Organic Chemistry - Notes Flashcards
Why are tertiary halogenoalkanes more reactive than primary and secondary halogenoalkanes?
- tertiary HALOGENOALKANES are less stable than primary and secondary
- but they form the most stable tertiary CARBOCATIONS due to the positive inductive effect on the three alkyl groups
- so tertiary halogenoalkanes undergo nucleophilic substitution more readily
Why do tertiary halogenoalkanes undergo Sn1?
- Due to the bulky alkyl groups surrounding the central carbon attached to the halogen, there is not enough space for the nucleophile to attack
- so first the carbon-halogen bond must break without the interference of any other molecules (unimolecular).
- then the carbocation forms and the nucleophile can attack
addition reaction
a reactant is added to an unsaturated molecule to form a single product
substitution reaction
an atom/ group of atoms are replaced with a different atom/group of atoms
elimination reaction
a pair/ group of atoms is removed from a molecules
hydrolysis reaction
a molecule is split apart when it reacts with water
three ways alkane fuels are obtained
- fractional distillation
- cracking
- reforming
Cracking
converts larger alkanes into smaller, more useful alkanes and ethene
cracking conditions
600-700 degrees to vapourise
silica, aluminium oxide, zeolite catalyst
thermal cracking
takes places at high temperatures and pressures WITHOUT a catalyst
Which bonds does catalytic cracking break
and
what is catalytic cracking mainly used to produce?
C--C bonds motor fuels (branched and cycloalkanes) + aromatic compounds
reforming
processing of straight chained hydrocarbons into branched chained alkanes and cyclic hydrocarbons for efficient combustion
Why do we carry out reforming?
straight chained alkanes do not burn evenly in car engines, they cause ‘knocking’ in the engine. Cyclohydrocarbons burn more SMOOTHLY and are BETTER for modern high performance engines.
reforming conditions
- 500 degrees
- platinum/rhodium catalysts
What does a repeating unit drawn out look like?
single bonds
brackets
n
When are addition polymers formed? and what are they?
when monomers containing double bonds are polymerised
they are the repeating unit of monomers
What do the monomers of polymers have to have?
a double bond (which is then broken in polymerisation)
Property of addition polymers (reactivity)
unreactive due to strong C-C and C-H bonds
Disposal of polymers [2]
- non-biodegradable so take up space in landfills
- no groups which can be attacked by water or natural organisms so cannot decompose naturally
recycling of polymers [4]
- polymers sorted into type (automatically with infrared)
- melted and remolded
- saves crude oil
- expensive in energy and man power
polymer incineration [4]
- burnt at high temps
- burning process used for energy generation (high temps prevent poisonous gases from entering the air)
- greenhouse gases such as CO2 produced
- if incomplete combustion then CO produced
polymers as feedstock for cracking [2]
- waste polymers can be used as feedstock for cracking (allows new polymers to be formed)
- process involves decompoistion. polymer heated with no oxygen then decomposes into smaller molecules that can be used as fuel
Life Cycle Assessment polymers [3]
- material, energy, space used to dispose of them
- materials and energy used to make
- materials and energy used to maintain
polymers improvements [2]
- remove waste gases produced during incineration
- make plastics which are biodegradable (eg. polyethanol)
alcohol general formula
CnH2n+1OH
Combust alcohols with a what flame?
As chain length increases, alcohols become…
CLEAN flame
less easy to burn because they are less volatile (don’t go up in a whoosh as fast)
Alcohols react with PCl5 to produce chloroalkanes
Eg. C2H5OH + PCl5 –> C2H5Cl + HCl + POCl3
> HCl produced gives of steamy white fumes > fume cupboard needed due to HCl > room temperature > SUBSTITUTION REACTION >
What can the alcohol and PCl5 reaction be used to test for?
-OH groups - (but first you must eliminate other things that react with PCl5 eg. carboxylic acids and water). If you have a neutral liquid containing no water and you get a violent reaction with steamy white fumes then there is an alcohol present.
Alcohols react with 50% concentrated H2SO4 and potassium bromide
KBr + H2SO4 –> HBr + KHSO4
HBr + alcohol –> alcohol[Br]+ H20
(eg. HBr + C2H5OH —> C2H5Br + H20)
- heat under reflux
- distil off product after about 20 minutes
alcohols reaction with iodine and red phosphorus
- substitution reaction
- moist red phosphorus
- warm the alcohol with the reactant
partial oxidation of primary alcohols
forms aldehydes AND WATER
limited amount of potassium dichromate (VI) solution in dilute sulphuric acid mix alcohol and reagents add alcohol dropwise, WARM GENTLY distill out aldehyde as it forms [O]
Full oxidation of primary alcohols
forms carboxylic acids AND WATER
eg. propan-1-ol would go to propanoic acid
potassium dichromate (VI) solution in dilute sulphuric acid
HEAT UNDER REFLUX
excess potassium dichromate and acid distill off product when the reaction finishes (collect distillate between 139-143 degrees)
[O]
oxidation of secondary alcohols
forms ketones AND WATER
eg. propan-2-ol would go to propanone
potassium dichromate (VI) solution in dilute sulphuric acid
add alcohol dropwise
mix alcohol and reagents
HEAT UNDER REFLUX
distill off product collecting distillate between 77-81 degrees.
