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96 terms

Kaplan MCAT OChem Ch.8: Aldehyde and Ketones

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carbonyl
has unique ability to behave as either Nu or electrophile
aldehyde
terminal func group
formaldehyde
methanal

http://upload.wikimedia.org/wikipedia/commons/0/0f/Formaldehyde-2D.png
acetaldehyde
ethanal

http://pages.uoregon.edu/ch111/images/ethanal.gif
propionaldehyde
propanal

http://faculty.lacitycollege.edu/boanta/LAB102/Organic%20Isomers_files/organi30.png
butyraldehyde
butanal

http://upload.wikimedia.org/wikipedia/commons/d/d6/Butyraldehyde_flat_structure.png
valeraldehyde
pentanal

http://upload.wikimedia.org/wikipedia/commons/d/d6/Butyraldehyde_flat_structure.png
-carbaldehyde
aldehyde attached to ring
formyl-
aldehyde doesn't hold priority
ketone's not specificed by number (c-1)
propanone (acetone)

butanone

cyclic ketones
propanone (acetone)
http://pages.uoregon.edu/ch111/images/propanone.gif
butanone
http://upload.wikimedia.org/wikipedia/commons/6/62/Butanone-structure-skeletal.png
cyclic ketone
http://www.chemicalregister.com/upload/cr/108-94-1.png
common name for ketone c
two alkyl alphabetized followed by word "ketone"
ketone as a substituent
prefix oxo-
form-
one-carbon compound
acet-
two carbon compound
dipole of carbonyl
greater than dipole of an alcohol because this lacks a H
dipole of carbonyl
in sol, dipole moments cause these to line up => rise in BP (but less than that of alcohols, because no H bonding)
aldehydes
more reactive towards Nu than ketones
carbonyl O
more EN => draw electrons away from C => making C electrophilic
dipole of carbonyl
inc. intermolecular forces and BP relative to alkanes
types of aldehyde/ketone synthesis
oxidation of alcohols

ozonolysis of alkenes

friedel-crafts acylation
oxidation of alcohols (aldehydes)
from partial oxidation of a primary alcohol
oxidation of alcohols (aldehydes)
only reagent used is PCC
oxidation of alcohols (ketones)
oxidation of secondary alcohol
oxidation of alcohols (ketones)
since no risk of oxidizing too far:

-Na or K dichromate

-chromium trioxide (Jones's reagent)

-PCC
PCC
dry, nonhydrating oxidizing reagent
ozonolysis of alkenes
these oxidatively cleaved to form aldehydes and ketones
ozonolysis of alkenes
whether you get aldehyde or ketones depends on whether you started w/ mono- or disub these
ozonolysis of alkenes
breaks these using ozone
friedel-crafts acylation
produces aromatic ketones (aldehydes if R = H) in form of R-CO-Ar
types of rxns w/ aldehydes and ketones
enolization and rxns of enols

addition rxns

aldol condensation

wittig rxn

oxidation and reduction
types of addition rxns of aldehydes and ketones
hydration

acetal and ketal formation

rxns w/ HCN

condensation w/ Ammonia derivatives
alpha protons of carbonyl compounds (enolization)
relatively acidic (pKa = 20) due to resonance stabilization of conj base.

electrons up to oxygen
alpha protons (enolization)
good probability of reattaching to partially neg. oyxgen instead of carbon
(enolization)
in solution, aldehydes and ketones exist as mix of two isomers: keto and enol,
enol
unsat. alcohol (DB and alcohol)
tautomers
differ in placement of H of two isomers

eq. more towards keto
tautomerization/enolization
process of interconverting keto and enol
enol
important intermediates
enolate carbanion
acts as Nu

can be created w/ SB (LDA abd KH)
1,3-dicarbonyl
extra acidic since there are two carbonyls to delocalize neg charge,
1,3-dicarbonyl
used to make the carbanion
carbanion
once formed, this Nu reacts via Sn2 mech w/ alkyl halides or ά-B unsaturated carbonyl compounds
michael additions (aldehyde and ketones)
once formed, this Nu reacts via Sn2 mech w/ ά-B unsaturated carbonyl compounds
michael additions (aldehyde and ketones)
carbanion attachest to unsaturated carbonyl at the B-position owing to resonance form
addition rxn (aldehyde and ketones)
Nu add. to a carbonyl
addition rxn (aldehyde and ketones)
carbon is electrophile
addition rxn (aldehyde and ketones)
Nu attacks => covalent bond to C => breaks pi bond in C=O => electrons pushed up to oxygen => tetrahedral intermediate
addition rxn (aldehyde and ketones)
if no good LG => carbonyl will not re-form => final prod identical to intermediate

