Unit 4.8 - Organic synthesis and Analysis Flashcards
What type of reactions do double bond reactions tend to be?
Addition
How are addition polymers produced?
From alkenes, where the double bond id broken to form a repeating unit
Describe a polymer repeating unit
No double bond
Saturated
How should a repeating unit always be shown?
With extended bonds through the brackets showing that it bonds to other repeating units on both sides
When do condensation polymers form?
When a water molecule is removed from the species of a reaction
How are polyesters formed?
In a reaction between dicarboxylic acids and a diol (a dialcohol), producing an ester linkage
Type of linkage in a polyester
Ester
Common example of a polyester
Terylene, known as PET
What is Ethan-1, 2-diol present in?
Antifreeze
What is given off when a dicarboxylic acid and a diol produce an ester linkage in a polyester?
Water
what else can you also make an ester linkage with with an alcohol?
a dioyl chloride
another word for ethan-1,2 - diol
ethylene glycol
what would be eliminated in the reaction between a carboxylic acid and an acid chloride?
HCl
How are polyamides formed?
In a reaction between a dicarboxylic acid (or a diol chloride) and a diamine
What is the removed during the reaction to form polyamides?
A molecule of water
What is left when a molecule of water is removed during a reaction between a dicarboxylic acid (or a dioyl chloride) and a diamine?
An amide linkage
Common examples of polyamides
Nylon - 6,6 and Kevlar
Explain all of the differences between addition polymerisation and condensation polymerisation
If the monomer is an alkene, then addition polymerisation occurs
No small molecule is lost and the polymer is the only product, then addition polymerisation has occurred
If a small molecule e.g - H2Oor HCl is produced along side side the polymer then a condensation polymerisation has taken place
The monomer(s) contain function groups such as -NH2, -COOH, -OH or -COCl then condensation polymerisation occurs
The chain contains the amide link -C(O)N(H) or an ester linkage -OC(O)- then condensation polymerisation has occurred
The chain only consists of carbon atoms then addition polymerisation has occurred
Properties of addition polymerisation
The monomer is an alkene
No small molecule is lost
The chain only consists of carbon atoms
Properties of condensation polymerisation
A small molecule e.g - H2O or HCl is produced
The monomer(s) contain functional groups such as -NH2, -COOH, -OH, -COCl
The chain contains an amide link -C(O)N(H) or an ester linkage -OC(O)-
Why are many of the reaction in organic chemistry laborious?
Since when you react two organic reagents you will produce some undesired products
Impurities
Undesired products
Name for undesired products
Impurities
What will there also be when trying to form something in a reaction except for the usual impurities?
Unreacted starting materials in the mixture
Purification
For a pure sample, we need to separate the product from the mixture
Separating the product from the mixture for a pure sample
Purification
Why do many organic reactions not go to completion as required?
Other products may be produced, and some unreacted starting product may remain
What’s an important part of any organic preparation?
The separation and purification of the products
What will you also have in the reaction products when producing ethyl ethanoate?
Ethanol and ethanoic acid that’s unreacted and some water that also forms
Miscible liquids
Will mix and dissolve in each other
Liquids that will mix and dissolve in each other
Miscible
What’s important to note about the solution produced when making ethyl ethanoate?
All of the four compounds present are miscible with each other
What would we see when making ethyl ethanoate and why?
A colourless liquid
All four compounds are miscible with each other
What conditions could the products be in depending on the reaction?
Could be an insoluble solid, may be present in solution or as immiscible liquids
What does each mixtures of products after an organic reaction need?
A different method of separation
When can distillation be used to separate the products from the other substances present in the reaction mixture?
If the product does not decompose at or below its boiling temperature and the boiling temperature is not too high
What separation technique can we use If the product does not decompose at or below its boiling temperature and the boiling temperature is not too high ?
Distilllation
When can simple distillation be used to separate a product from the other substances present in the reaction mixture?
If the boiling temperature of the product differs by a reasonable amount (perhaps 20 degrees Celsius or more) from the boiling temperatures of the other compounds present
What can simple distillation also be used for?
Separating a volatile liquid from other substances in the mixture that are not volatile
What is used to separate a volatile liquid from other substances in the mixture that are not volatile?
Simple distillation
What separation technique can be used if the boiling temperature of the product differs by a reasonable amount?
