CH6: Organic Chemistry I Flashcards
What are isomers? And the 2 types?
Molecules that have same molecular formula, but atoms arranged differently
2 types :
Structural
Stereoisomers
What is a structural isomer and the 3 types?
Molecular formula is same, but structural formula is different
1. CHAIN ISOMERS
Carbon skeletons is arranged differently (straight chain or branched) - so have similar chemical properties, but physical properties (BP /MP ETC) are different due to to different shape
-
POSITIONAL ISOMERS
Functional group attached to different carbon atom - physical/chemical properties are different -
FUNCTIONAL GROUP ISOMERS
Same atoms can be arranged into different functional groups - physical/chemical properties are different
General forumula of alkanes ?
CnH2n+2
Saturated hydrocarbons - all C-C bond are single bonds
What is bond fission and the 2 types?
Breaking of a covalent bond
HETEROLYTIC FISSION - bond breaks unevenly , with one the bonded atoms receiving both electrons
- forms CATION and ANION (bc one gain electrons , the other loses it )
HOMOLYTIC FISSION - bond breaks evenly/each bonding atoms receives one electron
- forms 2 radicals (particles that have an unpaired electron)
How are halogenoalkanes formed from alkanes? What are the 3 stages?
Halogens react with alkanes in PHOTOCHEMICAL reactions - started by light
- hydrogen atom is substituted by chlorine/bromine - RADICAL SUBSTITUTION REACTION
3 stages to process :
Initiation
Propagation
Termination
What is the initiation stage ?
UV lights breaks the Cl-Cl or Br-Br bond
- produces 2 radicals in homolytic fission reaction
What is the propagation stage?
Radicals are used up/ created in a chain reaction
- free radicals will react with unreative alkanes to form an ALKYL RADICAL and hydrogen halide
- this radical can attack another chlorine/bromine to from a halogenoalkane/regenerate chlorine/bromine free radicals
Cl. + CH4 —> CH3. + HCl
CH3 . + Cl2 —> CH3Cl + Cl.
What are termination reactions ?
2 radicals join together to make a stable molecule
What are the problems of free radical substitution?
Further substitution
Excess chlorine reacted with methane in the presence of UV light - causes further substitution and could produce CH2Cl2, CHCl3, CCl4
- nuisance because have to separate chloromethane from 3 unwanted products
Substitution of different carbon atoms - causes mixture of structural isomers
What is cracking?
Breaking lager hydrocarbons into smaller , more useful hydrocarbon fractions
What re the 2 types of cracking?
Thermal cracking - requires high temps(1000C)/pressure (70 atm) produces a lot of ALKENES
Catalytic cracking - lower temps(450 C)/pressure , but need catalyst (aluminium oxide/zeolite) to produce aromatic hydrocarbons
What is reforming and why do we need to do this?
Reforming : Converting straight chain alkanes into branched chain alkanes /cyclic hydrocarbons
Needed because : straight chan alkanes are more likely to explode , rather than combust , when compressed in engine —> CAUSE KNOCKING
How does complete/incomplete combustion of ALKANES cause pollution?
Complete combustion : forms CO2and H2O
Incomplete combustion: forms CO , Cand H20
Burning alkanes can also form :
- unburnt hydrocarbons - react with NO2 and SO2 to produce PAN in photochemical smog
- carbon particulates
- sulfur/nitrogen oxides
How s carbon monoxide harmful?
Toxic and odorless gas
- binds to haemoglobin in blood before oxygen can
- so oxygen deprivation in body
How are oxides of sulfur/nitrogen harmful?
Fuels containing sulfur are burnt forming SULFUR DIOXIDE GAS —> converted into sulfuric acid
High pressure/temp in car engines cause NITROGEN OXIDES TO FORM —> converted into nitric acid
BOTH CAUSE ACID RAIN - destroys environment /plants/buildings
- makes rivers acidic - harmful to aquatic animals
How are particulates harmful ?
Carbon particles (particulates ) from incomplete combustion FORM SOOT
- damage lungs /cause respiratory problems
- damage buildings - corrode them
- global dimming
How are catalytic converters used to remove pollutants ?
- use platinum catalyst to change into harmless/less harmful gases
Eg : 2NO + 2CO —> N2 + 2CO2
Nitrogen monoxide and carbon monoxide converted to nitrogen and carbon dioxide
NO is REDUCED
CO is OXIDISED
What are biofuels and the 3 types?
Renewable fuels
BIODIESEL - made by refining renewable fats/oils
BIOETHANOL - made by fermentation
BIOGAS - made/released when organic waste breaks down
Why are biofuels seen as carbon neutral ?
- Bc CO2 produced from biofuels is absorbed by plants for growth
- biodiesel/biogas can be made from waste that would go to landfill
- biofuels can provide money for LEDCS , as they have space to grow crops needed , as less land needed for fuels
Drawbacks of biofuels ?
- cost of converting engines/machinery for biofuels instead of petrol/diesel
- countries don’t have space to produce plants to make biofuels , bc needed for food production
- rainforest cut down to provide land
- shortage of fertile soils
Fractional distillation of crude oil?
