Topic 6 Organic Flashcards
Complete combustion
All of the atoms in the fuel are fully oxidised
Hydrocarbon + oxygen —-> carbon dioxide + water
Incomplete combustion
All of the hydrogen atoms in an alkane molecule are converted into water, but some of the carbon atoms can form gaseous carbon monoxide or solid carbon.
-Not fully oxidised
Partially incomplete: Hydrocarbon + oxygen –> carbon monoxide + water
Fully incomplete: Hydrocarbon + oxygen –> carbon + water
Carbon monoxide
-A toxic gas that causes death
-It acts by preventing the transport of oxygen around the body
-It is colourless and odourless, so people breath it into their lungs without knowing
-It is known as the ‘silent killer’
Catalytic converters
-Metals such as platinum, rhodium and palladium are spread thinly over a honeycomb mesh to increase the surface area for reaction
-A common type is known as a three way catalyst because it can remove three different pollutants: carbon monoxide, unburned hydrocarbons and oxides of nitrogen
-As the exhaust gases from the engine pass through the catalytic converter several reactions can occur.
Platinum in a catalytic converter
Collects oxygen atoms and lets them bind with carbon monoxide to form carbon dioxide.
Rhodium in a catalytic converter
Removes oxygen from nitrogen oxide pollutants and converts it to nitrogen and oxygen.
Palladium in a catalytic converter
Collects oxygen atoms and binds them with carbon monoxide to form carbon dioxide, molecules of unburnt fuel residue recombine with the oxygen due to the extreme heat resulting in more carbon dioxide and water.
Renewable
Energy can be remade quicker than it is being used up
Non-renewable
Fuel/energy is being used up faster than it can be made
Carbon neutral
Don’t produce carbon/greenhouse gases
Chlorofluorocarbons (CFCs)
Chlorofluorocarbons have been responsible for depleting the ozone layer as they attack and destroy ozone molecules
What is homolytic fission?
The process of breaking a covalent within a molecule leading to the formation of radicals. (A type of bond fission that involves the dissociation of a given molecule).
What is a radical?
A species with an unpaired electrons.
Mechanism, Step 1: initiation
-Formation of radical –> breaking Cl2 into individual atoms (UV is used)
-Involves homolytic fission
Cl2 —> Cl* + Cl*
(*- free radical species)
Mechanism, Step 2: propagation
-Free radical is very reactive and so can remove a H from methane to produce a new radical
Cl* + CH4 –> HCl + CH3* (super reactive which leads to
the start of a new equation)
CH3* + Cl2 –> CH3Cl + Cl*
-Both steps form one radical and one molecule
-Chlorine radicals are very reactive species and when they collide with methane molecules they react by removing a hydrogen atom.
Mechanism, Step 3: termination
-Radicals combine to form molecules
Cl* + Cl* –> Cl2
CH3* + Cl* –> CH3Cl
CH3* + CH3* –> C2H6
Alkene general formula
CnH2n
Overlapping in sigma and pi bonding
-The strength of a bond is dependent on the extent of overlapping.
-In the case of the sigma bond, the overlapping of orbitals takes place to a larger event
-Hence, the sigma bond is stronger in comparison to the pi bond because in the pi bond, the extent of overlapping is smaller.
Alkane general formula
CnH2n+2
Combustion in alkenes
Alkenes are hydrocarbons so like alkanes will burn in air or oxygen. The flame will be smokier than that of an alkane because of the higher percentage of carbon in the molecule.
Alkenes are rarely burned as fuels because they have other more useful reactions.
Mechanism for addition of alkanes
Need pictures
Electrophile
An electron-deficient species that are attracted to an electron-rich center.
(A species that will accept an electron pair).
What do the curly arrows in addition mechanism represent?
Electron density
Unsymmetrical alkanes
An unsymmetrical alkane is one in which the atoms on either side of the carbon carbon double bond are not the same.
An unsymmetrical attacking molecule is one in which the atoms are different.
Major product of mechanism
The product that is produced in the greatest amount in a chemical reaction.
Minor product of mechanism
A reaction product that is not produced in the greatest amount in a chemical reaction.
Addition polymerisation rules
-High temperature and pressure are required
-The alkene molecules are called monomers
-The polymer is named by writing ‘poly’ followed by the name of the monomer brackets
Recycle
Converting into other materials
Incineration
Heat energy to heat homes or factories or to generate electricity
Feedstock
Break down polymer waste into gases (mostly H2 and CO) then use these to male chemicals (often polymers).
