Topic six Flashcards
What is an electrophile
A positive species that is attracted to areas of high electron density
Chloroalkanes can be formed from both alkenes and alkanes.
Ethene can be converted into chloroethane.
Identify, by name or formula, the reagent for this conversion.
HCL (g)
Ethane is an alkene so undergoes electrophilic substitution the H is slightly positive and the cl is slight negotiate
Dif between electrophillic substitution and addition
Addition - Alkenes have pi bond attracting electrophiles ,double bond breaks and electrons donated to electrophile carbocation intermediate forms nucleophile attacks carbocation intermediate
Substitution - occurs due to delocalised pi electrons making it stable to resist addition therefore substitution occurs
What is a nucelophile
A species that donates a pair of electrons usually attracted to positive charge the carboncation intermediate
How does bromine water differentiate between alkanes and alkene
Turns alkene colourless due to electrophillic addition
What are the conditions to carry out hydrolysis of halogenoalkane
We use and aqueous solution of NAOH or potassium hydroxide
We add ethanol and heat under reflux
Why do we add ethanol when hydrolysing halogenoalkanes
To increase the solubility
Make experiment to find relative rates of hydrolysis of halogenoalkanes
Use water bath to control temperature
In separate test tubes we add aqueous silver nitrate to water
We add equal amounts of Dif halogenoalkanes to each test tube
Water is nucelophile will react with halogenoalkanes so will hydrolyse halide ion which reacts with silver nitrate to produce precipitate we measure how long it takes for precipitate to form
When we do the experiment to find how much precipitate forms why don’t we use hydroxide ions why do we use water
Because the silver nitrate will react with hydroxide to produce silver hydroxide which is the false precipitate
Explain the results of precipitate formed and colours
1- bromopentane forms cream precipitate slowly
1-chloropentane forms white precipitate very slowly
1-idopentane forms yellow precipitate very fast
Carbon-halogen bond must break c-I has relatively low bond enthalpy ,as u move down bond enthalpy deacreases
What do double carbon bonds consist of
Pi bond and sigma bond
Why are pi bonds attacked by electrophiles
Have high electron density so positive electrophile will attack
Why are sigma bond stronger than pi bonds
Weaker sideways overlap of p orbitals in a π bond, compared to strong head-on overlap in a σ bond.
Electron density in a π bond is above and below the bond axis, making it less stable than a σ bond.
Name 2 types of structural isomers
Chain and position isomers as they have the same molecular formula but Dif structural formular
What is a chain isomers
Have same molecular formula but longest carbon chain is Dif this is caused by branching
What does knocking mean
Alkanes explode at their own accord due to fuel or air in the engine being compressed
Why is termination step important
Removes free radicals so stops chain reaction
What does thermal cracking require
Heat and high pressure
What does catalytic cracking require
Uses a zeolite catalyst at Minimal pressure high temperature
Where is e/z isomerism seen
In unsaturated or ring compounds that have the same molecular formular but Dif shapes
What are the limitations of cis and trans
Can’t be used when we have three or four Dif groups so we use higher atomic number priority groups to determine e/z
Explain margarine production
Naturally occurring vegetable oils are unsaturated so when reacted with H2 we get a c-c bond which changed the properties of oil converting it to solid
What catalyst ,temp ,pressure and reagent does our reaction with steam use when alkene turn into alcohols
Catalyst we use is phosphoric acid or sulfuric acid
Reagent -steam
Temp -300 degrees
Pressure 60-70atm
What can alkene be oxidised and acidified by
Kmno4 potassium manganite and its a very powerful oxidising agent
What happens when alkene are shake with cold dilute potassium manganate
Purple colour turns colourless and product is a diol
How can the fact that potassium manganate when shaken with an alkene turns purple to colourless test between an alkene and alkane
An alkane won’t change colour it will stay purple whereas and Alkene will go colourless
What happens in the addition reaction of an alkene with hydrogen halide and what is regent conditions mechanism type of reagent and type of bond fission
The h atom acts as an electrophile accepting the electrons from the c=c bond in the alkene
Regent -hcl or hbr
Conditions -room temp
Mechanism -electrophilic addition
Type of reagent and-electrophile H delta positive
Bond fission -hetrolytic
How can halogens be used to test If a molecule is unsaturated
Only alkene will undergo electrophilic addition with a halogen when we use bromine water if it’s an alkene it will go from orange to colourless showing the addition taking place and alkane will remain orange as it’s saturated so addition does not occur
What is addition polymerisation
Reaction where many monomers that contain c=c bonds join to form long chains
What are the products of addition polymerisation
Polymer
What acc happens in addition polymerisation
Monomers have c=c bonds
Breaking of pi bond allows molecules to link together
Monomers join in long continuous chain
No by products formed
What is a polymer
Longer chain molecule made up of many repeating units
What makes polymers unreactive
They are Saturated and usually non polar
What does the rate of reaction when forming an alcohol from a halogenoalkane depend on
The type of halogen in the halogenoalkane -the stronger the C-X bond the slower the rate of reaction
Which halogenoalkane will not react to form an alcohol and which halogenoalkane will react the fastest
Fluroalkanes don’t react but iodoalkanes react very fast
Apart from the hydroxide ion, what can the formation of an alcohol from a halogenoalkane also use as the nucleophile?
