Aldehydes and ketones Flashcards
What is the similarity between aldehydes and ketones?
Both contain a carbonyl group C=O, which is the basis for their chemistry
How are aldehydes named?
Replacing the “e” of the corresponding alkane with “al”. E.g. ethanal
How are ketones named?
Replacing the “e” of the corresponding alkane with “one”. E.g. Propanone
Resonance is an important feature of carbonyl groups, what does resonance mean?
There are two forms or states of the carbonyl group to show visually.
In both cases the oxygen is negative or delta negative, and the carbon is positive or delta positive
Polarity is an important feature of carbonyl groups, what does it mean?
Reaction may be either nucleophilic or electrophilic
What feature of an aldehyde / ketone might be acidic?
The hydrogen attached to the carbon adjacent to the carbonyl group. It’s even more acidic (likely to lose a proton) if it’s between two carbons
Keto-enol tautomerisation. What does this mean?
Carbonyls exist in equilibrium with the enol form of the molecule. Although carbonyl is usually the predominant one
The O of carbonyl groups may form what type of intermolecular bonds?
Hydrogen bonds, with the hydrogens attached to other electronegative atoms such as O’s or N’s
Aldehydes and ketone will form what, when dissolved in an excess of primary alcohol?
Hemiacetals and hemiketals, respectively
Describe the two steps of the reaction where aldehydes/ketones may become hemiacetals/hemiketones
- The most charged species (+, the hydrogen) attracts electrons from the delta negative oxygen, leaving a carbocation intermediate.
- The second step involves the delta negative oxygen from the alcohol quickly attracted to the current most charged species(+, carbon).
- A proton is lost which regenerates the catalyst, and produces the hemiacetal or hemiketal. Now the proton may attract electrons from -OH forming H2O, a good leaving group. Again the delta negative oxygen on the alcohol is attracted to the positive carbocation. And again the alcohol releases its proton, regenerating the catalyst, producing an acetal or ketal
When do imines and enamines formed?
When aldehydes and ketones are allowed to react with amines
What is primary amine?
A nitrogen compound with the general formula R-NH2, where R represents an alkyl or aryl group.
In an imine the carbonyl group of the aldehyde or ketone is replaced with a C=N-R group
What is a secondary amine?
A nitrogen with the general formula R2N-H, where R represents aryl or alkyl groups.
Forms an enamine when reacts with an aldehyde or ketone
What is a aldol condensation?
A base catalysed reaction of aldehydes and ketones that have a-hydrogens. The intermediate, an aldol, is both and aldehyde and an alcohol. The aldol undergoes a dehydration reaction producing a carbon-caarbon double bond in the condensation product, an enal (alkene + aldehyde)
