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

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