Organic Chemistry- Aldehydes and Ketones I Flashcards
Aldehydes and ketones both contain what?
Carbonyl
What is carbonyl?
A double bond between a carbon and an oxygen
What is the difference between aldehyde and ketone?
Is what is attached to the carbonyl carbon
What is the most common funtional group in organic chemistry? Why?
The carbonyl group
First carbonyl is a component of many different functional groups (carboxylic acid, ester, amides, anhydrides)
The carbonyl has the unique ability to behave as either a nucleophile (as in condensation reactions) or an electrophile (as in nucleophilic addition reactions)
What is a ketone and aldehyde?
Ketone has two alkyl groups bonded to the carbonyl
Aldehyde has one alkyl group and one hydrogen.
Carbonly is never a terminal group in Ketone or Aldehyde?
Ketone
Aldehyde and ketones are _____ compounds.
Strong-smelling compounds.
Volatile carbonlys are found where? Examples?
In many spices, including cinnamon, vanilla, cumin, dill, and ginger.
How are aldehydes named?
By replacing the -e at the end of the alkane name with the suffix -al
What are the common names for the 1st five aldehydes?
Formaldeyde Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde
When aldehydes are named as substituents, what should you do?
Use the prefix oxo-
What is the IUPAC name for Formaldehyde?
Methanal
What is the IUPAC name for acetaldehyde?
ethanal
What is the IUPAC name for propionaldehyde?
Propanal
What is the IUPAC name for butyraldehyde?
butanal
What is the IUPAC name for valeraldehyde?
Pentanal
How does the name change if the aldehyde is attached to a ring?
The suffix -carbaldehyde is used intead
How are ketones named?
by replacing the -e with the suffix -one
How do you name ketones with their common names?
The two alkyl groups are named alphabetically, followed by -ketone
How does the name change when ketones are named as substituents?
Use the prefix oxo- or keto-
What are the physical properties of ketones and aldehydes governed by?
The presence of the carbonyl group.
The dipole of the carbonyl is stronger than what? Why?
The dipole of an alcohol because the double-bonded oxygen is more electron-withdrawing than the single bond to oxygen in the hydroxyl group
What hppens in solution with the carbonyl dipole?
The dipole moments associated with these polar carbonyl groups increase intermolecular attractions, causing an elevation in boiling point relative to their parent alkanes
Aldehydes and ketones have _____ more _____ than those of alcohol, but the _____ in _____ is less than alcohols because _______.
Have dipoles more polar than those of alcohols, the elevation in boiling point is less than that in alcohols because no hydrogen bonding is present.
In reactions, aldehydes and ketones both act as what? Why?
Aldehydes and ketones both act as electrophiles, making good targets for nucleophiles. This is due to the elecctron-withdrawing properties of the carbonyl oxygen, which leaves a partial positive charge on the carbon.
Generally, aldehydes are more ______ toward ______ than ketones because Why?
Reactive toward nucleophiles than ketones because they have less steric hindrance and fewer electron-donating alkyl groups.
How can aldehydes be produced?
From the partial oxidation of a primary alcohol, although only by pyridinium chlorochromate (PCC) With any stronger oxidants, aldehydes will ocntinue to be oxidized to carboxylic acids
How can ketones be produced?
The oxidation of a secondary alcohol. This can be performed using regeants ranging from sodium or potassium dichromate salts, to chromium trioxide, to PCC. When oxidizing a secondary alcohol, there is no concern for oxidizzing too far because the reaction will stop at the ketone stage no matter what.
What is the most important reaction mechanism on the MCAT?
The general reaction mechanism of nucleophilic addition to a carbonyl
Aldehydes, ketones, and more complex molecules share what general reaction mechanism?
The nucleophilic addition to a carbonyl
The C=O bond is what? Which makes it what?
Polarized with a partial positive charge on the carbonyl carbon and a partial negative charge on the oxygen. This makes the carbonyl carbon an electrophile, ripe for nucleophilic attack
When a nucleophile attacks a C=O bond, what happens?
If forms a covalent bond to the carbon, breaking the pi bond in the carbonyl. The elecctrons from the pi bond are pushed onto the oxygen atom. Oxygen happily accepts extra electrons due to it electronegativity. Breaking the pi bond forms a tetrahedral intermediate.
