Topic 6: Organic Chemistry I 2️⃣ Flashcards
What is a hydrocarbon
Compounds that contain hydrogen and carbon only
What is a homologous series
A series of compounds which similar properties, same general formula and same functional group. Differ by CH2
What is structural formula
A way if representing the molecules that shows the atoms carbon by carbon with attached hydrogens and functional groups
Eg. CH3CH2CH2CH2CH2CH2CH2CH3
What is displayed formula
A way of representing the molecules that shows how all the atoms are arranged and all the bonds between them
What is the general formula & functional group of an alkane
CnH(2n+2)
C-C
What is the general formula & functional group of an alkene
CnH(2n)
C=C
What is the general formula & functional group of alkynes
CnH(2n-2)
C-C triple bond***
What is the general formula & functional group of alcohols
CnH(2n+1)
-OH
What is the general formula & functional group of halogenalkanes
CnH(2n+1)
-Hal
What is the general formula & functional group of aldehydes
RCOH
-CHO
What is the general formula and functional group of ketones
CnH(2n)O
C=O
What is the general formula and functional group of carboxylic acids
CnH(2n+1)
-COOH
What is the general formula and functional group of Ethers
R-O-R
What is the general formula and functional group of primary amines ?
RNH2
What is the skeletal formula
A simplified organic formulae which only shows the carbon skeleton and associated functional groups
What is an addition reaction
A reaction where 2 or more molecules join together to form another molecule
What is polymerisation
Many monomers join together to make a long chain polymer
What is an elimination reaction
A reaction where atoms or small groups are lost from adjacent carbon atoms (common products removed are halides/H2O)
What is a substitution reaction
A reaction where an atom or group (eg.hydroxide ion) is replaced with another
What is a hydrolysis reaction
A reaction where a molecule is split by adding H+ and OH- (derived from water).
Often require a catalyst of acid or alkali
What is an oxidation reaction
A reaction where a species loses electrons. Other ways to describe it is a gain of oxygen or removal of hydrogen
What is a reduction reaction
A reaction where a species gains electrons. Other ways to describe it is the loss of oxygen and gain of hydrogen
What does a full curly arrow represent
Movement of 2 electrons
What does a half curly arrow represent ?
Movement of one electron
What are the three types of reagents
Nucleophiles
Electrophiles
Radicals
What are nucleophiles
They are electron pair donors
They can be either negatively charged or have lone pair electrons
They are attracted to electron poor centres
What are electrophiles
They are electron pair acceptors.
They can be either positively charged or have an area of electron deficiency
They are attracted to negative ions and electron rich centres
What are radicals
They have an unpaired electron which means they are very reactive
As a result their products are a complete mixture
What is a chain isomer
Carbon chain gets arranged differently
What are position isomers
Possible when there are functional groups can be put in different positions on the carbon chain
What are functional group isomers
Structural isomers that have different functional groups, leading to very different physical and chemical properties
What are the types of structural isomer?
Chain isomer
Position isomer
Functional group isomer
Stereoisomer
What are stereoisomers
Compounds with the same structural formula but different arrangement in 3D space
What is the difference between E/Z isomers
E= entgegen (opposite)
Z= zusammen (together)
What are the Cahn-Ingald-Prelog rules to determine whether a stereoisomer is an E/Z isomer when the carbons have different groups attached to them
Draw dashed line across the centre of the double bond
Atoms with a larger atomic number are given higher priority (1)
If the atoms directly bonded to the carbon are the same you move to the next one
How can you differ between a cis/trans stereoisomer
Cis- the same groups are on the same side of the double bond
Trans- the same groups are on opposite sides of the double bond
Why is refluxing used in organic chemistry
Useful as can be used for:
- flammable or volatile substances
- slow reactions
- continuous evaporation and condensation
- anti bumping granules in round bottomed flask
What is distillation and how is it used in organic chemistry
Gentle heating of a mixture, lowest boiling point substance evaporates first
You can compare this to known boiling points
Used in making primary alcohols
How and why is 1st stage of separation (separating funnel) used in organic chemistry
Used if product is not soluble in water
Denser layer is drawn down
Removes soluble impurities from product
How to use it :
Pour mixture into funnel
Add water
Shake the mixture and allow layers to separate
Run off two layers after having removed the stopper
How and why is the 2nd stage of separation (drying) used in organic chemistry
You will have some water left over in your product so…
Use a drying agent such as anhydrous magnesium sulfate or calcium chloride, then filter
How does fractional distillation work (crude oil)
Crude oil is evaporated/vaporised
Then condensed back into a liquid
Liquids of different boiling points condense at different levels
Define the term ‘fraction’
Molecules of a similar chain length
After fractional distillation but before the fuels are used as fuels what has to happen
They are refined - sulfur compounds are removed
Why do sulfur compounds have to be removed before a fuel can be used as a fuel ?
