4b Flashcards
how can C=O be made
oxidation of alcohols
partial oxidation of a primary alcohol
aldehyde
- 2e-
full oxidation of a primary alcohol
carboxylic acid
-2e-
from a carboxylic acid to an aldehyde
reduction
+ 2e-
aldehyde to a primary alcohol
reduction
-2e-
oxidation of a secondary alcohol
forms a ketone
nothing but a ketone
- 2e-
what is used as an oxidation agent to go from a primary alcohol to a aldehyde
PCC (pyridinum chlorochromate)
PDC (pyridinium dichromate)
how come using PCC AND PDC stops oxidation at an aldehyde
bc they are mild oxidation agents
they cannot fully oxidise the primary alcohol to a carboxylic acid.
what oxidising agent is used to fully oxidise a primary alcohol into a carboxylic acid
KMnO4
what is used to oxidise a secondary alcohol info a ketone
KMnO4
(CrO3 + H+ )
Na2Cr2O7
how many electrons are lost in the oxidation from a primary alcohol to a carboxylic acid
4!!
2 to get an aldehyde,, then 2 more to get a carboxylic acid.
what is jones oxidation
from a primary alcohol to a carboxylic acid using CrO3 and H2SO4 + H2O
what is the intermediate in a jones oxidation
the aldehyde is an intermediate
in a jones oxidation reaction,, are all functional groups oxidised
yes!! other primary alcohols or aldehydes will also be oxidised!
jones oxidation with a secondary alcohol
secondary alcohol + CrO3 + H2SO4 + H2O
gives a ketone!!
can ketones be oxidised
nope!!
can phenols be oxidised
nope!!
there is no H’s on the alpha carbon
what is MnO2
a mild oxidising agent
what can MnO2 oxidise
prim alcohols to aldehydes
aldehydes to carboxylic acids
secondary to ketones
is C=O electrophilic or nucleophilic
electrophilic
what reactions occur at the C=O
acid base reactions
oxidation reduction reactions
additions (reversible or irreversible)
what reactions can occur on the alpha C next to the C=O
acid base reactions to form enolates
enolate reactions can then occur as they act as a nucleophile (O- near a CC double bond)
what’s an enolate
C=C — O-
act as nucs
formed by acid base reactions of an alpha C next to a C=O
what shape is C=O
trigonal
name a reducing agent
HBr
alkene + HBr
1,2 addition reaction.
= attacks H
then Br attacks CC+
ketone + HBr
O attacks the H
then Br attacks the C
lone pair on O can kick off the Br to form a ketone again (as the ketone is more stable)
intermediate can’t be isolated
if the nucleophile attacking the C=O is a good leaving group,, what can occur
the lone pairs on O can kick off the nuc as it’s a good LG.
addition occurs,, then elimination occurs.
what’s special abojt the O on C=O
it’s weakly basic
as the O on C=O is weakly basic,, hat can it interact with
a bronsted acid
a lewis acid
bronsted acid
donated H
lewis acid
accepts e-
when the O on C=O acts as a base and attacks an electrophile (H+) what then happens
the O will be +.
resonance can now occur and make the C more +.
gives the aldehyde// ketone conjugate acid CC+ character
this reaction is also reversible (the O attacking a H+ // electrophile)
what’s a gem diol
when 2 OH are bonded to the same C.
what is another way of explaining a gem diol
it’s a ketone or aldehyde hydrate.
how do we form a ketone hydrate // gemdiol
O attacks a H+
H2O attacks the C
de protonate the H2O using H2O
u now have a gemdiol
R, R, OH, OH
this rea is reversible + the OH can grab a H,, lone pair of other OH can kick off the water, H on OH can be attacked by water + removed to give a ketone
what reaction gives a gem diol
a 1-2 addition of water
H2O + H2O gives (rev reaction)
OH -
H3O+
at low ph there is a bunch of
H3O
high con
at high ph there is a bunch of
OH -
high conc
when is OH- a good leaving group
in strongly basic conditions
high pH!!
aka lots of OH around it
what could favour certain products from forming
the bond angles!!
double bond but 60* when it wants to be 120* isn’t favoured!!
