Aldehydes and Ketones (Chapter 17) Flashcards
Hybridizations within Aldehyde/Ketone
- The carbon (C) is sp2-hybridized.
- The oxygen (O) is sp2-hybridized.
Reagents: Jones Oxidation
- NaCr2O7, H2SO4
- CrO3, H2SO4, H2O
1° Alcohol → Aldehyde
PCC
Pyridinium Chlorochromate
Jones Oxidation of a 1° Alcohol yeilds a Carboxylic Acid.
2° Alcohol → Ketone
- Jones Oxidation
- PCC
1° Alkyl Benzene → Ketone
Jones Oxidation
Oxidation: PCC vs. Jones
Jones Oxidation requires an aqueous acid (i.e. H2O), whereas PCC involves a non-aqeuous acid.
Allylic Alcohol → Aldehyde/Ketone
Oxidation via MnO2
MnO2 is a mild oxidant (i.e. it cannot oxidize non-allylic alcohols or alkenes).
Product of Allylic Alcohol Oxidation
- α,β-Unsaturated Aldehyde (if 1° Alcohol)
- α,β-Unsaturated Ketone (if 2°/3° Alcohol)
Alkene → Aldehyde/Ketone
Ozonolysis
Reagents: Ozonolysis
- O3, CH2Cl2
- Zn, CH3COOH
Terminal Alkyne → Ketone
Hg(II)-Catalyzed Hydration
Oxymercurtion
Hg(II)-catalyzed hydration is a Markovnikov addition reaction.
Reagents: Hg(II)-Catalyzed Hydration
HgSO4, H2O, H2SO4
Hydration: Markovnikov vs. Anti-Markovnikov
- Markovnikov: Alcohol (—OH) adds to the most substituted carbon.
- Anti-Markovnikov: Alcohol (—OH) adds to the least substituted carbon.
Terminal Alkyne → Aldehyde
Hydroboration-Oxidation
Hydroboration-oxidation is an anti-Markovnikov addition reaction.
Reagents: Hydroboration-Oxidation
- BH3
- H2O2, NaOH
Benzene → Aldehyde/Ketone-Substituted Benzene
Friedel-Crafts Acylation
Reagents: Friedel-Crafts Acylation
Acyl Halide + Lewis Acid
Geminal Diol vs. Vicinal Diol
Gem-Diol vs. Vic-Diol
- Geminal Diol: A compound containing two alcohol groups (—OH) are bonded to the same sp3-hybridized carbon atom.
- Vicinal Diol: A compound containing two alcohol groups (—OH) are bonded to adjacent sp3-hybridized carbon atoms.
Aldehyde/Ketone → Geminal Diol
Hydration
The hydration of aldehydes/ketones can be acid-catalyzed OR base-catalyzed.
Geminal Diol → Aldehyde/Ketone
Dehydration
The hydration of aldehydes/ketones is reversible.
Why must the carbonyl Oxygen be protonated in acid-catalyzed nucleophilic addition?
Addition to Aldehydes/Ketones
The nucleophile present under acidic conditions is too weak to add to the carbonyl Carbon without prior protonation of the carbonyl Oxygen.
Protonation of the carbonyl Oxygen increases the partial-positive charge on the carbonyl Carbon, which allows the weak nucleophile to add to the Carbon.
Nucleophile: Hydration of Aldehyde/Ketone
- Basic Conditions: OH–
- Acidic Conditions: H2O
Work-Up Step: Hydration of Aldehyde/Ketone
- Basic Conditions: Protonation via H2O
- Acidic Conditions: Deprotonation via H2O
Equilibrium Preference of Aldehyde/Ketone Hydration
- Hydration of ketones will favor the reagent (i.e. Ketone) over the product (i.e. 2° Gem-Diol)
- Hydration of aldehydes will favor neither the reagent (i.e. Aldehyde) nor the product (1° Gem-Diol).
- Hydration of formaldehyde will favor the product (i.e. Methanediol) over the reagent (i.e. Formaldehyde).
- Hydration of acyl halides will favor the product (i.e. Halide Gem-Diol) over the reagent (i.e. Acyl Halide).
The alcoholic addition to aldehydes/ketones has an identical equilibrium preference trend.
