Last Bit of Yr13!!! Flashcards
Which are the two ways you can form nitriles?
From aldehydes + ketones
From haloalkanes
What are the reagents needed for the formation of nitriles from aldehydes + ketones?
React aldehyde/ketone with H2SO4 + NaCN
What is the mechanism for forming nitriles from aldehydes + ketones?
Nucleophilic addition
What is the equation for forming nitriles from aldehydes + ketones?
CH3CH2CH2CHO + HCN —-> CH3CH2CH2CH(OH)CN
H2SO4/NaCN go across the arrow
Name CH3CH2CH2CH(OH)CN
2 - hydroxy pentane nitrile
What is the nucleophile in forming nitriles from aldehydes + ketones?
CN-
What are the reagents needed for formation of nitriles from haloalkanes?
React haloalkane with NaCN or KCN in ethanol
What is the mechanism for forming nitriles from haloalkanes?
Nucelophillic substitution
What is the equation for forming nitriles from haloalkanes?
CH3CH2Cl + NaCN —-> CH3CH2CH2CN + NaCl
Name CH3CH2CH2CN
Butane nitrile
What is the nucleophile in forming nitriles from haloalkanes?
CN-
Can you use nitriles as intermediates to form other organic substances?
YES
What happens if you reduce a nitrile?
Form amine
What happens if you hydrolyse a nitrile?
Form carboxylic acid
What are the reagents for reducing a nitrile?
H2
Ni catalyst
What is the equation for reducing a nitrile?
CH3CH2CN + 2H2 —-> CH3CH2CH2H2
Ni across arrow
Name CH3CH2CH2H2
Propylamine
What are the reagents for hydrolysis of nitrile?
Heat
Dilute aqueous HCl
What is the equation for hydrolysis of nitrile?
CH3CH2CN + 2H2O + HCl —-> CH3CH2COOH + NH4Cl
Name CH3CH2COOH
Propanoic acid
Name NH4Cl
Ammonium chloride
What are the six steps for synthesising aspirin?
Prepare organic substance Prepare aspirin Filter under reduced pressure Recrystallisation Filter under reduced pressure again Determine melting point of aspirin
What happens in “Prepare organic substance”?
Add NaOH to oil of wintergreen
Reflux - 30 mins
Leave to cool
Add HCl to neutralise
What happens in “Prepare aspirin”?
React 2-hydroxy benzoic acid (salicylic acid) with ethanoic acid
Add drops of conc acid
Warm mixture in water bath till solid dissolves
What happens in “Filter under reduced pressure”?
Cool mixture
Filer under pressure using Buchner funnel
What happens in “Recrystallisation”?
Slowly add minimum amount of hot solvent (ethanol) to impure aspirin
Sample will dissolve
Cool mixture to allow recrystallisation
What happens in “Filter under reduced pressure again”?
Filter under reduced pressure using Buchner funnel
Wash purified aspirin in cold water
Why do you wash aspirin in cold water?
As it isn’t very soluble in cold water
What happens in “Determine melting point of aspirin”?
Use melting point apparatus
Insert sample into melting point tube
Slowly increase temperature
Record the range over when it starts to melt
Impurities = lower melting point = wider range
What is an alternative method for “Determine melting point of aspirin”?
Set up Thiele Tube
Attach capillary tube to thermometer using rubber band
Use micro-burner to slowly heat side arm of Thiele Tube
When solid starts to melt remove heat + record temperature
What are the three types of chromatography?
Paper
TLC
Gas
What is the stationary phase in paper?
Paper
What is the mobile phase in paper?
Solvent
What does it mean if the dot remains under the line?
Not soluble in that solvent
Where should the amount of solvent be up to?
Below pencil line
How do you calculate Rf value?
Solvent front
What are the problems with paper?
Components can have similar Rf values
Unknown substances appear
What is the stationary phase in TLC?
Silica coated on piece of plastic
What is the mobile phase in TLC?
Solvent
What is the method for TLC?
Base line drawn in pencil + place dots along line
Plate places in beaker of solvent (below pencil line)
Lid placed on to ensure atmosphere of tank saturated wit volatile solvent
As solvent moves up mixture separates into components
Solvent reaches top of plate + plate removed
Solvent front noted + solvent left to evaporate
What happens if the substance is colourless?
