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Chemistry > Analysis and organic synthesis > Flashcards

Analysis and organic synthesis Flashcards

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1
Q

What is the reaction from an alkane to a haloalkane?

A

Reagent: Halogen
Condition: UV light
Mechanism: Free radical substitution

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2
Q

What is the reaction from an alkene to an alkane?

A

Reagent: Hydrogen and a nickel catalyst
Condition: 150°C
Mechanism: Electrophilic addition / hydrogenation

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3
Q

What is the reaction from an alkene to a haloalkane?

A

Reagent: Hydrogen halide
Condition: Room temperature
Mechanism: Electrophilic addition

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4
Q

What is the reaction from a haloalkane to an alcohol?

A

Reagent: NaOH (warm aqueous alkali)
Condition: Heat under reflux
Mechanism: Nucleophilic substitution

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5
Q

What is the reaction from an alcohol to a haloalkane?

A

Reagent: NaX and H2SO4
Condition: Heat under reflux
Mechanism: Nucleophilic substitution

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6
Q

What is the reaction from an alkene to an alcohol?

A

Reagent: Steam and H2SO4 or H3PO4 catalyst
Condition: 300c and 60-70 pressure.
Mechanism: Hydration/electrophilic addition.

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7
Q

What is the reaction from an alcohol to an alkene?

A

Reagent: Concentrated acid catalyst
Condition: Heat under reflux
Mechanism: Elimination / dehydration

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8
Q

What is the reaction from a (secondary) alcohol to a ketone?

A

Reagent: K2Cr2O7 (potassium dichromate) and H2SO4
Condition: Heat under reflux
Mechanism: Oxidation

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9
Q

What is the reaction from a (primary) alcohol to an aldehyde?

A

Reagent: K2Cr2O7 and H2SO4
Condition: Distillation
Mechanism: Oxidation

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10
Q

What is the reaction from a (primary) alcohol to a carboxylic acid?

A

Reagent: K2Cr2O7 and H2SO4
Condition: Heat under reflux
Mechanism: Oxidation
Or from an aldehyde.

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11
Q

What is infrared spectroscopy?

A

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.

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12
Q

What is the result of infrared spectroscopy?

A

It is used to identify molecules by the different peaks at different frequencies that occur.
Different peaks represent different functional groups.

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13
Q

What is the application of IR spectroscopy?

A

Breathalysers and monitoring pollutants.

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14
Q

How is IR spectroscopy used in breathalysing?

A

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.

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15
Q

How is IR spectroscopy used in monitoring pollutants?

A

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.

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16
Q

What is infrared radiation and atmospheric gases?

A

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.

17
Q

What is mass spectrometry?

A

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.

18
Q

How do you find the molecular mass of the compound?

A

The molecular ion peak.
This has the highest mass/charge ratio, ignoring the M+1 peak.

19
Q

What is the M+1 peak?

A

A small peak one unit right of the moleculuar ion peak.
This is because 1.1% carbon is present as the carbon-13 isotope.

20
Q

What is fragmentation?

A

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.

21
Q

What is the process of identifying compounds from combined techniques?

A

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.

22
Q

What are common fragment ions?

A

CH3+ = 15
CH3CH2+ = 29
CH3CH2CH2+ = 43
OH+ = 17
C=O+ = 28
COCH3+ = 43

23
Q

Why is reflux used in some reactions?

A

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.

24
Q

How is reflux good?

A

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.

25
Q

What is the reflux set up?

A

The flask is clamped by the neck, containing reactant and anti-bumping granules.
The condenser is placed on top of the flask in an upright position.
It should have no stopper on top so pressure does not build up.
Water enters through rubber tubing at the bottom and leaves at the top.

26
Q

What is distillation?

A

Used to separate liquids with different boiling points.
The substances will evaporate out of the mixture in order of increasing boiling point.

27
Q

What is the process of distillation?

A

A thermometer is placed at the neck of the condenser and shows the boiling point of the substance that is evaporating at that time.
If the boiling point of the pure product is known, it shows when it’s evaporating and so condensing.

28
Q

What is the set up for distillation?

A

The flask is clamped and connected to the still head, a second clamp is fitted to the reciever adaptor.
Rubber tubing brings water to the bottom and removes it from the top.
A flask collects the distillate.

29
Q

What is redistillation?

A

Mixtures with volatile liquids can be purified this way.
If a product and its impurities have different boiling points, then the impure product is heated again, with the temperature strictly controlled, in the same way as distillation.

30
Q

What is separation?

A

If the product is insoluble in water a separating funnel can be used to remove any impurities that do dissolve in water - salts or alcohols etc.

31
Q

What is the process of separation?

A

The mixture is poured into a separating funnel, and water added.
The funnel is shaken and allowed to settle.
The organic layer is usually less dense than the aqueous layer, so is on top.
The stopper is then opened and the aqueous layer allowed to run off so the product can then be collected.

32
Q

What are drying agents?

A

The organic layer after separating will have trace amounts of water, so needs drying.
Add an anhydrous salt (magnesium sulfate, calcium sulfate, or calcium chloride).
The salt binds to any water present to become hydrated.

33
Q

What is the appearance of the drying agent reaction?

A

The drying agent will be lumpy when first added - so more needs adding.
All the water has been removed when you can swirl the mixture and it looks like a snow globe.
The mixture should have gone from cloudy to clear, and the drying agent settled to the bottom. This can then be filtered.

34
Q

What is the order of purification of a liquid?

A

Separating funnel
Anhydrous salt
Redistillation

Chemistry (24 decks)

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