Reactivity Trend of Carbonyl Groups
Hemiacetal vs. Acetal
- Hemiacetal: A compound containing an alcohol group (—OH) and an ether group (—OR) are bonded to the same sp3-hybridized carbon atom.
- Acetal: A compound containing two ether groups (—OR) are bonded to the same sp3-hybridized carbon atom.
Aldehyde/Ketone → Hemiacetal/Acetal
Alcohol Addition
- The addition of one equivalent of alcohol is required to synthesize the hemiacetal.
- The addition of two equivalents of alcohol is required to synthesize the acetal.
Hemiacetal/Acetal → Aldehyde/Ketone
Alcoholic Addition to Aldehyde/Ketone is Reversible
Alcohol Cleavage
- Hemiacetal: Alcohol cleavage can occur in acidic conditions OR basic conditions
- Acetal: Alcohol cleavage can occur ONLY in acidic conditions.
Conditions of Alcohol Addition to Aldehydes/Ketones
- Hemiacetal: Alcohol addition can occur in acidic conditions OR basic conditions
- Acetal: Alcohol addition can occur ONLY in acidic conditions.
Reagents: Hemiacetal Cyclization
Starting Material: Compound contantaining Aldehyde Group AND Alcohol Group
- Acid-Catalyzed: H+, H2O
- Base-Catalyzed: OH–, H2O
Reagents: Acetal Cyclization
Starting Material: Compound contantaining Ketone Group AND Alcohol Group
- Acid-Catalyzed: H+, H2O
- Base-Catalyzed: OH–, H2O
When is the ring-formation of cyclic hemiacetals/acetals favored?
Hemiacetal/Acetal cyclization reactions are thermodynamically favorable if the product is a five-membered ring or six-membered ring.
Aldehyde/Ketone → Cyclic Acetal
Ethanediol Protection
The cyclic acetal is highly stable/unreactive under basic conditions.
Reagents: Ethanediol Protection/Deprotection
- Protection: 1,2-Ethanediol, H3O+
- Deprotection: H3O+
Cyclic Acetal → Aldehyde/Ketone
Ethanediol Deprotection
The 1,2-Ethanediol protection of aldehydes/ketones is reversible.
Properties of Cyclic Acetals
- Unreactive w/ Strong Nucleophiles
- Highly Stable under Basic Conditions
- Highly Unstable under Acidic Conditions
The Ethanediol deprotection of aldehydes/ketones occurs in acidic conditions ONLY.
Cyclic Thioacetal → Aldehyde/Ketone
Ethanedithiol Deprotection
The 1,2-Ethanedithiol protection of aldehydes/ketones is reversible.
Aldehyde/Ketone → Cyclic Thioacetal
Ethanedithiol Protection
The cyclic thioacetal is highly stable/unreactive under basic conditions and acidic conditions.
Reagents: Ethanedithiol Protection/Deprotection
- Protection: 1,2-Ethanedithiol, ZnCl2
- Deprotection: HgCl2, H2O, CaCO3
Aldehyde/Ketone → Methylene Group
Cyclic Thioacetal
- Ethanedithiol Protection
- Raney-Nickel Reduction
Reagents: Raney-Nickel Reduction
Raney-Ni, H2
Cyclic Thioacetal → Methylene Group
Raney-Nickel Reduction
Imine
Any compound that contains a Carbon-Nitrogen double bond (C=N).
The nitrogen atom of the imine is sp2-hybridized. (This hybridization causes the C=N–R structure to be bent.)
Enamine
A compound containing an alkenyl substituent attached to the Nitrogen atom.
The Carbon atom of the C—N is double-bonded to another Carbon (C=C).
Aldehyde/Ketone → Imine
1° Amine Nucleophilic Addition
Ammonia Nucleophilic Addition
The 1° amine nucleophilic addition to aldehydes/ketones occurs in neutral conditions OR weakly acidic (i.e. pH = 4–5) conditions.
Reagents: 1° Amine Elimination
H2O
The 1° amine nucleophilic elimination ONLY occurs in neutral conditions OR weakly acidic (i.e. pH = 4–5) conditions.
