organic 2 Flashcards
are ketones or enols favoured + why
ketones
C-H bond and C=O bonds are stronger than C=C and O-H
enol
C=C - OH
ketone and water
hydrate == gemdiolke
ketone + alcohol
acetal
ketone + CN-
cyanohydrin
ketone + amine
then product + NaBH4
immine
then amine
alpha proton
protons on C adjacent to C=O
ketone to enol form
tautomerisationnnn
10^-7 Keq
ketone and enols areee
tautomers
are ketons or enols preferred
ketones
the individual bond strengthd are stronger.
going from carbonyl to an enol is an example of what
an intramolecular proton transfer.
the less acidic // stable the H is,, the less likely tautomerisation will occur.
are enols formed from ketones only
nopeee
carbonyls too
aka aldehydes and esters can also form enolssss
bc enol is just the c=c - OH formed by losing an alpha H+.
aldehyde or enol
aldehyde favoured
ester or enol
ester favoured but not as much as an aldehyde
bc EDG makes C more partially negative,, so the H e- arent really wanted.
diketone or enol
enolllll
the O-H - - - O-
HYDROGEN BONDINGG
which stabilises the molecule.
and the system itself is conjugated making it more stable
cyclic ketone or enol
enol
bc the tautomer is a phenollllll
which is highly favoured DUE TO AROMATICITY
O-H - - - - O- meaning between carbonyls
hydrogen bonding
very strong ]very stabilising
base and ketone give rise to what
- on the C u remove the alpha H’s from
- on the O u resonate the e- to. (enolate formed)
the O loves the - more!!!!
so u start the aroow and attack nucs from there.
which enolate form can be used to react with nucs
borh
but from C is preferred
attack from alpha C- to nucleophile issss
orbital overlap
soft
-c - c=o
attack from O- to nucleophile isss
hard
charges and electrostatic interactions.
what is pka of alpha Hs dependent on
groups next to it
fg next to the C=O
resonanance forms
larger pka means
less acidic proton
more stable proton
acetaldehyde + its alpha h pka
Ch3 - c=o - h
13.5
acetone and its pka
Ch3 c=o Ch3
ch3 on other side donates to C=o via induction,, C is more p- so doesnt rlly want the H e-
so H is more stable
more stable. = more pka
so 20
ethyl acetate and ph
CH3 - C=O - OEt
OEt : donates towards c=o
c is less positive
doesnt rlly want the H’s e-
H is more stable,, higher pka,, less acidic
25
what is an aldol reaction
where aldehydes and ketones react and join to give
B-hydroxy aldehydes // ketones
whats needed for an aldol reaction
base
to remove the alpha H
aldol condensation conditions and product
strong acid/ base + heat
aldehyde + aldehyde –> aldol ,, then remove H20 to give a double bond and a c=o
explain base catalysed aldol condensation
remove alpha proton from one of the molcules and resonate this up to the O to give O- and a double bond.
O- reforms c=o and double bond used to attack other carbonyl,, move e- to the o –> o-.
protonate the o- to give OH.
remove alpha protons and resonate the e- to the o –> o- and a double bond.
from o- to double to kick off OH.
what is eneded inn a base catalysed aldol condensation and why
high heat and conc base
bc OH is a bad LG
E1cb elimination
acid catalysed aldol condensation (removing H2o)
o on c=o bonds to H,, turns into O+ - H
alpha hydrogen is removed and O is neutralised, but double bond is formed. and O+ - H
other carbonyl is hydrogeneated - C =O+ - H
O: from carbonyl to double bond attacks the C=o of the other molecule and neutralises O.
OH binds to H from O+ -H and neutralises O. ,, h2o is formed
alpha protons are attcked and H20 is removed
carbonyl and base
make an enolate
make the enolate c=c-o-
attack the other thing.
make sure u draw the arrow all the way to smt good and change the charge after.
