Organic Chemistry

what is the order of naming?

• carboxylic acid

• Ester

• Aldehyde

• Ketone

• Alcohol

Suffix and functional group of carboxylic acid:

• -oic acid

• COOH

• O=C-OH

Suffix and functional group of esters:

• -oate

• O=C-O

prefix, suffix and functional group of aldehydes:

• oxo-

• -anal

• O=C-H

Prefix, suffix and functional group of ketones:

• oxo-

• -one

• C=O

prefix, suffix and functional group of alcohol:

• hydroxy-

• -ol

• C-OH

are alkanes polar?

• Non-polar as electronegativity of carbon and hydrogen are similar

• Only form van der waals forces

boiling points of alkanes:

• longer the chain the higher the boiling point

• Alkanes with branched chains have lower boiling points as they cannot pack as closely together as unbranched chains, van der waals forces are less effective

solubility of alkanes:

• insoluble in water

• Water molecules held together by stronger hydrogen bonds

• Alkanes mix with non-polar liquids

alkanes reactivity:

• unreactive

• Don’t react with acids, bases, reducing or oxidising agents

What is petroleum?

• mixture of mainly alkane hydrocarbons

• Can be separated by fractional distillation

How does the fractionating tower work?

• crude oil heated in furnace

• Mixture of liquids and vapours passes into a tower that is cooler at the top and hotter at the bottom

• Vapours passes up tower until they arrive at a tray with temperature lower than their boiling point, where they condense into liquid

• Mixture of liquids that condenses on each tray is piped off

• Shorter chain hydrocarbons are nearer the top

what are the different fractions and their uses?

• gases = fuels on site

• Gasoline/ petrol/ naphtha = cars

• Kerosene/ paraffin = jet fuel, lighting

• Diesel oil = lorries and taxis

• Lubricating oil and waxes = candles, engine oil

• Fuel oil = ships, power stations

• Tar/ bitumen = surfacing roads, roofing

what does cracking mean?

• longer hydrocarbon chains are broken into shorter lengths

• Involves breaking of C-C bonds in alkanes

• Produces shorter alkanes chains and alkenes

What are the two cracking types:

• thermal cracking

• Catalytic cracking

define thermal cracking:

• heating alkanes at 700-1200K, 7000kPa

• Produces high percentage of alkenes

define catalytic cracking:

• heating alkanes at 720K, slight pressure

• Zeolite (silicon dioxide and aluminium oxide) catalyst

• Produces motor fuels, aromatic hydrocarbons

What are fuels?

• substances that release heat energy when they undergo combustion

• Alkanes are fuels

Define complete combustion of alkanes:

• combustion occurs in sufficient oxygen

• Alkane + O2 —> carbon dioxide + water

define incomplete combustion of alkenes:

• combustion occurs in limited oxygen

• Alkane + oxygen —> carbon monoxide + water

• Even less oxygen soot (carbon) can be produces

What are the pollutants?

• carbon monoxide - poisonous gas

• Nitrogen oxides - react with water vapour and oxygen to form acid rain

• Sulfur dioxide - acid rain

• Carbon particulate - exacerbate asthma, cause cancer

• Unburnt hydrocarbons - photochemical smog

• Carbon dioxide - greenhouse gas

• Water vapour - greenhouse gas

which pollutants are produced in the internal combustion engine?

• nitrogen oxides

• Carbon monoxide

• Carbon

• Unburned hydrocarbons

how to remove pollutants from internal combustion engines?

• Catalytic converters, reduce output of pollutants

• Honeycomb made of ceramic material coated with platinum and rhodium

• Honeycomb provides large surface area

• Polluting gas reacts with metal to form less harmful products

• Hydrocarbons + nitrogen oxides — > nitrogen + carbon dioxide + water

Explain use of flue gas desulfurisation:

• Fossil fuels may contain sulfur cmpounds

• When they are combusted, they can produce sulphur dioxide, which reacts with oxygen and water to sulphuric acid

• SO₂(g) + 1/2O₂(g) + H₂O(l) —> H₂SO₄ (l)

• Flue gas = gas given out by power stations

method of flue gas desulphurisation:

• slurry of calcium oxide and water sprayed onto the flue gas

• calcium oxide, water, sulphate reacts together to form calcium sulfite, further oxidised to calcium sulphate (gypsum)

• Gypsum can be sold to make builder’s plaster and plasterboard

• Or use calcium carbonate

Why do alkanes not react with halogens in the dark?

• not enough energy as the activation energy

• Required UV

what reaction takes place in the formation of a halogenoalkane?

• Free radical substitution reaction

• Hydrogen in alkane replaced by halogen atom

Explain free radical substitution:

INITIATION:

• Cl₂ -UV—> 2Cl.