When fuels are burnt, sulfur would react with oxygen producing sulfur dioxide
This results in acid rain when dissolved in water
Do branched or unbranched molecules have a lower boiling point ?
Branched molecules
Why do branched molecules have a lower boiling point
Due to reduced surface area, the magnitude of intermolecular forces is also reduced
What is an octane number ?
Measure of a performance of a fuel
A higher octane number means a smoother start when starting an engine - knocking
What are the two methods of making branched and cyclic alkanes
Reforming
Cracking
What does reforming involve
Uses a catalyst and high temperatures
Changes structure of alkane
What are the two types of cracking and what do they need
Thermal cracking - uses temperature and pressure (produces alkenes + alkanes)
Catalytic cracking - uses a catalyst, temperature and pressure ( produces aromatic compounds)
What does the catalyst determine in cracking
Which aromatic compound is formed / produced
Why do we crack?
Higher demand
Forms shorter chain alkanes and alkenes
Shorter chain alkanes ignite more easily- reduced knocking
Shorter chain alkanes are used in making polymers
Shorter chain alkanes are useful starting materials in organic synthesis
What are the products of complete combustion
Water and carbon dioxide
What are the products of incomplete combustion
Carbon dioxide
Water
Carbon monoxide
Carbon
other pollutants from combustion of fuels:
sulfur dioxide
nitrogen oxides
The process of halogenation of an alkane takes place in which 3 stages?
Initiation
Propagation
Termination
Describe the process of initiation
The halogen molecule is split by homolytic fission forming 2 halogen radicals
The rest of the reaction occurs with no further energy input
photodissociation- absorption of light that causes the bond breaking
Describe the stage of propagation
During the halogenation of alkanes the halogen radical with then go on to react with an alkane
It is a rapid process which continues until no more reactant remains (chain reaction)
Describe the stage of termination
Step at the end of radical substitution, where 2 radicals combine to form a molecule
There are a number of different possibilities due to the different radicals that are formed
What are the problems with free radical substitution
If there is an excess of a halogen in the reaction mixture you could produce di- tri- and tetr-…..
you can reduce the chance of this by having an excess of alkane molecules
If you have a carbon chain which is longer than two you full get a mixture of structural isomers
Why do we need alternative fuels?
Primary fuels today are fossil fuels problematic as…
-burning them releases co2 and other pollutants contributing to climate change
-finite source = unsustainable
Therefore carbon-neutral renewable alternative fuels are being developed
What are the 3 main types of biofuel?
Biogas
Bioethanol
Biodiesel
Why are biofuels in general better?
They can be produced at the rate they are used = renewable
Due to the carbon in biofuels being absorbed from the atmosphere, it’s use as a fuel makes minimal difference to the atmospheric proportion of co2
How is biogAs produced?
When organic waste is broken down by microorganisms Anaerobically
What is biogas composed of and how does that make it useful?
Composed primarily of methane and co2
-methane can be oxidised in combustion to release energy = gas can be used as a fuel
How can biogas be used to produce bio methane ?
Is often refined by removing co2 & other contaminants.
Bio methane is compositionally the same as natural gas so can be used to release energy using the same infrastructure
How is bioethanol produced?
Fermentation of plant matter often using enzymes or bacteria
(The sugar for fermentation is extracted from crops grown specifically for the production of bioethanol)
What has to happen to bioethanol before it can be used as a fuel ?
What are the benefits of bioethanol ?
Ethanol has to be separated from the much larger amount of water before it can be used as a fuel- requires energy
Ethanol increases the octane number of the fuel blend and reduces pollutants by providing more oxygen for compete combustion
How is biodiesel produced ?