What should be asked any time a carbonyl is opened?
Can I reform the carbonyl?
What needs to be present for the carbonyl to reform?
A good leaving group
What happens if a leaving group is not present as is the case for aldehydes and ketones?
Generally O- will accept a proton from the solvent to form a hydroxyl group, resulting in an alchol
What happens if a leaving group is present as is the case with carboxylic acids and their derivatives?
The carbonyl double bond can reform, pushing off the leaving group
In the presence of water, aldehydes and ketones react to form what?
Geminal Diols
What happens in the hydration reaction forming a geminal diol?
The nucleophilic oxygen in water attacks the electrophilic carbonyl carbon. This hydration reaction normally proceeds slowly, but we can increase the rate by adding a small amount of catalytic acid or base
How are hemiacetals and hemiketals formed?
One equivalent of alcohol is added to an aldehyde or ketone
How can hemiacetals and hemiketals be recognized?
By the retention of the hydroxyl group
In baseic conditions what is hemiacetal and hemiketal?
The halfway step is the endpoint
When two equivalents of alcohol is added, what happens and what forms?
The reaction proceeds to compltions, resulting in the formation of an acetal or ketal.
What occurs during the formation of acetal or ketal?
A nucleophilic substitution reaction and is catalyzed by anhydrous acid. The hydroxyl group of a hemiacetal or hemiketal is protonated under acidic condition and lost as a molecule of water. A carbocation is thus formed, and another equivalent of alcohol attacks this carbocation, resulting in the formation of an acetal or ketal.
Acetals and ketals are frequently used for what?
As protecting groups for ccarbonyl functionalities
Molecules with protecting groups can esily be what?
Converted back to ccarbonyls with aqueous acid and heat
Why do nitrogen and nitrogen based functional groups act as good nucleophiles?
Due to the lone pair of electrons on nitrogen, and react readily with the electrophilic carbonyls of aldehydes and ketones
How is an imine formed?
Ammonia adds to the carbon atom and water is lost
What is an imine?
A compound with a nitrogen atom double-bonded to a carbon atom.
What is a condensation reaction?
A small molecule is lost during the formation of a bond between two molecules
What is a nucleophilic substitution?
Nitrogen replaces the ccarbonyl oxygen
What are some common ammonia derivatives that react with aldehydes and ketones?
Hydroxylamine (H2N-OH)
Hydrazine (H2N-NH2)
Semicarbazide (H2N-NH-C(O)NH2)
What forms when hydroxxylamine reacts with an aldehyde or ketone?
Oximes
What forms when hydrazine reacts with an aldehyde or ketone?
Hydrazones
What forms when a semicarbazide reacts with an aldehyde or ketone?
Semicarbazones
How are enamines formed?
Imines and related compounds undergo tautomerization
What do enamines contain?
Both a double bond and a nitrogen-containing group
What is a common nucleophile on the MCAT?
Hydrogen cyanide (HCN)
What does hydrogen cyanide contain?
Both a triple bond and an electronegative nitrogen atom
Is HCN acidic or basic?
Acidic with a pKa of 9.2
As a nucleophile, what does hydrogen cynade do?
After the hydrogen dissociates, the nucleophilic cyanide anion can attack the carbonyl carbon atom
Hydrogen cyanide reacting with aldehydes or ketones produces what?
Cyanohydrines once the oxygen has been reprotonated
How does a cyanohydrin gain its stability?
The newly formed C-C bond
Aldehydes occupy the middle of what?
The oxidation-reduction spectrium, the are more oxydized than alcohols but less oxidized then carboxylic acids
Where are ketones on thee redox spectrum?
They are as oxidized as secondary carbons can get
What are examples of strong oxidizing agents that can cause aldehydes to oxidize further to carboxylic acids?
Potassium permanganate (KMnO4) Chromium trioxide (CrO3) Silver (I) oxide (Ag2O) Hydrogen peroxide (H2O2)
Aldehydes and ketones can also undergo _____ to form alcohol?
Reduction
Reduction of aldehydes and ketones is often performed by what?
Hydride reagents
What are the most common hydride reagents seen on the MCAT?
Lithium aluminum hydride (LiAlH4) Sodium borohydride (NaBH4)
Which of the two hydride reagents are often used when milder conditions are needed?
Sodium borohydride (NaBH4)