Water - but it is very slow
Why is the hydroxide ion a better nucleophile than water in the formation of an alcohol?
OH- carries a full negative charge and the O in H20 only carries a partial negative charge
What happens if we add silver nitrate solution in ethanol to the reaction of halogenoalkanes with water?
The silver ions will react with the halide ions as soon as they form, giving a silver halide precipitate
What do we need to do in order to form a primary amine from a halogenoalkane?
An ethanolic solution of excess ammonia is heated under pressure with a primary halogenoalkane
Why is an excess of ammonia used in the formation of a primary amine?
The product is more reactive than ammonia so further substitutions could occur
What kind of reaction is a nucleophilic substitution?
One in which a nucleophile attacks a carbon atom which carries a partial positive charge
Why will halogenoalkanes undergo nucleophilic substitution?
Due to the polar C-X bond
X has higher electronegativity than C
What are primary carbocations?
They have one alkyl group attached to the positively charged carbon (Secondary have 2 and tertiary have 3 alkyl groups?
What does the alkyl group create?
A positive inductive effect
What does the electron pushing effect place more of on the carbocation as the number of alky! groups increase?
More negative charge on the carbon as you go from primary - secondary - etc.
Reduces overall positive charge on carbon
How well did you know this?
What is spread over more atoms as you go from primary - secondary - etc. carbocations?
Positive charge
What happens if the charge is spread over more atoms in carbocations?
Ion is more stable
What can be used to explain the different reactivities of halogenoalkane substitution reactions and why?
Bond energies - these reactions involve breaking the C-X bond
Which halogenoalkane has the weakest C-X bond?
The C-I bond requires the least energy to break so is the weakest
Which halogenoalkanes are the least likely to undergo substitution reactions?
Fluoroalkanes
What can be used to measure the rate of hydrolysis of halogenoalkanes?
Acidified aqueous silver nitrate
What is set up initially in the experiment to measure the rates of hydrolysis?
3 test tubes in a 50 degrees celsius water bath, with a mixture of ethanol and acidified silver nitrate
What do we need to do to measure the rates of hydrolysis?
Add a few drops of chloroalkane, bromoalkane and an idodoalkane to each test tube and start a stop watch
Time how long it takes for the precipitates to form
What is the fastest nucleophilic substitution reaction in the rate of hydrolysis experiment?
Yellow silver iodide precipitate
(C-I bond has lowest bond enthalpy so ions form the fastest)
What is the slowest nucleophilic substitution reaction in the rate of hydrolysis experiment?
White chloride precipitate
(C-Cl bond has highest bond enthalpy so ions form slowest)
Why will a silver fluoride precipitate not form in the rate of hydrolysis experiment?
It is soluble - confirms fluoroalkanes are least reactive and iodoalkanes are most
What can we predict from the rate of hydrolysis experiment?
Any halogen below iodine in group 7 of the periodic table will form a silver halide precipitate even quicker
What reacts the quickest when comparing the rates of hydrolysis in primary, secondary and tertiary halogenoalkanes?
