Unit 6 Flashcards
aldehydes, ketones and alcohols
What is an aldehyde?
Has a c=o at the end of a molecule
What is a ketone?
Has a c=o in the middle of the molecule
What are some properties of aldehydes and ketones?
Polar
miscible with water
volatile
What is the suffix for an aldehyde?
Al
What is the suffix for a ketone?
one
How can you make an aldehyde from a primary alcohol?
By adding PCC (weal oxidising agent)
How can you make a ketone from a secondary alcohol?
potassium dichromate and sulphuric acid. (K2cr207 & h2so4) acidic conditions are best can just put (H+)
What can ozonolysis be used for?
To find the position of a double bond
What is ozonolysis?
Splitting of a double bond and inserting oxygens creating two carbonyl derivatives. Two molecules with c=o will be formed
What is PCC
A weak oxidising agent that is selective so can be used to oxidise a primary alcohol to an aldehyde
How can you produce benzaldehyde? (using chlorine)
React methylbenzene and chlorine in UV (form free radical) light then reflux to get benzaldehyde
How can you reduce benzoyl Chloride to get benzaldehyde? (aromatic)
Reduce benzoyl chloride using hydrogen and palladium catalyst mixed with barium sulfate
Why do addition reactions take place on aldehydes and ketones?
the c=o is polar as o is very electronegative. This slight positive charge on the C allows for nucleophilic attack which breaks the double bond (pi) and means H+ can be attached to the o (OH) as its down in acidic conditions
How do aldehydes and ketones react with water?
to form diols/hydrates but they arent very stable
What happens when you react an aldehyde with a alcohol?
Form an ether it can be used to protect ketone groups from further reaction
What colour does Na2Cr207 turn in the presence of an aldehyde
Goes from orange to green
Ketones are very hard to oxidise true or false?
True
Why is there difference in reactivity between aldehydes and ketones
Aldehyde is more reactive. as its less sterically hindered
less inductive groups (e- donating trying to stabilise) so the carbon centre is more + than in a ketone
Test for the carbonyl group? (aldehyde or ketone)
2-4 dinitrophenylhydrazine. If theres aldehydes or ketones present there will be an orange precipitate formed
Test for aldehydes?
Tollens reagent. Clear solution will turn like a silver mirror.
Can also use Fehlings solution which will turn from blue to orange
What happens if you condensate two aldehydes?
you make an aldol (2 functional groups)
What do alcohols contain?
OH hydroxyl group
what are primary secondary and tertiary alcohols
Primary- Carbon with the OH is bonded to 1 other C
Secondary- Carbon with the OH is bonded to 2 other Cs
Tertiary- Carbon with the OH is bonded to 3 other Cs
Phenol- bonded to benzene
What numbers correspond to Ortho?
1,2
What numbers correspond to Meta?
1,3
What numbers correspond to para
1,4
How do you get from an alkene to an alcohol?
An acid catalyst and water
How do you get from a carboxylic acid to a alcohol?
Lithium aluminium hydride in acidic conditions
How do you get from a halogen alkane to an alcohol?
Sodium hydroxide
Why do alcohols have high boiling points?
Hydrogen bonding and permanent dipole to dipole attractions
Small alcohols are miscible in water but this decreases with the size of the alkyl group
Alkyl group is non polar. The polar hydrogen bonds between OH is what makes it miscible so if you increase non polar bit you decrease solubility
Alkyl group decreases acidity in alcohols, why?
more Ch3 bonds push electrons to the O
Halogens increase acidity in alcohols, why?
They pull electrons towards themselves making H+ even more positive
Why is phenol more acidic than another alcohol?
Phenol is much more stable as the delocalized electrons can distribute the charge. Because it is stable it doesn’t mind losing the H as much. Also the H gets even more positive
Reduction of aldehydes and ketones using sodium borohydride gives what?
Alcohols
How can you get and alcohol from aldehydes and ketones?
Reduce them using sodium borohydride
Reacting an alcohol with sulfuric acid gives?
An alkene
Reacting an alcohol with sodium dichromate and sulfuric acid gives what?
Carboxylic acid
Reaction of an alcohol with PCC gives?
An aldehyde
