Organic Chemistry I Flashcards
What is a Hydrocarbon?
A compound that consists of hydrogen and carbon only
Define Saturated
Contains single carbon-carbon bonds only
Define Unsaturated
Contains a C=C double bond
Test for unsaturated compounds
Add Bromine Water which turns the solution from orange to colourless
Define Molecular Formula
shows the actual number of each type of atom
Define Empirical Formula
shows the simplest whole number ratio of atoms of each element in the compound
Define General Formula
algebraic formulae for a homologous series
Define Structured Formula
the minimal detail that shows the arrangement of atoms in a molecule
Define Displayed Formula
show all the covalent bonds present in a molecule
Define Skeletal formula
shows the simplified organic formula, shown by removing hydrogen atoms from alkyl chains, leaving just the carbon skeleton and functional group
Define Homologous Series
Families of organic compounds with the same functional group and general formula
Features of a Homologous series
- They show a gradual change in physical properties
- Each member differs by CH2 from the last
- same chemical properties
General Formula and suffix of Alkanes
General Formula : CnH2n+2
Suffix: -ane
Suffix of Alkanes (branched)
alkyl-
Functional group and prefix of Alkenes
-ene
C=C
Functional group and suffix of Halogenoalkanes
-ane
Functional Group : C-X
Prefix : Fluor-, Chloro- , Bromo - , Iodo-
Functional group and prefix of Alcohols
CnH2n+1OH
Functional group : -OH
Suffix : -ol
Functional group and suffix of Aldehydes
(insert fg)
Suffix: -al
Functional group and suffix Ketones
(insert fg)
suffix: -one
Carboxylic acids
(insert fg)
suffix: -oic acid
State the stem names for the number of carbons 1-10.
Meth Eth- Prop- But- Pent- Hex- Hept- Oct - Non- Dec-
What are the IUPAC rules
Name the stem name (no.of carbons) Name ending - Functional group Complex Molecules Longest chain with functional group Side chain - prefix Carbon numbered to give functional group lowest number
What are the type of reactions?
Polymerisation Elimination Hydrolysis Addition Substitution Reduction Oxidation
What is Polymerisation?
Joining smaller monomers together to form a very long chain
What is Elimination?
Some atoms break away from a larger molecule
What is Hydrolysis?
Splitting a molecule into 2 using OH- or H+ from an H2O molecule
What is Addition?
Joining molecules together to form longer ones
What is Substitution?
Replacing one atom with another on a molecule
What is Reduction?
When a species gains electrons in a reaction
What is Oxidation?
When a species loses electrons in a reaction
What do chemical mechanisms show?
The movement of electrons during a chemical reaction
What does the curly arrow indicate?
the movement of a pair of electrons
they always start from an area with electrons (lone pair or double bond)
They end where you are moving the electrons to or the formation of a new bond
What are the type of mechanisms?
Radical substitution
Electrophilic addition
Nucleophilic substitution
Define Structural Isomers
same molecular formula different structures
chain
Positional functional
Define Stereoisomers
They have the same structural formula but have a different spatial arrangement of atoms
Why do E-Z Isomers exist?
Due to restricted rotation about c=c bond
Which series can exhibit E-Z Isomerism?
Alkenes
When do E-Z isomerism arise?
There is a restricted rotation around c=c double bond
There are two different groups/atoms attached to both ends of the double carbon
What is classed as a priority group?
The atom with the bigger atomic number is classed as the priority group
When is a stereoisomer labelled Z
If the priority groups on the same side of the double bond
When is a stereoisomer labelled E
If the priority atom is not the opposite side of the double bond
What is the general formula for alkanes?
CnH2n+2
What are alkanes and cycloalkanes ?
saturated hydrocarbons
What are alkanes used as?
Alkanes are used as fuels
What are the ways in which alkane fuels can be obtained?
fractional distillation
Cracking
Reforming of crude oils
Which mixture is mainly consisting of alkane hydrocarbon?