[O]
Why can tertiary alcohols not be oxidised by potassium dichromate (VI) ?
they have no hydrogen atom on the carbon bonded to the OH group
alcohols and phosphoric acid reaction
alcohol —(phosphoric acid)—> alkene + water
dehydration
elimination
warm, under reflux
producing alkenes from alcohols provides a possible to route for making polymers without using monomers derived from crude oil (bc eventually crude oil will run out)
In the partial oxidation of alcohols, why do you distill out the aldehyde as it forms?
to prevent further oxidation into a carboxylic acid
When is reflux used?
when heating organic reaction mixtures for a long time.
It prevents organic vapours from escaping by condensing them back into a liquid.
What NOT to do when heating something under reflux?
DON’T seal the end of the condenser because gases will build up and cause an explosion
classic AS reaction using reflux?
Full oxidation of primary alcohols –> carboxylic acids
classic AS reaction using just distillation (no reflux)?
partial oxidation primary alcohols –> aldehydes
observation when a primary alcohol –> aldehyde/carboxylic acid (depending on if it is partial or full oxidation)
orange dichromate solution –> green (colour of Cr3+ ions)
What do anti-bumping granules do when added to the flask in reflux or distillation?
prevent vigorous boiling by providing a larger SA for bubbles to form on. Smaller bubbles form instead of large ones.
What is sometimes used other than a bunsen burner to heat organic chemicals?
electric heater because organic chemicals are flammable
When is distillation used?
to separate an organic product from its reaction mixture. Need to collect distillate at approximate boiling point range of the desired liquid.
Purifying an organic liquid (6 steps)
- put impure product distillate into separating funnel
- wash this product by a) add sodium hydrogencarbonate solution (shake and release pressure from CO2 produced) OR b) add saturated sodium chloride solution
- allow layers to separate in the funnel then run and DISCARD THE AQUEOUS layer
- organic layer (that has just been separated) into clean, dry conical flask and add three spatulas of drying agent (anhydrous sodium sulfate) to dry the organic liquid
- decant liquid (now all the water has been sponged up by the drying agent) into a distillation flask
- distill to collect pure product
Purifying organic liquid - washing step - what do the washing substances do?
sodium hydrogencarbonate - neutralises any remaining reactant acid
saturated sodium chloride - helps separate the organic and aqueous layers
two things that drying agents (when purifying organic liquids) should be?
1) insoluble in the organic liquid
2) not react with the organic liquid
In the preparation of bromoalkanes from alcohols, why is (fully?) concentrated sulphuric acid not used?
because it would oxidise the -ide to -ine (bromide to bromine)
two examples of drying agents
anhydrous sodium sulfate
anhydrous calcium chloride
How to get a correct measure of boiling point?
thermometer just above the surface of the boiling liquid, measuring the temperature of the saturated vapour
solvent extraction
compounds are separated based on their relative solubilities
preparation and purification of liquid organic compounds
(1) - prep
(2) - solvent extract - 6 steps
- heat mixture under reflux
- distill mixture (crude distillation - no thermometer required)
-distillate placed in separating funnel for further purification
—————————————————————————-
solvent extraction: - liquid mixed with water to remove general impurities and sodium carbonate solution to remove acidic impurities
- stopper in and funnel inverted and gently moved back and forth
- to release pressure whilst mixing invert funnel (with stopper in) and open tap briefly
- once acid impurities/other impurities have been removed (no more bubbles produced), the sodium carbonate solution layer/(or if another solvent was used to remove impurities) is run off.
- after discarding that final solvent solution (the thing added to get rid of impurities) the liquid is added to a drying agent that removes water
- after drying, liquid decanted and filtered through small tuft of mineral wool in pear shaped flask + DISTILL SECOND TIME
after heating under reflux what apparatus should be used to separate the two layers?
separating funnel
talk about the bottom layer when two layers form after use of a separating funnel
the more dense layer contains the impurities and is usually the bottom layer
after heating under reflux, when using a separating funnel to get two layers, which layer would you want to retain?
the layer that ISN’T the aqueous layer (so the less dense layer without the impurities)
DISCARD AQUEOUS LAYER
if it is the long prep and purification process, what is the final final step
distill the liquid a SECOND time, using a thermometer, collect the distillate between insert exact temp depending on liquid
What safety precaution should be taken during the solvent extraction step using water and sodium hydrogencarbonate solution?
releasing pressure in separating funnel; put stopper in, invert funnel, open the tap to release pressure
During the solvent extraction with water and sodium hydrogencarbonate solution, which layer should be retained?
