Aldehydes and Ketones

  • Created by: Hindleyc
  • Created on: 04-12-18 14:53
What are carbonyls?
Either aldehydes or ketones- compounds with a C=O bond
1 of 55
When is it an aldehyde?
When the C=O is on the end of the chain with an H attached -anal
2 of 55
When is it a ketone?
When the C=O is in the chain -one
3 of 55
What intermolecular forces are in carbonyls?
pure carbonyls cannot hydrogen bond but bond instead by permanent dipole forces
4 of 55
What is their solubility like?
Smaller carbonyls are soluble in water because they can form hydrogen bonds with water
5 of 55
What is the C=O bond? why?
Polarised because O is more electronegative than carbon.
6 of 55
What does this positive carbon do?
Attract nucleophiles
7 of 55
What about in comparison to the C=C bond in alkenes?
C=O is stronger and doesn't undergo reactions easily
8 of 55
What is this in contrast do?
Electrophiles that are attracted to the C=C
9 of 55
What is the oxidising agent that causes alcohols and aldehydes to oxidise?
Potassium dichromate - K2Cr2O7
10 of 55
What does a primary alcohol oxidise to? then?
Aldehyde, Carboxylic acid
11 of 55
12 of 55
Dont oxidise
13 of 55
What is the key point from these reactions
Aldehydes can be oxidised to carboxylic acids but ketones can't be oxidised
14 of 55
Reagents and conditions for oxidation of aldehyde to carboxylic acid
Potassium dichromate solution and dilute sulphuric acid, heat under reflux
15 of 55
Orange dichromate ion (Cr2O7^2-) reduced to the green Cr 3+ ion
16 of 55
General equation
17 of 55
How else can aldehydes be oxidised- what is this used for?
Using Feelings or Tollens reagent- test for presence of aldehyde group
18 of 55
Active substance in Tollens
Complex ion [Ag(NH3)2]+
19 of 55
How is it formed?
Mixing aq ammonia and silver nitrate
20 of 55
heat gently
21 of 55
Aldehydes only are oxidised by TR into a carboxylic acid - silver ions reduce to silver atoms
22 of 55
Aldehyde: Silver mirror forms coating inside of test tube
23 of 55
results in no change
24 of 55
Reagent for Fehlings test?
FS containing blue Cu2+ ions
25 of 55
Heat gently
26 of 55
Aldehydes are oxidised by feelings into a carboxylic acid so copper ions reduced to copper oxide
27 of 55
Blue Cu^2+ ions in solution change to a red precipitate of Cu2O. Ketones don't react
28 of 55
What can carbonyls do?
Be reduced
29 of 55
Using what?
Reducing agents such as NaBH4 (sodium tetrahydridoborate) or LiAlH4 (Lithium tetrahydridoaluminate) will reduce carbonyls to alcohols
30 of 55
NaBH4 in aqueous ethanol
31 of 55
Room temperature and pressure
32 of 55
What will aldehydes by reduced to?
Primary alcohols
33 of 55
What will ketones be reduced to?
Secondary alcohol
34 of 55
Nucleophilic addition steps. C=O
The oxygen is slightly negative and Carbon slightly positive
35 of 55
what next
H- ion attracted with lone pair of electrons.bonds to carbon but carbon has too many bonds so breaks the double bond. electrons to oxygen atom
36 of 55
What next
Lone pair of electrons on negative oxygen attracted to H+ bond
37 of 55
Where is the H+ from
water or weak acid
38 of 55
What does NaBH4 contain
source of nucleophilic hydride ions ( :H-) which are attracted to the +ve carbon in C=O bond
39 of 55
Overall eqn reductant?
40 of 55
What can happen because its planar?
can attack either side
41 of 55
What does the additions of hydrogen cyanide to carbonyls form?
42 of 55
Carbonyl to hydroxynitrile
43 of 55
Sodium cyanide (NaCN) and dilute sulphuric acid
44 of 55
Room temp and pressure
45 of 55
Nucleophilic addition
46 of 55
What the NaCN supply
Nucleophilic CN- ions
47 of 55
What does the H2SO4 supply?
H+ ions needed in second step of mechanism
48 of 55
49 of 55
When naming?
CN becomes part of main chain and carbon no 1
50 of 55
What could we use for this rxn? why not? what's used instead?
HCN but is a toxic gas that is difficult to contain. instead KCN/NaCN - still toxic because of cyanide ion
51 of 55
Steps of nucleophilic addition of KCN in dilute acid
1. nucleophile attacks slightly positive C forming bond so ejects- one of covalent bonds (pair of electrons) move onto O atom in intermediate stage
52 of 55
oxygen -ve charge as gained electrons so within solution H+ so proton forms bond with H ion
53 of 55
What do aldehydes and unsymmetrical ketones form?
Mix of enantiomers when they react with KCN followed by dilute acid
54 of 55
What is KCN?
55 of 55

Other cards in this set

Card 2


When is it an aldehyde?


When the C=O is on the end of the chain with an H attached -anal

Card 3


When is it a ketone?


Preview of the front of card 3

Card 4


What intermolecular forces are in carbonyls?


Preview of the front of card 4

Card 5


What is their solubility like?


Preview of the front of card 5
View more cards


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Reactions resources »