Biodegradable
Broken down by microbes in the environment. However, they are often plant based so land is needed to grow the plants.
The three main ways of putting polymer waste to other uses
-Recycling
-Incineration
-Use as chemical feedstock
The first stage of recycling
Sorting: there are many types of polymers which can’t be processed together so need to be sorted.
The second stage of recycling
Processing: involves chopping the waste into small pieces and washing it; this material is then used to make new materials such as melting, moulding sonf fibre production.
What does an incinerator do?
-Converts polymer waste into heat energy.
-Can be used to heat homes, factories or to generate electricity.
-Most of the atoms in the polymers end up in a gaseous products which pass into the atmosphere via a chimney.
Concerns about incineration
Air pollution- this is because as well as hydrogen and carbon, there are other elements in the polymer waste gases released into the atmosphere.
Advantages of polymers over traditional materials
-They can be manufactured on a large scale
-They are lighter in weight that traditional alternatives
-They are unreactive and so can be used to contain many substances for long periods
Advantages of incineration
-Converts polymer waste into heat energy
-Can be used to heat homes, factories or used to generate electricity
Disadvantages of incineration
-A lot of air pollution due to other elements in the polymer waste. These pollutants are difficult to remove from the waste gases released into the atmosphere.
What are halogenoalkanes?
-A homologous series of compounds in which one or more hydrogen atoms in an alkane are replaced by a halogen atom.
-Halogenoalkanes are important as many are reactive and can be converted into other more valuable products.
Naming halogenoalkanes
1) Place the prefix flour, chloroformed, bromo, iodo before the name of the parent alkane
2) Denote the position of the halogen as the carbon attached has to be the lowest number
3) Put the halogens in alphabetical order preceded by their position number
How are halogenoalkanes classified?
By the number of alkyl groups attached to the C atom bonded to the halogen:
Primary- the halogen is attached to a carbon that is attached to one other carbon
Secondary- the halogen attached to a carbon that is attached to two other carbons
Tertiary- the halogen attached to a carbon that is attached to three other carbons
Preparations of halogenoalkanes- from alkanes
CH4(g) + Cl2(g) –> CH3Cl(g) + HCl(g)
-UV light is needed
-Free radical substitution mechanism
-A mixture of products obtained
Preparations of halogenoalkanes- from alkenes
-Reaction of alkenes with hydrogen halides at room temperature produces halogenoalkane with one hydrogen atom:
CH3CH–CHCH3 + HBr –> CH3CH2CHBrCH3
-Alkenes react with halogens to form halogenoalkanes containing two halogen atoms:
CH3CH–CH2 + Br –> CH3CHBrCH2Br
Preparations of halogenoalkanes- from alcohols
Alcohols react with phosphorus halides or hydrogen halides to form halogenoalkanes
C2H5OH(l) + PCl5(s) –> C2H5Cl(l) + POCl3 + HCl(g)
CH2CH2CH2OH(l) + HCl(aq) –> CH2CH2CH2Cl(l) + H2O(l)
Electronegativity in halogenoalkanes
Halogenoalkanes contain a halogen atom with an electronegativity higher than that of carbon so the C-X bond is polar.
Electronegatives decrease down group 7 so the polarity of the C-X bond also decreases.
The carbon joined the halogen is always slightly positive or electron-deficient. This makes it susceptible to attack nucleophiles.
Nucleophiles
Nucleophiles are either negative ion or molecules with slightly negative atom.
They use a lone pair of electrons to attack
Accepts protons and donates electrons.
Hydrolysis
Cold water slowly hydrolyses halogenoalkanes, replacing the halogen atoms with an OH group to form alcohols eg.
CH3CH2CH2(l) + H2O –> CH3CH2CH2OH(l) + H+ + I-(aq)
The water acts as a nucleophile. This is a substitution reaction.
Substitution reaction with hydroxide ions
CH3CH2Br + OH+(aq) –> CH3CH2OH + Br-(aq)
The reaction is quicker with water and the rate increases further if the mixture is heated.
(Nucleophilic substitution)
Substitution with cyanide ions
-Halogenoalkane is heated under reflux with a solution of potassium cyanide in ethanol.
