Reactions And Mechanisms 1 Flashcards
Name the functional groups only containing σ bonds
Alcohols
Ethers
Amines
Halides
Functional groups containing π bonds
Alkenes Alkynes Aldehydes Ketones Carboxylic acids Esters Acid halides Anhydrides Amides Nitriles
What are the primary considerations for molecular interactions?
HOMO/LUMO interactions
Electrostatic interactions
The best bonding interaction is between which two things?
HOMO of the nucleophile
LUMO of the electrophile
What do curly arrows represent?
Movement of a pair of electrons from a filled orbital (HOMO) to an empty orbital (LUMO)
Order the nucleophile types in order of nucleophilicity
-ve charge > lone pair > π bond > σ bond
Order the electrophile types in order of electrophilicity
Empty orbital > π* orbital > σ* orbital
Where is the strongest interaction with a nucleophile and a carbonyl?
π* on the C
What is the best source of hydride for reducing an aldehyde or a ketone?
Sodium borohydride
NaBH4
What are the two types of organometallic reagents?
R-Li
R-MgBr
How are the organometallic reagents synthesised?
R-X -(Mg, Ether)-> R-MgBr
R-X -(2Li, Ether)-> R-Li + Li-X
What is the third way to synthesise an alkynyl organometallic reagent?
Use a strong nitrogen base
Such as NaNH2
NaNH2 made from reacting Na + NH3
What are the two reaction steps for reacting an organometallic reagent with an aldehyde/ketone?
- R-MgBr
2. H2O
Why must organometallic reagent reactions be done in two steps?
They are incompatible with water
Water destroys the organometallic by protonating the carbanion
How are hydrates formed?
Reacting water with aldehydes or ketones
How are hemiacetals and acetals formed?
Reacting alcohols with aldehydes or ketones
Why is it easier to form hydrates from aldehydes over ketones?
As the bond angle is reduced from 120 to 109.5
Harder to form hydrate with ketones as steric clash is increased in the product
Acid and base catalysts can be used in both hydrate and hemiacetal formation, what do the do?
Acid: make the carbonyl more electrophilic by protonation
Base: make the nucleophile more nucleophilic (deprotonation)
Why can acetals only be formed using acid catalysis?
An OH group must be made into a good leaving group
That can’t happen in basic conditions
What is one way to determine which leaving group is best?
Consider the acidity of the conjugate acids formed from the anions upon leaving
Strongest acid makes for the best leaving group
Why do organometallic reactions generate a tetrahedral product and not a trigonal product?
None of the leaving groups are good
