Topic 6 - Organic Chem I Flashcards
What is the IUPAC ?
system for naming organic compounds
What is the process in naming an organic compound ?
- find stem - longest carbon chain with most side-chains
- add functional group
- put any side-chains as a prefix in alphabetical order with the number of the carbon it is bonded to
- multiple identical side-chains or functional groups use di-,tri- or tetra- (ignore when putting in alphabetical oder)
what is homologous series
several organic compounds that have the same functional group and general formula
what is an addition reaction
joining two or more 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 reaction
when a species loses electrons
what is a reduction reaction
when a species gains electrons
what do curly arrows show in a mechanism
to show how electron pairs moves around when bonds are made or broken
what is radical substitution mechanism
radical substitution of halogens in alkanes to make halogenoalkanes
what is electrophilic addition mechanism
addition of halogens and hydrogen halides to alkenes to make halogenoalkanes
what is nucleophilic substitution mechanism
nucleophilic substitution of primary halogenoalkanes with aqueous potassium hydroxide to make alcohols and with ammonia to make amines
what are nucleophiles
electron pair donors (negatively charged ions/species with lone pair)
electron rich - attracted to electron poor places
attracted to Cδ+ atom (replaces the halogen)
what are electrophiles
electron pair acceptors (positively charged ions/species)
electron poor - attracted to electron rich areas
Hδ+ attracted to C=C bond (electron rich)
what are radicals
have an unpaired electron
very very reactive
react with anything (+ve, -ve or neutral)
what are isomers
two molecules with the same molecular formula but different atomic arrangement
what are structural isomers
different structural arrangement of atoms
what are the 3 types of structural isomer and explain
- chain isomer
- where the carbon skeleton arranged differently
- similar chem properties
- dif physical properties - positional isomer
- skeleton/functional group same but functional group attached to dif carbon
- dif physical properties
- possibly dif chem properties - functional group isomers
- same atoms arranged into different functional groups
- very dif physical properties
- very dif chem properties
Why might it be tricky to spot a structural isomer
atoms rotate as much as they like around C-C bonds
What is bond fission
breaking a covalent bond
what are the 2 types of bond fission
homolytic fission
heterolytic fission
what is heterolytic fission
the bonds break unevenly with one of the bonded atoms receiving both electrons from the bonded pair
two dif substances can be formed (eg. cation and anion)
X↷Y →X⁺ + Y⁻
what is homolytic fission
bond breaks evenly and each bonding atom receives one electron from bonded pair
two ‘radicals’ formed
X-Y →X● + Y●
what are photochemical reactions
reactions started by light
What do radical substitution reactions need to start
UV light
what are the three stages in a radical substitution reaction
initiation
propagation
termination
what is the initiation stage in radical substitution reaction (use example of Cl₂ + CH₄ →CH₃Cl + HCl )
where radicals are produced
1. sunlight provides enough energy to break Cl-Cl bond
(photodissociation)
2. bond splits equally (homolytic fission) 2Cl●
what is the propagation stage in radical substitution reaction (use example of Cl₂ + CH₄ →CH₃Cl + HCl )
radicals used up & created
(chain reaction)
- chlorine radical attacks methane molecule
Cl● + CH₄ →CH₃●+ HCl - new methyl radical attacks another chlorine molecule
CH₃● + Cl₂ →CH₃Cl + Cl● - new chlorine radical can attack another methane molecule and so on until all chlorine and methane has been used up
what is the termination stage in radical substitution reaction (use example of Cl₂ + CH₄ →CH₃Cl + HCl )
radicals are destroyed
- two free radicals join to make a stable molecule
- several possible termination reactions
eg Cl● + CH₃● →CH₃Cl
What are the 2 problems with radical substitution reactions (use example of Cl₂ + CH₄ →CH₃Cl + HCl )
- end up with a mixture of products
eg if trying to make chloromethane but there is too much chlorine, dichloromethane, trichloromethane or tertachloromethane can also be produced
- can take place at any point on carbon chain - mixture of structural isomers
what is the best way to reduce chance of by-products in a radical substitution reaction (use example of Cl₂ + CH₄ →CH₃Cl + HCl )
excess of methane - greater chance for chlorine radical to collide only with methane molecule and not a chloromethane molecule
describe the fractional distillation process of crude oil
- crude oil vaporised at 350℃
- vaporised crude oil goes into fractionating column and raises up through the trays
- largest hydrocarbon doesn’t vaporise at all - bp too high = runs at bottom as residue
- colder further up column so condenses at dif temperatures
- drawn off at dif levels on trays
what are the 3 main methods for obtaining hydrocarbons from crude oil
fractional distillation
cracking
reforming
what is the purpose of bubble caps in fractional distillation
deflects the rising vapour down into the condensed liquid on the tray
condensed liquid continuously runs off from the tray and would be collected
bubble caps makes the separation more effective.