60* when it’s meant to be 109.5 is more favoured!!
in 1-2 addition reactions with C=O,, how does the nuc attack
at 107*
burgi dunitz trajectory
what can decrease the rate of a 1-2 addition
steric hinderance to do burgi dunitz trajectory.
this is why aldehydes are more reactive than ketones. (H vs R group)
are 1-2 additions reversible
they can be!!
both irreversible + reversible
where does the nuc attack the C in C=O
at 107*
in the pi**
🦋 shape
the O then attacks an electrophile
what is between the C=O bond
nothing!!
there is a node —— that way.
asymmetric ketones can give what
enantiomers due to different stereogenic centres
what is a cyanohydrin
R, R, OH, CN
what process makes a cyanohydrin
1-2 addition using NaCN + H2O
steps in the 1-2 addition to make cyanohydrin addition
CN- attacks the C
e- go to the O
O attacks H2O H
cyanohydrin is made
this is reversible!!
cyanohydrin to ketone
1-2 elimination
lone pair on OH kick off CN
OH is now +
base removes the H from OH
ketone is formed
alcohol to aldehyde
MnO2
secondary alcohol to ketone
MnO2
cyclo hexane + alcohol to aldehyde
PCC
PDC
ketone to cyanohydrin
NaCN
H2O
MeOH
what is equilibrium influenced by
influenced by factors that determine reactant and + product stability
what makes a C=O more stable
if it’s more substituted
are ketones or aldehydes more stable
ketones!!
more substituted C=O
more steric hinderance of burgi dunitz trajectory
is ketone addition or aldehyde addition more favoured
aldehyde addition is more favoured
less hinderance of burgi dunitz trajectory.
less stable C=O as less substituted
what substituents on the C=O favour addition
EWG
make the C more +
gem diol derivative is favoured
C=O and a EDG
C=O is less electrophilic
gem diol derivatives are not favoured
addition is less favoured
C=O and large substituents
addition isn’t favoured
gem diol derivatives aren’t favoured
stability of the C=O usually dictates what stability
reactant stability.
ketone + aldehyde stability
what dictates product stability
the steric hinderance.
ketones -> 2 R groups,, close together than before, tetrahedral in shape when gem diols are formed : less stable. the gemdiol is favoured less than the ketone.
ketone addition product is less favoured than the aldehyde addition product.
aldehydes in terms of pro and rea stability
rea = less stable
pro = more stable
ketones in terms of pro and rea stability
rea = more stable
pro = less stable
ketone hydration under acidic conditions to form gem diols or ketone hydrates
use H3O+ (acidic conditions)
protonate the C=O
H2O attacks the C
H2O is deprotonated
all reversible reactions
hydration of ketones under basic conditions
use of OH
OH attacks the C and e- move to the O
O attacks H20 Hydrogen (its protonated)
gem diol is made. with OH-
reversible reaction
what’s a hemiacetal
R H OR OH
from an aldehyde
use of alcohol
what’s a hemiketal
R R OH OR
ketone + alcohol to hemiketal
hemiacetal synthesis
aldehyde O attacks the H
alcohol attacks the C
H on alcohol bonded is deprotonated by alcohol
hemiacetal is made!!
hemiketal synthesis
ketone O attacks the H
alcohol attacks the C
alcohol H is deprotonated by alcohol
hemiketal is made!!
are cyclic hemiketal and hemiacetal more stable than acyclic ones
yes!!!
cyclic ones will be favoured over the reactant.
the reactant will be favoured if the product is an acyclic hemiacetal or hemiketal!!
what is an acetal
R H
OR OR
how is an acetal made
aldehyde + H3O+ + alcohols + H20
acetal synthesis mechanism
aldehyde O attacks H3O+
alcohol attacks C
e- move up to O
water deprotonates alcohol
OH on hemiacetal attacks H3O+ H
lone pair on alcohol kicks of the water
alcohol attacks the C (O is stabilised)
alcohol is deprotonated
acetal is formed
how is the back reaction of acetal synthesis made
presence of excess H2O and a catalyst
what’s a ketal
like an acetal but with 2 RS
R R
OR OR
what’s the ketal mechanism
same as the acetal mechanism
excess alcohol + H
how is the back reaction of ketal synthesis obtained
excess H2O
acid catalyst
what is glucose
hydroxyaldehyde
6 membered cyclic hemiacetal
what is ribose
5 membered cyclic hemiacetal
maltose
glucose + glucose
cellulose
polymer of glucose bridged by acetal bridges
key points of the jones reaction
prim alcohol to carboxylic acid.
CrO3 + H2SO4 –> CHROMIC ACID ( Cr OH OH =o =o )
O: attacks Cr
=o forms o-
water removed, alcohol forms, deprotonation, aldehyde forms
water attacks,, hydrated aldehyde forms,, CrO3 + H2SO4 must be used again to get the carboxylic acid.
1 electron movement for MnO2
weak oxidising agent
benzyllic and allylic alcohols to aldehydes
O: attacks Mn and O on Mn attacks H
deprotonation makes O neutral
1 e- movement from alpha H and =O to form OH
other e- from =O goes to Mn. forms a radical on alpha C.
radical and O - Mn electrons form a double bond + other e- goes to Mn
