Organic Chemistry

What are fractions separated by in fractional distillation?

• The boiling points of each substance

• This is decided by how many carbon and hydrogen atoms the molecule contains

What is the process of fractional distillation?

• Crude oil enters the fractionating column which is hot at the bottom and cool at the top

• Crude oil is heated so vapours rise

• The different fractions condense at different heights according to their boiling points and are tapped off as liquids

• Vapours of hydrocarbons with very high boiling points will immediately condense into liquid at the higher temperatures lower down and are tapped off at the bottom of the column

• Vapours of hydrocarbons with low boiling points will rise up the column and condense at the top to be tapped off

• The fractions containing smaller hydrocarbons are collected at the top of the fractionating column as gases

• The fractions containing bigger hydrocarbons are collected at the lower sections of the fractionating column

 

What is petroleum?

A mixture consisting mainly of alkane hydrocarbons that can be separated by fractional distillation

What is crude oil made from?

• alkanes

• cycloalkanes

• arenes (compounds with a benzene ring)

Why is cracking needed?

Smaller hydrocarbon fractions are in significantly higher demand than higher hydrocarbon fractions so they are broken down into smaller, more useful compounds

What is the process of catalytic cracking?

• Large hydrocarbon molecules are fed into a steel chamber and heated to a high temperature and then passed over an aluminium oxide catalyst

• The chamber does not contain any oxygen to prevent combustion of the hydrocarbon

• When a large hydrocarbon is cracked, a smaller alkane and an alkene is formed

What are the 2 types of cracking?

• Thermal cracking: high temperatures and high pressure and produces alkanes and a lot of alkenes

• Catalytic cracking: lower temperature and slight pressure in the presence of a catalyst( zeolite or aluminium oxide) to produce mainly aromatic hydrocarbons

What are the economic reasons for cracking alkanes?

• Petroleum fractions with shorter carbon chains are in higher demand than larger fractions

• To make use of excess larger hydrocarbons and to supply demand for shorter ones, larger hydrocarbons are cracked

• The products of cracking are more valuable than the starting materials

What is the primary use for alkanes?

Fuels

What are the word equations for the combustion of alkanes (complete and incomplete)?

In excess oxygen

• Alkane + oxygen → carbon dioxide and water

In a limited supply of oxygen

• Alkane oxygen → carbon monoxide +water

Reduced supply of oxygen

• Alkane + oxygen → carbon (soot) + water

What are the products of an internal combustion engine?

• NO_x

• CO

• carbon

• unburned hydrocarbons.

What are the environmental impacts of the products of an internal combustion engine?

• CO: CO can bind to haemoglobin taking the place of where oxygen/CO2 should be binding, meaning oxygen cannot be transported to organs and CO2 cannot be removed

• Oxides of nitrogen: can react with unburnt hydrocarbons to produce smog, nitric acid causes acid rain which caused corrosion of buildings

How can gaseous products from internal combustion engines be removed?

• Catalytic converters are fitted on cars

• Platinum is coated on honeycomb to provide a large surface area for reactions to take place

Equations include:

• Oxidation of CO → CO₂: (2CO+O₂ → 2CO₂)

• Reduction of NO → N₂: (2CO + 2NO → 2CO₂ + N₂)

• Oxidation of unburnt hydrocarbons:

  (C_nH_2n+2 + (3n+1)O → nCO₂ + (n+1)H₂O)

What happens in the combustion of hydrocarbons containing sulfur?

Sulfur dioxide is produced that causes air pollution

What is sulfur scrubbing/flue gas desalination?

• Waste gases are passed into a scrubbing chamber

• A wet slurry of calcium oxide and calcium carbonate is sprayed onto the gases

• CaO and CaCO₃ can both be used as they react with sulfur dioxide in the following reactions:

• CaO + 2H₂O + SO₂ + ½ O₂ → CaSO₄.H₂O

• CaCO_{3 +} ½ O₂ + SO₂ → CaSO₄ + CO₂

Name and outline the mechanism for the reaction of methane with chlorine

• Free radical substitution

• Cl₂ → 2Cl∙

• Cl∙ + CH₄​ → CH₃∙ ​+ HCl

• CH3∙ ​+ Cl₂​ → CH₃​Cl + Cl∙

• Cl∙ + Cl∙→ Cl₂

• CH₃∙​ + Cl∙→ CH₃​Cl

What is the test to identify an alkene?

• Shake with bromine water

• If alkene is present, solution turns from orange to colourless

What is the test to identify a halogenoalkane

• Add aqueous sodium hydroxide and warm gently

• Acidify with nitric acid

• Add silver nitrate

• If halogenoalkane present, precipitate forms (Cl=white, Br=cream, I=yellow)

What is the test to identify an alcohol?

