carbonyl compounds Flashcards
what is the carbonyl group?
C=O
what is the functional group and general formula for aldehyde
- RCHO
- (C double bonded to O, single bond to H and R)
what is the functional group for a ketone
RCOR’ (C double bonded to O)
how do you differentiate between an aldehyde and a ketone?
- in an aldehyde C=O is at the end, in a ketone it is attached to an inner carbon
- aldehydes end in -al, ketones end in -one
- aldehydes can be oxidised, ketones can’t
how do you name aldehydes
- al suffix
- (C=O is on the end of chain)
how do you name ketones
- -one suffix
- (designate number for which carbon C=O is on)
what kind of intermolecular forces do molecules with the carbonyl group have? why?
- permanent dipole-dipole due to the polar C=O bond
- (O is negative)
how soluble are carbonyl groups in water? what influences solubility?
- yes
- form hydrogen bonds between water molecules and oxygen of C=O
- as C chain length increases, solubility decreases
what bond in carbonyl compounds is usually involved in reactions?why?
- C=O
- due to the polarity of the bond difference in electronegativity between C and O
what is the strongest bond in carbonyl compounds?
C=O
why is the addition of HCN important?
- increases the length of the carbon chain by 1 carbon atom
- allowing more useful molecules to be made
will the product of HCN added to a carbonyl compound have optical isomers? why?
- yes they will
- in the aldehyde/ketone the carbonyl carbon is planar
- :CN- can attack from either side above or below
- forming two enantiomers
what is the name of the product when HCN is added to a carbonyl compound
hydroxynitriles
(OH and CN groups)
what carbon is the OH group attached to in a hydroxnitrile formed from a ketone
inner carbon
what carbon is the OH group attached to in a hydroxnitrile formed from an aldehyde
terminal carbon
what is Fehling’s solution? what colour is it?
- copper complex ions
- blue
what happens when an aldehyde is added to fehiling’s solution?
reduced to Cu+ ions → colour change to brick red ppt
what happens when a ketone is added to Fehiling’s solution?
no visible change → stays blue
how do you test for a carbonyl compound?
- use Brady’s reagent (H2SO4 dissolved in methanol)
- if a carbonyl compound is present an orange precipitate is formed
- can be identified against a library of known melting points of derivatives (carbonyl compounds produces different derivatives)
what is in tollen’s reagent?
silver complex ions [Ag(NH3)2]+ in colourless solution
what happens when an aldehyde is added to tollens reagent?
silver mirror forms
as Ag+ is reduced to Ag (s)
what happens when a ketone is added to tollens reagent?
no visible change
what is another oxidising agent for alcohols and aldehydes? what change in colour does this undergo?
- acidified potassium dichromate (VI) - H2SO4 and K2Cr2O7
- colour change from orange → green
what are the reducing agents for aldehydes and ketones? what ions does this release in solution?
- NaBH4 (sodium tetrahydriodoborate III)
-releases H- ion
how do you convert an aldehyde to form a carboxylic acid?
- oxidation of aldehydes using Cr2O7 2- / H+
- i.e K2Cr2O7/H2SO4
what is the name for the mechanism of a reduction of an aldehyde
nucleophilic addition
when reduced what do aldehydes form
primary alcohols
when reduced what do ketones form
secondary alcohols
how do you represent a reducing agent
[H]
what is an aldehyde oxidised into
carboxylic acid
