Carbonyl Chemistry Flashcards
Why are alpha hydrogens acidic?
aldehydes/ketones can have their proton removed by a base and from a carbanion
the carbanion can form an enolate via resonance
- resonance stabilises the carbanion
- the enolate/stable species contributes to the acidity of the alpha hydrogens
- the electron withdrawing group (carbonyl) makes the hydrogen more easily removed
What bases are normally involved in the formation of bases?
NaOH - water soluble
n-buytllithium - organic base
LDA (lithium disopropylamide) - organic base
What are the different types of aldol condensation reaction?
base catalysed reaction between two aldehydes - forms a beta hydroxy aldehyde
acid catalysed reaction between two aldehydes - forms an alpha beta unsaturated ketone
reaction between two ketones - forms an alpha beta unsaturated ketone
What are the steps in an aldol condensation reaction?
1st - addition of an appropriate base to form an enolate
2nd - nucleophilic attack at the carbonyl
3rd - protonation
4th - dehydration
Why does the beta hydroxy aldehyde undergo dehydration at the end of the reaction? What is the benefit of it occurring?
dehydration occurs spontaneously
the dehydrated product is more stable than the non-conjugated carbonyl due to
- delocalisation of electrons
- extended pi system
What is a crossed aldol reaction? How can it be made to be successful?
crossed aldol reaction can be between two aldehydes or two ketones
to be successful one of the reactant must not have any alpha hydrogens
- if both have alpha hydrogens, then it can have too many possible products to be useful
What is the Claisen Schmidt reaction?
base catalysed reaction between an aldehyde and a ketone
forms an alpha beta unsaturated ketone
Why is the aldol reaction of nitroalkanes useful? How does it occur?
is able to produce amines after reduction of the final product (alpha beta unsaturated nitroalkane)
occurs via catalytic hydrogenation with a platinum or raney nickel catalyst
What is a Claisen Condensation reaction?
base catalysed condensation reaction between two esters
base - sodium ethoxide
forms a beta ketoester
Why can’t sodium hydroxide be used in a claisen condensation reaction?
sodium hydroxide is too strong of a base
- it would hydrolyse the ester
ester = carboxylic acid and alcohol
What is the Dieckman cyclisation reaction? What does it produce?
condensation reaction involving a 1,6-diester
reaction is base catalysed and has an acid workup
produces a cyclic beta ketoester
How are different products formed from a Dieckman cyclisation reaction?
a 1-6 diester gives a 5-membered ring
a 1-7 diester gives a 6-membered ring
