Isomers And Carbonyls Flashcards
What is a stereoisomer
Isomers with the same structural formula but different spatial arrangements of atoms
When does optical isomerism occur
When a carbon atom has 4 different functional groups attached to it
What are enantiomers
2 compounds that are optical isomers of each other (non superimposeable mirror images )
How do optical isomers work
They have similar physical and chemical properties but they rotate plane polarised light by the same amount but in opposite directions
What is a race mate / racemic mixture
A mixture containing a 50/50 mixture of 2 enantiomers
Why are racemic mixtures not detected by polarimeters
They don’t rotate plane polarised light
How is a race mate formed
When a reactant or intermediate has a original planar group in the molecule and is approached from both sides by an attacking species
There is an equal chance of it being attacked from both sides so an equal amount of each enantiomer is formed
What are 2 reactions that form racemates
An unsymmetrical alkene with HBr in Electrophilic addition
Nucleiphilic addition of HCN to aldehydes and unsymmetrical ketones
What are crabonyls
Compounds with the C=O bond
Why are smaller carbonyl soluble in water
They can form hydrogen bonds with the water
Why do carbonyls not undergo addition reactions easily
How do they attract nuceliphiles
The C=O is strong
The bond is polarised as O is more electronegative than carbon
What do primary alcohols oxidise to
Aldehydes then carboxylic acids
What do secondary alcohols oxidise to
Ketones
What is the oxidising agent used to oxidise alcohols
Acidified potassium dichromate solution
Or potassium dichromate solution and dilute sulfuric acid
How do you test for aldehydes
Heat gently with tollens reagent and silver mirror forms
Heat gently with fehlongs solution and brick red precipitate forms
What is the reducing agent for reducing carbonyls
NaBH4
What are aldehydes reduced to
Primary alcohol
What are ketones reduced to
Secondary alcohols
What is the mechanism for reducing alcohols
Nucleophilic addition
What is another way carbonyls can be reduced
Catalytic hydrogenation
Using hydrogen and a nickel catalyst
At a high pressure
How are hydroxinitriels formed
What are the conditions
What is the mechanism
Reacting carbonyls with HCN ( dilute sukfiric acid and CN source )
Room temp and pressure
Nuecliphikic addition
What type of acids are carboxylic acids in terms of strength (2)
They are weak acids as they only slightly dissociate in water
But they are strong enough to displace carbon dioxide from carbonates
Why do carboxylic acids dissolve in water
They form hydrogen bonds with water molecules
How do carboxylic acids differ in strength based on chain length
The alkyl groups are electron releasing, a bigger chain lengths makes it more negative and less stable
So acids are weaker as they get biggger
How do carboxylic acid strength differ with halogens
They are electron withdrawing so it makes it less negative and more stable
So stronger
How are carboxylic acids tested
React with Na/CO3 or aqueous NaHCo3 to form effervescence when Co/2 released
What is the only carboxylic acid that can be oxidised nd why
Methanoic acid
Its structure effectively has an aldehyde group so it forms carbonic acid when oxidised (this can decompose to give oxygen )
What is an esterification reaction
Carboxylic acid + alcohol -»> ester + water
How are esters named
The anoate from the carboxylic acid
The eyl from alcohol
What are 3 users of esters
Perfume
Flavourings
Plasticisers for polymers
Why do esters not form hydrogen bonds
They are polar but don’t form hydrogen bonds because there in no hydrogen bonded to a highly electronegative atom
What is the solubility of esters
What is their bp like
Almost insoluble in water
Lower bp than the hydrogen bonded carboxylic acid they come from
How do plasticisers work
They allow polymer chains to move more easily which makes it more flexible
How can esters be hydrolysised (2)
Either heating with an acid or with sodium hydroxide
What are the reagents and conditions for hydrolysis of esters using an acid
Dilute hydrochloric acid
Heat under reflux
What is formed when an ester is hydrolysed by acid
A carboxylic acid and an alcohol (opposite of esterification )
What is the problem with hydrolysis by acid of esters
It is a reversible reaction that doesn’t give a good yield of products
What are the regents and conditions for ester hydrolysis with sodium hydroxide
Dilute sodium hydroxide
Heat under reflux
Why is the hydrolysis of esters with NaOH not reversible
The carboxylic salt produced is an anion of the carboxylic acid which is resistant to attack by weak nucleophiles like alcohols so the reaction is not reversible
How do you convert the carboxylic acid salt to a carboxylic acid form
Add a strong acid
What is glycerol used in and why
Cosmetics food and glues
It forms hydrogen bonds very easily and is readily soluble in water
How so biodiesel formed
Vegetable like or fats reacting with methanol to form methyl esters (biodiesel ) and glycerol
What is the difference between acyl chloride and carboxylic acids
They are much more reactive
What do acyl chlorides form when reacting with water
A carboxylic acid and HcL
What do acid anhydrides form when reacting with water
2 carboxylic acids
What do acyl chloride form when reacting with alcohol
Ester + Hcl
What do acid anhydrides form when reacting with alcohols
Ester + carboxylic acid
What do acyl chlorides form when reacting with ammonia
What is an observation
Primary amide + NH4Cl
White smoke of NH4CL
What do acid anhydrides form when reacting with ammonia
Primary amide + ammonium salt
What does an acid andydride form when reacting with primary amine
N substituted amide
What does acyl chloride form when reacting with primary amine
N substituted amide
What is the mechanism called for the reaction of acyl chlorides and acid anhydrides
Nucleophilic Addition Elimination
