Chapter 6: Aldehydes amd Ketones I: Electrophilicity and Redox Flashcards
What is a carbonyl?
A carbonyl is a carbon double bonded to an oxygen.
Found in carboxylic acids, ketones, aldehydes, esters, amides, anhydrides, etc.
Why is the carbonyl one of the most common functional groups in organic chemistry?
The carbonyl group is one of the most common functional groups in organic chemistry for two reasons:
It is a component of many different functional groups including carboxylic acids, ketones, aldehydes, esters, amides, anhydrides, etc.
Can act as a nucleophile (as in condensation reactions) or an electrophile (as in nucleophilic addition reactions)
All of the molecules in the image have carbonyl carbons.
Where (terminal or middle) will we find aldehydes? Ketones?
Volatile carbonyl aromas.
How do we name aldehydes?
How do we name aldehydes attached to rings?
The suffix -carbaldehyde is used.
How are ketones named?
We see the prefix form- and acet- often.
What do those mean?
Is the dipole moment created by a carbonyl carbon significant regarding intermolecular forces?
How does it compare to an alkane?
How does it compare to hydrogen bonding?
What is the most common electrophile we will see on test day?
Describe the physical properties of aldehydes and ketones.
The physical properties of aldehydes and ketones are governed by the presence of the carbonyl carbon.
The dipole of the carbonyl carbon is stronger than the dipole of an alcohol because the double bonded oxygen is more electron withdrawing than the single bond of oxygen in the hydroxy group.
The boiling point is less than alcohol’s because no hydrogen bonding is present.
In reactions, aldehydes and ketones both act as electrophiles, making good targets for nucleophiles.
Aldehydes are more reactive toward nucleophile than ketones because they have less steric hindrance and fewer electron donating alkyl groups.
What are the mechanisms that produce aldehydes and ketones?
An aldehyde can be obtained from the partial oxidation of a primary alcohol through pyridinium chlorochromate (PCC: C5H5NH[CrO3Cl])
Stronger oxidants will oxidize aldehydes to carboxylic acids (also obviously therefore Primary alcohols will completely oxidize to carboxylic acids in the presence of a strong oxidizing agent)
Key tones can be obtained from the oxidation of a secondary alcohol (chromates, chromium trioxide, PCC) When oxidizing a secondary alcohol, the reaction will stop at the ketone stage.
Concept check 6.1
Why is the carbonyl carbon important in organic chemistry and reactivity?
Molecule when a nucleophile attacks, a carbonyl carbon?
The carbonyl group is polarized, with a partial positive charge on the carbonyl carbon and a partial negative charge on the oxygen. This makes the carbonyl carbon and electrophile, right for nucleophilic attack.
What makes a good leaving group?
A good leaving group in organic chemistry is one that readily departs with its bonding electrons, and is relatively stable on its own. This stability is often achieved by being a weak base, as strong bases tend to be highly reactive and unwilling to leave. Other factors contributing to a good leaving group include size and resonance stabilization.
A good leaving group is the conjugate base of a strong acid. This means the leaving group is relatively stable and doesn’t readily grab a proton back
Larger atoms or groups are generally better leaving groups because they can better distribute the negative charge they carry when they leave, making them more stable
If a leaving group can be stabilized by resonance, where the negative charge is delocalized over multiple atoms, it becomes a better leaving group
Good leaving groups are weak bases, meaning they have a low affinity for protons and are more stable as anions
A good leaving group should be stable as a negative ion or neutral molecule after it leaves the molecule
Examples of good leaving groups:
Halides (I-, Br-, Cl-):
Iodide is the best leaving group among the halides, followed by bromide and then chloride.
Sulfonates (OTs, OMS):
These are excellent leaving groups because they can readily form stable anions.
Neutral molecules:
Water (H2O), alcohols, and amines can also be good leaving groups if they are in the right context.
Which reactivity, size, and qualities make a good leaving group?
WEAK BASES (conjugate base of a strong acid) because the leaving group is stable and doesn’t readily grab a proton back (low affinity for protons)
LARGER atoms or groups are better leaving groups. They better distribute their negative charge when they leave, making for more stability.
Halides (I better leaving group than F BECAUSE IT IS BIGGER)
Sulfonates: mesylates and tosylates
Water (in protic solvent)
Which reactivity, size, and qualities make a poor leaving group?
Compounds that have strong affinity for protons and electrons.
Strong bases (hydroxide ions)
Draw the generic nucleophilic attack of ethanal
OH IS NOT A GOOD LEAVING GROUP
What is a nucleophile? Electrophile? Leaving group?
A nucleophile will have excess electron density, negatively charged atom or polyatomic ion or something with a lone pair
Electrophile has electron deficiency, like a carbonyl carbon or a carbon covalent bonded to an electronegative species.
Leaving group. Accept bond, lose bond.
Good leaving groups: Weak bases, halides (larger halides make better leaving groups) water sometimes (like in the formation of hemiacetals hemiketals ketals and acetals).
Poor leaving groups: strong bases of weak acids (like -OH), small halides, alkyl anions (CH3-), RO- (alkoxides)
Which way do the arrows go in a reaction?
The arrow starts at the election and toward the carbon atom with electron deficiency.
The arrows go from a bond and to a nucleus.
SN2 recap
Backside attack of nucleophilic attack of an electrophile by a nucleophile.
2 refers to the fact that it is a bimolecular transition state. ONE STEP. Sort of half bind each attached to the carbon. Trigonal bipyrimidal shaped intermediate.
Causes inversion of stereochemistry if the attack is on a chiral center.
