A-Level Chemistry - Topic 6 - Organic Chemistry I (PART 1 - "The Basics" - "Fuels")

What does a general formula show and what is an example?

an algebraic formula that can describe any member of a family of compounds

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e.g. Cn H2n+1 = alkanes

What does a empirical formula show and what is an example?

the simplest whole number ratio of atoms of each element in a compound

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e.g. C4H10O

What does a molecular formula show and what is an example?

the actual number of atoms of each element in a molecule

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e.g. C4H10O

What does a structural formula show and what is an example?

shows the arrangement of atoms CARBON BY CARBON

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with the attached hydrogens and functional groups

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e.g. CH3CH2CH2CH2OH

What does a skeletal formula show and what is an example?

shows the bonds of the carbon skeleton only

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(with any functional groups)

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H and C aren’t shown

What does a displayed formula show and what is an example?

shows how all the atoms are ARRANGED

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and shows the bonds between them

What system is used for naming organic compounds

IUPAC

What are members of a homologous series?

a bunch of organic compounds that have the same functional group and general formula

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consecutive members of a homologous series differ by -CH2-

What is the prefix/suffix for alkane , branched alkanes, alkenes and halogenoalkanes?

alkane = ane

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branched alkanes = alkyl (-yl)

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alkenes = ene

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halogenoalkanes = -chloro/bromo-/iodo-

What is the prefix/suffix for alcohols, aldehydes, ketones, cycloalkanes and carboxylic acids?

alcohol = -ol

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aldehydes = -al

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ketones = -one

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cycloalkanes = cyclo-…-ane

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carboxylic acids = -oic acid

What is an addition reaction?

the joining of two+ molecules together to form a larger molecule

What is a polymerisation reaction?

joining together lots of simple molecules to form a giant molecule

What is an elimination reaction?

when a small group of atoms breaks away from a larger molecule

What is a substitution reaction?

when one species is replaced by another

what is a hydrolysis reaction?

splitting a molecule into two new molecules by adding H+ and OH- derived from water

what is an oxidation/reduction reaction?

oxidation = any reaction in which a species loses electrons

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reduction = any reaction in which a species gains electrons

what is a “mechanism”?

diagrams that break reactions down into individual stages to show how substances react together

how do curly arrows work in a mechanism?

starts at the bond/lone pair where the electrons are at the beginning of the reaction

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points to where the new bond is formed at the end of the reaction/to the atom where the electrons go

what is a nucleophile?

electron pair donors

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often negatively charged ions/species that contain a lone pair of electrons

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electron rich, so attracted to places that are electron poor

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what else are nucleophiles attacked by?

molecules with polar bonds

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since they have 𝛿+ areas

what are electrophiles?

electron pair acceptors

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often positively charged ions or w/ 𝛿+ areas

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electron poor, so attracted to places that are electron rich

what do electrophiles “like” to react with?

negative ions

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atoms w/ lone pairs

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the electron-rich areas around a C=C bond

What are radicals?

species with an unpaired electron

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= v. reaction

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= will react with ANYTHING: positive, negative or neutral

what is a problem with radical’s reacting with anything in sight?

probably end up with a mixture of products

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= radical reactions aren’t useful if after a PURE product

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could also take place anywhere along the carbon chain

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= a mixture of structural isomers can be formed

what do isomers have in common (and not)?

the same molecular formula (the actual number of atoms in each element in a molecule)

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but the atoms are arranged differently

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what are structural isomers?

isomers that have different STRUCTURAL ARRANGEMENTS of atoms

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but the same molecular formula despite having a different structural formula

what are the 3 types of structural isomer?

chain isomers

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positional isomers

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functional group isomers

what is a chain isomer?

the carbon skeleton can be arranged differently

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= a straight chain OR branched in different ways

what similarities/differences to chain isomers have with each other?

similar chemical properties

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but physical properties (e.g. b.p.) will change due to the shape change

what is a positional isomer?

the skeleton and the functional group could be the same

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only with the functional group attached to a different carbon atom

what differences do positional isomers have with each other?