• Add acidified potassium dichromate solution

• If primary/secondary alcohol present, solution turns from orange to green

• No colour change if tertiary alcohol present

What is the test to identify an aldehyde?

• Warm with Tollen’s reagent/Fehling’s solution

• If aldehyde present, either silver mirror forms or blue solution turns to a red precipitate

What is the test to identify a carboxylic acid?

• Add sodium hydrogen carbonate

• If carboxylic acid present, carbon dioxide gas formed

What is mass spectrometry used for?

Identifying organic compounds by determining their molecular formula

How can the Mr be deduced from mass spectroscopy?

• The highest molecular ion peak represents the intact ion and is therefore the Mr of the molecule

Why is high resolution mass spectrometry beneficial?

• It can measure to 4 decimal places making it easier to distinguish molecules with a similar Mr

What is the process of infrared spectroscopy?

• A spectrophotometer irradiates the sample with infrared electromagnetic waves

• It detects the intensity of the wavelength of IR radiation which goes through the sample

• Covalent bonds absorb the infrared radiation, causing them to vibrate

• The molecules will only vibrate at a specific frequency

• Depending on the rest of the molecule, each vibration will absorb specific wavelengths of IR radiation which are also shown as the reciprocal of the wavelength

What is the resonance frequency?

The specific frequency at which the molecules will vibrate to stimulate larger vibrations

Why can infrared spectroscopy often not be used alone?

Some absorption bands overlap eachother

What is the fingerprint region?

The region of the infrared spectroscopy below 1500 that is unique to each molecule

How does the absorption of infrared in carbon dioxide, methane and water vapour link to global warming?

• Molecules of greenhouse gases in the atmosphere absorb the infrared radiation emitted by the sun

• They re emit some of it back towards the Earth keeping it warm (the greenhouse effect)

• Burning fossil fuels and leaving rubbish to rot in landfills has caused a rise in greenhouse gas concentration which means more heat is being trapped and the Earth is getting warmer

What is the structure of an alkene?

• Unsaturated hydrocarbon

• Electron dense double bond

What is a sigma bond?

• Formed from the end to end overlap of atomic orbitals

• Only done by S and P orbitals

What is a pi bond?

• Sideways overlap of adjacent P orbitals

• 2 lobes that form the bond lie above and below the plane to maximise overlap of P orbitals

What are single, double, and triple bonds made of?

• Single bond: sigma bond

• Double bond: 1x sigma bond, 1x pi bond

• Triple bond: 1x sigma bond, 2x pi bond

What are the conditions required for electrophilic addition?

• Alkene

• Electrophile (halogens, halogen halide, sulfuric acid)

What is the process of electrophilic addition with halogens?

• C=C bond induces a dipole in the halogen molecule

• δ⁺Br acts as an electrophile and is attacked by the electrons in the C=C bond

• The C=C double bond breaks and one halogen attached to one of the carbons

• The other halogen⁻ ion attacks the other carbon

• A dihaloalkane forms

What is the process of electrophilic addition with a halogen halide?

• The halogen halide is is polar

• The C=C bond attacks the Hδ⁺, forming a carbocation intermediate.

• The Br⁻ ion attacks the carbocation.

• A halogenoalkane forms

What is the process of electrophilic addition with sulfuric acid?

• H₂SO₄ is polar

• The C=C bond attacks the Hδ⁺, forming a carbocation intermediate.

• The OSO₃H⁻ ion attacks the carbocation.

• Alkyl hydrogen sulfate forms

• If you add water under heat, an alcohol will form

What is the test for unsaturation?

• Compound is shaken with bromine water

• If unsaturated, addition will take place causing the solution to decolourise

What is a carbocation?

• Positively charged carbons with only 3 covalent bonds

• These can be either primary, secondary or tertiary depending how many alkyl groups are attached

Why are tertiary carbocations the most energetically stable?

• Alkyl groups push electrons away from themselves towards the positively charged carbon

• This causes the carbocation to become less positively charged

• Charge is spread around the carbocation which makes it more energetically stable

What is Markovnikov’s rule?

In an addition of a halogen halide to an alkene, the halogen ends up bonded to the most stable carbon atom

Why are addition polymers unreactive?

• No double bonds

• Main carbon chain is non-polar

What is the IUPAC rule for naming addition polymers?

• Identify monomer

• add “poly” and brackets

What are the uses of poly(chloroethene) (PVC)?

• Drain pipes

• With a plasticiser can be made flexible enough to be a pool liner

What is the role of a plasticiser?

• Makes polymers more flexible

• Prevents polymer chains from being close to one another by disrupting Van de Waals forces, allowing them to slide over each other

What IMF are present in polyalkanes?

