3.8 Aldehydes and ketones Flashcards
What is the carbonyl group
C=O
What is the functional group and general formula for an aldehyde
RCHO (C double bonded to O, single bond to H and R)
end
What is the functional group for a ketone
RCOR’ (C double bonded to O)
middle
How do you name aldehydes
-al suffix (C=O on the end of a chain)
How do you name ketones
-one suffix (designate number for which carbon C=O is on)
What kind of imfs do molecules with the carbonyl group have? Why
Permanent dipole-dipole due to polar C=O bond (O is delta negative)
How soluble are they in water? What influences solubility
Yes - form hydrogen bonds between water molecules and oxygen of C=O
As C chain length increases, solubility decreases
Which bond in carbonyl compounds is usually involved in reactions, why
C=O due to the polarity of the bond
Large difference in electronegativity between C and O
What is the strongest bond in carbonyl compounds
C=O
Draw a mechanism for the nucleophilic addition of HCN to a carbonyl compound
Why is the addition of HCN important
Increases the length of the carbon chain by one carbon atom - very useful
Will the product of HCN added to a carbonyl compound have optical isomers, why
Yes
In the aldehyde/ketone the carbonyl carbon is planar, so the :CN- can attack from either above or below, forming enantionmers
What is the name of the product when HCN is added to a carbonyl compound
Hydroxynitriles (OH and CN groups)
What happens when an aldehyde is added to Fehling’s solution
Reduced to CU+ ions –> colour change to brick red ppt
What happens when a ketone is added to Fehling’s solution
Stays blue
What happens when an aldehyde is added to Tollen’s reagent
Silver mirror forms as Ag+ reduced to Ag(s)
What happens when a ketone is added to Tollen’s reagent
No visible change
What is another oxidising agent for alcohols and aldehydes? What is the colour change
Acidified potassium dichromate (VI) - H2SO4 and K2Cr2O7
Colour change from orange to green
What is a reducing agent for aldehydes and ketones
What ions does this release in solution
NaBH4 (sodium tetrahydridoborate (III), releases an H- ion
Write an equation for the reduction of pentan-2-one and for 3-methylbutanal
CH3COCH2CH2CH3 + 2[H] -> CH3CH(OH)CH2Ch2CH3
CH3CH2CH2(CH3)CHO + 2[H] -> CH3CH2CH2(CH3)CH2OH
Draw and name a mechanism for the reduction of an aldehyde
Nucleophilic addition
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