the layer with the stuff you began with (eg. bromoethane)
Fractional distillation
1) crude oil heated and fed into fractionating tower
2) fractions separated according to boiling point (small molecules with low b.p at top) - top of tower cooler (where small molecules vapourise)
4) Different sized fractions condense at different heights due to different boiling points
5) fractions are collected
In car engines the gases are ejected before combustion is complete..
because this achieves maximum power. However it causes carbon monoxide and unburned hydrocarbons that are ejected to cause pollution
1) carbon monoxide
2) unburned hydrocarbons
3) fuels containing sulfur
4) combustion taking place at high temps in car engines
5) unturned petrol engines
1) poisonous, reduces capacity of blood to carry oxygen by irreversibly binding to haemoglobin
2) unburnt hydrocarbons react with air in the presence of sunlight to produce photochemical smog that causes serious breathing problems
3) fuels containing sulfur converted to SO2 in combustion, mixes with water droplets forming acid rain
4) high temps allow nitrogen and oxygen to combine forming oxides of nitrogen which combine with water droplets and form acid rain
5) diesel engines and unturned petrol engines tend to form carbon particulates (eg. soot) which pollute the air
What do catalytic converters do?
change poisonous molecules such as CO and various nitrogen oxides into less harmful molecules (eg. CO2 and N2)
What catalysts do catalytic converters use?
expensive metals (platinum/rhodium/palladium) as heterogenous catalysts (honeycomb of ceramic material coated with a thin layer of metal)
What happens if lead is adsorbed onto a catalytic converter?
it is a catalyst poison, stops the catalytic converter from working.
example equation of catalytic converter converting some gases
2CO + 2NO –> 2CO2 + N2
Disadvantages of biofuels
- less land to grow crops
- rainforests cut down
- less fertile soil
What are biofuels? + two examples
:))
formed from plants and carbon neutral
biodiesel and bioethanol (all formed from renewable resources)
Free radical substitution example: INITIATION
bromine + ethane
Br2 –> 2Br *
Free radical substitution example: PROPAGATION
bromine + ethane
Br* + C2H6 –> C2H5* + HBr
C2H5* + Br2 —> C2H5Br + Br*
Free radical substitution example: TERMINATION
bromine + ethane
Br* + Br* —> Br2
C2H5* + C2H5* –> C4H10
Br* + C2H5* —> C2H5Br
Free radical substitution example: INITIATION
chlorine + CHCl3 (chloroform)
Cl2 –> 2Cl*
Free radical substitution example: PROPAGATION
chlorine + CHCl3 (chloroform)
Cl* + CHCl3 –> CCl3* + HCl
CCl3* + Cl2 —> CCl4 + Cl*
in the first propagation step of free radical substitution, what is knocked off of the reactant to form the first radical other than the Cl2 or Br2 or whatever it is
a hydrogen
What can Cis/trans and E/Z be assigned to?
How to go about working out Cis/trans or E/Z isomerism
anything with a C=C and three different groups attached can be named by cis/trans and also E/Z
But things where there are 4 different groups all together can ONLY be named using E/Z, NOT cis/trans
split vertically and choose the highest priority group on the LHS and the highest on the RHS
split horizontally and determine if it is cis/trans (or if there are 4 different groups then if it is E/Z)
alkene + potassium manganate (VII) –> diol
colour change depending on acidified/alkaline
acidified (VII) with H2SO4 = purple solution to colourless
(VII) made slightly alkaline with sodium carbonate solution = dark purple solution to dark green to dark brown precipitate
manganate (VII) ions are…
STRONG OXIDISING AGENTS
carbonyl group
a functional group composed of a C=O bond
what is the thing about aldehydes and ketone being oxidised
aldehydes can be further oxidised to carboxylic acids, ketons CANNOT
what does the presence of the hydrogen atom in aldehydes mean?
they are very easy to oxidise, they are strong reducing agents
Why can ketones not be oxidised?
they don’t have a hydrogen atom on one side of the C=O bond.
What is the only way a ketone can be oxidised?
with very very very very strong oxidising agents like potassium manganate (VII) but even this is done destructively, breaking C-C bonds
What is the reagent in the fehling’s test and what are the conditions?
fehling’s solution containing blue Cu2+ ions
heat gently
Fehling’s solution : what is happening and what is the observation
aldehydes are oxidised by fehling’s to a carboxylic acid. The copper (II) ions are reduced to copper (I) oxide.
in the presence of an aldehyde the blue Cu2+ ions in the solution change to a red Cu2O precipitate
Tollen’s reagent?
ammoniacal silver nitrate (sodium hydroxide, ammonia, silver nitrate solution)
Tollen’s reagent what happens and observation?
aldehydes oxidised by Tollen’s to a carboxylic acid, producing a ‘silver mirror’ and Ag+ gains e- (is reduced)
how to determine if a halogenoalkane will undergo elimination or substitution?
water - encourages substitution
ethanol - encourages elimination
but the CLASSIFICATION is the most determining:
primary - mainly substitution
secondary - both substitution and elimination
tertiary - mainly elimination
