Organic Chemistry Flashcards
3.3.1
what are the 6 different types of formulae?
- Molecular: shows the actual number of atoms of each element in a compound
- Empirical: shows the simplest whole number ratio of atoms of each element in a compound
- General: the simplest algebraic formula of a member of a homologous series
- Structural: shows arrangement of atoms and, when it’s necessary, the bonds between them
- Displayed: shows arrangement of all atoms in a molecule and between bonds
- Skeletal: a ‘stick-like’ drawing that shows the bonds between carbon atoms only; each c atom is a corner
3.3.1
What is a homologous series?
A homologous series of organic compounds is a group of organic compounds ALL containing the same functional group.
Molecules from the same homologous series:
* Have similar chemical properties.
* Show a gradual change in physical properties.
* Can be represented by a general formula as they differ from one another by -CH2.
A common example: alkanes.
3.3.1
What are alkanes?
- Alkanes: saturated hydrocarbons - contain single covalent bonds only with general formula CnH2n+2.
- Methane, ethane, propane, butane, pentane
3.3.1
What are the 9 homologous series and what are their prefixes and suffixes?
- Alkenes; suffix = -ene
- Alkanes; suffix = -ane
- Alcohol; prefix = hydroxy-, suffix = -ol
- Haloalkanes; prefix = chloro-, bromo-, …
- Aldehydes; suffix = -al
- Ketones; prefix = -one, suffix = -oxo
- Carboxylic acid; suffix = -oic acid
- Nitriles; prefix = none, suffix = -nitrile
- Amines; prefix =amino-, suffix = -amine
3.3.1
What is an isomer?
An isomer is a molecule with the same molecular formula as another (it’s made of the same atoms) that’s arranged differently. There are a few types of isomerism…
3.3.1
What are the 2 types of isomerism?
- Structural isomerism
- Stereoisomerism
3.3.1
What is structural isomerism?
To be a structural isomer of another molecule, the molecule in question must have the same molecular formulae but different structural formulae.
3.3.1
What are the 3 types of structural isomerism?
- Chain isomerism
- Positional isomerism
- Functional group isomerism
3.3.1
What is chain isomerism?
–> Chain isomerism: 2 or more ways of arranging the carbon skeleton
- Chain isomers have similar chemical properties but slightly different physical properties.
- The more branched the isomer, the fewer the van der Waals forces between molecules and the lower its b.p
3.3.1
What is positional isomerism?
–> Position isomerism: when the functional group is bonded at different positions on the carbon chain.
- Position isomers have the same carbon skeleton and the same functional group - it is only the position of the functional group which changes
3.3.1
What is functional group isomerism?
Functional group isomerism: same molecular formula but containing different functional groups.
3.3.1
What is stereoisomerism?
Stereoisomerism: same structural and displayed formulae but different arrangement of bonds in space.
3.3.1
What is E/Z or Geometric isomerism?
E/Z or Geometric isomerism: occurs as a result of restricted rotation about the planar carbon to carbon double bond. It’s when each double bonded carbon atom is bonded to 2 different groups.
- Single bonds can easily rotate. However, C=C double bonds have restricted rotation because of the pi bond, so the groups on either end of the bond can be imagined to be ‘frozen’ in one position.
3.3.1
How do we name E/Z isomers?
E isomer: groups are on the opposite side of the C=C bond.
Z isomer: groups are on the same side of the C=C bond (on ‘Zame Zide).
3.3.2
What are alkanes?
they are saturated hydrocarbons - contain single C-C bonds
3.3.2
What is Crude Oil/Petroleum and what can it be separated into?
it is a mixture consisting mainly
of alkane hydrocarbons that can be separated into fractions by fractional distillation
3.3.2
What are the 6 steps in fractional distillation?
1) The crude oil is heated up to about 350°C and most turns into a gas.
2) The vaporised crude oil goes into the bottom of the fractionating column and rises up through the trays.
3) The largest hydrocarbons don’t vaporise at all, because their b.p. are too high - they just run to the bottom as liquids.
4) There is a temp. gradient in the fractionating column, which means it is hotter at the bottom and becomes progressively cooler towards the top.
5) Because b.p. of alkanes ↑ as the molecules get larger, the larger molecules with the higher b.p. turn back to liquids nearer the bottom, + the smaller molecules with the lower b.p. turn back to liquids nearer the top. This creates fractions as different molecules condense at different temperatures.
6) The hydrocarbons with the lowest b.p. don’t condense and come out of the top of the column as a gas.