SN1, SN2 from Professor Dave
Draw generic hydration (presence of water) of aldehyde and ketone using acetaldehyde and acetone.
What does this produce?
In the presence of water, aldehydes and ketones react to form geminal diols (1,1-diols)
Recall that geminal means on the same carbon and vicinal means attached to adjacent carbons
What are hemiacetals and hemiketals?
Aldehydes and ketones can be treated with alcohols.
When one equivalent of alcohol (the nucleophile in this reaction) is added to an aldehyde or ketone, the product is a hemiacetal or hemiketal.
Hemiacetals and hemiketals can be recognized by the retention of the hydroxyl group.
Hemiacetals and hemiketals are cyclic compounds formed when an alcohol adds to the carbonyl group of an aldehyde or ketone, respectively. They are intermediate products in the formation of acetals and ketals.
Draw the formation of a hemiacetal and a hemiketal. What causes this?
Addition of equimolar concentration of alcohol to solution will produce hemiacetals and hemiketals.
Draw the formation of acetal and ketals. What causes this?
Addition of alcohol to solution will produce acetals and ketals.
Once the hemiacetal or hemiketal is formed, hydroxyl group is protonated and releases as water. Alcohol attacks, forming an acetal or ketal.
What is produced when an acetal or ketal is mixed two equivalents of alcohol?
Understand that in an acid solution the oh can leave. Usually oh is a poor leaving group as it is a strong base of a weak acid (water).
The resulting molecule would be an acetal or ketal and water.
The hemiacetal and hemiketal will react into acetals and ketals as the hydroxyl group is protonated and the alcohol attacks again.
What kind of reaction is the formation of acetals and ketals with the addition of alcohol to aldehydes and ketones, respectively?
When two equivalent of alcohol are added to aldehyde or ketones, the resulting products will be an acetal or ketal.
This is an SN1 reaction (unimolecular nucleophilic substitution reaction, loss of leaving group formation of carbocation intermediate)
In the hemiacetals and hemiketals, which is the nucleophile and which is the electrophile?
Pay attention here.
First step is formation of hemiacetal or hemiketal (a necleophilic addition reaction) where alcohol is the nucleophile and carbonyl carbon is electrophile.
Second step is the formation of acetals and ketals from hemiacetals and ketals and the electrophile is a carbocation formed from an SN1 reaction.
Do nitrogen and nitrogen based functional groups act as good nucleophiles?
What is the product of a nitrogen based functional group and an aldehyde or ketone (primary nitrogen and secondary nitrogen)
Imine is formed. Enamine is formed. Respectively for primary and secondary nitrogens (fact check this)
Draw an amine. Draw an imine.
Draw the condensation reaction that occurs when nitrogen or nitrogen based functional groups (like ammonia) is added to a ketone.
What kind of reaction is this considered. Condensation and what?
This is considered a condensation reaction and is also an example of nucleophilic substitution.
Draw the reaction of methylamine and acetone.
What is an enamine?
Draw formation of an enamine.
Tautomer form of an imine.
What are cyanohydrins?
What acts as a classic nucleophile of cyanohydrins?
Aldehydes and ketones produced stable cyanohydrins when exposed to hydrogen cyanide (HCN, pKa 9.2 (relatively acidic) as a nucleophile)
Draw the formation of a cyanohydrin with the addition of HCN to acetone.
What kind of reaction is this?
Draw formation of:
Germinal diol from aldehyde
Nucleophilic addition to aldehyde
Hemiacetal formation
Acetal and ketall formation
Imine and enamine formation
Cyanohydrin formation
Concept check 6.2
Where on the redox spectrum do aldehydes and ketones lie?
Aldehydes occupy the middle of the redox spectrum:
They are more oxidized than alcohols, but less oxidized than carboxylic acids. (Recalling that aldehydes are terminal functional groups; ie all aldehydes have primary carbons)
Ketones are as oxidized as secondary carbons can get.
What occurs when aldehydes are further oxidized?
What kind of oxidizing agents will do this?
What oxidizing agent will not oxidize an aldehyde? Remember this one.
Aldehyde will oxidize to carboxylic acids with any oxidizing agent stronger than pyridunium chlorochromate (PCC):
KMO4, CrO3, Ag2O, H2O2, chromate solutions (CrO4 2-)
What occurs when aldehydes in ketones are reduced?
What reagents are commonly seen as reducing agents?
The addition of reducing agents such as lithium aluminum hydride (LiAlH4, a strong reducing agent) and sodium borohydride (NaBH4, a milder reducing agent) will reduce aldehydes and ketones to alcohols.
Ketones are easily reduced to their respective alcohol is using hydride reagents.
Concept check 6.3
Chapter 6 mastery 1
Chapter 6 mastery 2
Chapter 6 mastery 3
I needed to draw the first step of the reaction to see it.
Chapter 6 mastery 4
Draw it. This is a condensation reaction, it is also a nucleophilic substitution reaction.
Chapter 6 mastery 5
A strong oxidizing agent will oxidize an aldehyde to a carboxylic acid. This was just a matter of finding which one matched
Chapter 6 mastery 6
Strong reducing agents will reduce a ketone to an alcohol
Chapter 6 mastery 7
Chapter 6 mastery 8
Chapter 6 mastery 9
Draw it.
Chapter 6 mastery 10
Draw it. Get good with nomenclature.
Chapter 6 mastery 11
Chapter 6 mastery 12
Chapter 6 mastery 13
What is glutaraldehyde?
Glutaric acid?
It’s just an aldehyde naturally produced by reduction of glutaric acid.
Chapter 6 mastery 14
Chapter 6 mastery 15
