Topic 6: Organic I Flashcards
Define Isomer
Molecules with the same molecular formula but different arrangements of their atoms in space.
Define Structural Isomerism
Same molecular formula but different structural formula.
Define Stereoisomerism
Same structural and molecular formula but atoms occupy different positions in space.
What are the types of Structural Isomerism?
Chain, positional, and functional group
What are the types of geometric stereoisomerism?
E/Z and cis-trans
Can an E isomer be a cis or trans isomer?
Trans
Do Z isomers have the priority groups on the same or opposite sides?
Same (On Ze Zame Zide)
What is cracking?
The conversion of long hydrocarbon chains to smaller hydrocarbon chains.
What can the products of cracking be?
Smaller alkenes and an alkane
Smaller alkenes and a cycloalkane
Branched alkenes and a branched alkane
What can be done with the alkenes produced by cracking?
The alkenes can be used in addition polymerisation reactions to make other useful substances such as polyethene.
Why is Reforming important?
Straight chain alkanes make poor quality petrol and so converting them is important for making good fuel.
What are the steps in cracking?
A long hydrocarbon chain is heated until it vaporises. The vapour is then passed over a heated catalyst such as silica-alumina or zeolites. Thermal decomposition reaction takes place.
What happens during reforming?
Straight chain alkanes are converted into cyclic compounds - first to cyclic compounds then to aromatic hydrocarbons. Hydrogen gas is a biproduct.
What are problems with the combustion of alkanes?
Air pollution, incomplete combustion producing carbon monoxide and unburnt hydrocarbons.
Other products include sulfur dioxide, sulfur trioxide, and nitrous oxides, which contribute to acid rain.
How reaction occurs in catalytic converters?
2NO + 2CO -> N2 + 2CO2
Adsorption, reaction, and desorption
What does heterolytic cleavage produce?
Ions
What does homolytic cleavage produce?
Free Radicals
What is the equation for finding the formal charge?
Formal charge = Non-bonding electrons + 1/2 bonding electrons
Would the ammonium ion act as a nucleophile, an electrophile, or neither?
Neither. It cannot act as a nucleophile because it has a positive charge and there is no lone pair on the N. It is usually not considered a electrophile as the N+ cannot accept a pair of e-. However, it can be considered to have electrophilic properities as the H atoms are electrophilic and are subject to attack.
Why is a tertiary carbocation the most stable?
The inductive effect: electron density is passed through the C-C bond to the positive carbon, stabilising the C+. The more R groups around the C+, the greater the inductive effect.
What is the test for alkenes?
Add bromine solution (which is reddish-brown). Solution turns colourless if alkene present.
What is electrophilic addition?
The addition of an electrophile to a double bond.
Name 4 electrophilic addition reactions.
Hydrogen (hydrogenation)
Hydration -steam
Hydrogen Halide (HX)
Halogens (XX)
What are the fractions produced by fractional distillation? Give them in order from longest to shortest chains.
Bitumen: roads and roofs
Fuel oil: fuel for ships, power station
Diesel: Fuel for cars, lorries, buses
Kerosene: Aircraft fuel
Gasoline: Fuel for cars
(Refinery) Gases: Bottled Gas
What are the two types of cracking?
Describe the conditions required and products for each?
Thermal cracking: Requires high temperatures (up to 1000 oC) and high pressures (up to 70atm) and produces alkanes and a lot of alkenes.
Catalytic cracking: Lower temperatures (around 450 oC) and slight pressure in presence of zeolite or aluminium oxide catalyst to produce mainly aromatic hydrocarbons.
What is the catalyst used in reforming?
Platinum
Why are straight chain alkanes bad fuels?
They are more likely to explode, rather than combust, inside the engine. This is known as knocking, and makes the combustion less efficient.
How is CO formed as a pollutant?
CO is formed by the incomplete combustion of hydrocarbons in car engines.
How are NOx compounds formed as pollutants?
Oxidation of nitrogen from the air in car engines.
What is the consequence of NOx as a pollutant?
Dissolve in and react in water with oxygen to form acid rain.
How are biodiesel, bioethanol, and biogas formed?
Biodiesel: made by refining renewable fats and oils.
Bioethanol: made by fermentation.
Biogas: made/released when organic waste breaks down.
What are the benefits of biofuels?
Often considered carbon neutral - though not completely correct as carbon dioxide produced during refinement and transport of plants.
Biodiesel and biogas can reduce waste going to landfill.
What are the drawbacks of biofuels?
The cost of converting engines and machinary to run on biofuels instead of petrol/diesel.
Many developed countries don’t have the space to be able to produce enough plants to make the biofuels because the land is needed for food production.
What are the conditions needed for the reaction between ethene and hydrogen?
Pt/Ni catalyst
Heat
What is the product of hydrogenation reactions?
Alkene + H2 -> Alkane
What are the conditions needed for the reaction between steam and alkenes?
Phosphoric acid catalyst.
Heat
What is the product of the reaction between alkenes and steam?
Alcohols
What are the conditions needed for the reaction of alkenes with hydrogen halides?
Room temperature
What is the product of the reaction between Hydrogen Halides and alkenes?
Halogenoalkanes - the major (markovnikov) and the minor (anti-markovnikov) products.
What is an application of hydrogenation in industry?
Manufacture of margarine - the unsaturated vegetable oils are hydrgenated forming saturated vegetable oils which solidifies it.
What is needed for the oxidation of Alkenes?
Cold dilute KMnO4/H+ (acidified potassium manganate)
Shake the alkane with “
What is the colour change associated with the oxidation of alkenes?
Pale purple -> Colourless
What is the product of the oxidation of alkenes?
