Ch 20 Aldehydes And Ketones Flashcards
How do you name an aldehyde
-al,the number one carbon is the carbonyl carbon. Cyclic aldehydes are named carbaldehyde
What happens when you protonate a ketone?
It is subject to attack by a weak Nu- because it become more electrophilic
How do you name a ketone?
-one, alkyl alkyl naming ,position with locant
How do you convert a primary alcohol into an aldehyde?13.10 draw several reactions
PCC/CH2Cl2-treatment with a strong oxidizing agent
Ozonolysis of Alkenes 9.11 draw several reactions
1)O3, 2)DMS,ozonolysis will Cleave a double bond.
How does resonace effect the electrophilicity of a carbonyl group? Draw the resonance structure.
One of the resonance structures exhibits a positive charge on the carbon atom, indicating that the carbon atom is deficient in electron density (d+)
How does induction effect the electrophilicity of a carbonyl group?
Inductive effects also render the carbon atom deficient
in electron density. As a result, this carbon atom is particularly electrophilic and is susceptible to attack by a nucleophile.
In general why are aldehydes more reactivce than ketones?
- Steric effects. A ketone has two alkyl groups (one on either side of the carbonyl) that contribute to steric interactions in the transition state of a nucleophilic attack. In contrast, an aldehyde has only one alkyl group, so the transition state is less crowded and lower in energy.
- Electronic effects. Recall that alkyl groups are electron donating. A ketone has two electrondonating alkyl groups that can stabilize the d+ on the carbon atom of the carbonyl group. In contrast, aldehydes have only one electron-donating group
The d+ charge of an aldehyde is less stabilized than a ketone. As a result, aldehydes are more electrophilic than ketones and therefore more reactive.
What are the step in the nucleophilic addation under basic conditions? Draw the mechanism.
What are the step in the nucleophilic addation under acidic conditions? Draw the mechanism.
What is a hydrate? How is one formed?
When a aldehyde or ketone is treatedwith water, the carbonyl group can be converted into a hydrate. A hydrate has two OH groups.
In a Hydrate formation where does the equilibrium postion sit? What are the exception?
The position of equilibrium generally favors the carbonyl group rather than the hydrate, except in thecase of very simple aldehydes, such as formaldehyde:
What are the step in a base catalyzed hydration? Draw the Mechanism
What are the step in a acid catalyzed hydration? Draw the Mechanism
What is an acetal and how is it formed? What are the common acids used?
In acidic cinditions and aldehyde or ketone will react with to molecules of alcohol to from an acetal.
TsOH and H2SO4(sulfuric acid ) are the commonacids used.
Why is an acid catalyst used in an acetal formation.
the acid catalyst serves an important role in this reaction. Specifically, in the presence of an acid, the carbonyl group is protonated, rendering the carbon atom even more electrophilic.
This is necessary because the nucleophile (an alcohol) is weak; it reacts with the carbonyl group more rapidly if the carbonyl group is first protonated.
What are the step to form an acetal?
The first three steps produce an intermediate called a hemiacetal and (2) the last four steps convert the hemiacetal into an acetal:
Why are acetals good protectiong groups?
Acetal formation is a reversible process that can be controlled by carefully choosing reagents and conditions. acetal formation is favored by removal of water. To convert an acetal back into the corresponding aldehyde or ketone, it is simply treated with water in the presence of an acid catalyst. In this way, acetals can be used to protect ketones or aldehydes.
LAH would reduce everything
How is an imine formed?
in mildly acidic conditions, an aldehyde or ketone will react with a primary amine to from an imine.
What is the mech for a imine formation?
(1) The first three steps produce an intermediate called a carbinolamine
(2) the last three steps convert the carbinolamine into an imine:
How is an emamine formed?
in acidic conditions, an aldehyde or ketone will react with a secondary amine to from an enamine.
What is a Wolff-Kishner Reduction?
the reduction of a hydrazone to an alkane under strong basic conditions and heat.
this transformation provides a two step procedure for reducing a ketone to an alkane.
How are acetals,imines and enamines
acetals are hydrolized with aqueous acid to afford the corresponding aldehyde or ketone and alcohol
imines and enamines also undergo hydrolysis when treated with aqueous acid to form ketone.
How are thiosacetal formed?
in acidic conditions and aldehyde or ketone will react with two equivalents of a thiol to form a thioacetal. The mech is analogous to acetal formation.
What is Raney nickel and what does it do?
When treated with Raney nickel, thioacetals undergo desulfurization, yielding an alkane. Raney Ni is a porous, Ni-Al alloy, in which the surface has adsorbed hydrogen atoms.
What happen when an aldehyde or ketone is treated with a hydride reducing agent? What is the mech
When treated with a hydride reducing agent, such as lithium aluminum hydride (LAH) or sodium borohydride (NaBH4), aldehydes and ketones are reduced to alcohols.
What is a cyanohydrin and how is one formed?
When treated with hydrogen cyanide (HCN), aldehydes and ketones are converted into cyanohydrins, which are characterized by the presence of a cyano group and a hydroxyl group connected to
the same carbon atom.
In the presence of a catalytic amount of base, a
small amount of hydrogen cyanide is deprotonated to give cyanide ions, which catalyze the reaction
Why are cyanohydrins useful in syntheses?
the cyano group can be further treated to yield a range of products.
In the first example, the cyano group is reduced to an amino group. In the second example, the cyano
group is hydrolyzed to give a carboxylic acid.
What is the Witting reaction?
This reaction can be used to convert a ketone into an alkene by forming a new C-C bond at the location of the carbonyl group. The phosphorus-containing reagent that accomplishes this transformation is called a phosphorus ylide. An ylide is a neutral molecule that contains a negatively charged atom (C- in this case) directly attached to a positively charged heteroatom (P+ in this case).
draw a Friedel-crafts acylation of benzene
When treated with a peroxy acid, ketone can be converted into ____.
ester via the insertion of an oxygen atom
an unsymmertical ketone is treated with a peroxy acid to forms a regioselective ester. Why
because isopropyl group migrates more rapidly than the methyl group during the rearrangentment step of the mech , migratory aptitude -the migration rates of different groups.
H>3>2,Ph>1>methyl
when benzylic aldehyde is treated with preoxy acid what is formed
benzoic acid
