Organic Chemistry - Topic 6 Flashcards
What is a hydrocarbon
a compound consisting of hydrogen and carbon only
What is a saturated compound
Contain single carbon-carbon bonds only
What is an unsaturated compound
A compound that Contains carbon to carbon double bonds
What is the molecular formula
The formula which shows the actual number of each type of atom
What is the empirical formula
The formula that shows the simplest whole number ratio of atoms of each element in the compound
What is the general formula
algebraic formula for a homologous series e.g. CnH2n
What does the structural formula show
the arrangement of atoms in a molecule e.g butane: CH3CH2CH2CH3 or CH3(CH2)2CH3,
What does the displayed formula show
All the covalent bonds present in a molecule
What is the bond angle and shape around the carbon atom in a saturated hydrocarbon
Shape: tetrahedral
Bond angle: 109.5
What is the homologous series
families of organic compounds with the same functional
group and same general formula
What is a functional group
An atom or group of atoms which when present in different molecules
causes them to have similar chemical properties
Functional groups of
alkanes,
alkenes,
alcohols,
halogenoalkanes,
aldehydes,
ketones,
carboxylic acids
esters
Alkanes: c-c
Alkenes: c=c
Alcohol:C-OH
Halogenoalkane: c - halogen
Aldehyde: O =C- H
Ketone: C = O
Carboxylic acid: O=C-OH
Ester: O = C - O
What are the prefix/suffix of ,
aldehydes,
ketones,
esters
Carboxylic acid
Alcohol
Alcohol: prefix: hydroxy suffix: ol
Aldehyde: suffix: al prefix: formyl
Ketone: suffix: one prefix: oxo
Esters: suffix: yl - oate e.g methylethanoate
What is the order of priority for the different homologous series except esters (highest first)
Carboxylic acids >aldehydes>ketones>alcohols>alkenes>halogenoalkanes
Rules for naming alcohols
1) alcohols have a high priority than halogenoalkanes and alkene so they usually start on the lowest carbon when with a halogenoalkane and alkene
2) if there is more than one alcohol then you add an e on the stem of the name e.g Ethane-1,2-diol NOT ethan - 1,2 - diol
3) if the compound has another functional group in addition to the OH that is higher in priority than the OH can be named with the prefix hydroxy and the higher priority keeps it’s suffix e.g 2-hydroxypropanoic acid
4) if there is more than one OH we use diol triol ect…
Rules of naming aldehydes
1) an aldehydes name ends in al
2) if there are two aldehydes then the di is put before the al and an e is added onto the stem e.g pentanEDIal
Rules of naming ketones
1) Ketones end in -one
2) When ketones have 5C’s or more in a chain then it needs a number to show the position of the
double bond. E.g. pentan-2-one
3) two ketone groups then di is put before – one and e is added onto the stem
Rules of naming carboxylic acids
1) always ends in oic acid
2) numbering starts at the carboxylic acid as it’s the highest priority
3) if there is a carboxylic acid at either end it’s called a dioic acid and the e is added into the stem
Rules of naming carboxylic acids
1) always ends in oic acid
2) numbering starts at the carboxylic acid as it’s the highest priority
3) if there is a carboxylic acid at either end it’s called a dioic acid and the e is added into the stem
What are structural isomers
same molecular formula different structures
What are chain isomers
Compounds with the same molecular formula but different structures of the carbon skeleton
What are position isomers
Compounds with the same molecular formula but different structures due to different positions of the same functional group on the same carbon skeleton
What are stereoisomers
Isomers that have the same structural formulae but have a different spatial arrangement of atoms
What causes E-Z isomerism to arise
1) When there is restricted rotation around the C=C double bond.