• Halogen broken into halide ions

• The halide ions are free radicals, highly reactive

• UV light required

PROPAGATION:

• halide ions takes hydrogen atom

• Cl. + CH₄ —> HCl + .CH₃

• Carbon is now a free radical

• Methyl free radical then reacts with halogen atom

• .CH₃ + Cl₂ —> CH₃Cl + Cl.

TERMINATION:

• free radicals are removed

• .Cl + .Cl —> Cl₂

• .CH₃ + .CH₃ —> C₂H₆

• .Cl + .CH₃ —> CH₃Cl

what are chain reactions and are they important?

• other products being formed as well as main ones

• Produces mixture of products

• They are important for the ozone layer

• CFCs (chlorofluorocarbons) form a chain reaction in the stratosphere

• CFCs used in aerosol sprays, C-Cl bonds released into the atmosphere where UV rays break down bond to form Cl radicals

• Cl. + O₃ —> ClO. + O₂

• ClO. + O₃ —> 2O₂ + Cl.

• Chlorine radical therefore acts as a catalyst in the breakdown of ozone into oxygen

Why is the ozone layer important?

• protects the Earth from harmful exposure to too many UV rays

• Too much UV rays can cause skin cancer

are halogenoalkanes polar?

• halogenoalkanes are polar as they have a C-X bond

• However not polar enough to make then soluble in water

What is a nulceophile?

• Lone pair donor

• Reagent that attacks and forms bonds with positively/ partially charged carbon atoms

• Nucleophiles are negatively charged

what reaction do halogenoalkanes go under?

• nucleophillic substitution

What are some nucleophiles for nucleophilic substitution reaction?

• hydroxide ions takes -..OH

• Ammonia ..NH₃

• Cyanide ion -..CN

• NaOH aqueous, warm

• KCN ethanolic, warm

• NH₃ excess concentrated ammonia dissolved in ethanol at pressure in sealed container

Outline nucleophilic substitution:

• lone pair on nucleophiles attacks carbon

• Curly arrow from C-X bond to X

uses of nucleophilic substituion:

• useful to introduce new functional groups into organic compounds

• Halogenoalkanes can be converted into alcohols, amines, nitriles, carboxylic acid

what are some nucleophiles for elimination reaction?

• KOH ethanolic, hot

Outline elimination reaction:

• OH- ion acts as a base INSTEAD of a nucleophile

• Lone pair on OH- attacks H

• Arrow from H-C bond to C-C bond of adjacent carbon

• Arrow from adjacent C-X bond to X

• Forms an alkene

why are alkenes unsaturated molecules?

Contain at least one C-C double bond

why a double bond cannot rotate?

• p-orbital on each carbon

• Two orbitals overlap to form an orbital with a cloud of electron density above and below the single bond called a pi-orbital

• Pi-orbital means the bond cannot rotate

What are electrophiles?

• lone pair acceptors

• E.g. H+ ions

• Alkenes are susceptible to attacks by electrophiles as the C=C bond is very electron rich

what mechanism do alkenes undergo with electrophiles?

• electrophilic addition

• Carbocation formed

• 4 types of electrophilic addition

Electrophilic addition with Br₂ (aqueous) :

• arrow from carbon double bond to Br

• Arrow from Br-Br bond to second Br

  2)

• one Br now bonded with C

• Other bromine ion now a nucleophile

• Arrow from lone pair on Br- to positive carbon

electrophilic addition with HBr:

• arrow from double carbon bond to H

• Arrow from H-Br bond to Br

  2)

• H attached to carbon

• Br now a nucleophile and an ion

• Arrow from lone pair to positive carbon

electrophilic addition with H₂SO₄ (Concentrated, cold):

• arrow from double bond to hydrogen

• Arrow from H-O bond to O

  2)

• Oxygen is a nucleophile

• Arrow from lone pair on oxygen to positive carbon

electrophilic addition with H₂O and strong acid:

• Acid needed as a catalyst

• arrow from double bond to H+

  2)

• Arrow from lone pair on oxygen of another molecule to positive Carbon

  3)

• Arrow from H-O bond to positive O+ AND -H+

what is a carbocation?

product of electrophilic addition

What are the different carbocations?

• primary carbocation = positive carbon attached to one R group

• Secondary carbocation = positive carbon attached to two R groups

• Tertiary carbocation = positive carbon attached to three R groups

which carbocation is most stable?

tertiary, secondary, primary

which carbocation is the major product?

carbocation that is a more stable intermediate is the major product

What are polymers?

large molecules made of repeating units (monomers)

what are addition polymers?