Tertiary
When can u use cis and trans
When the same element is used on ether side of molecule if it’s not base it on probity groups and use e and z
What is the reaction between alkenes with hydrogen ,regent ,conditions ,type of reaction,change in functional groups and what is this reaction used for in the industry
Reagent - hydrogen
Conditions - nickel catalyst
Type of reaction -addition/reduction
Change in functional group alkene to alkane
No electrophiles involved it’s just an addition and it’s used to make margarine
What is an addition reaction
a reaction where two molecules react
together to produce one
Reactions of alkenes with bromide/chlorine
Change in functional group
Reagent, conditions,mechanism,electrophile ,type of bond fission
Change in function group alkene to dihalogemoalkane
Regent bromine dissolved in organic solvent
Conditions -room temp
Mechanism -electrophile br delta positive
Type of bond fission - hetrolytic
Reaction of bromine water with alkenes
Regent ,conditions type of reaction
Observations
Regent - bromine dissolved in water
Conditions - room temp
Type of reaction electrophilic addition
Observations orange to colourless
Reaction of potassium manganate with alkene
Change in function group
Conditions
Type of reaction
Observations
Reagent
Function group alkene to diol
Conditions - room temperature
Reagent -potassium manganate in acidified solution
Observations purple goes colourless
Oxidation
How are nitrogen oxides formed
Nitrogen oxides form from the reaction between N2 and O2 inside the car engine.
The high temperature and spark in the engine provides sufficient energy to break strong N2 bond
What are catalytic converters made of
platinum, palladium, rhodium
Hydration of alkenes to form alcohols
Regent
Catalyst
Temp
Pressure
Regent is steam which is water in gas form
Catalyst -phosphoric or sulfuric acid
Temp -300c
Pressure 60-70 atm
What does hydration mean in terms of hydration of alkenes
It means addition of water
Halogenoalkane to an alcohol
Regent
Conditions
Mechanism
Nucleophile
Regent -potassium or sodium hydroxide
Conditions -in aqueous solutions heat under reflux
Mechanism -nucelophillic substitution
Nucleophile-OH-
Why when doing the reaction of a halogenoalkane to an alcohol do we need aqueous conditions rather than ethanol conditions
solvent is changed to ethanol an
elimination reaction occurs and an alkene would be produced rather than an alcohol through nucelophillic substitution
Why is aqueous silver nitrate in ethanol used to test the rate of reactivity of halogenoalkanes
When aqueous silver nitrate is added to a halogenoalkane the Halide will combine to form a silver halide precipitate as the halogenoalkane will undergo nuclearphilic substitution with water releasing the free halide which then reacts with silver nitrate to form precipitate ,but the precipitate only forms once the halide has left the halogenoalkane and so the rate of pecipitate formation can test the rate of reactivity as the quicker it’s formed the quicker substitution is and so greater reactivity the rate depends on bond strength between c-X
What are the expected result when a halogenoalkane reacts with silver nitrate in ethanol
Iodoalkanes (C-I) hydrolyze fastest → Yellow precipitate (AgI)
Bromoalkanes (C-Br) hydrolyze moderately → Cream precipitate (AgBr)
Chloroalkanes (C-Cl) hydrolyze slowest → White precipitate (AgCl) highest bond enthalpy
When a halogenoalkane is reacted with silver nitrate why is it done In ethanol
Because halogenoalkane
are insoluble in water as non polar but soluble in ethanol so it allows the halogenoalkane to mix with the silver nitrate
Potassium cyanide to produce nitriles from halogenoalkane
Purpose
Reagent
Conditions
Reactiontype
Nucelophile
Purpose- extend carbon chain
Conditions -ethanol solution heat under reflux
Reaction type nucelophillic substitution
Nucelophile CN-
Ammonia to produce primary amine from a primary halogenoalkane
Reagent
Conditions
Reaction type
Nucleophile
Reagent -excess NH3
Conditions - ethanol solution,heat under pressure
Reaction type - nucelophillic substitution
Nucleophile -NH3
Ethanoic potassium hydroxide to produce alkenes from halogenoalkane
Regent
Conditions
Reaction type
Base
Reagent -KOH ethanoic potassium hydroxide
Conditions-heat under reflux
Reaction type -elimination
Base OH - acts as base removing H+
As ethanol is used eliminations occurs forming alkene if water was used substitution would occur forming alcohol
Polyethene properties and what it’s used for
is used to make plastics bags,
buckets, bottles. It is a flexible, easily moulded,
waterproof, chemical proof, and low density
plastic.