Simple distillation
Example of simple distillation
The distillation of 2-chloro-2-methyl propane from its mixture with 2-methylpropan-2-oil and hydrochloric acid
When is fractional distillation used?
If the boiling temperatures are closer together
What is used to separate if boiling temperatures are closer together?
Fractional distillation
What is used during fractional distillation and why?
A fractionating column, which enables more efficient separation of the products to occur
Give 2 examples of using fractional distillation
-the separation of ethanol obtained from the fermentation of sugars is more effective if fractional distilllation is used
-the primary separation of the products present in crude oil (petroleum) is also carried out by fractional distillation
What reaction technique is used to separate compounds that decompose just before or at their boiling temperatures or have very high boiling tempatures?
Distillation is carried out under reduced pressures (vacuum distillation) or steam distillation can be used
When is distillation carried out under reduced pressures (vacuum distillation) or is steam distillation used?
For compounds that decompose just before or at their boiling temperatures or have very high boiling temperatures
What does pressure do to the boiling point of a compound?
The lower the pressure, the lower the boiling point of a compound
What is vacuum distillation?
When there’re less pressure exerted on the vapour since this decreases the compounds boiling temperature
Give an example of reduced pressure distillation working
The alkane dodecane C12H26 boils at 216 degrees under atmospheric pressure (101kpa) but at 92 degrees if the pressure is reduced to 1.3kpa
What do we need to work out when working with miscible liquids?
Which is the organic layer and which is the aqueous layer
Which layer is discarded and which layer is kept with miscible liquids?
Discard the aqueous layer
Keep the organic layer
What are the 2 methods of determining what out organic layer and what our aqueous layer is when working with miscible liquids?
Use density data
Keep adding deionised water
How do we use density data to work out which layer is an organic layer with miscible liquids?
The lower density one will be on top
Explain properly how we would use deionised water to see which layer is an organic layer with miscible liquids
Keep adding deionised water to see which layer grows
There will still be water present in the organic product, which is what we keep
In order to get a dry product (dry = no water) we should add a drying agent for example calcium chloride or magnesium sulphate, which are hygroscopic (absorb moisture)
We could then use this in fractional distillation and compare its boiling point with literature values to know that its been purified well
Drying agents \examples
Calcium chloride
Magnesium sulphate
Why are calcium chloride and magnesium sulphate examples of drying agents?
They’re hygroscopic (absorb moisture)
How can we tell if something has been purified well?
Use it in fractional distillation and compare its boiling point with literature values
Example of organic products that are sensitive to heat
Esters
What do some organic products do upon excessive heating and why?
Decompose
They’re sensitive to heat
Which separation technique do we use if organic products are sensitive to heat and decompose upon excessive heating?
Steam distillation
When do we use steam distillation?
When organic products are sensitive to heat and may decompose upon excessive heating
Which industry is steam distillation very important n?
The perfumery industry
Why is steam distillation so important in the perfumery industry?
Essential oils extracted from plants may decompose if heated to their boiling temperatures at atmospheric pressure
How does steam distillation work?
Steam is passed into the reaction mixture and the volatile compounds present pass over with steam, and condense in the receiving flask
What is one of the most widely used oils in the perfume industry? Explain how it is used
Rose oil
Steam distillation of rose oil gives an oil (containing a number of different compounds) and water from the condensed vapours
What do we look at during solvent extraction?
The solubility of a product in different solvents
What is solvent extraction?
A method that depends on the differing solubility of a compound in two immiscible solvents
Give an example of a differing solubility of a compound in different immiscible solvents
Iodine is about 90x more soluble in tetrachloromethane than in water
What happens if tetrachloromethane is added to an aqueous solution of iodine and the mixture shaken?
Most of the iodine is extracted into the tetrachloromethane layer
How do we separate 2 layers?
Using a separating funnel
What do we need to do if CO2 gas forms in a reaction that requires the use of a separating funnel?
Make sure to release pressure in the funnel periodically
What is used to separate a solid from a liquid?
Filtration
What is filtration used for?
Separating a solid and a liquid
How can filtration be carried out?
Using a filter paper and a funnel or sometimes with a plug of cotton wool to stop the solid
The use of what makes filtration quicker and why?