By refining (removing impurities from) renewable fats and oils
Fuel is produced by transesterification -process that converts fats and oils into biodiesel & glycerin (co-production)
What are the benefits of alternative fuels?
Considered almost carbon-neutral
Biodiesel and biogas can reduce the amount of waste going to landfill as the waste can be used to produce them
Biodiesel production could provide money for less developed countries as they have space to grow required crops
What are the drawbacks of alternative fuels ?
The high cost of converting engines & machinery to run biofuel instead of petrol/diesel
Many developed countries don’t have space to produce enlightened plants needed for biofuels as land is needed for food production
What does a catalytic converter do?
Removes environmentally polluting molecules from exhaust gases
Removes molecules that affect health from exhaust gases
What are the molecules that a catalytic converter removes?
Nitrogen oxides, carbon monoxide and unburnt hydrocarbons
Describe the structure of a catalytic converter
Contains small quantities of precious metal catalysts (solids) such as: platinum, rhodium & palladium.
Spread over a thin honeycomb mesh which increases the surface area
What are the stages of the reaction inside the catalytic converter?
CO and nitrous oxide molecules attach (adsorb) to the catalytic mesh
The catalyst weakens the bonds which allows them to react more freely
The products (CO2 and N2) are released (desorbed) from the catalytic mesh
What is incomplete combustion and when does it occur?
Occurs when there is insufficient oxygen present or because combustion is very rapid
All hydrogen atoms are converted to water
Some of the carbon atoms form gaseous carbon monoxide or solid carbon
What are the problems with carbon monoxide
Poisonous gas
Binds to haemoglobin in red blood cells preventing them from carrying oxygen to the body
Colourless gas - so harder to detect
Contributes directly to climate change as it participates in chemical reactions in the atmosphere which produce ozone
How are oxides of sulfur produced?
Some molecules in crude oil contain atoms of sulfur which can’t be removed by fractional distillation, cracking or reforming processes.
During the combustion of alkanes, these atoms of sulfur form sulfur dioxide and then react in the atmosphere to form sulfur trioxide
What are the problems with oxides of sulfur
Sulfur dioxide and trioxide are both acid gases which means that when the dissolve in water in the atmosphere they form sulfur out acid and sulfuric acid.
Both of which, contribute to the formation of acid rain (responsible for a lot of environmental damage)
How are oxides of nitrogen produced
High temperatures in cars causes nitrogen molecules in the air to react with oxygen
N(2) + O(2) ——-> 2NO
What is the problem with oxides of nitrogen
Nitrogen dioxide is acidic and can dissolve in the water is atmosphere to form nitric acid
Contributes to environmental damage in the same way as sulfuric acid
What are carbon particulates mainly formed from?
Fuel oil
Plastics
Diesel engines
Fires
Vehicle tail pipes
What problems do carbon particulates cause
Risk of strokes, cardiovascular events, coronary heart disease
They can reflect sunlight back into space which reduces the amount of sunlight that reaches the earth (global dimming)
What are the problems associated with unburnt hydrocarbons
Hydrocarbons in the atmosphere contribute to photochemical smog as well as absorbing infrared radiation
How can you test for unsaturation
Bromine water
Goes colourless if alkene is present
What are the physical properties of alkenes
Don’t dissolve in water as they are non-polar
As chain length increases, surface area increases, as does intermolecular forces = higher melting and boiling points
What is a double bond in an alkene made up from ?
A sigma bond (σ) and a pi bond (π)
Describe a sigma bond
Formed when 2 s-orbitals overlap end on
Describe a pi bond
Formed when 2 p-orbitals overlap side on
Why is a double bond not twice as strong as a single bond?
Because the pi bond is weaker than the sigma bond
Draw a diagram of double bond
Draw
What are the two requirements when making alkanes from alkenes
150 degreees and a nickel catalyst
(Process is called hydrogenation)
What type of reaction is making dihalogenalkanes
Electrophilic addition reaction
How can you determine the position of a halogen if the chain length is longer than two and unsymmetrical when drawing the mechanisms for making halogenalkanes?
It is to do with the stability of the carbocation - determines the products of the reaction
- The more carbon chains that are attached the more stable the carbocation
ie. A carbocation with 3 carbon chains attached is tertiary and the most stable -halogen would go there
When can major and minor products occur ?