Petroleum
What is a petroleum fraction?
mixture of hydrocarbons with similar chain length and boiling point range
Describe the process of fractional distillation.
oil is pre-heated then passed into a column
The fractions condense at different heights
The temperature of the columns decrease upwards
The separation depends on the boiling point
Boiling point depends on size of molecule
The larger the molecule the larger the London forces
Similar molecules condense together
And bigger molecules condense at the bottom at higher temperatures
What does the physical process of fractional distillation involve?
The splitting of weak London forces between molecules
What is cracking?
conversion of large hydrocarbons to smaller molecules by breakage of c-c bonds
What does the chemical process of cracking involve?
The splitting of strong covalent bonds so requires high temperatures
Outline reasons for catalytic cracking (3)
The petroleum fractions with shorter C chain are more in demand than larger fractions
To make use of excess larger hydrocarbons and to supply demand for shorter ones, longer ones are creaked
Products of cracking are more useful and valuable than the starting material. The smaller the alkane are used for motor fuels which burn more efficiently
What do higher Mr alkanes crack into ?
smaller Mr alkanes + Alkenes + hydrogen
What is reforming ?
The processing of straight-chain hydrocarbons into branched-chain alkanes and cyclic hydrocarbons for efficient combustion.
What are reformed products used for?
making motor fuels
What do fuels do?
release heat energy when burnt
Combustion of alkanes
alkanes easily burn in the presence of oxygen.
This combustion of alkanes is highly exothermic
Compare incomplete combustion and complete
incomplete combustion produces less energy per mole than. Complete combustion
Complete Combustion
In excess oxygen alkanes will burn with complete combustion
The products are CO2 + H2O
Incomplete Combustion
If there is a limited amount of oxygen then incomplete combustion occurs.
Produces CO and/or C
Why is carbon monoxide highly toxic?
To humans as CO can form a strong bond with hemoglobin in the RBC.
This is stronger bond than that made with oxygen and so prevents the oxygen attaching to the haem
Odourless gas - can cause death if it builds up in an enclosed space due to faulty heating appliances
What do Carbon (soot) lead to?
Causes global dimming reflection of the sun’s light
Where are sulfur containing impurities found?
In the petroleum fraction which produces SO2 when they are burned
Coal
High in sulfur content, and large amounts of sulfur dioxides are emitted from power station
What causes acid rain?
SO2 acidic and will dissolve in atmospheric water
Where do NO2 form from?
The reactions between N2 + 02 inside car engine
What are the environmental consequences of unburnt hydrocarbons?
contributes towards formation of smog
What do catalytic converters do?
These remove CO, NOx and unburnt hydrocarbons from exhaust gases, turning them into harmless CO2 N2 H20
What do converters have in them to give a large surface area?
they have a ceremony honeycomb coated with thin layers of catalyst metals: platinum, palladium, rhodium
Give 2 main examples of renewable plant based fuels
Alcohol and Biodiesel
How is alcohol produced?
ethanol can be produced from the fermentation of sugars from plants
How is Biodiesels produced?
By reacting vegetables oils with a mixture of alkali and methanol
Advantages of using Biofuels
reduction of use of fossil fuels which are finite resources
Renewable
Allow fossil fuels to be used as feedstock for organic compounds
No. risk of large scale pollution from exploitation of fossil fuels
Disadvantages of using Biofuels
less food crops may be grown
Land not used to grow food groups
Rain Forests have to be cut down to provide land
Shortage of fertile soils
What is a radical?
a species with an unpaired electron and is represented in mechanisms by a single dot
What is a radical formed by?
it is formed by homolytic fission of a covalent bond and results
Reaction of alkanes with halogens is known as?
Free radical substitution
What are the two ways in which covalent bonds are broken?
Homolytic Fission + Heterolytic Fission
What happens in a homolytic fission?
Each atom gets one electron from the covalent bond
What type of arrow is used to show the movement of one arrow?
one headed arrow
What happens in a heterolytic fission?
One atom gets both electrons
What does a two headed arrow show?
movement of a pair of electrons
Heterolytic Fission produces…
IONS
Reactions of alkanes with bromine / chlorine occurs in
uv light
Name the steps of free radical substitution
Initiation
Propagation
Termination
In general why do alkanes not react with many reagents
As the c-c bond and the c-h bonds are relatively strong
In initiation, what role does uv light have?
supplies the energy to break the Cl-Cl bond. It is broken in preference to the others as it is the weakest.