The use of fluted filter paper
The filtrate only needs to travel through one layer of filter paper and the paper only touches the funnel at the folds
What is fluted filter paper used for?
Making filtration faster
What’s another thing we can use for filtration?
Filtration using a Büchner funnel (vacuum filtration)
What needs to be done once the solid is in the funnel after filtration?
It needs to be washed with an appropriate solvent and dried in the air, or in a drying oven at a temperature below its melting temperature
When are the products obtained by crystallisation?
If the solid is present as a solute in solution
How are the products obtained if the solid is present as a solute in solution?
By crystallisation
Why would a solution be coloured when it’s supposed to be colourless?
Due to the presence of impurities
Why would a solution be coloured when it’s supposed to be colourless?
Due to the presence of impurities
What is used when a solution is coloured when it’s supposed to be colourless?
Decolourising charcoal
What does declourising charcoal do?
Absorbs the coloured impurities
How is decolourising charcoal used?
The solution is boiled with a little decolourisng charcoal to remove the colour and then filtered hot to remove the charcoal that contains the absorbed colour
What do we do after using decolorising charcoal?
The solution is filtered hot to remove the charcoal that contains the absorbed colour
How is a filtrate concentrated?
By boiling and is then cooled
How Dow e know that a solution has been sufficiently concentrated?
Crystals of the solute appear on cooling. These are filtered off and dried.
What does it mean if crystals of a solute appear on cooling?
The solution has been sufficiently concentrated
What is done to crystals of a solute?
They’re filtered off and dried
What does it mean mean if no crystals appear on cooling?
Then the solution needs to be made more concentrated
How do we know that a solution needs to be made more concentrated?
If no crystals appear on cooling
What type of solvent do we need to choose when extracting soluble solids from solution?
Where the solid dissolves poorly when cold but well when hot
When does extra care need to e taken when concentrating a solution?
If the solvent is flammable
What is used when concentrating a solution if the solvent is flammable?
Generally a water bath or some method of electrical heating, for example a hot plate is used
When would a solute need to be recrystallised?
When the solute obtained by crystallisation may not be pure
Essential steps for recrystallisation
- Dissolve impure solid in minimum amount of hot solvent
- If solid remains, filter this off whilst hot (hot filtration - place apparatus in oven or water bath)
- Allow solution to cool for crystals to form
- Filter crystals, was with cold solvent, dry
- Record melting temperature of solid and compare with literature values
Name 2 ways of measuring impurity
Comparing melting temperature to literature values
Use chromatography
Explain exactly how we would use melting temperatures as a way of measuring impurity
Impure —> melting temperature will be lower than its pure form and melts over a range of temperatures
Pure —> sharp melting temperature (1-2 degrees deviation from literature value)
Explain the melting temperature of an impure compound
Melting temperature will be lower than its pure form and melts over a range of temperatures
Explain the melting temperature of a pure compound
Sharp melting temperature (1-2 degrees deviation from literature value)
Empirical formula
Simplest whole number ratio of atoms
What is chromatography?
An analytical technique used to separate and identify component molecules in a mixture
What are the stages of chromatography?
The mobile phase and the stationary phase
The mobile phase of chromatography
A substance that allows molecules to move over or through the stationary phase
What can the mobile phase be n the form of?
A liquid or a gas, depending on the type of chromatography being carried out
What move further in the mobile phase?
More soluble products
The stationary phase
A substance that has affinity to molecules in the mixture being analysed
Relationship between the affinity of a molecule in the stationary phase and the distance it moves in the mobile phase
The greater the affinity of a molecule to the stationary phase, the shorter the distance it moves with the mobile phase
What’s the mobile and what’s the stationary phase in paper chromatography?
Mobile phase —> solvent you dip the paper in
Stationary phase —> the chromatography paper
What happens during paper chromatography for a more soluble product?
Moves further up the chromatography paaper
What type of products move further up the chromatography paper?
More soluble ones
what happens to less soluble product during paper chromatography?
Stick to the paper
What type of products stick to the paper during paper chromatography?
Less soluble ones
What does every component molecule in a mixture used in chromatography have?
A unique Rf value in a particular solvent mixture
What ones each molecule in a mixture have a unique Rf value for?
Particular solvent mixture
How is an Rf value calculated?
