[Year 1] WM Flashcards
How do you identify an alcohol?
R-OH
Suffix: -ol
ethanol, CH₃CH₂OH
How do you identify an aldehyde?
R-COH
Suffix: -al
propanal, CH₃CH₂CHO
How do you identify a ketone?
R-CO-R’
-one
propanone, CH₃COCH₃
How do you identify a carboxylic acid?
R-COOH
Suffix: -oic acid
butanoic acid, CH₃CH₂CH₂COOH
How do you identify an acid anhydrides?
(R-CO)₂O
-oic anhydride
ethanoic anhydride, (CH₃CO)₂
How do you identify an ether?
R-O-R’
-oxy-
methoxyethane, CH₃OCH₂CH₃
How do you identify an ester?
R-COO-R’
alkyl-____-anoate
methyl ethanoate, CH₃COOCH₃
What makes an alcohol primary?
If the carbon it is connected to, is connected to one other carbon.
What makes an alcohol secondary?
If the carbon it is connected to, is connected to two other carbons.
What makes an alcohol tertiary?
If the carbon it is connected to, is connected to three other carbons.
What happens when you oxidise primary alcohol?
Becomes an aldehyde (distillation) then carboxylic acid (reflux with excess oxidising agent).
What happens when you oxidise secondary alcohol?
Becomes a ketone (reflux).
What happens when you oxidise tertiary alcohol?
Cant be oxidised (unless you burn it).
What is used to oxides alcohols?
Acidified potassium dichromate (K₂Cr₂O₇).
- acts as the oxidising agent, so it reduces itself.
- Turn from orange (dichromate ions) to green (chromium ions).
What are you doing when you distil something?
You are removing the desired product as it is formed.
What are you doing when you reflux something?
Heating reactants and condensing any volatile products/reactants to carry on the reaction.
What type of reaction forms alkenes from alcohols?
An elimination reaction.
- By refluxing with sulfuric acid or phosphoric acid.
- By passing alcohol vapour over a solid catalyst (Al₂O₃). (need to be able to draw this).
Describe the mechanism to dehydrate alcohols using elimination.
- Lone pair on Oxygen attack H⁺ from the acid catalyst.
- The intermediate formed has a + charge on the oxygen.
- This oxygen can pull electrons in the C-O bond strongly to break the bond.
- This leaves an unstable carbocation intermediate. (water leaves)
- The carbocation loses a H⁺ from a neighbouring carbon to form a C=C bond as the electrons from the bond move.
- This leaves an alkene, water, and reforms the H⁺ from the acid catalyst.
How can esters be made from alcohols?
Reacting them with a carboxylic acid:
- using a sulfuric acid catalyst.
- -OH from carboxylic acid is removed.
- -OR from alohol bond in its place.
- The removed -OH bonds with -H from alcohol.
Or acid anhydride:
- A C-O bond in the acid anhydride is broken.
- -R from the alcohol takes its place.
- the remaining -OH in the alcohol bonds with the smaller fragment to form a carboxylic acid.
Know how to draw these.
How can haloalkanes be made from alcohols?
Via a substitution reaction (e.g. HBr).
- -OH replaced by -Br.
- -OH forms water with remaining -H.
What is phenol and how are they numbered?
- A benzene ring with an alcohol group.
- carbon with the alcohol is the 1-carbon.
How do you test for phenols?
Add iron(III) chloride.
If phenol exists a purple colour should form.
Why can phenols react with NaOH?
- They are weak acids as they are able to dissociate partially to form a phenoxide ion.
- This phenoxide ion can then bond to Na⁺.
(an react with other strong bases too)
How can you tell the difference between phenols and carboxylic acids?
Carboxylic acids can react with weak bases whilst phenols cannot.
So you react carbonates with them to identify.
How do you tell the difference between an alcohol and a phenol?
- Phenols can react with acid anhydrides and make an ester and carboxylic acid.
BUT
- Phenols cannot react with carboxylic acids.
WHILST
- alcohols can react with both.
THEREFORE
- you react them with carboxylic acids (using acid anhydrides as a control)
What apparatus is used during reflux and when is it used?
- Liebig condenser.
- Heating mantle or water bath.
Used when you need to heat volatile substances without losing them.
When is distillation used?
Used to separate substances with different boiling points.
Useful when you want to extract a chemical before it reacts any further.
How can we purify a volatile substance?
Distilation and separation.
Describe the method used for separation.
- Clamp separating funnel to a clam stand and add the products from distillation.
- Add water to dissolve soluble impurities. This forms an aqueous solution of impurities.
