Ketones and aldehydes Flashcards
what is a carbonyl group
C=O
what is an acyl group
a carbonyl group (C=O) bonded to a carbon group
what is a ketone
C=O bonded to two R groups
what suffix do ketones have
-one
when is “oxo” used for ketones
oxo describes the =O (the oxygen group)
what is an aldehyde
C=O bonded to an R group and an H
what suffix do aldehydes use
-al
when is “oxo” used for aldehydes
oxo describes the =O (the oxygen group)
what prefix do aldehydes use
formyl-
what shape does the C=O bond have
trigonal planar, sp2
describe the bond strength and length of the C=O bond
the C=O bonds are stronger but shorter than the typical sigma bond
T or F: the C=O bond has a dipole moment (explain)
true; C is electron poor while O is electron rich, and O pulls electron density towards it giving it a partial neg charge
what can IRs tell us about our molecule (in regards to the C=O)
it can show if C=O is present. We won’t know where or how many though
what can HNMR tell us about our molecule
the singlet’s position is what’s indicative of an aldehyde vs carboxylic acid
what does CNMR tell us about our molecule
carbonyls in a C13 NMR will stand out, near the 113 area (far left)
how do we prepare acids or ketones
oxidize an alcohol
what is the product when a 1 degree alcohol is oxidized
carboxylic acid
what is the product when a 2 degree alcohol is oxidized
ketone
what is the product when a 3 degree alcohol is oxidized
no reaction
what are some examples of things that go over the arrow in an oxidation reaction
- KMno4
- H+ and K2Cr2O3
- H+ and Na2Cr2O3
- H2Cr2O3
- CrO3 and heat (Jones)
what do you do if you want to oxidize a 1 degree alcohol into an aldehyde instead of an acid?
for a milder reaction you use PCC. It stops the reaction at an aldehyde
what is ozonolysis of alkenes (what is the reactant and product)
turns an alkene into a carbonyl (we get two of these products)
what happens in ozonolysis of alkenes
we split the double bond and make 2 of our products. Oxidation is happening on both sides
T or F: in ozonolysis of alkenes, if the reactant was asymmetrical we would get the same 2 products
false, an asymmetrical alkene would mean we get 2 different products
what is hydration of alkynes
turns an alkyne into a carbonyl
what happens in hydration of alkynes
we use acidified water with mercury as a salt. We’re doing oxidation of the carbon up to an alcohol, but we will continue to oxidize it all the way up to a carbonyl
what is reduction of esters to aldehydes
ester is reduced to an aldehyde
what happens when esters are reduced to aldehydes
we use DIBAL washed with acid to do this
what is reduction of nitriles
a nitrile (R-C-(triple bond)-N) is reduced into an aldehyde
what happens when nitriles are reduced
use DIBAL washed with acid
what is reduction of acyl halides
an acyl halide (C=O bonded to R and X) is reduced into an aldehyde + LiX
what happens in reduction of acyl halides
we use LiAIH4 (Or some other variation of LiAl). It is bulky
what are the different types of nucleophiles (5)
H-type, O-type, S-type, N-type, and C-type
T or F: H- is a nucleophile
false; it’s a strong base
since H- is a strong base and not a nucleophile, what do we use as our nucleophile
we use NaBH4 (think of it as BH3 and a hydride)
why do we use boron in the nucleophile for H-type nucleophiles
it’s not very large or polarizable, making the nucleophile selective
after H-type nucleophiles react and make a product, why do we get stuck
we get stuck because in order for the product to reform, it has to kick off either C or H, and none are good options
in H-type reactions, we get stuck at the product so how do we combat this, and what are we left with
we QUENCH the reaction. Use water or a dilute acid. this increases the amount of protons added to the reaction –> result is an alcohol
to show the overall carbonyl group reaction, is it in one step or two? what is it/are they? why?
2 steps, 1= reaction with LAH, 2=reaction with water. In two steps because LAH reacts violently with water. Product=enantiomers
to show the overall H-type reaction, is it in one step or two? what is it/are they? why?
it’s in 1 step because NaBH4 is more mild. The reaction is essentially the reverse of the oxidization of the alcohol
what is an O-type nucleophile
a nucleophile with oxygen
does an O-type nucleophile have a slower or faster attack than H-type? why?
slower attack than H; due to electron density
what is wrong with the product of an O-type reaction
it has a very good leaving group which will just leave
since the product of o-type has a leaving group that will leave, what can we do
we can either reverse to the starting materials or make the carbonyl group more electrophilic
in o-type, how do we make the carbon electrophilic
we use a catalytic amount of protons or do the reaction in acidic conditions
after making the carbon more electrophilic in o-type, what is the product and what is the outcome of this
positively charged oxygen on the product, so it will want the nucleophile
T or F: making the carbon more electrophilic in the o-type reaction is reversible
true; so we must use equilibrium arrows
describe the steps of the o-type reaction
- adding catalytic hydrogen to make the electrophilic carbon
- alcohol nucleophile attacks, product has a good LG
- a proton is lost (we get an X shaped product) and protonation occurs to get water as an LG
- water leaves, nucleophile attacks again, deprotonation occurs
- we’re left with a ketal or an acetal
what is the difference between a ketal and an acetal
ketal: two ethers that form from the original carbonyl
acetal: same as ketal but has an H group and an R instead of 2 R’s (comes from aldehyde)
in o-type, how can we drive the equilibrium towards a product
remove water will shift the reaction to the right
where in the o-type mechanism do we want to remove water to drive the reaction forward
in the 5th step:
- our reactant is X shaped and one of the subs is positively charged water
- we can remove water, which gives us a ketone bonded to an R
in o-type, what do we use to remove water
we use azeotropic distillation glassware – a dean-stark trap
how does a dean-stark trap work?
