ketones/aldehydes

Flashcard maker : Kaitlynn Baldwin
ketones
carboxylic acids
esters
aldehydes
acid chlorides
amides
Carbonyl Structure – 2 points
Carbon is sp2 hybridized
C=O is shorter, stronger and more polar than C=C
Ketones and aldehydes are good solvents for ____ and ____
water and alcohol. due to hydrogen bonding
Draw Mclafferty Rearrangement
The net result of this rearrangement is the breaking of the ?, ? bond, and the transfer of a proton from the gamma carbon to the oxygen.
An alkene is formed as a product of this rearrangement through the tautomerization of the enol.
Secondary alcohols are readily oxidized to ketones with ______ in ______or by _______
sodium dichromate (Na2Cr2O7)
sulfuric acid
potassium permanganate (KMnO4).
________ is selectively used to oxidize primary alcohols to aldehydes.
Pyridinium chlorochromate (PCC)
Ozonolysis of Alkenes
Friedel Crafts Reaction
Reaction between an acyl halide and an aromatic ring will produce a ketone.
Hydration of Alkynes
The initial product of Markovnikov hydration is an enol, which quickly tautomerizes to its keto form.
Internal alkynes can be hydrated, but mixtures of ketones often result.
Hydroboration-Oxidation of Alkynes
Hydroboration-oxidation of an alkyne gives anti-Markovnikov addition of water across the triple bond.
Synthesis of Ketones and Aldehydes Using 1,3-Dithianes
1,3-Dithiane can be deprotonated by strong bases such as n-butyllithium.
The resulting carbanion is stabilized by the electron-withdrawing effects of two polarizable sulfur atoms.
Alkylation of 1,3-Dithiane
Alkylation of the dithiane anion by a primary alkyl halide or a tosylate gives a thioacetal that can be hydrolyzed into the aldehyde by using an acidic solution of mercuric chloride.
Ketones from 1,3-Dithiane
The thioacetal can be isolated and deprotonated.
Alkylation and hydrolysis will produce a ketone.
Synthesis of Ketones from Carboxylic Acids
Organolithiums will attack the lithium salts of carboxylate anions to give dianions.
Protonation of the dianion forms the hydrate of a ketone, which quickly loses water to give the ketone.
Ketones from Nitriles
A Grignard or organolithium reagent can attack the carbon of the nitrile.
The imine is then hydrolyzed to form a ketone.
Aldehydes from Acid Chlorides
Lithium aluminum tri(t-butoxy)hydride is a milder reducing agent that reacts faster with acid chlorides than with aldehydes
Lithium Dialkyl Cuprate Reagents
A lithium dialkylcuprate (Gilman reagent) will transfer one of its alkyl groups to the acid chloride.
Nucleophilic Addition
A strong nucleophile attacks the carbonyl carbon, forming an alkoxide ion that is then protonated.
Aldehydes are more reactive than ketones.
The Wittig Reaction
The Wittig reaction converts the carbonyl group into a new C?C double bond where no bond existed before.
A phosphorus ylide is used as the nucleophile in the reaction.
Preparation of Phosphorus Ylides
Prepared from triphenylphosphine and an unhindered alkyl halide.
Butyllithium then abstracts a hydrogen from the carbon attached to phosphorus.
Mechanism of the Wittig Reaction – Betaine formation
Mechanism of the Wittig Reaction – Oxaphosphetane formation
Mechanism for Wittig
The oxaphosphetane will collapse, forming carbonyl (ketone or aldehyde) and a molecule of triphenyl phosphine oxide.
Hydration of Ketones and Aldehydes
In an aqueous solution, a ketone or an aldehyde is in equilibrium with its hydrate, a geminal diol.
With ketones, the equilibrium favors the unhydrated keto form (carbonyl).
Mechanism of Hydration of Ketones and Aldehydes
Hydration occurs through the nucleophilic addition mechanism, with water (in acid) or hydroxide (in base) serving as the nucleophile.
Cyanohydrin Formation
The mechanism is a base-catalyzed nucleophilic addition: Attack by cyanide ion on the carbonyl group, followed by protonation of the intermediate.
HCN is highly toxic.
Formation of Imines
Ammonia or a primary amine reacts with a ketone or an aldehyde to form an imine.
Imines are nitrogen analogues of ketones and aldehydes with a C?N bond in place of the carbonyl group.
Optimum pH is around 4.5
Mechanism of Imine Formation
Acid-catalyzed addition of the amine to the carbonyl compound group.
Mechanism of Imine Formation
Acid-catalyzed dehydration.
Other Condensations with Amines
Formation of Acetals
Formation of ketals
Mechanism for Hemiacetal Formation
Must be acid-catalyzed.
Adding H+ to carbonyl makes it more reactive with weak nucleophile, ROH.
Acetal Formation
Cyclic Acetals
Addition of a diol produces a cyclic acetal.
The reaction is reversible.
This reaction is used in synthesis to protect carbonyls from reaction
Acetals as Protecting Groups
Hydrolyze easily in acid; stable in base.
Aldehydes are more reactive than ketones.
Reaction and Deprotection
The acetal will not react with NaBH4, so only the ketone will get reduced.
Hydrolysis conditions will protonate the alcohol and remove the acetal to restore the aldehyde.
Oxidation of Aldehydes
Aldehydes are easily oxidized to carboxylic acids.
Oxidation of Aldehydes
Oxidation of Aldehydes
Reduction Reagents … can reduce ketones to secondary alcohols and aldehydes to primary alcohols.
Sodium borohydride, NaBH4
Reduction Reagents…is a powerful reducing agent, so it can also reduce carboxylic acids and their derivatives.
Lithium aluminum hydride, LiAlH4
Reduction Reagents…can reduce the carbonyl, but it will also reduce any double or triple bonds present in the molecule.
Hydrogenation with a catalyst
Sodium borohydride, NaBH4
NaBH4 can reduce ketones and aldehydes, but not esters, carboxylic acids, acyl chlorides, or amides.
Lithium Aluminum Hydride
LiAlH4 can reduce any carbonyl because it is a very strong reducing agent.
Difficult to handle.
Catalytic Hydrogenation
Widely used in industry.
Raney nickel is finely divided Ni powder saturated with hydrogen gas.
It will attack the alkene first, then the carbonyl.
Deoxygenation of Ketones and Aldehydes
The Clemmensen reduction or the Wolff-Kishner reduction can be used to deoxygenate ketones and aldehydes.
Clemmensen Reduction
Clemmensen Reduction
Wolff-Kishner Reduction
Forms hydrazone, then heat with strong base like KOH or potassium tert-butoxide.
Use a high-boiling solvent: ethylene glycol, diethylene glycol, or DMSO.
A molecule of nitrogen is lost in the last steps of the reaction.

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