what is the order to hydrocarbons produced in fractional distillation and their uses (from smallest to largest)
gases - camping gas
petrol - petrol (gasoline)
naphtha - processed to make petrochemicals
kerosene (paraffin) - jet fuel, petrochemicals, central heating fuel
gas oil (diesel) - diesel fuel, central heating fuel
mineral oil - lubricating oil
residue (fuel oil) - ships, power stations
residue (wax/grease) - candles, lubrication
residue (bitumen) - roofing, road surfacing
What is cracking
when heavier fractions are ‘cracked’ to make smaller molecules
breaks longer-chain into smaller-chain by breaking
C-C bonds
it is a random process = different mixture of products each time
Why is cracking done
higher demand of light fractions - less demand of heavier
things in higher demand = more valuable
what are the two types of cracking
thermal and catalytic
what is thermal cracking
produces lots of alkenes
high temperatures (up to 1000℃) and high pressures (up to 70 atm)
used to make valuable products eg polymers (plastics)
what is catalytic cracking
produces lots of aromatic compounds (those that contain benzene rings) and motor fuels
uses a zeolite catalyst (hydrated aluminosilicate)
slight pressure and high temp (450℃)
cuts cost
What is reforming
turns alkanes into cycloalkanes or aromatic hydrocarbons
converts straight-chain into branched-chain
uses catalyst - platinum stuck on aluminium oxide
Why is reforming done
to make comubstion more efficient by reducing the chance of knocking
knocking = alkanes explode of their own accord when the fuel in engine is compressed - straight-chain most like likely (eg petrol/diesel)
what is complete combustion of alkanes
only products = carbon dioxide and water
what is incomplete combustion of alkanes
not enough oxygen around
products = carbon monoxide, carbon and water
Why is carbon monoxide harmful
toxic
CO binds better than O₂ to haemoglobin = bind before O₂ can
less oxygen carried around body = oxygen deprivation
Why are sulfur dioxide and nitrogen oxides harmful
leads to acid rain
sulfur dioxide = from burning fossil fuels = dissolves in moisture in air = sulfuric acid
nitrogen oxides = produced from high pressures/temps in car engine (O₂ and N₂ in air react) = when escape to atm dissolves in moisture = nitric acid
why is acid rain harmful
destroys environment (veg and trees)
corrodes buildings/statues
kills fish in lakes
What are catalytic converters?
sit quietly in car exhaust and remove some pollutants from car emissions
How do catalytic converters work
have a honeycomb structure covered with platinum or rhodium catalyst
exhaust gases react on surface
1. carbon monoxide reacts with nitrogen oxides to form carbon dioxide and nitrogen
2. unburnt hydrocarbons and remaining carbon monoxide react with oxygen to form carbon dioxide and water vapour
what are biofuels
fuels made from living matter over a short period of time
what is bioethanol
ethanol made by fermentation of sugar from crops eg maize
what is biodiesel
made by refining renewable fats and oils eg vegetable oil
what is biogas
produced by breakdown of organic waste matter
How are biofuels still classed as carbon neutral if they release carbon dioxide when burnt
its the same carbon dioxide that was absorbed by the plants when growing
however carbon dioxide still give out while refining and transporting as well as when making the fertilisers/powering agricultural machinery when growing/harvesting
What is a set back of biofuel
petrol car engines would have to be modified to use fuels with high ethanol concentrations
land used to grow these crops can’t be used for food
What type of bond do single covalents make
sigma (σ) bonds
What is a sigma bond
two orbitals (can be 2 s, 1 s and 1 p or 2 p )overlap in a straight line in the space between two atoms
gives the highest possible electron density between two nuclei
Why is a sigma bond the strongest type of covalent bond
the high electron density between the two nuclei means there is a strong electrostatic attraction - high bond enthalpy
what type of bond do double covalent bonds make
sigma (σ) bond and a pi (π) bonds
What is a pi bond
two orbitals overlap sideways
‘above’ and ‘below’ molecular axis
(p orbitals)
why do pi bonds have a relatively low bond enthalpy
the electron density is spread out above and below nuclei
therefore electrostatic attraction is weaker
Why cant atoms in C=C bond not rotate around it ?