2) When there are two different groups/atoms attached both ends of the double bond
What functional group can posses E-Z isomerism
Alkenes
Why can’t alkanes posses E-Z isomerism
As there single carbon to carbon bonds can easily rotate
Rules for naming E-Z isomerism
1) if the priority group is on the same side then it is Z isomerism (Zame Zide)
2) if the priority group is in different side the it is E isomerism (Epposite side)
THE GROUPS DONT HAVE TO BE THE SAME ON EITHER SIDE IF THE DOUBLE BOND
What is the priority group in isomerism
The atom with the highest atomic number
Rules for naming cis trans isomers
1) Look at the group that is the SAME on both sides of the double bond
2) if the group is on the same side then it is a cis isomer
3) if the group is on different sides then it is a trans
Process of fractional distillation of crude oil
1) the crude oil is vaporised in a furnace
2) the crude oils vapours move up the fractioning column, the column is hotter at the bottom and becomes cooler at the top
3) as each alkane moves up the column at some point it will reach a temp which is cooler than its bp causing it to condense back to liquid and pass out of the column,
4) Boiling point depends on size of molecules, The larger the molecule the larger the London forces
5) the alkanes with shorter carbon chains condense near the top of the column due to their low bp whilst the longer chain alkanes condense at the bottom due to their high bp and alkanes with very long chains form a thick liquid called bitumen which is collected from the very bottom
What is cracking
conversion of large hydrocarbons to smaller molecules by breakage of C-C bonds
Equation for cracking
Large alkanes —> smaller alkanes+ alkenes + (hydrogen)
Both sides have to equal number of carbons and hydrogens
What is petroleum
A mixture consisting mainly of alkane hydrocarbons
What are petroleum fractions
A mixture of hydrocarbons with a similar chain length and boiling point range
What bonds are broken in fractional distillation and cracking
Fractional distillation: Weak London Forces
Cracking: Strong covalent bonds
Economic reasons for catalytic cracking
1) The petroleum fractions with shorter C chains are in more demand than larger fractions.
2) To make use of excess larger hydrocarbons and to supply and demand for shorter ones, longer hydrocarbons are cracked.
3) The products of cracking are more useful and valuable than the starting products. The smaller alkanes are used for motor fuels which burn more efficiently
What is catalytic cracking
a chemical process involving the splitting of strong covalent bonds so requires high temperatures
What is reforming
Turning straight chain alkanes into branched and cyclic alkanes and Aromatic hydrocarbons
Problems of the pollutants
- Carbon monoxide - is toxic to humans as CO can from a strong bond with haemoglobin in red blood cells. This is a stronger bond than that made with oxygen and so it prevents the oxygen attaching to the haemoglobin, causing death and starvation of oxygen.
- Nitrogen oxides - NO is toxic and can form smog , NO2 is toxic and acidic and forms acid rain
- Carbon dioxide - Contributes towards global warming
- Unburnt hydrocarbons - Contributes towards formation of smog
- Soot/particulates - Global dimming and respiratory problems
- sulfur dioxide - acidic and will dissolve in atmospheric water and can produce acid rain
How does nitrogen oxides form
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
N2 + O2 —> 2NO N2 + 2O2 —> 2NO2
How do catalytic converters help reduce the environmental problems of pollutants
They remove CO, NOx and unburned hydrocarbons from the exhaust gases, turning them into ‘harmless’ CO2, N2 and H2O.
2 CO + 2 NO —> 2 CO2 + N2
C8H18 + 25 NO —> 8 CO2 + 12½ N2
Describe and explain the structure of catalytic convertors
Converters have a ceramic honeycomb coated with a thin layer of catalyst metals platinum, palladium, rhodium – to give a large surface area.
Examples of renewable plant fuels (biofuels)
- Alcohols
- Biodiesel
How are biodiesel made
by reacting vegetable oils with a mixture of alkali and methanol
How are alcohols made
from the fermentation of sugars from plants
Advantages of biofuels
- Reduction of use of fossil fuels which are finite resources biofuels are renewable
- Use of biodiesel is more carbon-neutral
- Allows fossil fuels to be used as a feedstock for organic compounds
- No risk of large scale pollution from exploitation of fossil fuels
Disadvantages of biofuels
- Less food crops may be grown
- Land not used to grow food crops
- Rain forests have to be cut down to provide land
- Shortage of fertile soils
What is a free radical
A Free Radical is a reactive species
which possess an unpaired electron
What happens in heterolytic fission
One atom gets both electrons
Conditions of free radical substitution
UV light
Steps of free radical substitution
1) Initiation
2) Propagation
3) Termination
What happens in homolytic fission
Each atom gets one electron from the covalent bond
Free radical mechanism of the reaction of alkanes with chlorine
Initiation
Cl2 —> 2Cl.
Uv light supplies energy to break the Cl-Cl bond but UV light does not have enough energy to break C-H bond
Propagation
CH4 + Cl. —-> HCl + .CH3
.CH3 + Cl2 —-> CH3Cl + Cl.
Chlorine free radicals are very reactive so remove the H from methane leaving methyl free radicals
As the Cl free radical is regenerated it can react with more alkane molecules in a chain reaction
Termination
.CH3 + Cl. —> CH3Cl
.CH3 + .CH3 —> CH3CH3
Cl. + Cl. —> Cl2
WRITE USING STRUCTURAL FORMULA
Overall reaction for reaction of alkanes with chlorine
CH4 + Cl2 —> CH3Cl + HCl
What can promote further substitution
Excess halogens
E.g Excess Cl2 will trigger further substitution and could produce CH2Cl2, CHCl3 and CCl4
Propagation
CH3CL + CL. —> HCl + .CH2Cl
.CH2Cl + Cl2 —> CH2Cl2 + Cl.
