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)
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 delta -)
How soluble are they in water? What influences solubility?
Yes forms 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 a carbonyl compound, using :Nu- to represent the nucleophile
Slide 21
Draw a mechanism for the nucleophilic addition of HCN to a carbonyl compound
Slide 23
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 they will. In the aldehyde/ketone, the carbonyl carbon is planar, so the :CN- can attack from either above or below, forming two enantiomer
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
What is in tollens’ reagent?
Silver complex ions, 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
Draw and name a mechanism for the reduction of an aldehyde
Slide 47
Write an equation for the reduction of pentan-2-one and for 3xmethylbutanal