- Allow time for the solution to settle and 2 layers will form:
- The top layer is of impure products
- The bottom layer is of aqueous later containing water-soluble impurities.
- Remove the stopper and drain off aqueous layer.
After separation, you are left with impure products.
What must you do next? Describe the method.
Purification.
- Add impure products to a round-bottomed flask.
- Add anhydrous CaCl₂ as a dehydrating agent.
- This will remove all aqueous substances still remaining.
- Invert flask and leave for 20-30 mins.
After purification, you are left with impure products.
What must you do next? Describe the method.
(vacume) Filtration.
- Connect Buchner funnel and vacuum to a flask.
- Add filter paper to the Buchner funnel and dampen slightly to seal.
- Pour the reaction mixture through the top of the funnel with the vacuum line on.
- The vacuum creates a reduced pressure in the flask that pulls liquid through the filter paper leaving the solid in the Buchner funnel.
If you want the solid after vacuum filtration, what must you do next?
Purify the solid.
How do you purify a solid? Describe the method.
Recrystilation.
- Choose an appropriate solvent such that will dissolve the solid when hot but no when cold.
- Add just enough hot solvent to allow the impure solid to dissolve to get a saturated solution of impure product.
- Hot filter to get rid of insoluble impurities.
- Cool the solution slowly to allow crystals to form.
- Soluble impurities will remain dissolved as there is a smaller quantity fo them so takes longer to crystalise
- Filter and collect solid purified crystals.
- Wash with very cold to remove any remaining soluble impurities solvent and dry them off.
How can you measure the purity of a compound?
- Measuring the melting point.
- TLC
Describe the method for determining the purity of a compound via melting point analysis.
- Add a sample of a solid product to capillary tube and place in the heating element of a melting point apparatus.
- Slowly increase the temperature until the substance starts to melt.
- This will be a range from when the solid just starts to melt to full melts.
- Compare the melting points against data book values.
- If substance contains impurities the melting point be lower and the range will be larger.
Describe the method for determining the purity of a compound via TLC.
- Draw a pencil line on stationary phase (silicon dioxide or aluminium dioxide plate).
- Dissolve your solid product in a suitable solvent.
- Using a capillary tube, pipette solution of your product and a solution of known pure product onto the pencil line.
- Place in beaker and add mobile phase (liquid solvent) below the pencil line.
- Place lid over beaker to prevent evaporation.
- Allow solvent to move up close to the top and remove from beaker.
- Mark the solvent front and allow to dry.
- If the compound is colourless, observe with iodine (locating agent) or UV (using a fluorescent dye).
After chromatography how do you analyse it quantitatively?
By calculating its Rf value and comparing it with a library of known Rf values.
Rf = distance travelled by spot / distance travelled by solvent
(also dependent on temp, solvent used, make up of TLC plate)
It is difficult to use TLC for separating larger quantities.
What can be done instead?
Column Chromatograph.
- Pack burette with silica or alumina (stationary phase)
- Run mixture and solvent (mobile phase) through continuously.
- The different compound in the mixture run through the column at different rates.
- So you can collect the pure compounds at the bottom at different times.
What’s plotted during IR spectroscopy and how is it analysed?
Absorption of IR (which increases vibrational energy in covalent bonds) against Wavenumber (cm⁻¹).
There will be different peaks for different bonds in different functional groups.
What’s plotted during mass spectroscopy and how is it analysed?
Relative abundance - Mass/Charge ratio
It peaks at different m/z depending on the Mr of the fragments.
The M+ peak is for the molecular ion peak.
The M+1 peak is for the molecular ion peak but with carbon-13
What happens during fragmentation?
- A positive fragment and a radical are made.
- Only the positive charged fragment is detected.
When combining IR and mass spec, what order should they be analysed in?
- Find the functional groups present using IR.
2. Identify the structure from fragment patterns.
What are the 12 principals of green chemistry?
- Better atom economy: More feedstock incorporated into product and less waste.
- Prevention of waste products: Better than treating/disposing of waste.
- Less hazardous chemical synthesis: Using less hazards chemicals in reactions
- Design safer chemical products: Less toxic and hazardous products
- Use fewer solvents: Minimise use of organic solvents.
- Lower energy usage: Lower temp and pressure processes.
- Use renewable feedstock: Instead of depleting natural resources.
- Reduce reagents used and number of steps: As these can generate waste.
- Use catalysts, and more selective ones: Generally reduce energy usage and waste products.
- Design chemical products for degradation: when released into environment, should break down into innocuous products.
- Employ real-time process monitoring: To reduce waste products.
- Use safer chemical processes: that minimise releasing of gases, fires and explosions
