6.1.2: Carbonyl compounds 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)
What is the functional group for a ketone?
RCOR’ (C double bonded to O)
How do you name aldehydes?
-al suffix (C=O is 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 intermolecular forces do molecules with
the carbonyl group have? Why?
Permanent dipole-dipole due to the polar C=O
bond (O is ∂-)
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
Why is the addition of HCN important?
Increases the length of the carbon chain by one
carbon atom allowing more useful molecules to
be made.
Will the product of HCN added to a carbonyl
compound have optical isomers? Why?
Yes they will. In the aldehyde/ketone, the
carbonyl carbon is planar, so the :CN- can attack
from either above or below, forming two enantiomers.
What is the name of the product when HCN is added
to a carbonyl compound?
Hydroxynitriles (have OH and CN groups)
What is Fehling’s solution? What colour is it?
Copper complex ions, blue
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?
No visible change → stays blue
How do you test for a carbonyl compound?
Use Brady’s reagent - 2,4-dinitrophenylhydrazine
If a carbonyl compound is present an orange precipitate is formed
What is in Tollens’ reagent?
Silver complex ions in colourless solution.
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 change in colour does this undergo?
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
How do you convert an aldehyde to form a carboxylic acid?
Oxidation of aldehydes using Cr2O7
2-/H+ (i.e. K2Cr2O7/H2SO4)