water is separated from the reaction mixture via differences in density and miscibility. water is trapped and doesn’t return to the reaction
T or F: in o-type reactions, the stoichiometry of any alcohol we use is important
true;
what do we do if we only want to react with one of the subs on a molecule, and leave the other alone?
we need to use a diol as a protecting group
why are protecting groups useful?
if we want to react the less reactive sub on a molecule, the protecting group protects the one we want to keep
describe the mechanism of adding a protecting group. The reactant has a ketone we want to keep and an ester we want to reduce
the protecting group protects the ketone, and then we add a reducing agent and then water, making the ester into an alcohol. Then we wash with acidified water to convert it back into a ketone
describe the hydration of carbonyls to diols
- can happen under acidic or basic conditions
- the carbonyl can react with either H+ or OH- and water, producing a geminal diol (X shaped, with two OH groups)
T or F: a more electron deficient carbonyl = a slower reaction rate. Explain
false; a more electron deficient carbonyl = faster reaction rate
- if the carbon is electron rich, the nucleophile won’t want to attack it, so the carbon must be electron poor
what is the purpose of using S-type nucleophiles
used as tools to grow carbon chains by making a new C-C bond
what is used in s-type reactions?
start with an aldehyde, use dimercaptoethane and a lewis acid, product is a thioacetal
what are the reagent and product in s-type reactions
start with an aldehyde, end with a thioacetal
what is a thioacetal
a ketal, but instead of O we have S
in s-type reactions, why do we use a lewis acid
the lewis acid makes the carbonyl group more electrophilic than H+
in s-type, why do we want the lewis acid to make the carbonyl group more electrophilic than H+
then a strong base will deprotonate the thioacetal, because that H is going to experience a conjugate base that is stabilized
T or F: in s-type, we need a very strong base to remove the proton
true
in s-type, after the mechanism stuff, we’re left with a carbon nucleophile. What can we do now?
we can treat it with any of the substitutions we saw last semester
in s-type, what happens when we treat the carbon nucleophile with an alkyl halide?
the reaction creates a new C-C bond, and allows us to grow our carbon chain
in s-type, once we react the carbon nucleophile with an alkyl halide and create the new c-c bond, what two things can we do to remove the thioacetal
hydrolysis or desulfurization
describe hydrolysis to remove thioacetals
converts thioacetal to a ketone. Can be under acidic or basic conditions
describe desulfurization to remove a thioacetal
used when we don’t want acidic or basic conditions (it’s hydrogenation)
- converts thioacetal to a hydrocarbon chain with an R group
describe n-type reactions
carbonyl is treated with amines and water is removed, producing a product containing C and N (depends on what type of amine is used)
what is the product when a 1o amine is used
imine. R-N=C, with a lone pair on the N
T or F: 1o amine to produce an imine uses the same pathway that was used to produce a ketal
true
T or F: we get a mixture of products of imines if our starting materials are unsymmetrical
true
for finding the major product of imines, what do we need to consider
sterics between the R groups and the rest of the molecule
in n-type, what is our product when we use a 2o amine
an enamine. It’s an amine bonded to a vinyl carbon. Has 2 R groups from the N and a lone pair
what is special about the mechanism of 2o amine to enamine
similar steps to imine mechanism, except the secondary amine acts as a base instead of water to deprotonate
which carbon is deprotonated in a 2o amine reaction (n-type)
the alpha carbon (carbon next to the carbon of the double bond)
T or F: if our starting material is asymmetrical, we get a mixture of products in our 2o amine n-type reaction
true
in 2o amine –> enamine reaction, which product is our major product
the less substituted double bond is the major product
describe the clemmensen reduction
carbonyl treated under very acidic conditions to create a hydrocarbon
if we don’t want to use the harsh clemmensen reduction reaction, what can we do instead?
