Lecture 12. Mechanisms in Carbonyl Chemistry Flashcards
What do carbonyl compounds contain ?
C=O double bonds
What is a sigma bond ?
Head on overlap if sp2 hybrid orbitals
What is a pi bond ?
Side on overlap of p orbitals
What does a double bond contain ?
A sigma and pi bond
What are carbonyl groups susceptible to at carbon?
Nucleophilic attack
What does a nucleophilic attack on a carbonyl result in ?
A tetrahedral intermediate
What does the fate of the tetrahedral intermediate depend on ?
- Nucleophile
- Nature of carbonyl
- Reaction conditions
What way do aldehyde and ketone tetrahedral intermediates react ?
Tend not to react further
What way do ester and thioester tetrahedral intermediates tend to react ?
Will react further
What way do amides tetrahedral intermediates tend to react ?
Reluctant to react
What are aldehydes and ketones easily reduced to ?
Alcohols
What does nature use NADH for ?
A hydride source for reduction reactions
What are simple aldehydes susceptible to ?
Nucleophilic attack by even fairly poor nucleophiles like water forming hydrates
What does the extent of hydrate formation depend on ?
The structure of the carbonyl compound
How do larger substituents effect hydrate formation ?
Less favorable
What is hemiacetal ?
Very similar to hydrates, except the nucleophile is n alcohol rather than water
What form do sugars generally exist as ?
Cyclic hemiacetyls
How are hemiacetyls formed ?
Slowly. using either an acid or base to catalyse the reaction
How do acid catalysis effect the carbonyl group ?
Makes it more electrophilic
How does base catalysis effect the nucleophile ?
Makes it more nucleophilic
What can happen if a carbonyl has a potential leaving group on it ?
The tetrahedral intermediate formed after nucleophilic attack can collapse back to a new carbonyl compound
When are nucleophilic acyl substitution more successful ?
- The intended leaving group is a better leaving group than the nucleophile
- The electrophile is reactive enough
What leads to the formation of imines ?
The reaction of aldehydes or ketones with primary amines, in which the carbonyl oxygen is lost completely
What does imine formation often require ?
Acid catalysis