O- accept proton, making OH
addition rxn (aldehyde and ketones)
if good LG present => carbonyl reform
hydration (addition rxn)
water + aldehyde and ketones => gem-diols (1,1 diols)
hydration (addition rxn)
Nu oxygen of water attacked carbonyl carbon
hydration (addition rxn)
normally slow, but inc. rate by adding small amount of acid or base
acetal and ketal formation
aldehyde and ketone + alcohols (Nu)
acetal and ketal formation
one eq. of OH => hemiacetal or hemiketal

contains one OH

in base, rxn would stop here
acetal and ketal formation
two. eq. of alcohol => acetal or a ketal

in aldehyde => H is characteristic
acetal and ketal formation
catalyzed by anhydrous acid
acetal and ketal formation
used as protecting grou
ethylene group
protecting group
protecting group
molecules w/ these can easily be converted by to carboxyls w/ aq. acid and heat
rxn w/ HCN
Nu,

pKa = 9.2
rxn w/ HCN
after H disso. => Nu attacks carbonyl => cyanohydrins
cyanohydrin
formed after CN- attacks carbonyl, when O is protonated
condensation w/ Ammonia Derivatives
Ammonia as Nu + carbonyl => water is lost => imine
Nu sub
DB forms between C and N and a LG (water is kicked off)
common ammonia derivatives (H2NOH)
form oximes
common ammonia derivatives (hydrazine)
form hydrazones
common ammonia derivatives (H2NNHCONH2)
form semicarbonzones
imine
compound w/ N atom DB to a carbon atom
condensation rxn
reaction in which water is lose between two molecules
aldol condensation
Nu add to carbonyl in which aldehyde acts as both an electrophile (keto form) and Nu (enol or enolate form)
aldol formation
compound treated w/ catalytic base => enolate + carbonyl of another compound => aldol (aldehyde + alcohol)
enolate
more Nu since neg charge
aldol condensation
w/ strong base and high temp + kick off water => DB => a, B unsaturated aldehyde
aldol condensation
only use one type of aldehyde or ketone
the wittig reaction
swaps out C=O for a C=C
the wittig reaction
gets C=C by converting aldehydes and ketones into alkenes
the wittig reaction
first step is formation of phosphonium salt from Sn2 rxn of alkyl halide w/ Nu (C6H5)3P
phosphonium salt
P atom that has three aromatic phenyl group => good Nu and attacks partially pos. on alkyl halide
phosphonium salt
after attacks partially pos. on alkyl halide => it's deprotonated (lose proton of alpha carbon) w/ a SB => ylide
ylide/phosphorane
it's a zwitterion
phosphorane
this form has DB between C and P
the wittig reaction
aldehyde/ketone => alkene
ylide
type of carbanion, so has Nu prop.
ylide
when combined w/ aldehyde/ketone, attacks carbonyl C => intermediate called betaine
betaine
(specific type of zwitterion) that forms a four membered ring between O and P.

Ringed intermediate known as oxaphosphetane => decomposes to yield an alkene and triphenylphosphine oxide
oxi-red of aldehyde to carb acids
some ex, amles: KMnO4, CrO3, Ag2O, H2O2
oxi-red of aldehyde to alcohols
LAH and NaBH4 when milder conditions
oxi-red of aldehyde to to alkanes (two types)
Wolff-Kishne reduction

Clemmensen reduction
Wolff-Kishne reduction (oxi-red of aldehyde to to alkanes (two types)
carbonyl to hydrazone => hydrazone releases N2 when heated w/ base => alkane

useful when product is stable under basic conditions
Clemmensen reduction(oxi-red of aldehyde to to alkanes (two types)
aldehyde/ketone is heated w/ amalgated zinc in HCl
oxi-red of aldehyde to to alkanes by:
-Wolff (H2NNH2)
-Base (KOH)
-Ethylene glycol (high boiling solvent)
-Clemmensen (Hg(Zn), HCl)
aldehydes
oxidized to carb acd

reduced to primary alcohols
ketones
can't be further oxidized

reduced to secondary alcohols