What is polypropene used for
is a stiffer polymer, used in
utensils and containers and fibres in rope
and carpets.
What is a major drawback of incineration?
Some toxins can be released during incineration, such as acidic waste products like HCl from burning halogenated plastics
How do modern incinerators improve the incineration process
They burn more efficiently and remove most toxins and pollutants.
Do incinerators still release greenhouse gases
Yes
How does incineration impact the volume of rubbish?
greatly reduces the volume of rubbish.
Why is recycling polymers beneficial?
saves raw materials, as most polymers are made from crude oil, conserving precious resources.
What are some challenges of recycling polymers?
Sorting is required, which is expensive in terms of energy and manpower.
Polymers can only be recycled into the same type, so careful separation is needed.
What makes thermoplastic polymers suitable for recycling
They can be melted down and reshaped.
How can polymers be used as feedstock for cracking
They can be cracked into smaller molecules to make other chemicals and new polymers, saving raw materials
How are toxic gases like HCl removed from incinerator emissions
Waste gases are scrubbed with a base or carbonate. The base reacts with acidic HCl gas, neutralizing it.
How have chemists improved sustainability in polymer use?
They have developed biodegradable and compostable polymers, which can be made from natural substances like maize and starch
What is incineration
Rubbish is burnt, and the energy produced is used to generate electricity.
What is a carbocation intermediate ,what does its stability depend on , and why is a secondary carbocation the major product over primary
Unstable molecule that exists for a short period of time the stability of the carbonation depends on how many alkyl groups are bonded to it , secondary carbocation will be major product as its more stable as has 2 alkyl groups bonded so exists for longer periods of time so is more likely to form product
How does eletrophillic addition of alkene and halogen molecule acc work to get halogenoalkane
The high electron density of the pi bond repels the electron pair of the covalent bond in the bromine halogen molecule inducing a non permanent dipole ,the electron pair in the pi bond of the alkene are attracted to the positive bromine, and the positive bromine acts as an electrophile , the electron pair forms a covalent bond with this bromine atom ,at the same time the covalent bond between the 2 bromine atoms breaks and the pair of electrons now move to the other bromine atom . We now have a carbocation intermediate and a br atom with an electron pair, the br with electron pair is attracted to carbocation intermediate , it now forms a covalent bond with that carbon and we end up with a halogenoalkane
How does nucelophillic substitution acc occur
The lone pair of electrons on nucelophile is attracted to electron deficient carbon on the halogenoalkane as the c-x bond has a dipole , the nucelophile donates its pair of electrons to this positive carbon to form a covalent bond, however carbon can only have 4 covalent bonds ,so at the same time c-x bond breaks and electrons go to halogen atom (hetroyliytic fission) the halide leaves the halogenoalkane and we have substituted the nucelophile for the halogen
Combustion of alcohols
Alcohols combust with clean flame
C2H50H + 302=2c02+3h20
We add oxygen and get carbon dioxide and water
Reactions of alcohols with sodium
2ROH+2Na→2RONa+H2
Observations -effluscence
Mixture gets hot, soidum dissolves ,white solid product ,this reaction can test for alcohols
Aldehydes description ,functional group,position
Carbonyl compound they contain c=o functional group, the suffix is -al, the c=o functional group is ALWAYS on carbon -1
Ethanal
Propanal
Butanal
Ketones
Carbonyl compounds C=O functional group suffix -one, functional group is never on the end of carbon chain like in aldehydes,
Propanone
Butanone
We don’t need a name for where the c=o bond is if we have a symmetrical molecule when we have 5 carbons or more we need a number.