3.3.2
What are the different fractions?
- what are their carbon chains, and uses
- Refinery gases C1-C4; bottled gas for camping + stoves
- Gasoline C5-C12; car fuel (petrol)
- Naphtha C7-C14; making medicines + fabrics
- Kerosene C11-C15; jet engine fuel
- Diesel C15-C30; central heating fuel
- Fuel oil C30-C50; fuel in ships + power stations
- Lubricating oil C40-C50; wax for candles
- Bitumen C50+; roofing, road surfacing
3.3.2
What is cracking and what are the 2 types?
- Cracking: the breaking of C–C bonds in long chain alkanes to form a mixture of short-chained alkanes and alkenes.
- There’s two types of cracking: thermal cracking and catalytic cracking
3.3.2
What is thermal cracking
- the conditions needed for it
- Very high temp. (800-900°C)
- High pressure (up to 70atm)
- No catalyst required.
- High % of small-chain alkenes (used to make polymers e.g. poly(ethene) which is made from ethene).
3.3.2
What is catalytic cracking
- the conditions needed for it
- High temp. (450°C)
- Slight pressure
- Zeolite catalyst (hydrated aluminosilicate)
- Used mainly to produce branched alkanes (which burn more uniformly - used as motor fuels) + aromatic hydrocarbons (cycloalkanes).
3.3.2
What are the economic reasons for cracking?
- Demand for short-chain hydrocarbons is much higher than demand for long-chain hydrocarbons.
- There is a greater demand for:
- shorter chain alkanes as they are more volatile and are therefore better fuels. - short chain alkenes as they are more reactive than alkanes. They’re used to make polymers (plastics).
- The thing is, fractional distillation of crude oil produces a surplus of long-chain hydrocarbons and fewer short chain hydrocarbons than required.
- This explains why we crack long-chain hydrocarbons into more useful short-chain hydrocarbons by cracking.
3.3.2
What is the combustion of alkanes?
- Shorter chain alkanes (which have lower b.p.s than longer chains since they have weaker attractions between molecules) are valuable as ‘clean’ fuels.
- A fuel is a substance that reacts with oxygen releasing heat energy (combustion reactions are exothermic).
3.3.2
What occurs as a result of complete and incomplete combustion?
Complete Combustion
- In an excess supply of oxygen, alkanes burn to form carbon dioxide and water. This is complete combustion.
Incomplete Combustion
- If the supply of oxygen is limited, carbon monoxide or even just carbon is formed instead of, or as well as, carbon dioxide. This is incomplete combustion.
3.3.2
Why is complete combustion desirable?
- Carbon monoxide is poisonous
- Less energy is released during incomplete combustion.
- Soot (solid bits of carbon) can be produced from incomplete combustion. This causes dirty deposits, building up in engines and on roads. It is also causes respiratory problems.
3.3.2
What are the 6 pollutants produced by Combustion of Alkanes?
- Carbon dioxide (CO2)
- Carbon monoxide (CO)
- Unburnt hydrocarbons and oxides of nitrogen (NOx)
- Photochemical smog
- Acid rain
- Sulfur dioxide (SO2)
3.3.2
What are the effects of carbon dioxide (CO2)?
- Planet earths most hated molecule! It’s formed by complete combustion of hydrocarbons, such as petrol.
- It’s a greenhouse gas which contributes to global warming.
3.3.2
What are the effects of carbon monoxide (CO)
- Formed by incomplete combustion of hydrocarbons, such as petrol in the internal combustion engine.
- It is a colourless, odourless, poisonous (will literally kill you) gas.
3.3.2
What are the effects of Unburnt hydrocarbons and oxides of nitrogen (NOx)?
- Unburnt hydrocarbons are formed when not all of the fuel in the internal combustion engine combusts. They are greenhouse gases.
- Nitrogen oxides are produced when the high pressure and temperature in a car engine cause the nitrogen and oxygen atoms from the air to react together.
3.3.2
What are the effects of photochemical smog?
Unburnt hydrocarbons react with nitrogen oxides in the presence of sunlight (UV) to form ground-level ozone. Ground-level ozone is a major component of smog. It irritates people’s eyes, aggravates respiratory problems, and can causes lung damage.
3.3.2
What are the effects of acid rain?
When nitrogen dioxide escapes into the atmosphere, nitric acid is produced. Nitric acid falls dissolved in rain; the acid rain destroys trees, vegetation, and corroding buildings. It also corrodes statues, cliffs and kills fish in lakes.
