Year 12- Organic Chemistry Flashcards
What is a hydrocarbon?
Compound consisting of hydrogen and carbon atoms only
What is a structural formula?
Shows minimal detail of arrangement of atoms in a molecule, CH3CH2CH2CH3
What is a displayed formula?
Drew out to show all covalent bonds and atoms present in a molecule
What is the shape around a carbon atom in a saturated hydrocarbon?
Tetrahedral- bond angle is 109.5
What is a skeletal formula?
Simplified organic formula, shown by removing hydrogen atoms from alkyl chains, only showing carbon atoms and functional groups
What is a homologous series?
Families of organic compounds with same functional groups and general formula.
- They show gradual change in physical properties
- Each member differs by CH2
- Same chemical properties
What is the difference of the C=O bond in ketones and aldehydes?
Ketones- in the middle
Aldehydes- at the end
Ester functional group
Central carbon double bonded to an oxygen and single bonded to another oxygen
Which form- suffix or prefix- do double and triple C-C bonds take?
Suffix
Order of priority highest first
Carboxylic acids> aldehydes> ketones>alcohols>alkenes> halogenoalkanes
Which one takes precedence of taking the lowest number- functional group or branched chain?
Functional group
What do we do if there is more than one functional group or side chain?
List them in alphabetical order
What happens if the compound has an -OH group and a functional group that takes precedence?
Priority group gets suffix ending and OH can be names with the prefix hydroxy.
What happens in homolytic fission?
Each atom gets one electron from the covalent bond. This forms free radicals.
What is a free radical?
A reactive species that possesses an unpaired electron
What happens in heterolytic fission?
One atom gets both electrons
What is structural isomerism?
Same molecular formula but different structures/ structural formulae
What are the different ways structural isomerism can rise?
- Chain isomerism
- Position isomerism
- Functional group isomerism
What is chain isomerism?
Compounds with same molecular formula but diff structures of the carbon skeleton
What is position isomerism?
Compounds with same molecular formula but different positions of same functional groups on the same carbon skeleton.
What is functional group isomerism?
Compounds with same molecular formula but atoms arranged t give different functional groups
What is stereoisomerism?
Same structural formulae but different spatial arrangement of atoms
What are 2 types of stereoisomerism?
E-Z isomerism
Optical isomerism
What type of hydrocarbon exhibits E-Z isomerism?
Alkenes
Why do E-Z stereoisomerism arise?
- Restricted rotation around C=C bond
- 2 different groups/atoms attached to both ends of double bond
What is considered the priority group in E-Z isomerism?
The atom with the bigger atomic number
What is petroleum?
Mixture containing mainly alkane hydrocarbons
Fractional distillation of crude oil
- Oil is heated and passed into column
- Fractions condense at diff heights depending on their bp.
- Temp of column decreases upwards
- Bp depends on size of molecules: larger ones condense at the bottom at hotter temps and vice versa.
What is cracking?
Conversion of large hydrocarbons to smaller hydrocarbons by breaking C-C bonds
What do high mr alkanes form in cracking?
Smaller mf alkanes, alkenes and hydrogen
Economic reasons for cracking
- Shorter hydrocarbons are more in demand
- To make use of excess larger hydrocarbons
- Products are more valuable
Conditions of thermal cracking
High temp: 400-900 *C
High pressure: 7000kPa
Products of thermal cracking
Mostly alkenes and hydrogen
Conditions of catalytic cracking
Moderate pressure
High temp: 450*C
Zeolite catalyst
Product of catalytic cracking
Branched and cyclic alkanes and aromatic hydrocarbons
How can SO2 be removed?
By flue gas desulfurisation. Gases pass through scrubber containing basic calcium oxide which reacts with the acidic SO2 in a neutralisation reaction. Forms calcium sulfite, CaSO3.
What can calcium sulfite be used for?
To make calcium sulfate for plasterboard
How is nitrogen oxide formed?
Formed between nitrogen and oxygen in car engine. High temp and spark in the engine provides activation energy needed to break strong N-N bond.