By comparing the distance moved by the mobile phase and the molecule
Equation for working our Rf
Distance moved by the molecule/distance moved by solvent
What is chromatography a technique used for?
To separate substances from a mixture by their slow movement, at different rates, through or over a stationary phase
What has chromatography been developed to be able to do now?
So that mixtures of substances can be separated by using a number of different methods
How do we know which chromatography method to use?
They’re appropriate to the number and nature of the components present
How is chromatography now used in a quantitative way even though it as originally a qualitative method?
It’s often used in conjunction with mass spectrometry to identify individual components that are present in the mixture
Why is chromatography often used in conjunction with mass spectrometry?
To identify individual components that are present in the mixture
How is chromatography used in conjunction with mass spectrometry?
Chromatography separates the components. Inject the components through a mass spectrum = fragments it = can characterise the molecules
2 mechanisms for the separation process during chromatography
Partition
Adsorption
Which methods can be used to decide which dyes are present following chromatography?
Take IR spectrum and compare
Chromatography with a different solvent
TLC
Thin layer chromatography
What is the stationary phase in paper chromatography?
Water trapped in the cellulose fibres of the paper
What is the stationary phase in TLC?
A layer of silica (SiO) or aluminium oxide (Alp) coated onto a plastic or glass plate
What technique is similar to paper chromatography?
TLC
Explain how paper chromatography/TLC is carried out
Spots of starting materials in a suitable solution are placed at the bottom of a piece of chromatography paper or the initial solvent level below the spots
The solvent front then rises up the paper/plate, separating the mixture into a series of spots
When the solvent front has risen to a suitable level, the paper/plate is removed and dried
The position of the separated spots and the solvent front are notes and the distance that these have risen from the starting line is measured
What happens when the solvent front rise up the paper/plate during paper chromatography/TLC?
Rises up the paper, separating the mixture into a series of spots
Where do we measure zero from during chromatography?
The pencil line
Why do we draw our zero line with pencil during paper chromatography?
Since biro ink would be separated by the solvent
When do we have a solvent front?
Once the solvent has gone past all the spots
Where do we measure up to the spots during paper chromatography/TLC?
The centre of spots
How do we work out where the centre of spots are during paper chromatography?
Highest-lowest point of spot/2
What can we compare using paper chromatography?
The position of the spots for a known and unknown solute can be compared to see if they have travelled the same distance
What can we calculate from paper chromatography/TLC?
The Rf value
When is two-way separation used?
When the use of a particular solvent does not completely separate the spots
What do we use when the use of a particular solvent does not completely separate the spots during chromatography?
Use two-way separation
How is two-way separation done?
The dried chromatogram is rotated through 90 degrees and then a different solvent is used on it
When is the identification of spots easy during chomatography?
When they’re coloured
What is done when solutes produce colourless spots during chromatography ?
The chromatogram is sprayed with a suitable reagent that causes the spots to become coloured
What would we do with a chromatogram containing colourless spots of different amino acids?
Spray it with a solution of ninhydrin
Gently warm the paper = blue-purple spots appear that show the position of the different amino acids
What appear to show the positions of different amino acids following the addition of ninhydrin to a chromatogram?
Blue-purple spots
What’s the name for the process by which TLC separates amino acids?
Adsorption
Wha’s another method apart form spraying a chromatogram with ninhydrin that can be used to show the positions of colourless spots?
Shine UV light on the plate
What will happen when shining UV light on a chromatogram?
If the separated compounds are fluorescent, they will show a colour
Another way apart from a solution of ninhdyrin on the chromatogram and shining UV lights on the plate to see colourless spots
The plate itself can have a coating of fluorescent materials and then the plate is exposed to UV light. The spots then show up dark spots on a fluorescent background.
advantages of TLC over paper chromatography
Faster
The thin layer on the plates can be made from a variety of materials
Important uses in forensic science
What’s the most common type of gas chromatography?
Gas-liquid chromatography (GLC)
What happens during gas-liquid chromatography?
A gaseous mixture is passed “through” liquids particles supported on an inert (Unreactive) solid
GLC
Gas-liquid chromatography
How is the gaseous mixture swept into the column for GLC?
By a carrier gas
Carrier gases used in GLC
Hydrogen
Helium
Argon
Why are hydrogen, helium or argon chosen as carrier gases in GLC?