3.3.2
What are the effects of sulfur dioxide?
- The final bit of depressing pollution from Hydrocarbons found in crude oil is Sulphur Dioxide. Hydrocarbons in crude oil contain traces of sulphur which combusts to form sulphur dioxide.
- Sulphur dioxide reacts with water and oxygen in the atmosphere to form acid rain
3.3.2
What are the 2 methods to control pollution?
- Flue-gas desulfurisation
3.3.2
How are Catalytic converters used to control pollution?
- Gaseous pollutants found in the exhaust gases from internal combustion
engines of cars (like CO, unburnt hydrocarbons, and NOx) can be removed
by catalytic converters. - Catalytic converters consists of a ceramic ‘honeycomb’ coated in a thin
layer of catalyst metal (Typically platinum/palladium/rhodium).
➜ this ensures max. surface area, min. use of expensive metals. - The pollutants are converted to less harmful products
3.3.2
What is Flue-gas desulfurisation?
- how is it used to control pollution
- In cars, sulphur is mostly removed from the petrol used to prevent sulphur dioxide forming.
- However, in coal-burning power stations and factories the waste gas is passed through scrubbers containing an alkaline slurry of powdered calcium carbonate,(limestone) or calcium oxide mixed with water.
- When the flue gases mix with the alkaline slurry, the acidic sulphur dioxide gas reacts with the calcium compounds to form a harmless salt (calcium sulphate)
- This is useful, because there’s a lot of sulphur flying up those flues
3.3.2
How does the chlorination of alkanes work?
- Halogenoalkanes are the organic product of the photochemical reaction (in the presence of UV light) of a halogen atom with an alkanes.
- In these reactions, one or more hydrogen atoms are substituted by one or more halogen radicals.
- They are produced via a free radical substitution mechanism in a chain reaction.
3.3.2
What are free radicals, and how does free radical substitution work?
- Free radical substitution: a type of substitution where a radical replaces a different atom or group of atoms.
- Free radical: a species with an unpaired electron (one of them) in their outer shell- this unpaired electron makes them very reactive.
3.3.2
What do free radicals form and how are they represented?
- Free radicals form when a covalent bond splits equally, giving one electron to each species (this is called homolytic fission and happens to chlorine and fluorine in the ozone layer).
- A free radical in a mechanism can be shown by putting a dot next to it, like this: *CH3.
- The dot, *, is an e-
3.3.2
What occurs in the chlorination of alkanes?
- what are the 3 stages called
A mixture of methane and chlorine will not react on its own. But when exposed to UV light, we get a reaction and form chloromethane.
- A reaction mechanism shows each step in the synthesis of a chemical reaction. - The reaction mechanism for the synthesis of chloromethane has three stages as shown below: - This is a ‘Free Radical Substitution’ Mechanism.
- the 3 stages are: initiation, propagation and termination
3.3.2
What happens in the initiation stage?
Sunlight provides enough energy to break some of the Cl-Cl bonds - this is photodissociation.
* This step Involves homolytic bond breaking - the weakest bond is broken.
* The atom becomes a highly reactive free radical because of its unpaired electron.
3.3.2
What happens in the propagation stage?
- In propagation, free radicals are used up and created in a chain reaction.
- First, Cl* attacks a methane molecule:
- Next, the methyl free radical can then attack another Cl2. New Cl* can attack another CH4 molecule.
- The *Cl radial has been reformed. So, this process repeats over and over again
3.3.2
What happens in the termination stage?
- In a termination step, 2 free radicals form a covalent bond using the 2 unpaired electrons, making a stable molecule.
- This ends the reaction.
- The chances of this happening increase as the concentration of free radicals increases.
3.3.3
What is a halogenoalkane?
Halogenoalkane: an alkane with at least one halogen atom in place of a hydrogen atom.
* So, the functional group of this homologous series is a halogen atom attached to a C atom.
* They are named the same as the original alkane with a prefix indicating the halogen present:
* F = Fluoro-
* Cl = Chloro-
* Br = Bromo-
* I = Iodo-
3.3.3
Explain the 3 things halogenoalkanes can be classified as
- Haloalkanes can be classified as primary, secondary or tertiary:
- Primary Haloalkane; One carbon attached to the carbon adjoining the halogen.
- Secondary Haloalkane; Two carbons attached to the carbon adjoining the halogen.
- Tertiary Haloalkane; Three carbons attached to the carbon adjoining the halogen