- Crude oil is vaporised to 350 degrees
- Enters column and gets cooler as you go up
- Larger alkanes , have larger BP so condense lower
Smaller alkanes , have lower BP do condense higher up - Largest hydrocarbons have to high BP so don’t condense —> residue at bottom
Smallest hydrocarbons also don’t condense BP too low so drawn off as gases at top
What are sigma bonds?
- formed when 2 orbitals overlap , in straight line, in space between 2 atoms
- gives highest possible electron density between positive nuclei
- leads to strong electrostatic attractionbetween nuclei/shared pair of electrons
- HAVE HIGH BOND ENTHALPY
What is a pi bond?
Formed from sideways overlap of adjacent p orbitals
- electron density is spread out above/below the nuclei
- causes weaker electrostatic attraction between nuclei and shared pair of electrons , than sigma bond
- LOW BOND ENTHALPY
What is a double bond made up of?
A sigma bond and pi bond
What are stereoisomers?
Compounds that have same structural formula but different arrangement of atoms in space.
- because of lack of rotation around double bond (due to way p orbitals overlap to form Pi bond), some alkenes have stereoisomers
What is a E/Z isomer ?
E (trans) isomer have groups on opposite sides of double bond /carbon ring
Z (Cis) isomer have groups on same sideof double bond/carbon ring
How to work out if isomer is E or Z if all carbons have different groups attached to them?
Using Cahn-Ingold-Prelog (CIP) priority rules
- look at atomic number of first atom attached to CARBON
- higher the atomic number, the higher the priority
- if high priority on same side - Z isomer
- if high priority on opposite sides - E isomer
What’s an electrophilic addition ? What reactions are electrophilic addition?
The addition of an electrophile to a double bond
- double bond opens up / atoms added
The addition of :
Hydrogen
Steam
Hydrogen halide
Halogen
What are electrophiles?
Electron pair acceptors - short of electrons ,sp attract to areas with many electrons
- positively charged ions /polar molecules
Conditions and reaction of HYDROGEN + ALKENE?
How is this used in margarine manufacturing?
- produce ALKANE
Conditions :
NICKEL catalyst
150 degrees
Margarine is made by hydrogenating unsaturated veg oils . By removing double bonds, you increase MP of oil so its solid at room temp
HALOGEN + ALKENES - reaction?
Form dihalogenoalkanes
- halogens are added across the double bond
Test for alkenes?
Add bromine water - solution will decolourise if alkene is present
- because bromine is added across double bondso goes colourless and forms dibromoalkane
STEAM + ALKENE - reaction and conditions
Forms alcohol
Conditions : 300 degrees
60-70 atm
Phosphoric acid catalyst
ALKENES + HYDROGEN HALIDES - reaction?
Form HALOGENOALKANES
- if hydrogen halide is added to unsymmetrical alkene- 2 products
- the amount of each product depends on how stable the carbocation is
- carbocations with more alkyl groups are more stable - they feed electrons towards + CHARGE
(Tertiary is most stable - so more of this made)
Oxidation of alkenes using ACIDIFIED POTASSIUM MANGANATE (oxidising agent)
C2H4 + H2O + [O] —> C2H4(OH)2
- the purple solution turns colourless
Produced DIOL- alcohol with 2 -OH groups
- this can be used to test for alkenes, as alkanes don’t have double bonds, so wont oxidise this way
What is addition polymerisation? And what are polymers?
Where monomers (containing at least one C double bond) , form long chains of polymers
- double bond opens up
Polymers - long chain molecule made up of repeating units (monomers)
Ways of disposing polymers?
RECYCLING : reduce amount of waste going to landfill sites - reduces use of finite resources
Some can be recycled by MELTING/REMOULDING
Some can be CRACKEDinto monomers/ used as ORGANIC FEEDSTOCK
BURNED : if can’t be recycled (due to chemical composition ) , can be burned to generate electricity
- needs to be controlled to reduce toxic gases
E.g PVC contain chlorines so forms HCl
- scrubbers can neutralise gases like HCl
Principles for sustainable polymer manufacturing?
- use safe/environmentally friendly reactants
- use fewer chemicals/other materials
- use renewable raw materials
- use catalysts - keep energy use to minimum
- limit waste products
- produce polymers with long lifespan
What are biodegradable/compostable polymers ? Ands what are the advantage of these?
Biodegradable- Polymers that naturally decompose
- products can be used for other applications
- can be made from renewable raw materials, so wont run out
BUT SORTING/COLLECTING MEANS ITS MORE EXPENSIVE THAN NON BIODEGRADABLE OPTIONS
Compostable - polymers that are plant based
- CO2 released in decomposition is same as CO2 absorbed by plant, so not adding to CO2 in air
- save energy compared to oil based plastics
What are catalytic converters made from?
Ceramic honeycomb structure coated with a thin layer of catalyst metals (platinum, palladium,rhodium) —> give larger SA
Advantage of biofuels ?
Reduction of use of fossil fuels (which are finite)
Biofuels are renewable
More carbon-neutral
Fossil fuels can be used as feedstock for organic compounds
Less pollution