What do catalytic converters do?
Remove CO, nitrogen oxides and unburned hydrocarbons from the exhaust gases, turning them into harmless gases.
Mechanism of greenhouse effect
UV wavelength radiation passes through atmosphere to Earths surface and heats it up. Earth radiates out IR long wavelength radiation. The C=O bond in CO2 absorbs IR radiation so it doesn’t escape the atmosphere. Energy is transferred to other molecules in atmosphere by collisions so atmosphere is warmed.
Initiation stage- free radical substitution
- UV light supplies energy to break CL-Cl bond by homolytic fission
- Forms free radicals
Propagation stage- free radical substitution
1) CH4 + Cl* –> HCl + *CH3
2) CH3 +Cl2 –> CH3Cl +Cl
What are primary, secondary and tertiary haloalkanes?
Primary- one carbon attached to carbon adjoining halogen
and vice versa…
What reactions can halogenoalkanes undergo?
Elimination and nucleophilic substitution reactions
What is a nucleophile?
Electron pair donator
What is an electrophile?
Electron pair acceptor
Nucleophilic sub- Halogenoalkane (general)
- Nucleophile attacks positive carbon atom attached to halogen
- C-X bond breaks and this releases a negative halide ion
How can we compare the reactivity of halogenoalkanes?
- React it with aqueous silver nitrate
- A silver halide ppt forms as the halide leaving group combines with a silver ion
- The quicker the ppt forms, the faster the sub reaction
Precipitates formed from reacting aqueous silver nitrate with halogenoalkanes- colours
AgI- yellow
AgBr- cream
AgCl- white
What happens in nucleo sub reaction of a halogenoalkane and cyanide ions?- product, reagent, conditions
Product- nitrile
Reagent- KCN dissolved in ethanol/water mixture
Conditions- Heat under reflux
What happens in nucleo sub reaction of a halogenoalkane and aqu. hydroxide ions?- product, reagent, conditions
Product- alcohol
Reagent- potassium/sodium hyroxide
Conditions: aqu. solution, heat under reflux
What happens in nucleo sub reaction of a halogenoalkane and ammonia?- product, reagent, conditions
Product- amine
Reagent- NH3 dissolved in ethanol
Conditions: Heat under pressure in sealed tube
What happens in elim sub reaction of a halogenoalkane and alc. hydroxide ions?- product, reagent, conditions
Product- alkene
Reagent- potassium/ sodium hydroxide
Conditions- in ethanol, heat
What are chloroalkanes and chlorofluoroalkanes used for?
Solvents- CH3CCl3 used as solvent in dry cleaning
What is naturally-occurring ozone (O3) used for?
Layer in upper atmosphere thats beneficial as it filters out much of the suns harmful UV radiation
What is ozone, O3 like in the lower atmosphere
It is a pollutant and contributes to formation of smog
What do man-made CFCs do?
Form a hole in the ozone layer
What is now used instead of CFCs in refrigerators and air conditioners?
HFCs- safer as they don’t contain C-Cl bond which would break in CFCs by UV light.
How do CFCs form a hole in the ozone layer?
UV light breaks the C-Cl bonds which forms a chlorine free radical. The catalyses the decomposition of ozone in a free rad sub reaction.
Arrangement of bonds around C=C bond in alkenes
Planar- 120* bond angle
What does a C=C bond contain?
a pi and sigma bond
Why are pi bonds vulnerable to being attacked by electrophiles
They are exposed and have high electron density
What reactions do alkenes undergo?
Electophilic addition reactions
Electro add of bromine with alkenes- products, reagent and conditions
Products- dihalogenoalkane
Reagent- bromine
Conditions- room temp (not in UV light)
What is the intermediate in electro add. reactions?
Carbocations
Electro add. of HBr with alkenes- products, reagent and conditions
Products- halogenoalkene
Reagent- HBr or HCl
Conditions- room temp
If an alkene is unsymmetrical, what can be formed in an electro add reaction?