Why is the C-H bond not broken?
UV light does not have enough energy to break the C-H bond
Through which process has the bond broken in initiation and what does it form?
Homolytic Fission it forms Free Radicals
Write the equation for chlorine and methane in initiation.
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Write the equation for chlorine and methane in Propagation
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When the halogen free radical is formed in propagation what happens?
The halogen free radicals are very reactive and remove an H from the alkane leaving a methyl free radical
What does the methyl free radical react with in propagation
The methyl free radical reacts with a Cl2 molecule to produce the main product and another Cl free radical
What do all Propagation steps consist of?
a free radical in the reactants and in the products.
What happens when the halogen free radical is regenerated ?
As the halogen free radical is regenerated, it can react with several more alkane molecules in a chain reaction
When is the process terminated?
Collision of two free radicals does not generate further free radicals: the chain is terminated.
Write out the Termination equations for chlorine and methane.
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What is the general formula for alkenes?
CnH2n
Alkenes are ….
Saturated Hydrocarbons
Which bonds do the C=C bonds consist of?
C=C double covalent bond consists of one sigma (σ) bond and one pi (π) bond.
π bonds are … so….
They are exposed and have high electron density
They are therefore vulnerable to attack by electrophiles.
Formation of σ bond
One sp2 orbital from each carbon overlap to form a single C-C sigma σ bond
Rotation can occur around a sigma bond
Formation of π bond
The π bond is formed by sideways overlap of two p orbitals on each carbon atom forming a π-bond above and below the plane of molecule.
Restricted rotation about π bond
What is meant by the term electrophile
An electron pair acceptor
How many addition reactions of alkenes should you know ?
5
Alkenes -> Alkane
Hydrogenation
Reagent: hydrogen
Conditions: Nickel Catalyst
Type of reaction: Addition
How is hydrogenation used in industry?
Manufacture of margarine by catalytic hydrogenation of unsaturated vegetable oils is expected.
Draw ethene to ethane
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Alkenes to di-halogenoalkanes
Halogenation
Reagent: Bromine (dissolved in organic solvent)
Conditions: Room temperature (not in UV light)
Mechanism: Electrophilic Addition
Type of reagent: Electrophile, Br+
Type of Bond Fission: Heterolytic
Draw ethene to 1,2 dibromoethane
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What happens as the Br 2 molecule approaches the alkene
The pi bond electrons repel the electron pair in the Br-Br bond. This INDUCES a DIPOLE. Br2 becomes polar and ELECTROPHILIC (Brδ+).
What is seen when an intermediate is formed?
The INTERMEDIATE formed, which has a positive charge on a carbon atom is called a CARBOCATION
alkene -> halogenoalkanes
Addition of hydrogen halides Reagent: HCl or HBr Conditions: Room temperature Mechanism: Electrophilic Addition Type of reagent: Electrophile, H+ Type of Bond Fission: Heterolytic
Why is HBr a polar molecule?
HBr is a polar molecule because Br is more electronegative than H. The H δ + is attracted to the electron-rich pi bond.
Draw the mechanism for But-2-ene to 2-bromobutane
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If the alkene is unsymmetrical, addition of HBr/HCl can lead to …
isomeric products
In electrophilic addition the major product is formed via
The more stable carbocation intermediate
How do we determine which carbocation is more stable?
A carbocation intermediate is more 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.
What is the order of stability for carbocations
tertiary > secondary >primary
Alkene to Diol
Reagent: KMnO4 in an acidified solution Conditions: Room temperature
Type of reaction: Oxidation
Observation: purple colour of MnO4- ion will decolourise to colourless
Draw out the mechanism for propene to Propan-1,2-diol
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Which test can test for the alkene functional group and why?
Oxidation of KMnO4 at room temperature as it would not change colour with alkanes but for alkenes it would go from purple to colourless
Addition of bromine water with alkenes orange to colourless
Bromine water with alkenes
Reagent: Bromine dissolved in water Conditions: Room temperature Type of reaction: Addition
Observation: Orange colour of bromine water will decolourise to colourless
Draw the mechanism for Bromine water with ethene
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Hydration of alkenes to form alcohols
High temperature 300 to 600°C
High pressure 70 atm
Catalyst of concentrated H3PO4
Equation for hydration of ethene
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How do alkenes form polymers?
