Grasby Flashcards
What do you get when you react R-X (X is a halide) with NaCN
Nitrile
How can carboxylic acids be made from CO2
By reacting it with an organometallic reagent which breaks one of the C=O. this is then followed by an acid work up
What does a high pKa indicate
Strong acid
What does a low pKa mean
Strong base
Arrange these in terms of which is the best LG and state their pKa`s,
Amine, anhydride, acid chloride and alcohol
Chloride (HCl = -7)
Anhydride (RCOOH = 5)
Alcohol (ROH = 15)
Amine (RNH2 = 35)
If XH has a low pKa it shows that it is a…
good leaving group
How can esters be made from acid chlorides and anhydrides
React ROH with base
What role does the base play in ester formation from acid chlorides and anhydrides.
Takes a H from the alcohol group once it has attacked the carbonyl
What do you get when you react an acid chloride with a carboxylate salt eg MeCOO-
Anhydride
What do you get if you react an acid chloride with 2 equalivalents of an amine
Amide
Why are two equivalents of amines needed in the reaction with acid chlorides
One to form the amide and the other to mop up the acidic H
Esters and anhydrides can also be used to form amides but why is chloride preferred
Bigger yield
describe the schotten bauman conditions for the reaction of amides and why does this not produce a carboxylic acid.
2 equivalents of amine. NaOH and CH2Cl2.
This reaction takes place in the organic phase.
What makes a good nucleophile
Strong bases and molecules with high pKa`s
Order these in terms of decreasing electrophilicity
Ester, amine, chloride and anhydride
Chloride - anhyrdried- Ester - amine
How does the inductive effect increase electrophilicity
More inductive effects increases the electrophilicity
How does delocalisation affect electrophilicity
Decreases electrophilicity,however, lp in oxygen are lower in energy than lp in amides due to O being higher in electronegativity which means N donated lp
Why do anhyrdrides have high electrophilicity
Delocalisation is shared over two carbonyls
Can amides be made from carboxylic acid
No only from acid deratives
How are acid chlorides made from carboxylic acid
By reacting CA with SOCl2 or PCl5
How can electrophilicity be enhanced
protonate the carbonyl
how can leaving group ability be enhanced
By protonating the Lg
What conditions are needed for esterification
CA and an alcohol in acidic conditions
Why is acid needed in esterification
To protonate the carbonyl and OH and also the reaction does not occur at a practical rate without acid catalysis.
How to favour hydrolysis
XS water
To favour Esterification
Use XS solvent eg ROH and remove H2O by using a drying agent or by distillation
how are Lactones formed (Cyclic esters)
undergo intramolecular esterification.
functional groups more likely to interact if attached to same molecule
Why cant esters be made under basic conditions
a carboxylate salt is formed
What is transesterification
Conversion of one ester to another
Does transesterication involve protonation of electrophile and leaving group
yes
What do you get if you react esters with water under basic conditions.
Carboxylate salt and alcohol
In saponification once the OH has be deprotonated is the reaction reversible
No as the carboxylate salt is not a nucleophile
Why is an acid catalyst not needed when there is a good nucleophile
The nucleophile will be protonated turining it to a good one to a poor nucleophile.
Explain the effect increasing acid has on imine formation
increases untill pH 5 then decreases
How does an acid catalyst speed up the rate of imine formation
Converts poor lg into a good lg unitl pH 5
What do you get if you react an amide with water under acidic conditions
carboxylic acid
What do you get when an amide reacts with water under basic conditions
Carboxylic salt
What is required to hydrolyse nitriles
Water and H2SO4
What do you get when ROCL and an anhydride react with water
Carboxylic acid
Why can`t esters be made from ketones
Because the product is more reactive and will react with the reagent.
How are organocopper reagents made
CuBr is reacted with R-Li and ether at 78 degrees. which gives R2Cu-Li- and LiBr
What do you get when you react an amide with a R-Li (ether and H3O+)
aldehyde
What do you get when you react a nitrile with a grignard reagent followed by an acid workup
Ketone
What is reduced by NaBH4
Ketones and aldehydes
What is reduced by LiALH4 and acid workup
esters, anhydrides and chloride, even aldehydes and ketons
What do you get when you react amide and LiAlH4
amine
How do you get an aldehyde from an ester
reduce the ester with LiAlH4 followed by an acid work up and then react the alcohol with PCC, CH2Cl with no water.
Name some properties of amino acids
All chiral except glycine and have the same stereochemistry. At pH 7 as zwitterions
what do you get if you react an acid chloride and carboxylate salt
anhydride
What do you get if you react an ester with an amine and comment on the rate of reaction
Amide and reaction is slow
