Carbonyls Flashcards
what is the carbonyl functional group
C=O bond
draw a ketone
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Draw a aldhyde
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Write the equation of aldehydes undergoing oxidation
pg 134
what do aldehydes form when they undergo oxidation
they form a carboxylic acid
- goes from orange to green
What are the reagents needed for aldehydes to under go oxidation
- acidified potassium dichromate
- sulfuric acid
- under reflux
- heat gently
describe nucelophilic addition reactions
- carbonyls have C=C functional group
- makes them susceptible to nucleophilic attach on the slightly positive carbon atom,
- a nucelophile donates a pair of electrons to the electron deficient carbon atom, to form a new covalent bond
- the pie bond in the C=O breaks
- extra electron pair is donates to the neighboring hydrogen to form an alcohol group and stable product
WRITE OUT THE GENERAL MECHANISM FOR NUCLEOPHILIC ADDITION REACTIONS
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describe sodium tetrahydridoborate
- NaBH4
- reducing agent which is commonly used in organic synthesis
- compound is made of a BH4- ion which acts as a source of H- IONS
- used in water in aqueous solution
- Hydride ion is species that is involved in electrophilic addition and reduction of carbonyl compounds to alcohol
Write reducing equation of pentan-2-one
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draw out mechanism with sodium tetrahydridoborate
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describe hydrogen cyanide
- weak acid that will partially ionise in solution
- cynaide ion cannot react directly with carbonyl compounds but when the reaction is acidified the carbonyl functional group becomes more reactive as polarity of the C=O bond is increased
draw the equation of cyanide and water
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draw the reaction mechanism of hydrogen cyanide
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Whats the difference between aldehyde and ketones
- the C=O functional group is in different places on their carbon chain, this results in them having different chemical properties, their different reactions with the same reagents can be used to distinguish between these classes of carbonyl compounds
How can you test for a carbonyl group with Bradys reagent
- bradys reagent, this is a mixture of methanol, sulfuric acid and a solution of 2,4 - DNP,
- when this is added to an aldehyde and ketone a yellow/orange preciptate of 2,4 - dinitrophenylhydrazone derviate is seen
- doesnt happen with a carboxylic acid
How do you identify a specific aldehyde or ketone
- filtration
- recrystallisation
- dry the product
- then test for its melting point
- difficult for ketones as ketones with a similar chain length have similar boiling points this makes it challenging to experimentally distinguish between them, but the 2,4 - dinitiropphenylhydrozone derivatives have different melting points
Describe how tollens reagent works
- add sodium hydroxide solution is added to silver nitrate solution until a brown precipitate is formed
- dilute ammonia is added drop wise until brown precipitate redissolves
- used to distinguish between an aldehyde and a ketone, it reacts with the aldehyde to form a silver mirror precipitate but not a ketone
- this is because it is a weak oxidising agent and can react with carbonyl functional group in an aldehyde but not a ketone as when it is added to a ketone there is no reaction as ketones cannot be oxidised further
- silver ions are reduced and the aldehyde functional group is oxidized
- aldehyde turns into carboxylic acid
- DRAW THIS
reacting aldehydes and ketones with dichormate
heat with orange acidified dichromate Cr2O72-
- aldehyde turns from orange to green Cr(+6) = (+3), aldehyde is oxidised to a carboxylic acid, dichromate is reduced
- ketone remains orange
reacting with Fehling’s test for aldehydes and ketones
- heat with blue alkaline solution, Cu2+ and sodium hydroxide
- aldehyde - goes from blue solution to brick red preciptate (Cu2O), reduces copper ions from +2 to +1
- ketone remains blue
what are the physical properties of carboxylic acids
Solubility
- small carboxylic acids are very soluble in polar solvents such as water because hydrogen bonds can be formed between carboxylic acid functional group and water
- as hydrocarbon chain of carboxylic acid increases in size the solubility decreases this is because only the carboxylic acid can form hydrogen bonds with the water so as the molecule becomes longer then solubility decreases
What are the chemical properties for carboxylic acid
- they are weak acids as they partially ionize in solution releasing hydrogen ions from the carboxylic acid group
- draw this
- they react at a slower rate than with a strong acid as the pH is higher and therefore the concentration of H+ will be lower
draw the reaction of carboxylic acids with metals
2Na + 2CH3COOH = 2CH3CHOONa + H2
draw reaction of carboxylic acid with metal oxides
MgO + 2HCOOH = (HCOO)2Mg + H2O