reduced to Cu+ (s)
Cu^2+ + e- —> Cu+ (s)
-Tollens’ reagent-silver nitrate based Ag+ (aq)
-Colourless->silver
Ag+ (aq) reduced to Ag(s)
Ag+ + e- —> Ag
What causes the oxidation of food?
oxygen in the air
What does the oxidation of edible oils cause?
It gives food a rancid flavour