The carrier gas must not react with any of the substances
What does the column for GLC contain?
Fine solid material or is a hollow column whose walls are coated with a solid on which there is a liquid stationary phase
What s used instead of Rf in GLC?
RT
RT
Retention time
Retention time (RT)
The time taken form the sample ending the injection point and passing through the chromatography column before reaching the detector
The time taken form the sample ending the injection point and passing through the chromatography column before reaching the detector
Retention time (RT)
What factors does the efficient separation of the compounds in a mixture depend on?
Volatility of the compound itself
The column temperature
The length of the column
The flow rate of the carrier gas
What’s an important factor in separating compounds by GLC for similar compounds (e.g - those in the same homologous series)?
Their boiling temperatures
What vary enormously because of, for example, the volatility of the compound, the column temperature, the length of the column and the flow rate of the carrier gas?
Retention times
What does identification by retention time depend on?
The conditions being exactly the same
What is often done to the separated compounds following gas chromatography and why?
They’re led into a mass spectrometer, where a positive identification can be made since retention times can vary enormously so its best not to just rely on these
What can be done to compounds that have been led into a mass spectrometer following gas chromatography?
Positive identification can be made
GC-MS
Gas chromatography, mass spectrometry
What is the ABE fermentation process?
A method of bacterial fermentation that produces propanone (acetone), butan-1-ol and ethanol from starch
Which compounds will come of the column first?
Lowest boiling point
What does a faster retention time mean?
Comes off the column first
What would a lower boiling point mean in terms of retention time?
Lower boiling point = lower retention time
What does every substance have a unique one of?
A unique chromatogram
What does the area under a peak on a chromatogram represent?
How much of a substance you have
How do you work out how much of a substance you have from a chromatogram?
Use the area under the peak
What do you do if you’re asked to work out the % of a specific substance from a chromatogram?
Area of that substance/total area of all peaks x 100
What would be different if gas chromatography was carried out at a different temperature and why?
Relative peak areas would be different
Because it would be dependent on whether a substrate would decompose upon heating
Why would the relative peak areas on a chromatogram be different if gas chromatography was carried out at a different temperature?
Because it would be dependent on whether a substrate would decompose upon heating
HPLC
High performance liquid chromatography
When is high performance liquid chromatography used and why?
For heat sensitive substances that vaporise at high temperatures
To avoid them evaporating or decomposing, we use solvents that the substance will dissolve in
What do we use for heat sensitive substances that vaporise at high temperatures?
HPLC
Explain how HPLC works
The column is packed with solid particles (of uniform size) and the mixture sample is dissolved in a suitable solvent
The solution is then forces through the column at high pressure
What is the column packed with for HPLC?
Solid particles of uniform size
Applications of HPLC
Testing urine samples of athletes for the presence of banned substances
In food chemistry - antioxidants are added to fatty food products such as margarine and cream cheese to help prevent oxidation
What are added to fatty food products and why?
Antioxidants
To prevent oxidation
Most common antioxidants
BHA
BHT
Various esters of Gallic acid
Where can the C(CH3)3 group be found in the antioxidant BHA?
In the 2- or 5- positions in the ring
Spectroscopy
The interaction between light (em radiation) and matter
Spectroscopy techniques
Infra red (IR) spectroscopy
Nuclear magnetic resonance (NMR) spectroscopy
UV/Visible spectroscopy
Mass spectrometry (MS)
How do we read a mass spectrum?
Furthest peak to the right = molecular ion peak = Mr of the compound
The other peaks represent the possible fragments of the molecular ion
Which peak is the molecular ion peak on a mass spectrum?
The furthest peak to the right
What does a mass spectrum always keep and what does it discard?
Positive ions (the fragments) are kept
Discards negatives and radicles
How do we use IR spectroscopy?
Determine functional groups present using the data sheet
What is IR spectroscopy used in and how?
Breathalysers (sensitive to C-O, which is only in alcohols)
What makes an element nmr active?
An odd number of nucleons
Give 2 elements that are nmr active and are used for NMR spectroscopy + explain
C-13 and protons
Odd number of nucleons
What do the number of peaks on a carbon-13 nmr spectrum represent?
The number of carbon environments
What do the number of peaks on the proton nmr represent?
