organic 4 Flashcards
how do we form an enolate
we remove an alpha H and move e- to the carbonyl
what can we do with an enolate
we can use it to form bonds to other carbonyls!!!
is an enolate more reactive to a ketone or an aldehyde + why
an aldehyde!!
bc less inductive effect moving the e- towards the partially positive carbonyl
bc it only has 1 R group!!
what do end equivalents do
they help control the regioselectivity and reactivity of enolates and enols!!
what stops us from generating enols
if there’s no alpha protons to remove by the carbonyl
benzaldehyde + LDA reaction product and conditions
- 78*C
enolate but with Li bonded to the O!!!! and no negative charge
what is LDA
a strong and powerful base
kinda hindered so it helps us control the reaction
when
ketone is reacted with LDA,,, can we stop at the enolate
yessss
the reaction is rlly slow due to the low temp of -78*C!!!
what is LDA
lithium
di isopropylamide
N with 2 claw machine things and Li
describe the reaction between LDA and a ketone
Li-N bond attacks Alpha H
double bond attacks LI
u get an enolate type thing but with Li on the oxygen,, u still get the double bond aswell
LDA after reacting with a ketone isss
N claw claw H
bc u removed the Li but attacked the alpha H.
what does LDA attack
the least hindered alpha H
bc it’s a powerful but bulky base!!!
product of LDA a ketone and then the reaction with a carbonyl
Li- N attacks alpha H
double bond attacks Li
u get enolate but with Li on the neutral O.
u get H N claw claw as ur product
the Li enolate type thing then uses it’s lone pair and double bond to attack a carbonyl C.
the O will then be (+) bc it’s bonded twice to C and once to Li.
what is the lithium enolate called
lithium enolate
how does the powerpoint say lithium enols react
they say that the O -Li bond reforms the carbonyl
and that the double bond attacks the Carbonyl C
then the other Carbonyls double bond bonds with the Li.
this forms a little circle between the O’s and the Li.
this is then reacted with acid to get OH and a carbonyl on the original carbonyl.
ketone + TMS + Et3N
O bonded to TMS (single bond)
double bond between where the H was removed and the carbonyl
ketone + TMS + Et3N thermodynamic major product
most substituted double bond
ketone + TMS + LDA major kinetic product
TMS bonded to O (single bond)
double bond between the least hindered H that was removed and the carbonyl
LDA THINK LOW TEMP
kinetic product
least hindered H is removed
LDA IS USED SO LOW TEMP TOO
thermodynamic product
most stable double bond is formed
aldol reaction using the TMS enolate
lone pair on O reforms the carbonyl double bond
double bond attacks Carbonyl C
if ur enol product has a carbonyl on one end and smt else on the other,, what can u do to make the random group into an OH
u add H3O + and do a work up
how can we make benzaldehyde more reactive
add TiCl3
the carbonyl O is weakly basic so will attack TiCl3
TiCl3 is a strong lewis acid (accepts lone pair l)
benzaldehyde and TiCl3
makes benzaldehyde more reactive
u still have a carbonyl but the O is positive as it’s bonded twice to the C and once to the TiCl3
other things can then react with it. (enolates!!)
most important use of LDA
making lithium enolates
gets least hindered H
its a bulky base
what is a silyl enol ether
enolate but with SiMe3 bonded to the O (which is neutral)
ether functional group
R ‘ - O - R ‘2
where it’s a single bond
enol functional group
protonated enolate
OH near connected to a double bond
how to make a silyl enol ether
carbonyl + Me3SiCl (bc they’re hard)
the O attacks the Si
the Cl kinda just goes away.
hard + strong bond so favoured!!
