Carbonyls Flashcards
How do you form an aldehyde?
oxidation of a primary alcohol
How do you form a ketone?
oxidation of a secondary alcohol
Are carbonyls reactive or unreactive to electrophiles?
unreactive
How can nucleophiles react with carbonyls?
the carbon in the C=O bond is slightly positive as the O is electronegative
What are the properties of carbonyls?
polar
high MP and BP
soluble in water
Why is the MP and BP of carbonyls lower than alcohols and carboxylic acids?
there is no hydrogen bonding between molecules
Why do carbonyls have a high MP and BP?
permanent dipole-dipole interactions between molecules
What are the 4 reactions you need to know for carbonyls?
2,4-DNP
oxidation of aldehyde to carboxylic acid - Tollens test
nucleophilic addition x2:
1. reduction of carbonly compund to an alcohol
2. addition of HCN
What happens when an aldehyde or ketone react with 2,4-DNP?
produces and orange to yellow precipitate
How can you identify a sepcific carbonyl compound from reacting with 2,4-DNP?
finding the melting point of the recrystallised derivative and compare the MP to other known MP of carbonyl compunds
What is the method of recrystallisation?
- add minimum amount of hot solvent to dissolve crystals
- cool solution
- filter the crystals and rinse with cold solvent to leave them dry
What is tollens reagent made of?
silver nitrate
ammonium hydroxide
sodium hydroxide
How can an aldehyde be detected by Tollen’s test?
Tollen’s reagent oxidises aldehydes to carboxylic acids
warmed
silver ions are reduced to metallic silver producing a shiny silver mirror
What reducing agent is used to reduce carbonyls into alcohols?
NaBH4
What is a hydride ion?
H- = has 2 lone pairs
acts as a nucleophile to reduce carbonyls into alcohols
What is the steps of nucleophilil addition of carbonyls with hydride ions?
- H- acts as a nucleophile, attacking the slightly + carbonyl C
- the intermediate acts as a base, taking H+ from H2O
- leaves a Hydroxide ion and an alcohol
What is a hydroxynitrile?
an alcohol with CN (cyanine) attached
Why is a reagent needed for the reaction of a carbonyl with HCN?
HCN is a weak acid = only slightly dissociates into H+ and CN- in aq solutions
the undissociated molecure, HCN, is a weak nucleophile = reacts very slowly
What is the reagent used in reacting a carbonyl with HCN?
NaCN / H+ = acidified, aq, sodium cyanide solution
What happens to an aldehyde and ketone when added to Fehling’s solution?
aldehyde = forms dark red precipitate
ketone = stays blue
What is Fehling’s solution made from?
copper sulfate solution
what are enantiomers?
pair of molecules that are mirror images of each other
What are optical isomers?
stereoisomers so they have the same structural formula but different arrangement of atoms in space
they are non-superimpossable mirror images of each other
What is a chrial centre?
a central carbon atom with 4 different groups attached
why would a different reagent of HCN be used instead?
HCN is highly toxic so a different CN compound would be safer to use
How can nucleophilic addition of carbonyls lead to enantiomers being produced?
the carbonyl functional group is planar
so the nuceophile can attack from above or below the plane
aldehydes form chiral centres with 4 diff groups attached
so it can form opitcal isomers depending whether the nucleophile attacked from the top or bottom
ketone do not form chiral products = symmetrical