• made from alkenes

• Polymer named poly-

Properties of addition polymers:

• unreactive

• Rigid

why are addition polymers unreactive?

• made of strong non-polar C-C and C-H bonds

• Long chain of saturated alkane molecules

• Not attacked by biological agents therefore non biodegradable

what is the use of PVC?

• used for drainpipes, window frames

what do plasticisers do?

• prevents polymer chains from being close to one another so makes the polymer more flexible

• Disrupts van der Waals forces between chains, making them weaker

• Can make PVC flexible enough to make aprons

primary, secondary, tertiary alcohols:

• primary: carbon bonded to the OH has one R group

• Secondary: carbon bonded to the OH has two R groups

• Tertiary: carbon bonded to the OH has three R groups

physical properties of of alcohol:

• OH group means hydrogen bonding occurs between molecules

• Alcohols have higher melting/boiling points than alkanes with similar relative mass

• -OH group can form hydrogen bonds with water molecules, but non-polar hydrocarbon chain cannot

• Therefore shorter chains of alcohol are soluble in water, longer chains are not

what are the two ways ethanol can be formed?

• cracking crude oil

• Fermentation of glucose

describe formation of ethanol from crude oil:

• ethene produced from crude oil fractions that are cracked

• Ethene is hydrated, reaction needs phosphoric acid catayst

• CH₂=CH₂ + H₂O -(phosphoric acid)→ C₂H₅OH

• Fast, pure ethanol produced

describe formation of ethanol from fermentation:

• carbohydrates broken down into glucose

• Glucose converted into ethanol and carbon dioxide by enzymes from yeast

• slow, aqueous solution of ethanol produced

Why is formation of ethanol from fermentation carbon neutral?

• carbon dioxide absorbed and carbon dioxide released in the production of ethanol are theoretically the same, balances out

• Photosynthesising of plants absorbs 6 molecules of CO2

• Fermentation and combustion releases 6 molecules of CO2

Problems with ‘carbon neutral’ production of ethanol:

• doesn’t take into account carbon costs when transporting crops, fuel for transport, processing crops

• Food security and use of land

Combustion of aclohol:

alcohol + oxygen —> carbon dioxide + water

Elimination reaction of alcohol is always:

• dehydration

• -OH group and hydrogen atom of carbon next to OH group produces water molecules Alcohols

• Dehydrated with excess hot concentrated sulfuric acid OR passing vapour over heated aluminium oxide

• Forms alkene and water

oxidation of primary alcohol with alcohol in excess:

• Acidified potassium dichromate

• aldehyde formed

• Ethanol + [O] —> ethanal + H2O

Oxidation of aldehyde with reagent:

• Tollen’s reagent or Fehling’s solution

• Ethanal + [O] —> ethanoic acid

oxidation of primary alcohol in excess oxidising agent and reflux:

• forms carboxylic acid

• Ethanol + 2[O] —> ethanoic acid + H2O

what are the oxidising agents of alcohol:

• acidified potassium dichromate: orange to green

• Tollen’s reagent: forms silver mirror

• Fehling’s solution: blue solution to red-orange precipitate

test to distinguish aldehydes from ketones:

• add tollen’s reagent

• Presence of aldehydes will form silver mirror

• Aldehydes will oxidise to form carboxylic acid, oxidising tollen’s reagent

Oxidation of secondary alcohol:

• forms ketone and water

• Acidified potassium dichromate needed

why can’t tertiary alcohols and ketones be oxidised?

• not easily oxidised as C-C bonds ned to be broken rather than C-H bonds

What does it mean to heat in reflux?

• Heating at high temperature for a prolonged period of time

Reaction of aldehyde to an alcohol:

• Reduction

• NaBH₄ aqueous solution (reducing agent)

• Aldehyde + 2[H] —> primary alcohol

reaction of ketone to an alcohol:

• Reduction

• NaBH₄ aqueous solution

• Ketone + 2[H] —> secondary alcohol

What mechanism is in reduction:

nucleophilic addition

What are the reagents for nucleophilic addition:

• NaBH₄ aqueous- produces primary secondary alcohol

• KCN with dilute acid, aqueous- produces hydroxynitriles

outline the mechanism of NaBH₄ with a ketone:

• arrow from :H- to C

• Arrow from C=O to O

• —>

• H attached to C

• -O: attached to C

• Arrow from :O- to H+

outline the mechanism of KCN with a ketone:

• addition of HCN due to acid

• Arrow from :CN- to C

• arrow from C=O to O

• —>

• CN attached to C

• :O- attached to C

• Arrow from :O- to H+

define racemic mixture:

• 50/50 of each stereoisomer

• Isomers of non super imposable mirror images

• Formed from an equal chance of attack from above and below the plane