enol description
double bond OH
enolate description
double bond O-
lithium enolate description
double bond O - Li
silyl enol ether description
double bond O - SiMe3
making a silyl enol ether (3 ways)
enolate lone pair attacks Si
kicks off Cl
Et3N is then used to remove the enol H to neutralise the O
———————————————————
lone pair on O on a carbonyl attacks the Si of the Me3SiCl
kicks off Cl
Et3N uses its lone pair to take off an alpha H,, which is then resonated to give a neutral oxygen
———————————————————
lithium enolate bond attacks Si and removed Cl
forms the silyl enol ether just like that
do silyl enol ethers react with all carbonyls
nopeeee
the other carbonyl needs to be ‘activated’ using TiCl4 or another lewis acid
the lewis acid needs to be making the other carbonyls Oxygen positive
NEt3 will do whattt
it’s a base so it will steal a alpha H
it steals the one that will give the most stable double bond
the way the teacher draws the silyl enol ether being made
the O- attacks the Si - Me3
it kicks off the Cl
if u have like a diester,, so like 2 carbonyls on molecule but further apart,, the symmetric looking ones,, how is a hydrogen bond created
EtO- // base can attack the alpha H’s
this can form a double bond and make O-.
this can then attack a H to form OH. hydrogen bond forms between the carbonyl O and the OH
so it forms a little ring type thing with dotted lines where the hydrogen bond is.
bonding 2 diff carbonyls together + removing an OH from the added one!
do it with di carbonyl and benzaldehyde: with benzaldehyde being the other carbonyl!! so this would drop down
knoevenagel reaction
Eto removes an alpha H
forms a double bond and O-
the O- and double bond attacks another carbonyl and forms O-
O- forms OH
Eto removes remaining alpha H ,, forms a double bond and an O-
O- and double bond is used to form another double bond and OH is removed (LG) kinda a bad LG so we had to go the long way.
NaOH and H3O+ can be added to make the esters caerboxylic acids,, then H bonding between carbonyl O of 1 carb acid and OH of another carb acid. forms a ring type thing
then arrows from double to H thats H bonded. OH bond to C from carbonyl and then the other arrow to remove the carboxylic aciddd.
can tauterise it to give the ketone version using arrows: double bond attacks H,, OH bond makes carbonyl.
doetner modification meaning
malonic acid : carboxylic acids on both sides
with an aldehyde as another reactant
u add a new R group and remove the old one as its a CO2
decarboxylation
u get rid of some of the carbonyl groups
deotner modification fully
di carboxylic acid type thing
A hs are removed and it attacks a carbonyl
OH bonds are formed betwee nthe old carboxylic acid ends!! with the new thing sticking out but its OH and not O-.
then the bond between the original OH is moved to the C of the C=O near it,, then the middle bond is broken and given to the C connected to the R group and a double bond is formed. the OH of the new thing is also removed
💗
this gives u the beginning of the new thing with a c=c and the old carbonyl group at the endddd.
pyridine and piperidine is the base thing and H donor.
remember that this gives an allene and then the OH e- go to the C-O to give C=O,, and the double bond of the allene takes the H
making a carboxylic acid from an ester,,
remove the alpha Hs,, get the double bond to keep attacking Bromines
this will remove e- densigty from thr C of the carbonyl
an OH- can attack it and it moves to the carboyl O giving O-,, this is ussed to remove the bromines to give a carboxylic acid
if u see a long carbonyl,, aka a long chain with 2 carbonyls as a reactant,, and the product is a chain with a different R group and a double bond,, what do we do and what should we think. yk this girl 💗
okay so its a carbonyl so we know we probs neeed to form some sort of enolate,, and bc its a different R group we know that that is probably from the thing we reacted to. and bc enolates react with carbonyls we know that itll be ‘C=O - new.R’ and bc its a double bond we know we have to remove a water.
and to get rid of the old part of the chain,, we need to form a hydrogen bond and then kick CO2 off 💗
this would give us an allene which then needs to attack the H and move the OH e-to reform the C=O bond
ketone to carboxylic acid
attack alpha H with base
form an enolate and use this to react with Br-Br.
keep doing this until all H’s are Br.
attack the C in C=O with OH,, then use the O- to kick off the CHBr3 to give a carboxylic acid.