Initiation
CH3Cl + Cl2 —> CH2Cl2 + HCl
CH2Cl2 + Cl2 –> CHCl3 + HCl
CHCl3 + Cl2 —> CCl4 + HCl
Practice write the overall equation for these following reactions
1) formation of CCl4 from CH4 + Cl
2) formation of CFCl3 from CH3F + Cl
1) CH4 + 4 Cl2 —> CCl4 + 4 HCl
2) CH3F + 3 Cl2 —>CFCl3 + 3 HCl
How are pi bonds formed
sideways overlap of two p orbitals on each carbon atom forming a π-bond above and
below the plane of molecule
Characteristics of pi bond
- they are exposed and have high electron density so therefore are vulnerable to be attacked by species which ‘like’ electrons: which are called electrophiles
- they are weaker between sigma bonds
- there is restricted rotation about a pi bond
Characteristics of sigma bond
- rotation can occur
- high levels of attraction between nuclei and shared electrons so are very strong
What are addition reactions
reaction where two molecules react
together to produce one
What are addition reactions
reaction where two molecules react
together to produce one
Reaction of alkenes with hydrogen
1) what is produced
2) what is the reagent
3) conditions
4) type of reaction
Produced: Alkane
Reagent: hydrogen
Conditions: Nickel catalyst
Type of reaction: Addition
Reaction of alkenes with halogen
1) what is produced
2) what is the reagent
3) what are the conditions
4) what is the mechanism
Produced: dihalogenalkane
Reagent: Hydrogen halogen
Conditions: room temperature
Mechanism: Electrophilic addition
Reaction of alkenes with hydrogen halogen
1) what is produced
2) what is the reagent
3) what are the conditions
4) what is the mechanism
Produced: halogenoalkane
Reagent: Hydrogen halogen
Conditions: room temperature
Mechanism: Electrophilic addition
why is a carboncation intermediate stable
carbocation intermediate is stable because the methyl groups on either side of the positive carbon are electron releasing and reduce the charge on the ion which stabilises it.
Why is the secondary carbocation more stable and more likely to form a major product than the primary carbocation
As there are more alkyl groups attached to the secondary carbocation so has a stronger inductive effect,this is because the greater number of alkyl groups means that more electrons are pushed towards the positive charge, this provides it better stability as the positive charge is more reduced and because of this extra stability the secondary cation is more likely to form, resulting in it to form a major product
Order of stability for carbocation
1) Tertiary (most stable)
2) Secondary
3) primary (least stable)
Reaction of potassium maganate with alkenes
(TEST FOR DOUBLE BONDS OR ALKENES)
1) observation
2) what is the reagent
3) what are the conditions
4) type of reaction
1) purple colour of MnO4- ion will decolorisation to colourless
2) KMnO4 in acidified solution
3) Room temperature
4) Oxidation
Reaction of bromine water with alkenes
1) what is the observations
2) what is the reagent
3) what are the conditions
4) what is the mechanism
1) orange colour of bromine water will decolorisation to colourless
2) bromine dissolved in water (bromine water)
3) room temperature
4) Addition
Hydration of alkenes
1) conditions
2) product
1) temp: 300 to 600 degrees Celsius pressure: 70atm catalyst: concentrated H3PO4
2) alcohol
Formation of addition polymers (poly(alkenes))
1) reactant
2) type of reaction
1) alkenes
2) addition polymerisation
Why are poly(alkenes) unreactive
Due to the strong C-C and C-H bonds
What is poly(ethene) used for
- to make plastic bags and bottles
—
What is poly(propene) used for
- utensils
- containers
- fibres in rope and carpets
Methods of disposing waste polymers
- incineration
- recycling
- feedstock for cracking
What occurs during incineration
- rubbish is is burnt and energy is produced to generate electricity
- Some toxins can be released e.g HCl and greenhouse gasses can be emitted
Advantages of recycling polymers
- Saves raw materials
- Thermoplastic polymers can be melted down and reshaped.
Disadvantages of recycling polymers
- Polymers need collecting/ sorting- expensive process in terms of energy and manpower.
- Polymers can only be recycled into the same type – so careful separation needs to be done.