Van de Waals only

What are the conditions needed for free radical substitution?

• UV light or high temperature.

• Presence of halogen

• Reaction in a gas or non-polar solvent

What are the stages of free radical substitution?

• Initiation

• Propagation

• Termination

How does the initiation stage work in free radical substitution?

• UV light breaks halogen bond

• One electron from the bond goes to each halogen (single-headed arrows)

• Homolytic fission produces two halogen radicals

How does the propagation stage work in free radical substitution?

• Radical reacts with alkane, forming a alkyl radical

• Alkyl radical reacts with a new halogen molecule, forming a halogenoalkane and halogen radical

• Chain reaction continues.

How does the termination stage work in in free radical substitution?

• Radicals combine to form stable molecules:

• 2 halogen radicals → halogen molecule.

  Halogen radical + alkyl radical → halogenoalkane.

• 2 alkyl radicals → alkane.

What are the conditions needed for nucleophilic substitution?

• Aqueous solution

• Halogenoalkanes

• Suitable solvent: ethanol + water mix

How does nucleophilic substitution with an aqueous OH/CN work?

• Lone pair on OH⁻/CN⁻ attacks δ⁺ carbon in C–X bond.

• C–X bond breaks, forming halide ion with a lone pair

• Forms either an alcohol (with OH) or a nitrile (with CN)

How does nucleophilic substitution with an aqueous

NH3 work

First Attack (Ammonia as a Nucleophile):

• Ammonia donates a lone pair to the δ⁺ carbon in the C–Halogen bond

• The bond breaks, forming a halide ion

• A second molecule of ammonia removes the extra hydrogen from NH₃⁺ on the intermediate

• This forms a primary amine and ammonium ion⁺.

Secondary amine formation:

• The primary amine has a lone pair on the nitrogen and can act as a nucleophile

• It attacks another haloalkane leading to the formation of a secondary amine

• Formation of Tertiary Amine and Salt:

• The secondary amine ) can react further with another haloalkane

• This forms a tertiary amine

Formation of Quaternary Ammonium Salt:

• The tertiary amine ) reacts with one more haloalkane to form a quaternary ammonium salt

What are the conditions needed for an elimination reaction?

• Halogenoalkane hydroxide solution

• High temperature/concentration

How does an elimination reaction work?

• OH⁻ removes a proton (H⁺) from a carbon that is adjacent to the carbon-halogen bond

• Electron pair from the adjacent bond forms a C=C double bond between the carbon next to the halogen and the adjacent carbon

• Carbon-halogen bond breaks, releasing a halide ion

• Forms an alkene, halide ion and water

What are the conditions needed for electrophilic addition?

• Alkene

• δ⁺ species

How does electrophilic addition work with halogens?

• C=C bond induces a dipole in the halogen molecule

• δ⁺Br acts as an electrophile and is attacked by the electrons in the C=C bond

• The C=C double bond breaks and one halogen attached to one of the carbons

• The other halogen⁻ ion attacks the other carbon

• A dihaloalkane forms

How does electrophilic addition work with a halogen halide?

• The halogen halide is is polar

• The C=C bond attacks the Hδ⁺, forming a carbocation intermediate.

• The Br⁻ ion attacks the carbocation.

• A halogenoalkane forms

How does electrophilic addition work with sulphuric acid?

• H₂SO₄ is polar

• The C=C bond attacks the Hδ⁺, forming a carbocation intermediate.

• The OSO₃H⁻ ion attacks the carbocation.

• Alkyl hydrogen sulfate forms

• If you add water under heat, an alcohol will form

How are alcohols produced industrially?

Hydration of alkanes in the presence of an acid catalyst

How is ethanol produced industrially?

Fermentation of glucose and then separated by fractional distillation

What are the conditions needed for the fermentation of glucose?

• 35 degrees

• Anaerobic conditions

What is the equation for the production of ethanol via fermentation?

C₂H₁₂O₆ ^→ 2C₂H₅OH + 2CO₂

Why is the production of ethanol via fermentation considered to be carbon-neutral? Why is this considered to be invalid?

• When ethanol is combusted, the carbon dioxide released is offset by the carbon dioxide absorbed during photosynthesis

• Land use and deforestation for large scale ethanol production

• Fossil fuel usage in production (for heat/transport)

What is a biofuel?

A fuel derived from living matter

What is the mechanism for the formation of an alcohol by the reaction of an alkene with steam in the presence of an acid catalyst?

Electrophilic addition

What are the issues linked to decision making about biofuel use?

• Land use and deforestation

• Water use

• Impact on food security

• Displacement of communities

How are alcohols classified?

