Chapter 26 - Carbonyls Flashcards
How to remember than an aldehyde has a C=O at the end of the carbon chain?
aldehyDe enD
Why is a colour change from orange to green observed?
change in oxidation state of the chromium gives the colour change
the importance of adding CN to a carbonyl compound?
- inc no. of Cs in a molecule
- hydroxynitriles (product formed) are used in industrial processes
all carbonyl compounds contain a ?
C=O
Why do we use Brady’s reagent and recrystallise (ect) instead of just measuring the BP of the aldehyde/ ketone ?
BPs can be very similar, melting points of the precipitates have a much larger diff so easier to distinguish using this
the proper name for Tollens’ reagent is?
ammonical silver nitrate
How do we make Tollens reagent?
- add silver nitrate solution to a test tube
- add a few drops of NaOH, a pale brown precipitate forms
- add dilute ammonia drop-wise until the precipitate dissolves
after making Tollen’s reagent?
- add ketone/ aldehyde to the test tube
- place the test tube in a water bath
- DON’T USE A BUNSEN AS ALDEHYDES AND KETONES ARE FLAMMABLE
how to get rid of anti-bumping granules?
hot filtration
how are liquids always seperated?
distillation
how to determine purity of a substance?
- IR
- MS
- Measure BP, compare to data book
- pure substances melt over a narrow range of temps
aldehyde vs ketone?
H attached to C=O makes it an aldehyde
Ketones hv carbonyl bond in middle (made from secondary acl)
ketone ending?
-one
aldehyde ending?
-al
what happens when propanal is added to water?
- no mixing
- extra CH2 means molecule has greater SA so more induced dipole forces
what happens when propanone is added to water?
mixes
- dipole means H bonds can form w water
- less induced dipole forces than in propanal so easier to overcome
what happens when propanal is added to Na2Cr2O7 ?
- Oxidation: propanal + [O] ➡ propanoic acid
- orange ➡ green colour change
- Reduction: 14H+ + Cr2O7 2- + 6e- ➡ 2Cr3+ (green)+ 7H2O
what happens when propanone is added to Na2Cr2O7?
stays orange no oxidation occurs
what is Tollen’s reagent?
Oxidising agent
What happens when propanal is added to Tollens?
- Ox: propanal + [O] ➡ propanoic acid
- Red: Ag++ e- ➡ Ag (silver mirror)
what happens when propanone is added to tollens
- clear: precipitate dissolves in ammonia
- doesn’t oxidise; no silver mirror
what is Brady’s reagent also known as?
2,4-DNP
What does brady’s reagent do?
detects C=O
+ result is orange crystals
how to work out which aldehyde/ ketone from Brady’s + result?
- distil orange crystals
- measure BP
- compare to values in databook to identify
nucleophile definition?
a species w a lone pair of electrons that can be donated to form a dative covalent bond
in organic chemistry?
- Ox: addition of O2
- Reduction: addition of H
reduction of carbonyl compounds is?
- the opposite of oxidation
- primary/ secondary alcohols are produced
for carbonyl compounds to be reduced there must be ?
- powerful reducing agent - NaBH4 (aq)
- HAS TO BE IN WATER
Ketone to 2° alcohol equation?
ketone + 2[H] ➡ 2° alcohol
aldehyde to 1° alcohol equation?
aldehyde + 2[H] ➡ 1° alcohol
reduction of carbonyl compounds is?
nucleophilic addition (double bond remember)
reduction of CCs NA mechanism number of steps and arrows?
3 steps, 4 curly arrows (check for arrow on C=O)
Where do the hydride ions come from for the reduction of CCs?
BH4-
reaction of CCs w HCN?
- NOT A REDUCTION - CN & H added not just H
- either KCN/ HCN and H2SO4 are the reagents
what is the problem w HCN?
- toxic
- low BP - vaporises- dangerous
- so we make it
why do we react CCS w HCN?
It can be used to ⬆ the no. of Cs in an organic molecule which is useful for organic synthesis
what is produced by the reaction of CCs w HCN?
hydroxynitriles
hydrogen cyanide creation?
- happens in situ
- H2SO4 + NaCN ➡NaHSO4 + HCN (weak acid)
HCN reversible ➡H+ CN- nucleophile (has lone pair on C)
⭐ be careful when naming hydroxynitriles?
the C of the CN becomes C1
HCN + CC ➡ hydroxynitrile: number of steps/ arrows in mechanism?
- 3 curly arrows
- 2 steps
when writing mechanism of HCN + CC ⭐
remember to start w formation/ dissociation of HCN
the carbonyl bond is made up of?
1 sigma, 1 Pi bond
p orbitals overlap sideways to form the Pi bond