Carboxylic acids
Have a COOH functional group at end of carbon chain
Suffix- oic
Ethanoic acid
Propanoic acid
Oxidising a primary alcohol in 2 steps
A primary alcohol is oxidised to form a aldehyde and then further oxidised to form a carboxylic acid
C4H5OH+O=CH3CHO+H20
C4H5OH +2O=C2H3COOH +H20
Reaction of primary alcohol to aldehyde
Reagent ,conditions,observations
Partial Oxidation
Reagent -potassium dichromate solution and dilute sulfuric acid
Conditions -use limited dichromate warm gently and distil out aldehyde as it forms
The potassium dichromate is an oxidising agent causing alchohol to oxidise
Observations-orange dichromate ions reduces to green
Full oxidation of primary alcohols to carboxylic acid
Reaction,reagent,conditions,observations
Reaction-primary alcohol to carboxylic acid
Reagent - potassium dichromate solution and dilute sulfuric acid
Conditions-use excess dichromate solution and dilute sulfuric acid
Heat under reflux ,distill of product after reaction has finishes
Orange dichromate reduces to green
Why do we use limited pottasium dichromate for partial oxidation of primary alchohol to an aldehyde but excess for primary alchohol to carboxylic acid
So that the primary alcohol is only oxidised to an aldehyde, and not further to a carboxylic acid. Aldehydes can be further oxidised, so to stop the reaction at the aldehyde, you:
Use limited oxidising agent(the potassium dichromate)
Distil the aldehyde as it forms (removing it from the reaction mixture)
Why do we heat the solution under reflux for full oxidation of primary alchohol to carboxylic acid
You also heat under reflux to prevent any aldehyde from escaping before it can be further oxidised into a carboxylic acid
Oxidation of secondary alcohols to ketone
Reagent
Conditions
Is there further oxidation under these conditions
Reagent - pottasium dichromate solution and dilute sulfuric acid
Heat under reflux
There is no further oxidation of the ketone under these conditions
What’s the sulfuric acid for in alcohol oxidation
The sulfuric acid is used to acidify the potassium dichromate. This is essential because:
The dichromate ion
only acts as a strong oxidising agent in acidic conditions sulfuric acid provides the H⁺ ions needed for the redox reaction to occur.
Can tertiary alcohols be oxidised by potassium dichromate
Not at all, as no hydrogen bonded to a carbon with OH group
How can we distinguish between aldehydes and ketones ,chemical bases for reaction
The fact that aldehydes can be further oxidised to carboxylic acid is the chemical bases for experiments and ketones can’t be further oxidised
Fehilings benadic solution experiment to distinguish aldehydes from ketones
Reagent -fehilings solution containing blue cu 2+ions
Heat gently
Reaction-aldehydes are only oxidised by fehilings solution to carboxylic acid and copper (2) ions are reduced to copper oxide (1)
If aldehyde is present blue copper ions change to brick red precipitate of copper oxide
Ketones wont react at all solution stays the same colour blue
How can i further test for presence of carboxylic acid after fehilings test
Add sodium carbonate , if carboxylic acid is present it will fizz and c02 will be produced
How can i form a chloroalkane from an alchohol
We add HCL OR Pcl5 we would observe misty fumes of hcl can be used to test for alchohol
ROH+PCL5=RCL+POCL3
OR
ROH+HCL=RCH+H20
How would i form a bromoalkane from an alchohol
We can use anything that has a bromine ion like Kbr or NAbr you ad 50 percent concentrated sulfuric acid(not hcl or u get chloroalkane) the acid acts as a catalyst and ensures acid base reaction.
In step one bromine reacts with acid to form halogen halide in step 2 the hydrogen halide react with alcohol to form bromoalkane.
1)2Kbr +H2So4=HBR +K2SO4
2) ROH+HBR=RBR+H20
How can i form a iodoalkane
Use red phosphorus pcl3
3ROH +PCL3=3RI+H3PO3
How can i produce an alkene from an alchohol
Reagents
Conditions
Purpose
Role of reagent
Type of reaction
Regent -concentrated phosphoric acid
Conditions -warm under reflux
Role of reagent -dehydrating agent and catalyst
Type of reaction-acid catalyst elimination
Dehydration -removal of water molecule from a molecule
Purpose -provides a route to form polymers without using monomers derived from oil
Propanol will turn into propene plus a h20
Distillation definition
Separation technique to separate organic product from reacting mixture ,based on different boiling points
Why is gentle heating important during distillation of organic compounds?
