Aldehydes/ ketones Flashcards
(26 cards)
What ion does Tollen’s reagant contain?
⌊Ag(NH₃)₂⌋⁺
What is Fehling’s solution?
-Cu²⁺ ions dissolved in NaOH.
True or False
Aldehydes and ketones can only be oxidised, not reduced.
- False.
- Aldehydes can be reduced to form primary alcohols.
- Ketones can be reduced to form secondary alcohols.
What reducing agent is used to reduce aldehydes and ketones into primary and secondary alcohols?
- NaBH₄ - sodium borohydride- in aqeous solution.
How is the reducing agent NaBH₄ represented in an equation?
⌊H⌋
Overall equation for reduction of aldehyde to form primary alcohol.
Aldehyde + 2⌊H⌋–> primary alcohol.
Overall equation for reduction of ketone to form secondary alcohol.
Ketone + 2⌊H⌋ —> secondary alcohol.
True or False
Reduction reactions of aldehydes and ketones are examples of nucleophillic substitution.
- False.
- Examples of nucleophillic ADDITION.
True or False
In nucleophillic addition mechanism of aldehydes/ ketones forming alcohols, a lone pair moves from H+ ion to the CS+ in carbonyl group.
- False.
- Lone pair moves from hydride ion that comes from reducing agent.
What is the nucleophile in the nucleophilic addition reaction of reduction of aldehydes/ ketones to form alcohols?
H- ion.
Outline nucleophillic addition mechanism for forming alcohol from reduction of aldehyde/ ketone.
Diagram of mechanism on files
- Lone pair moves from hydride ion to CS+.
- Pair of electrons moves from C=O bond to OS-.
- Intermediate with O- is formed.
- Lone pair on O- moves to H+ ion.
Where does the H+ ion come from in the nucleophilic addition mechanism with NaBH4?
- From acid/ water that reducing agent is dissolved in.
true or false
nucelophilic addition mechanism for aldehydes/ ketones are different.
- False!
- Nucleophilic addition mechanism is exact same for both!
Where does the H- ion come from in mechanism of reduction of aldehyde/ ketone to form alcohols?
- Reducing agent: NaBH₄
What mechanism is reaction of KCN with aldehyde/ ketone?
- Nucleophilc addition.
What is formed when KCN reacts with aldehyde/ ketone? What acts as nucleophile in reaction?
- Hydroxynitrile formed.
- CN-
What two different substances can be used to produce CN- for the nucleophilc addition of aldehydes/ ketones? What different conditions are required?
- KCN: dissolved in acidic solution, dissociates into K+/ CN-.
- HCN: no acid required.
Outline nucleophillic addition mechanism for forming hydroxynitrile from aldehyde/ ketone.
- Lone pair from CN- moves to CS+.
- Pair of electrons moves from C=O bond to OS-.
- Intermediate with O- is formed.
- Lone pair moves from O- to H+.
Where does H+ come from in nucelophilic addition of aldehydes/ ketones to form hydroxynitriles?
- HCN: comes from H+ within HCN.
- KCN: comes from acid.
In electrophilic addition of ketones/ aldehydes using CN- ions, when will a mixture of enantiomers be formed?
- If you start with an aldehyde (other than methanal) / unsymetrical ketone.
Overall equations for electrophilic addition of aldehyde/ ketone using KCN.
Aldehyde:
RCHO (aq) + KCN (aq) + H+ (aq)–> RCH(OH)CN(aq) + K+ (aq)
Ketone:
RCOR’ (aq) + KCN (aq) + H+ (aq) –> RCR’(OH)CN (aq) + K+ (aq)
What are the 3 main risks associated with using KCN?
- Irritant.
- Very dangerous if ingested/ inhaled.
- KCN reacts with moisture to form toxic gas, HCN.
What 4 different ways can you reduce the risks of KCN?
- Wear lab coat to prevent clothing contamination.
- Wear goggles.
- Use fume cupboard to prevent exposure to toxic fumes.
- Wear gloves.
True or False
We add concentrated acid to KCN in nucleophilic addition of aldehydes/ ketones.
- False
- We add DILUTE acid to KCN.