different physical + chemical properties

what are functional group isomers?

the same atoms can be arranged into different functional groups

what differences do functional group isomers have with each other?

very different physical + chemical properties

what can atoms do as much as they like around single C-C bonds?

rotate as much as they like

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= what looks like an isomer may not be one

What are the two types of bond fission?

heterolytic

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homolytic

what is bond fission?

the breaking of a covalent bond

what is heterolytic fission?

when the bond breaks unevenly

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with one of the bonded atoms receiving both electrons from the bonded pair

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forms a positively charged cation and a negatively charged anion

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what is homolytic fission?

the bond breaks evenly

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each bonding atoms receive one electron from the bonded pair

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2 electrically charged radicals formed (with an unpaired electron)

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= both v. reactive

in what type of reaction do halogens react with alkanes?

photochemical reactions

what is a photochemical reaction?

a reaction that required uv light to get going

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(an example of a radical substitution reaction)

what happens during a photochemical reaction?

a hydrogen atom is substituted

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by chlorine/bromine

what are the three steps in a radical substitution reaction?

initiation

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propagation

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termination

what does the mechanism look like for the radical substitution reaction between chlorine and methane?

what is the problem with radical substitution reactions?

you end up with a mixture of products

when does a substitution reaction have to stop?

where there are no more H atoms to replace

what is petroleum a.k.a?

crude oil

what is crude oil?

a mixture of hydrocarbons

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mostly made up of alkanes

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massive range of hydrocarbons

what are the steps in fractional distillation?

1. crude oil is vaporized (about 350 degrees C)

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2. vapor goes into a fractionating column

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3. due to temperature gradient, the hydrocarbons cool and condense in different fractions

where do the longest chain hydrocarbons end up in the fractionating column?

bottom of the column

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due to having the highest boiling point of them all

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(could also be drawn away if the boiling point is too high to even evaporate)

what is the highest desired length of hydrocarbon?

shorter ones

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e.g. petrol + naphtha

what is cracking?

the breaking of long-chain alkanes into smaller hydrocarbons

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(which include alkenes)

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involving the breaking of the C-C bonds

what is the use for a 1-4 carbon chain hydrocarbon?

LPG

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camping gas

what is the use for a 5-12 carbon chain hydrocarbon?

petrol

what is the use for a 7-14 carbon chain hydrocarbon?

processed to make petrochemicals

what is the use for a 11-15 carbon chain hydrocarbon?

jet fuel

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petrochemicals

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central heating fuel

what is the use for a 15-19 carbon chain hydrocarbon?

diesel fuel

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central heating fuel

what is the use for a 20-30 carbon chain hydrocarbon?

lubricating oil

what is the use for a 30-40 carbon chain hydrocarbon?

ships

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power stations

what is the use for a 40-50 carbon chain hydrocarbon?

candles

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lubrication

what is the use for a 50+ carbon chain hydrocarbon?

roofing

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road surfacing

what are the 2 types of cracking

thermal

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catalytic

what happens in thermal cracking?

1. high temperature (around 100 degrees c)

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2. high pressure (up to 70atm)

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3. produces a lot of alkene

what are alkenes good for?

making polymers

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e.g. poly(ethene)

what catalyst is usually used in catalytic cracking?

zeolite catalyst = hydrated aluminosilicate

what are the conditions for catalytic cracking?

slight pressure

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high temperature (around 450 degrees c)

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zeolite catalyst

what is a zeolite catalyst in terms of aluminosilicate?

hydrated aluminosilicate

what do aromatic compounds contain?

benzene rings

what is a benzene ring?

contain a ring of 6 carbon atoms

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with a delocalised ring of electrons

what is knocking?

where alkanes expload oftheir own accord

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when the fuel/air mixture in the engine is compressed

what are the most likely hydrocarbons to cause knocking?

straight chain alkanes

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adding branched chains and cyclic hydrocarbons to the petrol makes knocking less likely to happen = more efficient too

what is the name of the process where straight-chain alkanes are converted into branched chain alkanes and cyclic hydrocarbons?

reforming

what does reforming require?

a catalyst

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e.g. platinum stuck on aluminum oxide

what does the reforming of hexane into cyclohexane look like?

hexane reformed into cyclohexane (and H gas)

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then: the H gas could be reformed into benzene (C6H6) and H gas

what could octane be reformed into?