2 products- major or minor product
What makes a carbocation more stable?
The methyl groups on either side of the positive carbon are electron releasing and reduce the charge on the ion, stabilising it
Order of stability of carbocations
tertiary>secondary> primary
Electro add. reaction of sulfuric acid with alkenes- stage 1
Product- alkyl hydrogensulfate
Reagent-conc. H2SO4
Conditions- room temp
Electro add. reaction of sulfuric acid with alkenes- stage 2
Products- alkyl hydrogensulfate —> alcohol
Reagent- water
Conditions- warm mixture
-Hydrolysis reaction
Industrially, how are alkenes converted to alcohols?
-Name conditions
In one stage, compared to the electro add. reaction with conc. sulfuric acid. They are reacted with water in the presence of an acid catalyst.
High temp: 300-600
High pressure-70 atm
Catalyst of conc. H3PO4
Bond angles in alcohols
H-C-H and C-C-O bonds are 109.5 *, tetrahedral
H-O-C bond is 104.5*, bent
Partial oxidation of primary alcohols- reagent, product, conditions, observations
-Forms aldehyde
Reagent- potassium dichromate solution and dilute sulfuric acid
Conditions-warm gently and distilled out
Observations- orange dichromate ions reduces to green chromium 3+ ions
Full oxidation of primary alcohols- products, reagent, conditions and observations
-Forms carboxylic acid
Reagent- potassium dichromate solution and dilute sulfuric acid
Conditions- use excess dichromate, heat under reflux
Observations- orange dichromate ions reduces to green Cr3+ ions
Why are anti bumping granules used?
To prevent vigorous, uneven boiling by making small bubbles form instead of big ones
Oxidation of secondary alcohols
- Forms ketones
- Use potassium dichromate solution and dilue sulfuric acid
- Heat under reflux
- Orange dichromate ions (Cr2O7 2-) reduce to green chromium ions
Why aren’t tertiary alcohols oxidised?
No hydrogen bonded to carbon with OH group
Tollen’s reagent test- reagent, conditions, reaction, observations
- Reagent formed by mixing aqu. ammonia and silver nitrate to form complex ion [Ag(NH3)2]+
- Heat gently
- Aldehydes only oxidised to carboxylic acid
- Silver ions reduced to silver atoms
- Silver mirror coats test tube
Fehlings solution- reagent, conditions, reaction and observations
- Contains blue Cu 2+ ions
- Heat gently
- Aldehydes only oxidise to carboxylic acids
- Blue Cu 2+ ions reduced to red pot of Cu2O
How can carboxylic acids be tested for?
Using sodium carbonate. It fizzes and produces carbon dioxide.
Reaction of alcohols with dehydrating agents
- Forms alkene
- Uses conc. sulfuric or phosphoric acid
- Warm under reflux
- This is an acid catalysed reaction
Forming ethanol by fermentation - reaction and conditions
Glucose —> ethanol + carbon dioxide
- Optimum temp is 38*. At lower temps, too slow and higher temps, yeast dies and enzymes denature
- Done in absence of air as it could oxidise ethanol to ethanoic acid
Advantages of fermentation method for ethanol
- Sugar is renewable
- Production uses low level tech
Disadvantages of fermentation method for ethanol
- Batch process is slow and gives high production costs
- Ethanol made isn’t pure and needs ro be purified by fractional distillation
- Depletes land used for crop
Forming ethanol from ethene- reaction and conditions
- Hydration reaction
- High temp- 300*
- High pressure-70 atm
- Strong acidic catalyst of H3PO4
Advantages of hydration of ethene for ethanol
- Faster reaction
- Purer product
- Continuous process, cheaper manpower
Disadvantages of hydration of ethene for ethanol
- High tech
- Ethene is non renewable
- High energy costs for pumping for high pressure
What is a biofuel?
Fuel produced from plants
Why is ethanol produced from fermentation a biofuel?
- Carbon neutral
- Any carbon dioxide given off when biofuel is burnt was extracted from the air by photosynthesis when the plant grew
