Analysis and organic synthesis Flashcards
What is the reaction from an alkane to a haloalkane?
Reagent: Halogen
Condition: UV light
Mechanism: Free radical substitution
What is the reaction from an alkene to an alkane?
Reagent: Hydrogen and a nickel catalyst
Condition: 150°C
Mechanism: Electrophilic addition / hydrogenation
What is the reaction from an alkene to a haloalkane?
Reagent: Hydrogen halide
Condition: Room temperature
Mechanism: Electrophilic addition
What is the reaction from a haloalkane to an alcohol?
Reagent: NaOH (warm aqueous alkali)
Condition: Heat under reflux
Mechanism: Nucleophilic substitution
What is the reaction from an alcohol to a haloalkane?
Reagent: NaX and H2SO4
Condition: Heat under reflux
Mechanism: Nucleophilic substitution
What is the reaction from an alkene to an alcohol?
Reagent: Steam and H2SO4 or H3PO4 catalyst
Condition: 300c and 60-70 pressure.
Mechanism: Hydration/electrophilic addition.
What is the reaction from an alcohol to an alkene?
Reagent: Concentrated acid catalyst
Condition: Heat under reflux
Mechanism: Elimination / dehydration
What is the reaction from a (secondary) alcohol to a ketone?
Reagent: K2Cr2O7 (potassium dichromate) and H2SO4
Condition: Heat under reflux
Mechanism: Oxidation
What is the reaction from a (primary) alcohol to an aldehyde?
Reagent: K2Cr2O7 and H2SO4
Condition: Distillation
Mechanism: Oxidation
What is the reaction from a (primary) alcohol to a carboxylic acid?
Reagent: K2Cr2O7 and H2SO4
Condition: Heat under reflux
Mechanism: Oxidation
Or from an aldehyde.
What is infrared spectroscopy?
A beam of IR radiation is passed through a sample of the chemical.
The IR radiation is absorbed by the covalent bonds, increasing the molecules vibrational energy.
Bonds between different atoms absorb different frequencies, and between different places in an atom.
What is the result of infrared spectroscopy?
It is used to identify molecules by the different peaks at different frequencies that occur.
Different peaks represent different functional groups.
What is the application of IR spectroscopy?
Breathalysers and monitoring pollutants.
How is IR spectroscopy used in breathalysing?
An accurate test to determine the alcohol level in a drunk driver.
The amount of ethanol vapour is found by measuring the intensity of the peak corresponding to the C-H bond.
This is not affected by water vapour in the breath (unlike O-H bond).
The IR spectrum can be used as evidence in court.
How is IR spectroscopy used in monitoring pollutants?
Measures the concentration of polluting gases in the atmosphere.
This includes carbon monoxide and nitrogen monoxide, present in car emissions.
The intensity of the C≡O or N=O bonds can monitor the levels.
What is infrared radiation and atmospheric gases?
Most IR radiation passes through the atmosphere and is absorbed by the earth’s surface.
However, some is re-emitted from the earth’s surface in the form of longer wavelength IR radiation.
Water vapour, CO2 and CH4 absorb this because it has the same frequency as the natural frequency of their bonds.
Eventually the vibrating bonds re-emit this energy as radiation that increases the temperature of the atmosphere, causing global warming.
What is mass spectrometry?
The molecules in the sample are bombarded with electrons and a molecular ion, M+ is formed when the bombarding electrons remove an electron from the molecule.
The y-axis shows the percentage abundance of ions.
The x-axis shows the mass/charge ratio.
How do you find the molecular mass of the compound?
The molecular ion peak.
This has the highest mass/charge ratio, ignoring the M+1 peak.
What is the M+1 peak?
A small peak one unit right of the moleculuar ion peak.
This is because 1.1% carbon is present as the carbon-13 isotope.
What is fragmentation?
The electrons make some of the molecular ions break into fragments.
These can be seen on the mass spectrum in a fragmentation pattern, which can be used to identify molecules and their structure.
This is done by working out what ions could make each peak.
What is the process of identifying compounds from combined techniques?
Use the composition to work out the empirical formula.
Use the mass spectrum to find the molecular mass, and therefore molecular formula.
Work out the functional groups present by the IR spectrum.
Use the mass spectrum to work out the structure from the fragmentation pattern.
What are common fragment ions?
CH3+ = 15
CH3CH2+ = 29
CH3CH2CH2+ = 43
OH+ = 17
C=O+ = 28
COCH3+ = 43
Why is reflux used in some reactions?
Organic reactions are slow and substances usually flammable and volatile.
In a beaker with a bunsen burner, they evaporate or catch fire before they can react.
How is reflux good?
The mixture is heated in a flask fitted with a vertical Liebig condenser, so the mixture can be continuously boiled.
As the vapours evaporate they condense and are recycled back into the flask, so have time to react.
Heating is electrical - mantel - so compounds can’t ignite.