2,5 - dimethylhexane

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= now branched = lower b.p.

what do you get when you undergo complete combustion with an alkane?

carbon dioxide

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water

what are the products of incomplete combustion?

carbon monoxide

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carbon

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water

where does combustion reactions happen?

between gases

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(so liquid alkanes have to be vaporised first)

are combustion reactions endo or exothermic?

exothermic

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= release heat

why do larger alkanes release more neergy per mol?

because they have more bonds to react

what are 2 examples of methane’s uses?

central heating

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cooking

what are the 3 fossil fuels?

coal

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oil

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natural gas

when do we use fossil fuels most often?

power stations

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transport

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heating

what are the pollutants formed by burning fossil fuels?

carbon monoxide

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unburnt hydrocarbons

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carbon particulates

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oxides of sulfur (NOx)

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oxides of nitrogen (NOx)

why is carbon monoxide toxic?

oxygen in bloodstream carried around by haemoglobin

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carbon monoxide binds better to haemoglobin than oxygen

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so it bids to the haemoglobin in bloodstream before oxygen can

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means that less oxygen can be carried around the body

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= oxygen deprivation

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= could be fatal (at v. high concentrations)

how does sulfur dioxide produce sulfuric acid that comes down in rain?

1. caused by burning fossil fuels that contain sulfur
2. sulfur burns to form sulfur dioxide gas
3. enters atmosphere + dissolves in the moisture
4. then converted into sulfuric ACID

how do oxides of nitrogen lead to acid rain?

1. oxides of nitrogen are produced when the high pressure and temperature in a car engine
2. = the nitrogen and oxygen in the air to react together


1. escapes into the atmosphere
3. dissolves in moisture and then converted into nitric acid = falls as acid rain

what are the problems with acid rain?

destroys trees + vegetation

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corrodes buildings + statues

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killing fish in lakes

what do catalytic converters do?

remove some pollutants from car emissions

what do catalytic converters prevent?

carbon monoxide

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oxides of nitrogen

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unburnt hydrocarbons

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= prevented being spewing out

how does a catalytic converter work?

using a platinum catalyst to change then into harmless gases / less harmful ones

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e.g. water vapor, nitrogen / carbon dioxide

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how does a catalytic converter convert nitrogen monoxide and carbon monoxide into nitrogen and carbon dioxide?

2NO(g) + CO(g) -→ N2(g) + CO2(g)

what will be the first hydrocarbon to go?

oil

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gets really scarce = become more expensive

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not sustainable to keep using fossil fuels unnecessarily

what are biofuels?

fuels made from living matter over a short period of time

what is bioethanol and how is it formed?

ethanol = made by the fermentation of sugar from crops (e.g. maize)

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AN EXAMPLE OF A BIOFUEL MADE FROM RENEWABLE RESOURCES

what is biodiesel and how is it fomed?

fats +/ oils (e.g. vegetable oil) = made by refining renewable fats and oils

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AN EXAMPLE OF A BIOFUEL MADE FROM RENEWABLE RESOURCES

what is biogas and how is it formed?

organic waste matter = breaks down, producing biogas

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AN EXAMPLE OF A BIOFUEL MADE FROM RENEWABLE RESOURCES

What do biofuels form when burnt but why isn’t this as bad as burning hydrocarbons?

carbon dioxide

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but it’s carbon dioxide that the plants absorbed while growing

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= classed as carbon neutral

what are the negatives of using biofuels?

carbon dioxide still given out:

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while refining = transporting the fuel

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while making the fetilisers

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while powering agricultural machinery used to grow and harvest the crops

what else could biodiesel and biogas be made from?

waste that would otherwise go to landfill

what is the issue with switching from petrol to biofuels to transport?

petrol car engines would have to be modified to use fuels with high ethanol concentrations

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(e.g. in bioethanol)