The number of hydrogen environments
What do we use the chemical shifts in NMR for?
Use the data sheet to identify types of carbon/proton
When are chemical shifts generally greater?
If the carbon atoms are closer to EN toms, and also for carbon atoms close to alkene groups
Why do we now see splitting patterns in the NMR spectra used?
Due to the high resolution used
Why would NMR spectra now have a different number of peaks?
Due to splitting patterns forming
Name for the little peaks seen around the big peaks in high resolution NMR spectra
Splitting patterns
Splitting patterns
Little peaks seen around the big peaks in high resolution NMR spectra
What do splitting patterns give us information about?
Neighbouring protons
Explain how splitting patterns give us information about neighbouring porotons
If we have 5 close peaks, there’s 4 neighbouring protons for that carbon
Name for the splitting pattern produced when n=0
Singlet
Name for the splitting pattern produced when n=1
Doublet
Name for the splitting pattern produced when n=7+?
Multiplet
n+1 rule
The peaks split not one more than the number of hydrogens on the neighbouring carbon atom
Are hydrogens bonded to Os seen as neighbouring hydrogens to a carbon atom? Explain
No - OHs are usually singlets
How are integration factors found?
By the area under the peak
Where are integration factors indicated?
Above the peak
What do integration factors indicate?
The number of identical hydrogen atoms corresponding to that peak
How can methylpropanal and butanone be distinguished even though they both give 3 peaks in their proton nmr spectra?
Because the integration factors of the peaks are different
Methylpropanal —> 6:1:1
Butanone —> 3:3:2
What 2 things must we do to prepare a sample for nmr analysis?
Choose a suitable solvent
Choose a standard
How do we choose a suitable solvent for nmr analysis?
Hydrogen atoms absorb radiation so its important to choose one that contains no hydrogen atoms
Suitable solvents for nmr analysis
CCl4 and CDCl3
Why must a standard be added for nmr analysis?
To calibrate the spectrum
Standard normally used for nmr analysis
Tetrmethylsilane (TMS)
Why is tetramethylsilane usually used as a standard for nmr analysis?
Produces a single, singlet peak which is very intense
Has highly shielded H atoms (=peak at a lower frequency than most organic molecules)
Is cheap and non-toxic
What does it do on an nmr spectrum when a standard has highly shielded H atoms?
Peaks at a lower frequency than most organic molecules
What happens to a TMS standard before an nmr spectrum is produced?
It’s usually erased
Explain, in terms of the electromagnetic spectrum why something would appear colourless
Doesn’t absorb in the visible region
How is distillation done?
Reduce the temperature of the mixture to below the lowest boiling temperature and let the mixture warm up slowly
Why would compounds form in approximately equal amounts in a reaction?
Intermediate carbocations have similar stabilities
How do we work out relative peak area on a 1H NMR spectrum?
It’s just however many hydrogen atoms are in each environment
Explain why the molar percentage of each compound cannot be used to find the percentage by mass of each component if the relative molecular mass of each component differs on a gas chromatogram
If relative molecular masses are different, the number of moles present in the chromatogram is not directly related to the mass of each component
Explain what happens to IR absorptions when going from one compound to another
Increase and decrease depending on the different bonds
why would compounds containing Cl or Br have a number of molecular ion signals?
since they have different isotopes
give examples of compounds that may have a number of molecular ion signals and explain
those containing Cl or Br
they have different isotopes
What do we get reduce yields from during a reaction?
Incomplete extraction by solvent
Incomplete distillation/decomposition of product
What do we need to remember to do when writing repeating units and reactants that form it and other products?
write n
What do we do with relative peak area ratios on 1H NMR spectra?
Show the ratio of atoms in each region (not the literal number at H atoms in each region)
What do we know is true when something undergoes “complete oxidation”?
That the products will add up to be the exact same length. (No minor products will make up for some of the atoms)
What does 2 oxygen atoms in each module suggest when not a carboxylic acid?
An ester
What do we use to safely heat?
An electrically heated water bath
Why do we use a “minimum amount of hot solvent” during recrystallisation?
So that the maximum amount of product can crystallise out on cooling
What does it mean if we can’t identify things from gas liquid chromatography?
Their retention times must be the same
Do chemically equivalent protons show splitting? Explain
No, they only split when there’s something different next door