because of the way the p-orbitals overlap to form a pi bond
What are stereoisomerisms
have the same structural formula but different arrangement
What are two types of stereoisomerism
Z-isomer
E-isomer
What is a Z-isomer
‘zusammen’ = together
both above/below double bond and bonded to different carbon
What is an E-isomer
‘entgegn’ = opposite
one above, one below double bond and bonded to different carbon
How does the E/Z system work even when all the groups are different in an alkene ?
atom with higher atomic number takes higher priority from each carbon
What are the conditions for the electrophilic addition reaction of ethene and hydrogen
nickel catalyst
150℃
How is margarine made
by ‘hydrogenating’ unsaturated vegetable oils
removing double bonds raises melting point of oil - solid at room temp
How do halogens react with alkenes to for dihalogenoalkanes (use example of bromine and ethene)
- double bond repels electrons in Br₂ - polarising it
- heterolytic fission (uneven) of Br₂ - the closer Br gives up bonding electrons to other Br and bonds to the C atom
(curly arrow from bond to atom) - creates carbocation intermediate
(curly arrow from Br electrons to +ve carbocation) - Br⁻ bonds to second carbon atom
What is a test for the presence of C=C bonds ?
add brown bromine water
shake
decolourises
How can alcohols be made from alkenes ?
through steam hydration
300℃ 60-70atm
solid phosphoric acid catalyst
eg. manufacture ethanol from ethene
How are alkenes oxidised to create a diol ?
shake alkene with acidified potassium manganate, purple solution becomes decolourised
diol is made (2 -OH groups)
What happens when a hydrogen halide is added to an unsymmetrical alkene
two products are formed
In an electrophilic addition reaction of hydrogen halides to an unsymmetrical alkene, what affects the amount of product ?
how stable the carbocation is
What carbocations are most stable
ones with more alkyl groups because they feed electrons to +ve charge
How does a hydrogen halide react with an alkene (use hydrogen bromide and propene as an example)
- partial +ve hydrogen attracted to double bond
- electrons in double bond polarise H-Br (repulsion)
- heterolytic fission (H+ bonds to one of C)
- Br with lone pair bonds to other C
major product =
2-bromopropane as more alkyl groups (more likely)
minor product =
1-bromopropane as less alkyl groups (less likely)
What is Markownikoff’s rule
the major product from an addition of a hydrogen halide to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrogens already attached
What is addition polymerisation
when the double bonds in alkenes open up and join together to make long chains of monomers
How do you draw the repeat unit in a polymer
brackets around repeat unit
double bond = broken to draw as ‘side-links’ through the brackets
write an ‘n’ bottom right corner of bracket
What are the 3 methods of disposing of polymers
bury
reuse
burn
Why can waste plastics be buried ?
landfill used when plastic is:
- difficult to separate from other waste
- not in sufficient quantities to make separation financially worthwhile
- too difficult technically to recycle
What are the different ways waste plastics can be reused ?
plastics like poly(propene) can be recycled by melting and remoulding them
some can be cracked into monomers and then used as organic feedstock to make more plastics or other chemicals
What is the purpose of burning waste plastics
the heat used to generate electricity
Why does the process of burning plastics need to be carefully controlled ?
to reduce toxic gases
eg polymers containing chlorine (eg PVC) produce HCl
How is the process of burning plastics carefully controlled ?
waste gases from combustion passed through scrubbers which neutralise the gases
also plastics can be sorted before burning to separate out any material that will produce toxic gas
What principles should chemists follow when they design a sustainable polymer manufacturing process ?
