Organic Chemistry Ch 6. Aldehydes and Ketones Flashcards
Aldehydes
Terminal functional groups containing a carbonyl bonded to at least one hydrogen, use the suffix -al and the prefix -oxo. In rings, they are indicated by the suffix -carbaldehyde
Ketons
Internal functional groups containing a carbonyl bonded to two alkyl chains, use the suffix -one and the prefix oxo- or keto-
Carbonyl
C=O, reactivity dictated by the polarity of the double bond, carbon has a partial positive charge and is therefore electrophilic
Carbonyl containing compounds
Have higher boiling points than equivalent alkanes because of dipole interactions
Alcohol containing compounds
Have higher boiling point than equivalent alkanes because of hydrogen bonding
Aldehyde synthesis
Commonly produced by oxidation of primary alcohols, weaker, anhydrous oxidizing agents like pyridinium chlorochromate (PCC) must be used or the reaction will continue to a carboxylic acid
Ketone synthesis
Commonly produced by oxidation of secondary alcohols, various oxidizing agents can be used such as dichromate, chromium trioxide, or PCC because ketones are the most oxidized functional group for secondary carbons
Nucleophilic addition reactions
When a nucleophilic attacks and forms a bond with a carbonyl carbon, electrons in the pi bond are pushed to the oxygen atom, if there is no good leaving group (aldehydes and ketone), the carbonyl will remain open and is protonated to form an alcohol, if there is a good leaving group (carboxylic acid and derivatives), the carbonyl will reform and kick off the leaving group
Hydration reactions
Water adds to a carbonyl, forming a geminal diol
Hemiacetal formation
When one equivalent of alcohol reacts with an aldehyde via nucleophilic addition
Hemiketal formation
When one equivalent of alcohol reactions with a ketone via nucleophilic addition
Acetal formation
When another equivalent of alcohol reacts with a hemiacetal via nucleophilic substitution
Ketal formation
When another equivalent of alcohol reactions with a hemiketal via nucleophilic substitution
Imine, oxime, hydrazone, and semicarbazone formation
When nitrogen and nitrogen derivatives react with carbonyls
Imine tautomerization
Imine enamines
Enamines
Can tautomerize with imines
Cyanohydrin formation
Hydrogen cyanide reacts with carbonyls
Aldehyde oxidation
Aldehydes can be oxidized to carboxylic acids using oxidizing agents like KMnO4, CrO3, Ag2O, H2O2
Aldehyde reduction
Can be reduced to primary alcohols using hydride reagents
Hydride reagents
Reduction agents such as LiAlH4 or NaBH4
Ketone oxidation
Cannot be further oxidized
Ketone reduction
Can be reduced to secondary alcohols using hydride reagents
Alpha carbon
The carbon adjacent to the carbonyl carbon, the electron withdrawing oxygen of the carbonyl weakens the CH bond on alpha carbons
Alpha hydrogen
Hydrogens attached to the alpha carbon, relatively acidic and can be removed with a strong base, the electron withdrawing oxygen of the carbonyl weakens the CH bond on alpha carbons
Enolate
Results from deprotonation of a enol and can be stabilized by resonance with the carbonyl, are good nucleophiles
Ketones and nucleophiles
Less reactive because of steric hinderance and alpha carbanion destabilization, the presence of an additional alkyl group crowds the transition step and increases its energy, the alkyl group also donates electron density to the carbanion, making it less stable
Keto from
C=0 form that aldehydes and ketone can exist in
Enol form
double bond+hydroxyl group, less common form of aldehydes and ketons
Tautomers
Mars that can be entered converted by moving a hydrogen and a double bond, the keto and enol forms are tautomers of each other
Michaels addition
An enolate attacks an alpha-beta unsaturated carbonyl, creating a bond
Kinetic enolate
Favored by fast, irreversible reactions at lower temperatures with strong, sterically hindered bases
Thermodynamic enolate
Favored by slower, reversible reactions at higher temperatures with weaker, smaller bases
Enamines
Tautomers of imines, like enols are the less common tautomer
Aldol condensation
Aldehyde or ketone acts as both nucleophile and electrophile resulting in the formation of a carbon carbon bond in a new molecule called an aldol, contains both aldehyde and alcohol functional groups, nucleophile is the notate form from the deprotonation of the alpha carbon, the electrophile is the aldehyde or ketone in the form of the keto tautomer
1) condensation reaction occurs when the two molecules come together
2) dehydration reaction occurs which result in an alpha-beta unsaturated carbonyl
Retro-aldol reactions
Reverse of aldol condensations, paralyzed by heat and base, the bond between an alpha and beta carbon is cleaved
Dehydration reaction
Results in a loss of a water molecule
