Carbonyl groups Flashcards
Give the meaning of the term racemic mixture
7.2 racemic mixture
Equal concentration of enantiomers / (optical) isomers
What is an enantiomer?
7.2 racemic mixture
Non-superimposable mirror image
Explain how a pair of stereoisomers can be distinguished.
7.2 racemic mixture
(Plane) polarised light
Rotated in opposite directions
What is plane polarised light?
7.2 racemic mixture
If passed through a polarising filter, the light vibrates in the same plane
What is a chemical property of an optical isomer?
7.1 optical isomerism
4 different groups attached
What are 2 physical properties of an optical isomer?
7.1 optical isomerism
Can arrange them in different ways to form 2 different molecules, and cannot be superimposed
How do you draw an optical isomer?
7.1 optical isomerism
Locate chiral centre, draw an enantiomer in a tetrahedral shape, and draw its mirror image
Why would testing the optical activity of a racemic mixture not be useful
7.2 racemic mixture
A racemic mixture contains equal concentrations of enantiomers.
Each enantiomer will rotate the plane of polarised light by an equal but opposite amount
There would be no net change in the plane of polarised light.
Name the type of reaction between an aldehyde or ketone with hydrogen cyanide
8.1 Aldehydes and ketones
nucleophilic addition
Are carboxylic acids strong or weak acids?
8.2 Carboxylic acids and esters
They are weak so they partially dissociate in water
Forming a carboxylate ion and a H+ ion
What is formed when a carboxylic acid reacts with a carbonate?
8.2 Carboxylic acids and esters
A salt, carbon dioxide and water
Why are carboxylic acids soluble in water?
8.2 Carboxylic acids and esters
Polar C=O and O-H bonds allowing them to hydrogen bond.
What happens to the solubility of a carboxylic acid as the chain length increases?
8.2 Carboxylic acids and esters
solubility decreases, because the size of the hydrophobic non-polar part of the molecule increases
What are the reagents and reaction conditions for esterification?
8.2 Carboxylic acids and esters
alcohol, carboxylic acid and H2SO4 catalyst
(heated)
How are esters named?
8.2 Carboxylic acids and esters
The prefix of the alcohol with -yl as a suffix and the prefix of the acid with-oate as the suffix. For example, ethanol and ethanoic acid would react to form ethyl ethanoate
What are the uses of esters?
8.2 Carboxylic acids and esters
- Perfumes and flavourings
- esters make good solvents in glues and prinking inks because they are polar so dissolve things easily, and evaporate easily from mixtures
Why do esters make good plasticisers?
8.2 Carboxylic acids and esters
Make things more flexible, molecules escape and plastic becomes brittle and stiff
What are the reaction conditions and product of the acid hydrolysis of an ester?
8.2 Carboxylic acids and esters
Reaction conditions - HCl catalyst, H2O, heat
Forms - carboxylic acid and an alcohol
(Reverse esterification)
Why is a high temperature required to melt fats?
8.2 Carboxylic acids and esters
They fit neatly together, increasing van der Waals forces between then and the energy required to overcome forces and melt them
- usually solids
Why are oils easier to melt?
8.2 Carboxylic acids and esters
Double bonds mean chains are bent and don’t pack together, decreasing the effect of van der Waals and requiring less energy
- usually liquid
What is formed from the hydrolysis of fats and oils?
8.2 Carboxylic acids and esters
React with sodium hydroxide to form a carboxylate ion (sodium salt, or soap) and an alcohol (glycerol)
How do you reverse the effects of hydrolysis of fats and oils?
Add HCl
How do you get biodiesel from vegetable oils?
React with methanol using strong alkali to get a mixture of methyl esters of long chain fatty acids
What is the test for an aldehyde?
Tollen’s reagent - silver mirror