use hydrazine to convert the carbonyl group into a hydrazone
what is hydrazine
N2H4
it’s N-N, where each N is bonded to 2 H’s and has a lone pair
what is hydrazone
H2N-N(with lone pair)=C(joined to the rest of the molecule)
what is the wolff-kishner reaction
reduction of a hydrozone. Performed under basic conditions, and N2 gas is produced
what is the driving force of wolff-kishner reactions
N2 gas production (irreversible)
what is the product of a wolff-kishner reaction
a fully reduced product from a carbonyl down to a straight chain
describe C-
acts as a strong base and is one of the strongest bases we have
what is an example of a C-type nucleophile (ie how might C- be written)
as BuLi (Bu=butane that’s negatively charged around Li+)
what can C- do since it’s negatively charged
it wants to deprotonate anything it can (ie water to create OH)
T or F: C- acts like a nucleophile
false, it’s so strong that it acts like a base
for C-type nucleophile questions, what will the C- be attached to
an organic species
describe the mechanism of a C-type reaction
C nucleophile attacks the carbonyl from the bottom, causing electrons from the double bond to go to the O (=X shaped product). Then, the electrons from the O attack the HX nucleophile, to create a cyanohydrin
name the product of C-type reactions
cyanohydrin
what’s the purpose of grignard reactions
insertion of magnesium (or lithium) into an alkyl halide
describe how polarization is affected in a grignard reaction
polarization is revsered when Mg is added into the molecule. This is because the carbon is more electron dense than Mg
prior to the grignard reaction, describe the dipole moment
partial positive carbon, partial negative X
after the grignard reaction, describe the dipole moment
partial negative carbon, partial positive Mg
what is X in the grignard reaction
we don’t use F much, so X=I, Cl, or Br
what are the conditions for a successful grignard reaction
- must be a polar aprotic solvent (ie Et2O)
- no water or alcohols! (because protons destroy the reagent RMgX)
what can we make with the grignard reagent (RMgX)
an alcohol
describe the process of using RMgX to make an alcohol
RMgX reactions with a carbonyl and an aprotic solvent, to make an X shaped molecule with a neg/ O. Then we quench it with water, making an alcohol
T or F: grignard reagents (RMgX) can be 1o, 2o, or 3o
true
which carbons make up the new c-c bond in the product of the grignard mechanism
the nucleophilic to the electrophilic carbon
what is the purpose of the wittig reaction
we want a new c-c bond, but not an alcohol like we saw with grignard
what molecule does the wittig start with
starts with triphenylphosphine; P(Ph)3
what is the formula of triphenylphosphine
P(Ph)3
describe triphenylphosphine
a phosphate with 3 phenyl groups (benzene rings) attached, and it has a lone electron pair. It’s bulky
what is the reagent of the wittig reaction
an alkyl halide
describe the mechanism of the wittig reaction
P(Ph)3 reacts with the alkyl halide via backside attack (Sn2), causing the leaving group X to leave. P(Ph)3 is now attached, and P has a positive charge. This is an intermediate.
Next, BuLi (strong base) deprotonates the carbon, which produces an YLIDE. Then we get hybrid resonance structures. Then the molecule attacks a carbonyl from the bottom, we get an X shaped molecule, it cyclizes, it rearranges, and we’re left with an alkene (new c-c bond was made) and P(Ph)3O
what is an YLIDE
a compound with a C- bonded to a P+, S+, N+, etc
T or F: wittig reaction produces a new c-c bond
true
in the wittig reaction, which carbons make up the new c-c bond
carbon of the carbonyl to the electropositive carbon of the alkyl halide
what is the result of the wittig reaction if you start with unsymmetrical starting material
a mixture of products
what happens to the wittig product when it’s oxidized
it reverts back to the original carbonyl
what are two “one-pot” reactions
cannizzaro and baeyer-villager
what is the starting material in the cannizzaro reaction
aldehyde
what is/are the products of the cannizzaro reaction
an alcohol and an acid
in what proportions are the cannizzaro products made
50/50
what are the 3 downfalls of the cannizzaro reaction
- only used for aldehydes
- the aldehydes must lack alpha hydrogens
- can only be done in basic conditions
in the cannizzaro reaction, does the OH- act as a nucleophile or a base
nucleophile, because we don’t have the conditions to deprotonate
describe the cannizzaro reaction mechanism
OH- attacks the aldehyde from the bottom, electrons move to make O-. We now have an X shaped intermediate with O-, H, OH, and Ph. The electrons then move away from the O-, the H leaves, and it bottom attacks the starting material (which then can react with water), creating 2 products
what is the baeyer-villager reaction
oxidation using per-acids (inserts an oxygen beside the carbonyl)
what are per-acids
carboxylic acid, but instead of OH we have an additional oxygen in there
what is the product of the baeyer-villager reaction
ester
what do we use to perform the baeyer-villager reaction
mCPBA
- benzene ring with Cl attached
- also has the per-acid attached
why is mCPBA used
it’s only mildly acidic (good because we aren’t using it for acidity), and it’s safer than other peroxides
describe the baeyer-villager mechanism
mCPBA is not a nucleophile, so the O of the carbonyl deprotonates it, giving it a neg charge=nucleophile. Nuc attacks, then we get intramolecular cyclization (concerted), then we get an alkyl shift of the R group = ester
describe the product of the baeyer-villager reaction if the starting material is symmetrical
you get one product
describe the product of the baeyer-villager reaction if the starting material is unsymmetrical
you have two products, but the yield is NOT 50/50
T or F: the products of the baeyer-villager reaction (if there’s 2) are always 50/50
FALSE
how do you determine the major product of the baeyer-villager reaction
there’s precedence of R group migration.
H>3>2>Ph>methide>1
compare the R groups of each product (R group is the one attached to the oxygen)