To avoid decomposition and to ensure components boil off at the correct temperature.
Why is reflux used
To heat a reaction mixture for a long time without losing volatile substances — vapours condense back into the reaction flask.
Why should you never seal the top of a reflux condenser?
Because pressure build-up from gases could cause the apparatus to explode.
What is the purpose of anti-bumping granules in distillation?
To ensure smooth boiling by forming small bubbles, preventing violent bubbling or sudden boiling (bumping).
Why are electric heaters (or heating mantles) used instead of Bunsen burners in organic reactions?
Because many organic compounds are highly flammable and can catch fire with a naked flame
What’s the function of a condenser in a distillation or reflux setup?
To cool hot vapours so they condense back into liquid form, preventing loss of volatile substances.
In a Liebig condenser, where should the water enter and exit?
Water in: bottom
Water out: top
(This ensures efficient cooling by keeping the condenser full of water.)
What piece of equipment is used to contain the reaction mixture during reflux or distillation?
Round bottom flask
What is the difference between reflux and distillation in terms of purpose?
Reflux: Used to heat a reaction mixture continuously without losing volatile reactants/products.
Distillation: Used to separate and collect components based on boiling points
What is the first step in purifying an organic liquid after distillation
Transfer the distillate (impure product) into a separating funnel.
How do you remove acidic impurities from an organic product?
Wash with sodium hydrogencarbonate solution, shaking and releasing pressure (from CO₂ gas produced
What’s the role of sodium chloride solution in purification?
It helps to separate the organic layer from the aqueous layer more clearly. Can be use along side of sodium hydrocarbonate solution
How do you separate the two layers in a separating funnel?
Allow the layers to separate, run off and discard the aqueous layer, and retain the organic layer.
What is added to the organic layer to dry it?
A drying agent such as anhydrous sodium sulfate.
What is an important property of the drying agent?
It must be insoluble in the organic liquid and not react with it.
After drying the organic layer, what’s the next step?
Carefully decant the liquid and distil again to collect the pure product.
What is the purpose of redistillation after purification?
To collect the fraction that boils at the exact boiling point of the desired pure product
What is the full steps of purifying organic liquid after distillation
Place the distillate in a separating funnel.
Wash with sodium hydrogencarbonate to neutralise any acidic impurities (release CO₂ gas carefully).
Add sodium chloride solution to help separate the layers.
Allow layers to settle, then remove and discard the aqueous layer.
Transfer the organic layer to a clean, dry conical flask.
Add a drying agent (e.g. anhydrous sodium sulfate) to remove water.
Filter or decant the dried liquid.
Redistil to collect the pure product at its boiling point.
Roles of sodium chloride and sodium hydrogen carbonate in purifying a organic liquid
Sodium hydrogencarbonate (NaHCO₃):
Used to neutralise acidic impurities, such as leftover carboxylic acids.
Produces CO₂ gas, so pressure needs to be released while shaking.
Sodium chloride
Helps to separate the organic and aqueous layers more clearly.
Solvent extraction process
Mix organic solvent with oil-water mixture in a separating funnel.
Separate the oil layer.
Distil to separate oil from solvent.
Add anhydrous CaCl₂ to dry the oil.
Decant to remove drying agent.
Measuring Boiling Point (BP):
Can be done using a distillation setup or a boiling tube in an oil bath.
Pressure should be recorded — pressure changes affect BP.
BP is useful for checking purity and identifying a substance.
Many substances have similar BPs, so precise measurement is essential.
For accuracy, measure the temperature of saturated vapour at boiling.
Why is measuring boiling point not always the best method for identifying a substance
Many substances have very similar boiling points, making it hard to distinguish between them.
Impurities can raise or lower the BP, giving inaccurate results.
Changes in pressure (e.g. atmospheric pressure) affect BP readings.
It’s more useful for checking purity than for definitive identification.
What are molecules with four Dif groups known as
Asymmetrical/chiral