Reagents: 1° Amine Nucleophilic Addition
R—NH2
NH3
The 1° amine can directly attack the carbonyl Carbon without protonation of the carbonyl Oxygen. (Primary amines are stronger nucleophiles that alcohols/water.)
Imine → Aldehyde/Ketone
1° Amine Elimination
The 1° Amine nucleophilic addition to aldehydes/ketones is reversible.
Why are amines stronger nucleophiles than alcohols?
- The lone pair electrons on the Nitrogen atom (of the amine) are more donatable due to Nitrogen having a lower electronegativity than Oxygen.
- The lone pair electrons on the Oxygen atom (of the alcohol) are less donatable due to Oxygen having a greater electronegativity than Nitrogen.
Why is 1° Amine Nucleophilic Addition ineffective in strongly acidic conditions?
The 1° amine will become fully protonated (to yield NH4+/NH3R+) under acidic conditions; the NH4+/NH3R+ is not nucleophilic.
Hemiaminal
A compound containing one alcohol group (—OH) and one amine group bonded to the same sp3-hybridized carbon atom.
Iminium Ion
A compound that contains a Carbon-Nitrogen double bond (C=N) with a positive charge on the Nitrogen.
The iminium ion is an intermediate compound formed during the 1°/2° amine nucleophilic addition to an aldehyde/ketone.
Oxocarbenium Ion
A compound containing an Oxygen-substituted carbonyl group with a positive charge on the Oxygen.
The oxocarbenium ion is an intermediate compound formed during acid-catalyzed reactions involving an aldehyde/ketone.
Enol vs. Enolate
- Enol: A compound containing an alcohol group bonded to a Carbon atom of an alkene (i.e. the alcohol group is adjacent to the alkene group).
- Enol: A compound containing an oxide bonded to a Carbon atom of an alkene (i.e. the oxide is adjacent to the alkene group).
- The π-bond electrons of the alkene are in conjugation with the Oxygen lone pair (of the alcohol/oxide).
- The enol form and enolate form are tautomers of one another.
Hydrazone
A compound containing a Carbon double-bonded to a Nitrogen (C=N) that is single-bonded to an amine group (—NH2)
R2—C=N—NH2
Hydrazone → Methylene Group
Basic Decomposition of Hydrazone
Aldehyde/Ketone → Hydrazone
Hydrazine Addition
Reagents: Hydrazine Addition
H2N—NH2
Reagents: Decomposition of Hydrazone
NaOH
Aldehyde/Ketone → Methylene Group
Hydrazone
- Hydrazine Addition
- Decomposition of Hydrazone
Aldehyde/Ketone → Enamine
2° Amine Nucleophilic Addition
2° Amine Nucleophilic Addition
R2—NH
Why is the 3° Amine Nucleophilic Addition to aldehydes/ketones impossible?
The tertiary amine does not contain a Hydrogen atom that can be transfered to the oxide ion (following attack of the amine).
Cyanohydrin
A compound containing a cyanide group (—CN) and an alcohol group bonded to the same sp3-hybridized carbon atom.
Aldehyde/Ketone → Cyanohydrin
Cyanide Nucleophilic Addition
The first step of the cyanide nucleophilic addition is reversible
Reagents: Cyanide Nucleophilic Addition
NaCN, HCl
The HCl must be added slowly to avoid the generation of the toxic HCN compound.
Aldehyde/Ketone → Alkene
Wittig Reaction
Nucleophilic Addition of Phosphorus Ylides
The Witting Reaction allows for the creation of a Carbon-Carbon double bond (C=C).
Mechanism: Phosphorus Ylide Formation
- SN2 Attack of 1°/2° Alkyl Halide by P(Ph)3
- Deprotonation (from C—H bond) via Strong Base
Why are Triphenylphoshine and Phosphorus Ylides good nucleophiles?
P(Ph)3 = Triphenylphosphine
- P(Ph)3: The Phosphorus lone-pair electrons are highly donatable due to the low electronegativity of Phosphorus.
- Phosphorus Ylide: The zwitterionic resonance structure places a negative charge on the Phosphorus-bonded Carbon atom.
Reagents: Phosphorus Ylide Formation
P(Ph)3 = Starting Reagent
- 1°/2° Alkyl Halide
- Organolithium Compound
Hydrazine
H2N—NH2