Use UV light
Chemically
How does it work if you use UV light?
Stationary phase has chemical that will fluoresce under UV light
Spots go white
How does it work if you do it chemically?
Ninhydrin
Ninhydrin sprayed on = amino acids go brown/purple colour
How does it work if you do it chemically?
Iodine crystals
Put dried plate in beaker of iodine crystals + put lid on
Spots turn brown
How does TLC acc work?
Silica gel form silicon dioxide
Surface of silica = very polar
So can form H bonds with OH group
+ London forces + permeant dipole-dipole
What is adsorption?
The adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface
How does TLC acc work?
Part 2
Solid stationary phase = pigment adsorbed onto surface of solid particles
Relative forces of attraction between stationary phase, mobile phase + pigment = separation
What does it mean if pigment has weak forces of adsorption?
Less polar = move further up
What does it mean if pigment has strong forces of adsorption?
More polar = moves less
What are the control measures of TLC?
Same solvent
Same temperature
Same stationary phase
What is gas - liquid chromatography?
Long column filled with liquid compounds
Sample vaporised + pushed through column by inert carrier gas
What inert gas is often used in GLC?
N2 or He
Why is GLC kept in an oven?
To control temperature
What does GLC work on?
Relative solubility compared to stationary phase
What is the stationary phase of GLC?
Liquid coated on tubes
What does GLC show because it works on solubility compared to stationary phase?
Different compounds will travel at different speeds
= different boiling points + temperature inside column
What is retention time?
The length of time a compound remains in a column
How do you calculate retention time?
Time taken from sample injected until max height for that compound
What does each peak in GLC correspond to?
Different compounds
What must you do after you calculate retention time?
Compare to known database
Which compound would come out last in GLC?
The most similar to stationary phase
Which compound would come out first in GLC?
The one that isn’t similar but has the least no. of H bonds
= more H bonds = stronger attraction with stationary phase
How do you calculate the composition of a mixture in GLC?
Area of triangle for peak = 0.5 X base X height
Work out total area = add them together
Area of peak/ total area X 100
How does mass spectroscopy work?
Sample injected
Vaporised in heated vacuum
Gas vapour bombarded with high energy e- forms positive ions in ionisation chamber
+ions accelerated
Ions travel through magnetic filed in drift region
Time taken for ions to reach detector is measured
What does it mean if the ions are heavier?
Move more slowly = take longer to reach detector
What does M/Z of molecule equal + why?
Mr
As weight of e- is negligible
What does the M+ peak equal?
The total Mr for the compound
What is abundance?
The relative amount of ions in the spectra - usually given as a percentage
What is the equation for mass spectroscopy?
M (g) —-> M+ (g) + e-
Outline how a mass spectrometer would show the presence of Fe
M/Z value around 56
Why use the word “around”?
Abundance of isotopes
Outline how the mass spectrum would show how many different isotopes of sulphur were present
Count no. of M/Z peaks around 32
Relative atomic mass of sulphur found on Mars is different from relative atomic mass of S found on Earth. Why?
Different isotopic abundances
What can excess ionisation do when it is transferred to the molecular ion?
Can cause it to fragment
What happens when it fragments?
Produces smaller positive ion + radical
Smaller positive ion detected
Fragment ions can be broken down further
What is the M+1 peak caused by?
Carbon - 13 isotope
What is the Mr of CH3+?
15
What is the Mr of C2H5+?
29
What is the Mr of C3H7+?
43
What is the Mr of C4H9+?
57
What is the Mr of OH+?
17
What are the example of CH3CH2OH splitting?
CH3CH2OH (g) —-> CH3CH2OH+ (g) + e-
CH3CH2OH+ (g) —-> CH2OH+ (g) + .CH3
CH3CH2OH+ (g) —-> CH3+ (g) + .CH2OH
CH3CH2OH+ (g) —-> CH3CH2+ (g) + .OH
Whys is GLC not suitable technique for analysing mixture of dyes?
Because dyes not easily vaporised