3.8 Aldehydes and Ketones Flashcards
Draw the displayed formula for ethanal.
(see page 1 in the chemrevise revision guide)
What is the functional group for an aldehyde?
C=O on the end of a chain with an H attached to the chain too.
(see page 1 in the chemrevise revision guide)
Draw the displayed formula for propanone.
(see page 1 in the chemrevise revision guide)
What is the functional group for an ketone?
If the C=O is in the middle of the chain.
see page 1 in the chemrevise revision guide
What is a carbonyl?
Carbonyls are compounds with a C=O bond.
They can be either aldehydes or ketones.
How do carbonyls bond?
Intermolecular forces in carbonyls.
Pure carbonyls cannot hydrogen bond, but bond instead by permanent dipole forces.
How soluble are carbonyls in water?
The smaller carbonyls are soluble in water because they can form hydrogen bonds with water.
Do carbonyls undergo addition reactions easily?
In comparison to the C=C bond in alkenes, the C=O is stronger and does not undergo addition reactions easily.
Are carbonyls polarised?
The C=O bond is polarised because O is more electronegative than carbon. The positive carbon atom attracts nucleophiles.
(see page 1 in the chemrevise revision guide)
What is an oxidising agent that causes alcohols and aldehydes to oxidise?
potassium dichromate, K2Cr2O7
When a primary alcohol is oxidised what is its functional group change?
primary alcohol -> aldehydes
When an aldehyde is oxidised what is its functional group change?
aldehyde -> carboxylic acid
When a secondary alcohol is oxidised what is its functional group change?
secondary alcohol -> ketone
When a tertiary alcohol is oxidised what is its functional group change?
tertiary alcohols do not oxidise.
When a ketone is oxidised what is its functional group change?
ketones do not oxidise.
What are the reagents and conditions when oxidising an aldehyde?
reagent - potassium dichromate (VI) solution and dilute sulphuric acid.
conditions - heat under reflux
Draw the equation when oxidising propanal.
(see page 1 in the chemrevise revision guide)
For oxidising aldehydes with Tollen’s reagent, what are the:
- Reagents
- Conditions
- Reaction
- Observation
- Equation
(see page 1 in the chemrevise revision guide)
For oxidising aldehydes with Fehling’s solution, what are the:
- Reagents
- Conditions
- Reaction
- Observation
- Equation
(see page 1 in the chemrevise revision guide)
What a 2 reducing agents for carbonyls?
- NaBH4 (sodium tetrhydridoborate)
- LiSlH4 (lithium tetrahydridoaluminate)
Will reduce carbonyls to alcohols.
What is the change in functional group when Aldehydes are reduced?
aldehyde -> primary alcohol
What is the change in functional group when ketones are reduced?
ketone -> secondary alcohol
Draw the equation for the reduction of propanal.
(see page 2 in the chemrevise revision guide)
Draw the equation for the reduction of propanone.
(see page 2 in the chemrevise revision guide)
Draw the mechanism for the reduction of propanone.
(see page 2 in the chemrevise revision guide)
Other than a reducing agent, what is another way carbonyls can be reduced?
Catalytic hydrogenation
What are the reagents and conditions for catalytic hydrogenation of carbonyls?
Reagent - hydrogen and nickel catalyst
Conditions - high pressure
(see page 2 in the chemrevise revision guide for some example equations)
When adding hydrogen cyanide to a carbonyl what is:
- The change in functional group?
- The reagents?
- The conditions?
- The mechanism?
carbonyl -> hydroxynitrile
reagent - sodium cyanide (NaCN) and dilute sulfuric acid.
The NaCN supplies the nucleophile CN- ions.
The H2SO4 acid supplies H+ ions needed in second step of the mechanism.
conditions - room temperature and pressure
mechanism - nucleophilic addition
Draw the equation of the formation of 2-hydroxy-2-methylpropanenitrile from a carbonyl
(see page 2 in the chemrevise revision guide)
Draw the equation of the formation of 2-hydroxypropanenitrile from a carbonyl
(see page 2 in the chemrevise revision guide)
Why would you use KCN/ NaCN instead of HCN when forming a hydroxynitrile?
We could use HCN but it is a toxic gas that is difficult to contain.
KCN/NaCN are still, however, toxic, because of the cyanide ion.
Draw the mechanism for formation of a 2-hydroxypropanenitrile form a carbonyl.
(see page 2 in the chemrevise revision guide)
Draw the basic displayed formula of the structure of any hydroxynitrile
(see page 2 in the chemrevise revision guide)
How is a racemate formed from a carbonyl?
Draw the mechanism reaction.
(see page 3 in the chemrevise revision guide)