Addition Polymerisation
Draw a general equation for addition polymerisation.
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Why are poly(alkenes) unreactive?
Poly(alkenes) like alkanes are unreactive due to the strong C-C and C-H bonds.
Poly(ethene) is used to make
used to make plastic bags, buckets, bottles. It is a flexible, easily moulded, waterproof, chemical proof, and low density plastic.
Poly(propene) is a
is a stiffer polymer, used in utensils and containers and fibres in rope and carpets.
What are the methods of disposal of waste Polymers
Incineration
Recycling
Feedstock for cracking
What are the stages of recycling?
Sorting
Processing
What happens when an incinerator takes in polymer wastes?
It takes in polymer waste and converts it into heat energy that can be used to heat homes and factories or generate electricity.
How do chemists limit the problems caused by polymer disposal by?
developing biodegradable polymers
removing toxic waste gases caused by incineration of plastics
How are halogenoalkanes classified?
As primary, secondary or tertiary depending on the number of carbon atoms attached to the C-X functional group.
What makes halogenoalkanes reactive?
Hydrogen and Carbon atoms have similar electronegativities, so their bonds are almost non-polar
Halogen atoms have a higher electronegativity than that of carbon.
(EN of halogens decreases down the group)
Which reactions do halogenoalkanes undergo?
Substitution or Elimination
What is meant by the term nucleophile?
A species that a donates a lone pair of electrons to form a covalent bond with an electron-deficient atom
In a Nucleophilic Substitution a curly arrow always starts at…
the centre of a bond or from the lone pair
When a halogenoalkane is added to water ….
A reaction begins but it may take a period of time to complete
The reactions that occur between water and halogenoalkanes can be represented by …
ROH-alcohol (no colour change seen)
RX + H2O -> ROH + HX
RX + H20 -> ROH + H+ + X-
What type of nucleophile is water?
A poor nucleophile but can react slowly with halogenoalkanes in a substitution reaction
What is used to compare the rate of hydrolysis reactions in halogenoalkanes
using aqueous silver nitrate in ethanol
How is the rate of formation of the precipitate used to compare the reactivity of halogenoalkanes ?
Aqueous silver nitrate is added to halogenoalkanes and the halides combines with the silver ions to form a silver halide precipitate - this only forms when the halides ion has left the halogenoalkane
The quicker the precipitate is formed in hydrolysis of halogenoalkanes…
the faster the substitution reactions and the more reactive the halogenoalkanes
The rate of substitution depends on …
the strength of the C-X bond, The weaker the bond the easier it is to break and the faster the reaction
In terms of bond enthalpy what is the trend in reactivity of chloro- , bromo-, ido- alkanes.
iodo > bromo > chloro
Which bonds hydrolysed the quickest in hydrolysis of halogenoalkanes and its colour ?
AgI - yellow (fastest to hydrolyse weak bond)
AgBr - cream
AgCl - white
Compare the relative rates of hydrolysis of the different classification of halogenoalkanes
Tertiary ( fastest to hydrolyse)
Secondary
Primary
Halogenoalkane to alcohol (2)
hydrolysis in aqueous silver nitrate in ethanol ( water acts as a nucleophile)
Aqueous potassium/Sodium hydroxide to produce alcohols heated under reflux ( hydroxide ions acts as nucleophiles)- heterolytic
Write an equation for the 1-chloropropane into propan-1-ol
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Draw the mechanism between the reaction bromoethane and aq potassium hydroxide
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Halogenoalkane to Nitriles
Heat potassium cyanide dissolved in ethanol under reflux (cyanide ion acts as a nucleophile)
Write an equation for conversion of bromoethane into propanenitrile
……
In the conversion of halogenoalkanes to nitriles, the organic product contains one more carbon atom than the starting material.. Why is this useful?
Increases the length of the carbon chain and is an important way to synthesise more complex compounds.