What is feedstock for cracking and what is the advantage
- This is when Polymers can be cracked into small molecules which can be used to make other chemicals and new polymers
- Saves raw materials
How do chemist remove waste products that are emitted by incarceration
By reacting the acidic HCL gas with a base or carbonate, neutralising it
What are primary secondary and tertiary halogenoalkane
Primary - One carbon attached to the
carbon atom adjoining the halogen
Secondary - Two carbons attached to the
carbon atom adjoining the halogen
Tertiary - Three carbons attached to the
carbon atom adjoining the halogen
What do nucleophile always have
A lone pair of electrons and act as electron pair donors
Define hydrolysis
the splitting of a molecule by a reaction with water
What is a Nucleophile
electron pair donator
(They always have a lone pair of electrons to donate)
What does the rate of substitution reactions depend on
The strength of the C-X bond as the weaker the bond the easier it is to break so the faster the reaction
What role does water play as a nucleophile
Water is a poor nucleophile but can react slowly with halogenoalkanes in a substitution reaction
How can you compare the rate of hydrolysis of halogenoalkanes
Add aqueous silver nitrate to the halogenoalkane, the quicker the silver halide precipitate forms the faster the reaction and more reactive the halogenoalkane
Order of rate of reaction of silver iodide, chloride and bromide
Fastest: silver iodide (yellow ppt)
Silver bromide (creamy coloured ppt)
Slowest: silver chloride (white ppt)
Why does iodoalkane forms a ppt with the silver nitrate the quickest compared to other halogenoalkanes
The iodoalkane forms a precipitate with the silver nitrate first as the C-I bond is weakest and so it hydrolyses the quickest
What are the conditions, reagents, mechanism and reaction for nucleophilic substitution with aqueous hydroxide ions
Reaction: halogenoalkane—-> alcohol
Reagent : potassium (or sodium) hydroxide (OH-)
Mechanism: Nucleophilic substitution (SN2)
Conditions: in aqueous solutions, heat under reflux
Draw the SN2 reaction between hydroxide ions and halogenoalkanes (bromopropane)
Pg 20 in Chemrevise
What happens if the solvent is changed from water to ethanol in the reactions of halogenoalkanes with aqueous hydroxide ions
An elimination reaction occurs instead of substitution
Why is OH- a stronger nucleophile than water
OH- has a full negative charge making it more strongly attracted to the carbocation
How do tertiary halogenoalkanes react with hydroxide ions
Through an SN1 reaction
Why do tertiary halogenoalkanes undergo an SN1 mechanisms with aqueous hydroxide ions rather than SN2
- As the tertiary carbocation is stabilised by the methyl groups surrounding the carbocation as the methyl groups shift their electrons towards the carbocation
- the bulky methyl (the number and the position of methyl groups) prevent the hydroxide ions from attacking the halogenoalkane in the same way as SN2
Why do primary halogenoalkane do not undergo SN1 reactions
As they would only form a unstable primary carbocation
Reagent, conditions, mechanism and reaction of nucleophilic substitution with ammonia and halogenalkane
Reagent: ammonia in dissolved ethanol
Conditions: heating under pressure in a sealed tube
Mechanism: nucleophilic substitution
Reaction: halogenalkane —-> amine
Draw the reaction of bromopropane with ammonia
Pg 21
Conditions, reagent, reaction and mechanism in the elimination with alcoholic (ethanol) hydroxide ions
Reaction: halogenoalkane —> alkene
Reagent: potassium (or sodium) hydroxide
Conditions: in ethanol, heat
Mechanism: elimination
Uses of halogenoalkanes
- refrigerenants
- fire retardants
- pesticides
- chloroalkanes and chlorofluoralkanes can be used as solvents
Bond angles in alcohols
- all H-C-H and C-C-O are 109.5 - because there are 4 bond pairs of electrons repelling to a position of minimum repulsion
- H-O-C bond is 104.5 - because there are 2 bond pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion (lone pairs repelling more than bind pairs so the bond angle is reduced)
What are the three types of alcohols
- Primary alcohol- are alcohols where 1 carbon is attached to the carbon adjoining the oxygen
- Secondary alcohols - alcohols where 2 carbon are attached to the carbon adjoining the oxygen
- Tertiary alcohols - alcohols where 3 carbons are attached to the carbon adjoining the oxygen
Test for alcohols
- React the alcohol with sodium
- reaction with PCl5
Observations with the reaction with sodium and alcohols
Observations:
- effervescence
- mixture gets hot
- sodium dissolves