-The halogen atom is replaced by the CN group and a nitrile is formed.
-Useful synthetic reaction as it increass carbon chain length.
Substitution with ammonia
-Warm a halogenoalkane with a concentrated solution of ammonia in ethanol.
-In a sealed tube to prevent gas from escaping.
-Produces a primary amine.
-The ammonia acts as a nucleophile.
-If excess ammonia is used, the ammonia salt is produced.
Alcohol structure
Primary, secondary, tertiary (depending on the amount of carbons attached to the carbon the OH group is bonded to).
Combustion
CH3CH2OH(l) + 3O2(g) –> 2CO2(g) + 3H2O(l)
Substitution by a halogen (Method 1)
The hydroxyl group can be replaced with a hydrogen atom (a different method is used for each halogen).
Reagent: phosphorus (v) chloride
Conditions: room temperature
Substitution by a halogen (Method 2)
The hydroxyl group can be replaced with a hydrogen atom (a different method is used for each halogen).
Tertiary alcohols can react with concentrated hydrochloric acid.
Reagent: conc. HCl
Conditions: room temperature
The reaction of the conc. HCl with primary alcohols is too slow for synthesis.
Bromoalkanes
Bromination of alcohols is carried out by treating the alcohol with Her that is in-situ from the reaction of potassium bromide with 50% conc. sulfuric acid.
Reagent: KBr + 50% conc. H2SO4
Conditions: warm the reaction mixture
Iodoalkanes
Iodoalkanes are prepared by treating alcohols with phosphorous (iii) iodine which is produced from the reaction of red phosphorus with iodine (Pl3 is unstable)
Reagent: P + I2
Conditions: heat under reflux
Dehydration
Reagent: concentrated phosphoric acid
Conditions: heating under reflux
This is an example of elimination.
Ketones
When a secondary alcohol is oxidised, that organic product belongs too a homologous series called ketones.
Formula of a ketone
RCOR
Aldehydes
When a primary alcohol is oxidised, the organic product belongs to a homologous series called aldehydes.
Formula of aldehydes
RHCO
A test that would distinguish a tertiary alcohol from a primary or secondary alcohol
Potassium dichromate
What is Felling’s solution
Tests for the presence of an aldehyde
Another test that can used to distinguish an aldehyde from a ketone
Tollins reagent
Homologous series definition
A homologous series is a group of organic compounds with the same functional group but each successful member differs by CH2.
(Compounds in the same homologous series will have the same general formula, and similar chemical properties).
Chain isomers
Add a methyl group/chain.
Structural isomers
Same molecular formula but different structural formula.
Position isomer
Change the position of something(eg. double bond, OH group).
Functional group isomer
Same molecular formula changes to a different homologous group (may become cyclic).
Stereoisomer
Same structural formula but different spacial arrangement eg. E/Z (restricted rotation around double bond).
Cis/trans isomer
Same as E/Z isomerism (cis-Z, trans-E).
Alkane physical properties: Boiling temperature
-Longer chain length, more intermolecular forces (London) therefore requires more energy to overcome these bonds
-Branched (methyl groups)- lower boiling temperatures as there’re fewer points if contact between adjacent molecules.
Alkane physical properties: Solubility
-Insoluble in water (can’t form hydrogen bonds)
-But dissolve readily in each other.
Alkane physical properties: Density
-Liquid alkanes are less dense than water
-Density increases as molar mass of alkane increases
Fractional distillation
-Petroleum preheated and pumped into fractioning tower
-Separates into fraction according to boiling points.
Cracking
-Large hydrocarbons into smaller hydrocarbons
-High pressures, temperatures without catalyst
-(Or) Lower pressures, temperatures with catalyst
-Zeolite catalyst used
(heavier fractions- fuels or cracked)
Reforming
-Hydrocarbon molecules rearranged into other molecules
-Important in the manufacture of petrol
-Straight alkanes into branched
Combustion (in alkanes)
-Alkanes burn when ignited in air
-Highly exothermic
Complete:
(when air is in excess)
CH4(g) + 2O2(g) –> CO2(g) + 2H2O(g)
Incomplete:
CH4(g) + 1.5O2 –> CO(g) + 2H2O(g)
N2 + O2 –> 2NO (nitric acid)
-pollutant- smog, asthma attacks
-acidic- acid rain, damage to buildings