When two possible products can be formed when making halogenalkanes
What is needed to make diols (2 alcohol groups)
Dilute acidified potassium manganate
What is recycling ?
Involves converting polymer waste into other materials
What is an incinerator ?
Converts polymer waste into energy
What does use of polymer waste as feedstock mean?
Involves converting polymer waste into chemicals that can be used to make new polymers
What is a biodegradable polymer?
One that can be broken down by microbes
What are the 3 ways polymer waste can be put to other uses?
Recycling
Incineration
Use as chemical feedstock
Describe the stages of recycling
1st stage is sorting -necessary as there are many types of polymer in use and mixtures of these types cannot be effectively processed together
2nd stage is processing - involves chopping the waste into small pieces and washing it
The material is then used to make new materials using methods such as moulding, melting and fibre production
Why is there little solid waste left after incineration
Because most of the atoms in the polymers end up in gaseous products which pass into the atmosphere via a chimney
Why is there opposition to incineration
Concerns about air pollution because of the other elements present in the polymer waste other than hydrogen and carbon.
These pollutants are very difficult to remove from the waste gases released into the atmosphere
What are the disadvantages of biodegradable polymers?
They are often made from plant material - land is needed to grow the plants
They are designed to breakdown in the environment, so when they do the carbon and hydrogen atoms they contain, cannot be directly used
What are halogenoalkanes
Compounds where at least one hydrogen in the alkane has been replaced by a halogen (can be primary, secondary or tertiary)
Why does boiling point increase as you go down the halogen group?
Each halide has more electrons resulting in a stronger dipole-dipole interaction
Why does boiling point increase as carbon chain length increases?
Larger surface area means more London forces
Why are halogenoalkanes prone to nucleophilic attack
Halogen is electronegative which draws the electron density from the C-Halogen bond towards the halogen, making the carbon slightly electron deficient
How does nucleophilic substitution occur in halogenalkanes (in this case use OH)
During hydrolysis the halogen atom is replaced by the hydroxide ion (or another nucleophile)
Donation of the electron pair leads to the formation of a new covalent bond between the oxygen (OH) and the carbon
The carbon-halogen bond breaks by heterolytic fission - both electrons from the bond move to the halogen, forming a halogen ion.
Define nucleophilic attack
Nucleophile attacks electron deficient carbon with its lone pair of electrons
Describe and explain the reaction of a halogenoalkane with water
- Halide is replaced with -OH group, producing an alcohol
- Hydrolysis reaction
- Halogenoalkanes do not dissolve in water so ethanol is used
- Can monitor the rate using silver nitrate
Describe and explain the reaction of a halogenoalkane with aqueous potassium/sodium hydroxide
- Another way to produce alcohols (quicker)
- Halide is replaced by OH group
- Can monitor the rate but acidification needs to be carried out with dilute nitric acid before the silver nitrate can be added
Describe and explain the reaction of a halogenoalkane with potassium cyanide
- Halide replaced with CN group (:C=-N-) <- triple bond - which increases the carbon chain length & forms a nitrate
- carried out under reflux with potassium cyanide in ethanol
Describe and explain the reaction of a halogenoalkane with ammonia (NH3)
-Halide is replaced by -NH2 group producing an amine
-Ethanol is used
-Ammonium salt is also produced
What are the 4 types of nucleophilic substitution reactions you need to be aware of ?
Reaction with water
Reaction with aqueous potassium hydroxide
Reaction with potassium cyanide
Reaction with ammonia
How can you measure the rate of hydrolysis of primary halogenoalkanes
Heated with aqueous silver nitrate and ethanol
Hydrolysis takes place and halide ions form
The aqueous silver nitrate reacts with the halide ion forming a precipitate
1/ time for precipitate to form = rate
What colour are the precipitates formed during reaction of halides with silver nitrate
Chlorine - white
Bromine - cream
Iodine - yellow
Which out of bond polarity and bold enthalpy takes precedence
Bond enthalpy
Why do we have to use ethanol to dissolve halogenoalkanes instead of water
Need to break dipole-dipole interaction in halogenoalkane
-breaking hydrogen bonding in water doesn’t release enough energy to break the above^^
Compare alkanes to alcohols
Alkanes are more volatile
Alkanes have lower boiling points
Alkanes are less soluble in water
Alkanes don’t have hydrogen bonding only London forces
Which type of alcohol (primary, secondary or tertiary) don’t undergo oxidation?
