Aromatic compounds Flashcards
Aliphatic compounds
organic compounds where carbon aoms form open chains or closed rings but does not contain a benzene ring in their structure
eg. ethane
what is an aromatic compound
organic compounds contaning a benzene ring in their structure
descibe the bonding in benzene
six carbon-hydrogen bonds formed by sigma bonds - 12 fixed electrons
six carbon-carbon single bonds formed by sigma bonds - 12 fixed electrons
three carbon-carbon double bonds are formed by 6 pi electrons
the 6 pi electrons are delocalised-free to move around the benzene ring
the carbon carbon bonds are a identical intermediate between single and double bonds
what are delocalised electrons
freely moving electrons and are shared between More than two electrons
explain how the kekule structure correctly describes benzene’s structure
the number of
six carbon-hydrogen bonds formed by sigma bonds - 12 fixed electrons
six carbon-carbon single bonds formed by sigma bonds - 12 fixed electrons
three carbon-carbon ‘double’ bonds are formed by 6 pi electrons
how many electrons in benzene not involved in bonding
12 electrons involved not involved in bonding
explain how the kekule structure DOES NOT correctly describe benzene’s structure
does not correctly describe the distribution of pi electrons
the kekule structure has the pi electrons localised to three double bonds but in reality the electrons are delocalised
all of benzenes carbon tp carbon bonds are an identical intermediate between double and single bonds
give two proprties of benzene that result form its unusual bonding structure and give evidence
*Lack of reactivity - benzene is very stable/ unreactive
expeirmental evidence - benzene will not decolourise red bromine water or acidified potassium manganate vii
(not undergo an addition reaction)
*unusual bond lenght- all of benzenes bonds are the same lenght, smaller than a single bond, larger than an dounle
Is benzene saturated or unsaturated? Is it an alkene?
neither, benzene is neither saturated or unsaturated, also not an alkene
give two other properties of benzene (not related to its bonding structure)
non polar molecule - doesnt dissolve in water
carcinogenic- causes cancer- health hazard
what is the average number of electrons shared between any two adjacent carbon atoms in 1.cytohexane 2.benzene
- 2 electrons, only single bonds
- 2 sigma always shared +2 delocalised electrons
explain the result for demostarting the solubilities of methane, thene, ethyne, methylbenzene
result
1 when bubbled from water, each gas does not dissolve and forces itself into syringe B,syringe B opens to almost 100cm3
2 when bubbled through cyclohexane: each gas does dissolved and syringe B remains mostly closed
methane, thene, ethyne, methylbenzene are all non-polar molecules
name common aromatic compounds
pharmaceuticals - paraceramol, ibuprofen
acid base indicators- methyl orange and phenolphthalein
food preservatives - bezoic acid and its salts ( sodium benzoate)
name the equipment needed for extracting clove oil from cloves by steam distillation
safety tube
steam generator
hot plate/ bunsen burner
steam trap
cloves in water
liebig condenser
emulsion of clove oil and water
what are immiscible liquids
liquids that do not mix
what is the principle of steam distillation
the boiling point of two immiscible liquids is below the boiling point of both liquids seperately
Why is steam distillation used to extract clove oil from cloves rather than direct disillation
clove oil has high boiling point, if it were distilled directly, the oil would decompose at the high tempertures
what is the main constituent present in clove oil, what natural product in present in clove oil
eugenol
Give two saftey percautions in extracting clove oil from cloves by steam distillation
1 - a safety tube is placed in the steam generator to prevent build up of pressure
2- gloves are worn when handleing the cloved, eugenol can burn the skin
comment on the positio of the saftey tube in the steam generator
below the water level to prevent steam from escaping
What is the purpose of a steam trap in extracting clove oil from cloves by steam distillation
collect any steam that has condensed and avoid it condensing into and filling up flask full of cloved
what two substances are collected during steam distillation
water and clove oil as an emulsion
What is an emulsion?
An emulsion is a dispersion of small droplets of ONE LIQUID (OIL) IN ANOTHER LIQUID in which it is not soluble
Describe the appearance of the water- clove oil emulsion/distillate collected during the steam distillation
Milky coloured
Why are whole cloves used rather than powdered cloves?
whole cloves contain more oil
Explain the method to Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction
Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction
add emulsion into a seperating funnel, using a dropper add cyclohexane.
stopper and shake(funnel is inverted when shaken) tap is opened to release the pressure of the vapourised liquid
allow aqueous layer to drain into a beaker, organic to drain seperatly into a conical flask
the aqueous layer will still contain some oil, precedure is repeated at least two more time to obtain the max amount of clove oil
What is liquid liquid extraction
used to separate two immisible liquids. a slovent is added in whcih one of the liquids will dissolve but the other will not
Why add cylohexane?
Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction
clove oil is soluble in cytohexane , water is not, adding ctyohexane dissolces the clove oil from the emulsion, doesnt dissolve water
would ethanol be a suitable solvent for use in the liquid liquid extraction
Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction
ethanol would not be a suitable solvent.
to remove the clove oil from the elmunsion a non polar solvent must be used.ethanol has a polar hydroxyl group and it would dissolve water from the elmusion
Saftey procedures
Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction
the eparating funnel is invertes when shaking, tap is gentaly opened to release the pressure, avoid pointing it at another person
Why is the washing and separating carried out three times?
Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction
the milkey colour is caused by the presence of deoplets of clove oil in the water as an emulaion, each wahing ectracts more oil
describe the methos in removing excess water
using a spatula, add anhydrous magnesium sulfate to the clove oil and ctyohexane mixture.
the anhydrous magnesium sulfate brinds with any water present in the mixture and forms clumps of hydrated magnesium sulfate.
filter clove oil/cytohexane mixture with flutef filter paper into a new preweighes conical flask to remove the clumps of hydrated magnesium sulfate/ excess anhydrous magnesium sulfate
rinse the orginal conical flask with cytohexane and filter again to ensure all clove oil is retrieved
why is anhydrous magnesium sulfate (MgSO4) added
Removing excess water
magnesium sulfate is a drying agent, absorbs and clumps any remaining water
How much anhydrous magnesium sulfate is added?
Removing excess water
add until it settles at the bottom of the flask and no longer clumps, all the water has been absorbed
why is the mixture filtered
Removing excess water
to remove any hydrated magnesium sulfate and excess magnesium sulfate from the mixture
why is fluted filter paper used
Removing excess water
fluted filter oaoer has a greater surface are- filtration will be quicker
Describe the method in isolating the oil
place clove oil/ cytohexane in a water bath in a fume cuboard @81 C and boil the cytohexane off to leave the clove oil isolated.
leave the concial flask in the fume cuboard overnight, ensuring cyclohexane will be evaporated
why is the filtered mixture placed under a water bath
In isolating the oil
cytohexane is a volatile organic solvent, boiing point in 81, the cytohexane is boiled off leaving the clove oil completely isolated behind
why is a hot plate NOT used
In isolating the oil
thr clove oil could boil off as well as the cytohexane
why is a bunsen burner not used to evaporate the cyclohexane
In isolating the oil
cyclohexane is a flammble solcent- it must never be heated with a bunsen burner
two industrial uses of clove oil
flavoring agent
perfumes, soaps
