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
What are aldehydes and ketones?
Carbonyl compounds, carbon group on end in aldehydes and in the middle in ketones
What are some hazards of KCN?
Toxic and flammable
What are some safety precautions for KCN?
Fume cupboard and water bath
What is formed when oxidising a primary alcohol?
Primary alcohol —> aldehyde —> carboxylic acid
What happens when you oxidise a secondary alcohol?
Secondary alcohol —> ketone
Fehling’s Solution
A solution made of two different solutions, A and B. A contains Cu2+ ions and B contains a complexing agent.
Upon reaction, copper forms along with a precipitate of copper(I) oxide
Tollen’s Reagent
A solution containing the complex ion [Ag(NH3)2]+.
Upon reaction, a silver precipitate forms along with ammonia
Can tertiary alcohols be oxidised?
no
Why are carbonyls polar?
The polarity of the C=O bond makes them polar molecules
Why are carbonyls susceptible to nucleophiles ?
Trigonal planar shape of the group
Why are shorter chain carbonyls soluble in water?
They can form h bonds with water molecules
Why are longer chain carbonyls not soluble in water?
As the chains become longer, there is a greater percentage of non-polar molecule
Which 3 types of reaction do carbonyls undergo?
- Addition
- Nucleophilic addition
- Redox
Example Q
Write an equation for the formation of methyl propanoate, CHCH2COOCH3, from methanol and propanoic acid.
CH3OH + CH2H5COOH —> CH3CH2COOCH3 + H2O
Acylation
The name for the formation of an ester, without needing a mechanism
what is an Addition-Elimination reaction
The name of the mechanism for the formation of an ester from a acyl chloride
What are the 3 acid derivatives
Esters
Acyl chlorides
Acid anhydrides
What are acyl chlorides?
Have the functional group CoCl, suffix is -oyl
What is given off when acyl chlorides are reacted with water?
Cl is substituted by oxygen or nitrogen and misty fumes of hydrogen chloride are given off and ethanoic acid
What are acid anhydrides?
Two identical carboxylic acid molecules, joined via oxygen
What does an acid anhydride and water produce?
2 ethanoic acids
How is aspirin made?
Made by reacting salicylic acid with either ethanoic anhydride or ethanoyl chloride to form the ester, ethanoic acid is made too
Why is ethanoic anhydride usually used?
It is cheaper, safer as less corrosive, reacts more slowly and doesn’t produce dangerous hydrogen chloride fumes
Why is separation used in the purification of organic compounds?
To remove any impurities that do dissolve in water, such as salts or water soluble organic compounds
How do you isolate the pure product?
Organic layer is usually less dense so should float, with impurities dissolved in lower layer which can be drained off