- white solid is produced
Observations with reaction with PCl5
Misty fumes of HCl
What is the reagent to form halogenoalkanes from an alcohol
Hydrogen halide
What is needed to make hydrogen bromide
Potassium bromide and 50% concentrated
H2SO4
Equation for the reaction of phosphorus (III) iodide with ethanol
PI3 + 3 CH3CH2OH —> 3CH3CH2I + H3PO3
Equation for the reaction of phosphorus (V) chloride with ethanol
CH3CH2OH + PCl5 —-> CH3CH2Cl + POCl3 + HCl
Oxidation reaction with primary alcohols to aldehydes conditions, reagent, observation
Conditions: warm gently and distil out aldehydes as it forms
Reagent : potassium dichromate
Observations: orange dichromate ion (Cr2O72-) reduces to the green Cr 3+ ion
How to represent the oxidising agent in an equation
[O]
What is a dehydration reaction
removal of a water molecule from a molecule
Dehydration reaction of alcohol reaction, reagent, conditions, mechanism, role of reagent
Reaction: Alcohol —> Alkene
Reagents: Concentrated phosphoric acid
Conditions: warm (under reflux)
Role of reagent: dehydrating agent/catalyst
Type of reaction: acid catalysed elimination
Why can’t tertiary alcohols be oxidised by potassium dichromate
because there is no hydrogen
atom bonded to the carbon with the OH group
Distillation reaction: of primary alcohol to aldehydes
Reaction, reagent, conditions and observations
Reaction: primary alcohol aldehyde
Reagent: potassium dichromate (VI) solution and
dilute sulfuric acid.
Conditions: use a limited amount of dichromate
and warm gently and distil out the aldehyde as it
forms [This prevents further oxidation to the
carboxylic acid]
CH3CH2CH2OH + [O] —-> CH3CH2CHO + H2O
Observation
Orange dichromate solution changes to green
colour of Cr3+ ions
Draw distillation equipment
Pg 26 Chemrevise
Draw distillation equipment
Pg 26 Chemrevise
Draw reflux equipment
Pg 26 Chemrevise
What does the condenser do in reflux
prevents organic vapours from escaping
by condensing them back to liquids
What is reflux
heating organic reaction mixtures for long
periods
What is distillation
Separating an organic product from its reacting mixture
Why should you never seal the end of a condenser
As the build up of gas pressure could cause the apparatus to explode. This is true of any apparatus where volatile liquids are heated
Reflux reaction: primary alcohols to carboxylic acid
Conditions
Reaction
Reagent
Observations
Reaction: primary alcohol —-> carboxylic acid
Reagent: potassium dichromate(VI) solution and dilute
sulfuric acid
Conditions: use an excess of dichromate, and heat
under reflux: (distil off product after the reaction
has finished using distillation set up)
CH3CH2CH2OH + 2[O] —-> CH3CH2CO2H + H2O
Observation
Orange dichromate solution changes to green colour of
Cr3+
Why are anti bumping granules added in the flask of both distillation and reflux reactions
prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles
How to purify an organic liquid
1) put the distillate of impure product into a separating funnel
2) wash product by adding either - sodium hydrogencarbonate solution , shaking and releasing the pressure from CO2 produced or Saturated sodium chloride solution
3) Allow the layers to separate in the funnel, and then run and discard the aqueous layer.
4) Run the organic layer into a clean, dry conical flask and add three spatula loads of drying agent (anhydrous sodium sulfate) to dry the organic liquid.
5) Carefully decant the liquid into the distillation flask
6) Distil to collect pure product
What does sodium hydrocarbonate and sodium chloride do during the purification of an organic liquid
Sodium hydrocarbonate - will neutralise any remaining reactant acid
Sodium chloride - will help separate the
organic layer from the aqueous layer
What conditions do the drying agents need to have during the purification of an organic liquid
•be insoluble in the organic liquid
• not react with the organic liquid
How to conduct a solvent extraction
1) Mix organic solvent and oil-water mixture in a separating funnel then separate the oil layer.
2) Distil to separate oil from organic solvent
3) Add anhydrous CaCl2 to dry oil
4) Decant to remove CaCl2
Draw a separating funnel
Pg 28 Chemrevise
How can you measure the purity of a substance
By measuring the boiling point
This can be done in a distillation set up or by simply boiling a tube of the sample in an
heating oil bath
Why isn’t measuring the boiling point the most accurate method of identifying a substance
several substances may have the same boiling
Does primary and tertiary halogenoalkane undergo an elimination or substitution reaction
Primary - substitution
Tertiary - elimination