- use reactant molecules that are as safe and environmentally friendly as possible
- use few other materials (solvents) - if so be environmentally friendly
- renewable raw material used wherever possible
- minimum energy use - catalysts
- limit waste products made - especially harmful ones
- make sure lifespan of polymer is appropriate for its use
What are biodegradable polymers made from
renewable raw materials eg starch or from oil fractions
What are the advantages of using renewable raw material
- won’t run out like oil
- when polymers biodegrade CO₂ produced - therefore if plant-based same CO₂ that was absorbed
What are the disadvantages to using renewable raw material for biodegradable polymers
need right conditions to decompose - need to collect and separate from non-biodegradable
more expensive at the moment
What is hydrolysis
when water breaks bonds
What happens when halogenoalkanes are hydrolysed
form alcohols
nucleophilic substitution reaction
What haolgenoalkane is hydrolysed the fastest
iodoalkanes
Explain the nucleophilic subsitution reaction of halogenoalkanes
- C-halogen bond is polar
- +ve carbon accepts electrons from nucleophile
- C-halogen bond breaks heterolytically (both electrons taken by halogen)
- halogen falls off as nucleophile bonds to carbons
What is a way to hydrolyse halogenoalkanes without water (nucleophilic substitution)
warm aqueous potassium hydroxide under reflux
(makes alcohol)
Why is water slower in the hydrolysis of halogenoalkanes ?
its a worse nucleophile than potassium hydroxide
What happens when cyanide ions react with halogenoalkanes
nitirile and halide ion formed
under reflux
potassium cyanide in ethanol
What happens when halogenolakanes react with ammonia
amine and ammonium formed
warm halogenoalkane with excess ethanolic ammonia
What helps identify an amine
smell fishy
How can halogenoalkanes undergo elimination reactions
- halogenalkane mixed with warm alkali (KOH) dissolved in ethanol
- heated under reflux
- products = alkene, water, eg KBr
How can alcohols react to produce chloroalkanes
alcohol + PCl₅ or HCl produces chloroalkanes
PCl₅ produces chloroalkane, HCland POCl₃
HCl produces chloroalkane and water
How can alcohols react to form bromoalkanes
alcohol + bromide ions
produces bromoalkanes
- acid catalyst (50% conc sulfuric acid)
produces bromoalkane and water
How can alcohols react to create iodoalkanes
- alcohol + PI₃
under reflux with red phosphorous and iodine
produces iodoalkane and H₃PO₃
How can alcohols be dehydrated to form alkenes
- alcohol + acid catalyst (conc phosphoric acid)
- heat
- water eliminated
What colour flame does ethanol make
pale blue
What can be used to mildly oxidise alcohols
acidified dichromate
What are primary alcohols oxidised to
- aldehydes (-al) R-CHO
- carboxylic acid R-COOH
What are seondary alcohols oxidised to
ketones (-anone) R=O=R
What are tertiary alcohols oxidised to
nothing
How to test for a solution is an aldehyde or a ketone
benedict’s solution (copper(II) ions dissolved in sodium carbonate)
heated with aldehyde - blue copper(II) ions reduced to brick-red precipitate copper (I) ions
heated with ketone - nothing
In oxidation of alcohols, what happens to the oxidising agent acidified dichromate (VI)
orange dichromate(VI) reduced to green chromium(III)
How to control how far primary alcohols are oxidised
to get an aldehyde:
- get out of oxidising solution asap
- heating excess alcohol with controlled amount of oxidising agent in distillation
to get carboxylic acid:
- alcohol oxidised vigorously
- under reflux
What is the only way to oxidise tertiary alcohols
burning them
Why is refluxing used
- ensure volatile organic substances aren’t lost
- organic reactions are slow and flammable and volatile
- therefore using bunsen burner = evaporate or catch fire
How does reflux work
- mixture heated in flask fitted with vertical Liebig condenser
- continuously boils, evaporates and condenses vapours
- recycles them back into flask
- gives time to react
note - heating should be electrical = avoid naked flames
What is distillation
separates substances with different boiling points
How does distillation work
- gently heat mixture in distillation apparatus
- thermometer shows boiling pt of substance evaporating
- if known bp of pure substance thermometer shows evap and therefore condensing
- place flask at open end of condenser to collect product
- when temp changing place different flask
How does separation work
- pour mixture into separating funnel, then add water
- shake and allow to settle
- organic layer and aqueous layer are immiscible
What does separation do
removes any water soluble impurities from product
How do you remove traces of water from a mixture
- add anhydrous salt (eg magnesium sulfate or calcium chloride)
- used as drying agent - binds to water to become hydrated
- when first added = organic layer is lumpy
- add more until all water removed (swirl to look like snow globe)
- filter mixture
How to detect impurities
boiling point higher than recorded value