• Primary: the carbon atom attached to the OH group is attached to one other carbon atom

• Secondary: the carbon atom attached to the OH group is attached to two other carbon atoms

• Tertiary: the carbon atom attached to the OH group is attached to three other carbon atoms

What types of alcohols can be oxidised and what do they form?

• Primary: oxidised to form aldehydes/carboxylic acids

• Secondary: ketones

What oxidising agents can be used to oxidise alcohols?

• Acidified potassium dichromate

• Acidified potassium manganate

What are the equations for the oxidation of primary alcohols?

• Alcohol + Oxidising agent [O] → Aldehyde + Water

• Aldehyde + Oxidising agent [O] → Carboxylic acid

What are the equations for the oxidation of seccondary alcohols?

Alcohol + Oxidising agent [O] → Ketone

How does how the method used to oxidise a primary alcohol determines whether an aldehyde or carboxylic acid is obtained?

• Strength of oxidising agent (strong oxidising agent means carboxylic acid produced)

• Reflux conditions produce carboxylic acids

What tests can be used to distinguish between alcohols and ketones?

• Fehling’s solution:

• Aldehydes reduce the Cu2+ ions, ketones do not

• Aldehydes produce a blue solution red precipitate, ketones remain blue

• Tollens’ reagent

• Aldehydes reduce the tollens’ reagent

• Aldehydes form silver mirror on the test tube, ketones have no reaction

How can alkenes be formed from alcohols?

Acid-catalysed elimination reactions

What can alkenes produced by acid-catalysed elimination reactions be used for?

Addition polymerisation without monomers derived from crude oil

What is empirical formula?

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

What is molecular formula?

The true number of atoms of each element in a compound

What is structural formula?

Shows the structural arrangement of atoms within a molecule

What is displayed formula?

Shows every atom and every bond in an organic compound

What is skeletal formula?

• Shows only the bonds in a compound and any non-carbon atoms

• Vertices are carbon atoms

• Hydrogen is assumed to be bonded unless stated otherwise

What is an isomer?

A molecule with the same molecular formula but a different arrangement of atoms within the molecule

What is a structural isomer?

• An isomer that has a different structural arrangement of atoms

• They could be straight or branched chains but still have the same molecular formula

What is a position isomer?

An isomer with the same function group of the molecule but a different position within the carbon chain

What is a functional group isomer?

An isomer with a different arrangement of the same molecular formula so that the molecule has a different functional group

What is a stereoisomer?

• An isomer where the atoms have a different spatial arrangement

• They have limited rotation around the carbon double bond

• E= functional groups on opposite sides

• Z= functional groups on the same side

What are the CIP priority rules?

The first atom which is directly bonded to the carbon with the double bond with the high Ar is given the higher priority

How is a branched alkane drawn and what is its prefix/suffix?

• CH3

• -yl

How is a alkene drawn and what is its prefix/suffix?

• Double carbon-carbon bond

• -ene

How is a halogenoalkane drawn and what is its prefix/suffix?

• Halogen bonded to carbon

• Fluoro/Bromo/Chloro/Iodo

How is a alchohol drawn and what is its prefix/suffix?

• OH group

• -ol

How is a aldehyde drawn and what is its prefix/suffix?

• Double carbon-oxygen bond on end

• -al

How is a ketone drawn and what is its prefix/suffix?

• Double carbon-oxygen bond in the middle

• -one

How is a cycloalkane drawn and what is its prefix/suffix?

• Cyclical structure of carbons

• Cyclo-ane

How is a carboxylic acid drawn and what is its prefix/suffix?

• Double carbon-oxygen bond

• OH group

• -oic acid

What are the affects of aqueous silver nitrate on different halogenoalkanes?

• Chlorides: white precipitate

• Bromides: cream precipitate

• Iodides: pale yellow precipitate

Why does the carbon–halogen bond enthalpy influence the rate of reaction?

• Bonds have to be broken during the reaction

• Therefore the stronger the bond, the slower the halogenoalkane is to react

What are the conditions needed for nucleophilic substitution?

• Halogenoalkanes

• Either OH-, Nh3 or CN-

What is the process of nucleophilic substitution?

With OH-/CN-

• Lone pair on OH⁻/CN⁻ attacks δ⁺ carbon in C–X bond.

• C–X bond breaks, forming halide ion with a lone pair

• Forms either an alcohol (with OH) or a nitrile (with CN)

With NH3

• Ammonia donates a lone pair to the δ⁺ carbon in the C–Halogen bond

• The bond breaks, forming a halide ion

• A second molecule of ammonia removes the extra hydrogen from NH₃⁺ on the intermediate

• This forms a primary amine and ammonium ion