Tertiary alcohols
What colour change is expected when an alcohol is heated with potassium dichromate (VI)
If primary / secondary : orange—-> green
If tertiary : no colour change
What can primary alcohols be oxidised to form ?
Aldehydes : gentle heating & distilled off as they are made
Carboxylic acids: prepared under reflux with
Both need reagent of potassium dichromate
What can secondary alcohols be oxidised to form?
Ketones : can’t be oxidised any further than this so reaction is carried out under reflux
How do you form an alkene from an alcohol?
Dehydration
- water molecule is removed from starting material
- done under reflux with an acid catalyst (H2SO4 or H3PO4)
How can we distinguish between an aldehyde and a ketone
oxidation reaction
Aldehydes oxidise easily, ketones don’t
Fehlings reagent (blue - red = aldehydes)
How can you form chloroalkanes from an alcohol?
Substitution reaction
Use phosphorus(V)chloride (s) - PCl5
How do you form bromoalkanes from alcohols
Substitution reaction
Use either …
- Hydrogen bromide - HBr
- Phosphorus(III)bromide - PBr3
Water is produced
How do you form iodoalkanes from alcohols?
Substitution reaction
Use phosphorus(III)iodide - unstable so made in situ using red phosphorus and iodine
What does a saturated hydrocarbon look like ?
No C=C bond (only single bonds)
Has maximum number of hydrogen atoms
What are the points of comparison between natural gas (fossil fuel) & biodiesel/ethanol (biofuel)
Biofuels:
Land use (a lot needed)
Yield (low but gradually increasing)
Manufacture/transport (no exploration or drilling costs. However costs in growing processing and transport)
Carbon neutrality (Much closer to being carbon neutral)
* Natural gas is opposite *
What is the symbol for oxidising agents ?
[O]
Why should you not heat a primary alcohol under reflux if you are intending for the reaction to not reach completion (obtain an aldehyde)
Because the alcohol would be oxidised and the condense back into the pear shaped flask where it would be further oxidised to form a carboxylic acid
What are the most common drying agents
anhydrous….
Magnesium sulfate
Calcium sulfate
Sodium sulfate
Give a summary of the drying process
- The drying agent is added to the organic liquid and the mixture is swirled or shaken and left for a period of time
- Before use the drying agent is powdery but after absorbing water it looks more crystalline
- If a bit more drying agent is added and it remains powdery this is an indication that the liquid is dry
- Drying agent is removed either by decantation or by filtration
What are the advantages/disadvantages of using simple distillation compared to fractional distillation as a way of purifying an organic liquid ?
- Easier to set up and quicker
-  should only be used if boiling temperature of the liquid being purified is very different from other liquids in the mixture (ideally a difference of more than 25°C) as it does not separate liquids as accurately
What are the four techniques used to purify an organic liquid
Simple distillation and
fractional distillation
solvent extraction
drying
If using solvent extraction to purify an organic liquid how should a solvent be selected ?
Should be immiscible with the solvent containing the desired organic product
the desired organic product should be much more soluble in the solvent added them in the reaction mixture
Give a summary of the process of solvent extraction
Place the reaction mixture in a separating funnel then add the chosen solvent (should form a separate layer)
Place the stopper in the neck of the flask and gently shake
Allow the contents to settle into two layers
Remove the stopper and open the tap to allow the lower layer to drain into a flask
How can we reduce knocking?
By having more branched chains -octane number is increased & knocking is reduced
Why is reaction between KCN (potassium cyanide) and halogenoalkane particularly useful in chemistry
Increases carbon chain length
Why is the reaction between halogenoalkanes and concentrated ammonia often heated in a sealed tube
Sealed tube prevents loss of ammonia gas and heating increases rate of reaction
Why do we leave testubes containing silver nitrate and ethanol in water bath for five minutes before adding the halogenoalkanes
To allow the solutions to equilibrate
When should you use. E/Z over cis/trans
E/Z is used when there are different groups on either side of the double bond
Cis/trans used when the groups are the same on either side of the double bond
Explain the trend in reactivity of halogenoalkanes
Decreases down the halogen group as C-Hal bond decreases in strength
State what is meant by the term structural isomer
Molecules which have the same molecular formula but different arrangement of atoms
