Isomerism and carbonyl compounds Flashcards
What is optical isomerism?
It is a type of stereoisomerism.
Optical isomers are non-superimposable mirror images of each other.
What is stereoisomerism?
Stereoisomers have the same structural formula but different spatial arrangement of atoms.
What is a chiral carbon?
It is a carbon atom that has four different groups attached to it.
What is a racemate/racemic mixture?
A mixture of equal amounts of enantiomers.
How is a racemic mixture formed from a compound containing a carbonyl group?
The carbonyl is planar
There is an equal chance that a nucleophile will attack from either above or below.
This means that an equal amount of enantiomer will be formed.
How do you know if a compound is an optical isomer?
Optical isomers rotate plane polarised light.
Why is a racemate not optically active?
Both enantiomers would rotate plane polarised light in equal and opposite directions
What is produced when an aldehyde is oxidised?
Carboxylic acid
Which reagents can be used to distinguish between aldehydes and ketones?
Tollen’s reagent
Fehling’s solution
What is the observation when Tollen’s reagent is used to test for aldehydes and ketones?
Aldehyde- silver mirror formed
Ketone- no visible change
What is the observation when Fehling’s solution is used to test for aldehydes and ketones?
Aldehyde- brick red precipitate
Ketone- no visible change
What are the conditions for the reduction of aldehydes and ketones back to alcohols?
NaBH4
in water with methanol
What are the conditions to produce hydroxynitriles?
KCN
followed by dilute acid
What is formed when aldehydes and unsymmetrical ketones react with KCN followed by a dilute acid?
A mixture of enantiomers
Identify the hazards of working with KCN
it is an irritant
extremely dangerous if ingested or inhaled
it can react with moisture to produce hydrogen cyanide which is a highly toxic gas
How can risks be reduced when working with KCN?
wear gloves, a lab coat, safety goggles
perform the experiment in a fume cupboard
What is the functional group of a carboxylic acid?
RCOOH
What is a carboxylic acid?
It is a weak acid which slightly dissociates into a carboxylate ion and a H+ ion
Give the reaction between carboxylic acids and carbonates
Carboxylic acid + carbonate → salt + carbon dioxide + water
Give the name, conditions and reaction between carboxylic acids and alcohols
Esterification
heat, conc. sulfuric acid(catalyst)
carboxylic acid + alcohol ↔ ester + water
What are the uses of esters?
food flavourings
perfumes
solvents
plasticisers
Give the reaction and conditions for the acid hydrolysis of esters
reflux with a dilute acid e.g. HCl
ester + water ↔ carboxylic acid + alcohol
Give the reaction and conditions for the base hydrolysis of esters
reflux with a dilute alkali such as NaOH
ester + OH- → carboxylate ion + alcohol
What are vegetable oils and animal fats?
Esters of glycerol
What are the properties of animal fats?
mainly saturated hydrocarbon chains
solid at room temperature
What are the properties of vegetable oils?
unsaturated hydrocarbon chains
liquids at room temperature
Give the reaction for the hydrolysis of oils and fats
Fats/oils + NaOH → glycerol + soap
What is biodiesel?
A mixture of methyl esters of long chain carboxylic acids
Give the reaction and conditions for the production of biodiesel
methanol, KOH(catalyst)
triester + methanol → glycerol + methylester
