Organic Synthesis And Analysis Flashcards
What factors might be considered when deciding on a synthesis route?
- Type of reaction
- Reagents
- Atom economy
- Byproducts
-Conditions
What condition is required for alkanes to undergo free radical substitution with halogens?
The reaction requires ultraviolet light
Name the process in which alkenes can react to form polymers?
Addition Polymerisation
What conditions and reactants are required for a halogenoalkane to form a nitrile?
KCN
Warm, reflux
What is the difference between miscible and Immiscible liquids ?
Miscible = mix with each other
Immiscible = do not mix forming some sort of definite layers e.g. oil and water
What is refluxing ?
- Continuous evaporation and condensation without loss
- Most organic chemicals are volatile and if heated they will evaporated and be lost, however by doing it under reflux this allows compounds to be heated without escaping the flask.
What is the process of recrystallisation ?
- Firstly the solute must be obtained via crystallisation, solution is concentrated via boiling and crystals form upon cooling.
- Crystals obtained need to be purified again (recrystallisation)
- Dissolve the crystals in the minimum amount of hot solvent
- Filter to remove impurities
- Allow to cool so crystallisation of the pure solid takes place
- Filter
- Wash the crystals with small amounts of solvent
- Dry between 2 pieces of filter paper at a temp lower than the melting point
What is Vacuum Filtration ?
Separating solid products from a solvent or liquid reaction mixture.
Mixture is poured through a filter paper in a Buchner Funnel.
Solid is trapped by the filter and liquid is drawn through the funnel into flask below
Faster then gravity filtration as air is forced through the paper by the application of reduced pressure
How is the purity of a sample commonly identified ?
using melting point determination
- The melting point of a substance is constant and does not alter
- Pure samples should melt over a range of 1 degree, whereas impure samples melt over a wider range
- The presence of even a small amount of impurity will lower the compounds mpts
What must you make sure when using melting point determination?
That the sample is dry
Percentage Yield Formula
Actual Yield / Predicted Yield x 100
How can you separate Immiscible liquids ?
Using a separating funnel
Or steam distillation - steam is passed into the reaction mixture and volatile compounds pass over with the steam and condense into a new flask
How can you separate miscible liquids?
Distillation - different boiling points
Fractional Distillation
How do scientists refer to accuracy?
- The percentage difference between the experimental result and the accepted value. The stated uncertainty in an experimental result should always be greater than this percentage accuracy
- Stating the estimated uncertainty by the number of significant figures given (metres vs micrometers)
How do scientists ensure reliability ?
- Defined as the repeatability or consistency
- If an experiment is repeated multiple times and gives the same results it is reliable
How do scientists ensure validity ?
- Valid experiment is one that fairly test the hypothesis.
- All variables are kept constant apart from those being investigated
- All systematic errors are eliminated
Which reactions allow chain length to increase?
- HCN and aldehyde / ketones forming hydroxynitriles
- KCN and halogenoalkane forming a nitrile
- Aromatic only = Friedan Crafts reaction
Which reactions allow the chain length to decrease?
- Heating a carboxylic acid or its salt with soda slime giving a decarboxylation reaction
- Triiodomethane reaction = methyl ketone with iodine in alkaline solution
What is polymerisation?
Small molecules (monomers) combine together to form a long chain molecule (polymer)
What is condensation polymerisation?
Has 2 types of monomers and the polymer and a small molecule (water ) are produced
What is chromatography?
A technique for separating and analysing small quantities of chemicals in a mixture
All chromatography techniques involve a stationary phase and a mobile phase
What is thin layer chromatography (TLC)?
Uses a layer of silica or aluminium oxide coated onto a glass plate as the stationary phase.
A spot o fixture is placed about 10mm from the bottom. It is the suspended into about 5mm of solvent.
As the solvent travels up the plate, the compound separate
How can the compounds separate in TLC be identified?
By their Rf value
Rf = Distance moved by component
——————————————-
Distance moved by solvent front
What is gas liquid chromatography (GLC)?
Highly sensitive method for separating organic mixtures
-Sample gases are carried through the column by inert gas.
- The time taken for the compound to come out of the column is the retention time.
- The relative area of each peak gives the percentage of each compound present in the mixture