Diol
What problem do polymers face for disposal?
The low reactivity of many polymers makes them ideal for certain uses but at the same time creates problems with their disposal as many polymers are non-biodegradable.
One method of disposal is landfill.
What are the benefits of recycling polymers?
Reduces waste going to landfill.
Reduces the used of finite resources such as crude oil.
What are the drawbacks to recycling polymers?
Time-consuming as requires sorting.
If mixing occurs, it can produce an unusable mix of polymers.
Some polymers can release toxic chemicals when recycled such as PVC which releases chlorine.
What are the pros and cons of incinerating polymers?
Polymers can be incinerated (especially ones which are not suitable for recycling) and this can be used to generate energy.
This causes environmental pollution (release of CO2, HCl, and more).
What is the main benefit of feedstock recycling?
Works with unsorted and unwashed polymers.
What is feedstock recycling?
Where waste polymers are broken down, by chemical and thermal processes, into monomers, gases and oils.
What are some ways chemists have tried to limit the problems posed by polymer disposal?
Designed reactions to remove toxic waste: eg. CaO (s) + 2HCl (aq)→ CaCl2 (aq) + H2O (l)
Biodegradable polymers
Compostable polymers
What is needed for the formation of alcohols from halogenoalkanes?
An aqueous solution of NaOH or KOH.
Heat
What determines the rate of the reaction between OH- ions and halogenoalkanes?
The stronger the C-X bond, the slower the rate of reaction: fluoralkanes do not react at all but iodalkanes have a very fast rate of reaction.
Can you use water for the formation of alcohols from halogenoalkanes?
The reaction is very slow. The hydroxide ion is a better nucleophile than water as it carries a full negative charge whereas in water the oxygen atom only carries a partial charge.
How can the rate of reaction for the formation of alcohols from halogenoalkanes be measured?
If silver nitrate solution in ethanol is added to the solution, the silver ions will react with the halide ions as soon as they form, giving a silver halide precipitate (which causes a colour change)
What is needed for the formation of nitriles from halogenoalkanes?
Ethanolic cyanide ions (KCN/HCN for example).
Heat
What is needed for the formation of amines from halogenoalkanes?
Excess (2x) ethanolic ammonia.
Heat and high pressures.
Why is an excess of ammonia needed for the formation of amines from halogenoalkanes?
An excess of ammonia is used because the product is more reactive than ammonia so further substitution reactions could occur.
What is needed for the formation of alkenes from halogenoalkanes?
Ethanolic NaOH.
Heat
How would you classify the reaction between halogenoalkanes and ethanolic sodium hydroxide?
Elimination reaction.
What are the conditions needed for homolytic fission?
Temp > 450 oC
UV Light
Which bond is most likely to break during the formation of free radicals?
The bond with the lowest bond enthalpy/ the weakest bond
What are the three steps involved in free radical substition?
- Initiation
- Propagation Steps
- Termination Step
Why do free radical subsitution reactions have a low yield?
Lots of unintended products form in other termination steps.
What is the trend in solubility of halogenoalkanes?
Solubility decreases the longer the hydrocarbon chain.
What is the trend in boiling points of halogenoalkanes?
Boiling point increases the longer the hydrocarbon chain.
What are the features of an SN2 substitution mechanism?
Concerted mechanism (happens in one step)
Inversion of configuration
Transition state containing attacking and leaving groups
What are the reagents and conditions used for the dehydration of alcohols?
Heat under reflux
Conc sulfuric/phosphoric acid catalyst
What is the colour change associated with the oxidation of alcohols?
Orange -> Green
Cr2O7^2- ions reduced to Cr^3+
(acidified potassium dichromate)
What are the products of the oxidation of primary alcohols?
Aldehyde (distillation) or carboxylic acids (reflux)
What is the product of the oxidation of secondary alcohols?
Ketones (heat under reflux)
When does an SN1 reaction mechanism for the nucleophilic substitution of halogenoalkanes occur?
Steric hindrance prevents SN2
Primary carbocation is too unstable
How many steps are involved in an SN1 mechanism?
2
What is the role of the hydroxide ion in elimination reactions?
Base
What conditions should be used for the nucleophilic substitution of halogenoalkanes with hydroxide ions?
Aqueous solution
heat under reflux
How do you increase the yield of the ester in an esterification reaction?
Add a dehydrating agent such as anhydrous mangesium sulfate. This removes water as the reaction progresses so the position of eqm is shifted towards the ester.
What are the reagents and conditions needed for the chlorination of alcohols?
PCl5 and dry alcohol
How do you use PCl5 to test for alcohols?
Add PCl5 to dry alcohol, HCl produced and test for HCl (steamy fumes) by adding NH3 which creates white smoke (NH4Cl)
What reagents and conditions are needed for the bromination of alcohols?
To produce HBr:
Heat under reflux and add KBr and 50% sulfuric acid
HBr reacts with alcohol to produce halogenoalkane
What reagents and conditions are needed for the iodination of alcohols?
Warm mixture of damp red phosphorus and iodine to produce PI3. Add PI3 to alcohol
What is the purpose of anti-bumping granules?
Provide a surface for small bubbles to form, keeps the reaction under control and the boiling smooth.
Without, large bubbles would form or an explosion of liquid would go down the condenser.
How do you test for alcohols
Include method and observation for positive result
- (for primary and secondary alcohols) add acidified potassium dichromate and reflux - colour change from orange to green indicates presence of alcohol
- Add PCl5 to dry sample, HCl produced and test for HCl (steamy fumes) by adding NH3 which creates white smoke (NH4Cl)
1st test would show a positive result for anything which can reduce dichromate ions