Halogenoalkanes to Primary Amines
Reagent: NH3 (ammonia) dissolved in ethanol
Conditions: Heating under pressure in a sealed tube
Mechanism: Nucleophilic Substitution
Type of reagent: ammonia acts as nucleophile
Why is the sealed tube needed for production of primary amines from halogenoalkanes ?
The sealed tube is needed because ammonia is a gas and would otherwise escape from the apparatus before reacting.
To produce a high yield of amine from halogenoalkane ….
The ammonia is used in excess which reacts in a second step to produce amine
Draw the mechanism for the reaction between chloroethane and ammonia
SEE FC
Halogenoalkane to Alkene
Reagents: Ethanolic Potassium/Sodium hydroxide
Conditions:In ethanol; heat
Mechanism: Elimination
Role of Reagent: Base OH-
How does the structure of halogenoalkanes affect whether it is substitution or elimination that occurs?
primary tends towards substitution
tertiary tends towards elimination
What are some uses of halogenoalkanes?
refrigerants
fire retardants
pesticides
How can alcohol be classified?
primary, secondary , tertiary
How many alkyl groups are attached to each classification of alcohol?
1- primary ROH
2- secondary R2CHOH
3- tertiary R3COH
If combustion is complete with alcohol the products are
carbon dioxide and water
Combust with clean flame
C2H5OH + 3O2 -> 2CO2 + 3H20
Alcohol to halogenoalkanes
Halogenation (replacing OH- in alcohol with halogen)
different method needed for each halogen ( adding halogen simply does not work)
Chlorination requires (2)
Phosphorus (v) chloride (white solid PCL5)
Vigorous at room temperature hence the reaction mixture does not require heating
Chlorination produces …
Two inorganic products: phosphorus oxychloride and hydrogen chloride
CH3CH2CH2OH+PCL5-> CH3CH2CH2CL +POCL3+ HCL
Chlorination of tertiary alcohols
alcohol needs only to be mixed (by shaking) with concentrated hydrochloric acid @ rtm
Bromination requires….
using a mixture of potassium bromide and 50% concentrated sulfur acids
Reaction mixture warmed with alcohols
Bromination eqns
2 eqns -> the inorganic reagents
KBr + H2SO4 -> KHSO4 + HBr or
2KBr + H2SO4 -> K2SO4 + 2HBr
CH3CH2CH2CH2OH+HBr-> ch3ch2ch2ch2Br+ H2O
Iodination requires …..
using a mixture of red phosphorus and iodine
They reaction mixture including the alcohol is heated under reflux
Iodination eqns
2 eqns -> inorganic reactants first react to form PI3
2P+3I2 -> 2PI3
3C2H50H + PI3 -> 3C2H5I + H3PO3
Inorganic phosphonic acid formed
Alcohols to Alkenes
Elimination Dehydration
Heating the alcohol with concentrated phosphoric acid
Water - inorganic product
Which classifications of alcohols can be oxidised and why?
primary and secondary as you are able to remove the hydrogen of OH + hydrogen from the carbon atoms joined to OH group
What are the products of oxidation?
Ketones - Secondary
Aldehydes - Primary - further oxidised to Carboxylic Acids
For oxidation of alcohols the reagents used include….
a mixture of potassium dichromate(VI) and dilute sulfur is acid
How do we distinguish between Aldehyde and Ketones?
Reagent: Fehling’s solution containing blue Cu 2+ ions.
Conditions: heat gently
Reaction: aldehydes only are oxidised by Fehling’s solution into a carboxylic acid and the copper (II) ions are reduced to copper(I) oxide
Observation: Aldehydes :Blue Cu 2+ ions in solution change to a red precipitate of Cu2O. Ketones do not react
CH3CHO + 2Cu2+ + 2H2OCH3COOH + Cu2O + 4H+
How is the presence of carboxylic acid tested for?
By addition of sodium carbonate. It will fizz and produce carbon dioxide
What are the two different practical techniques for oxidation?
heating under reflux
Distillation with addition
When is the apparatus heating under reflux used in terms of oxidation of alcohols?
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+ ions
When is the apparatus distillation with addition used in terms of oxidation of alcohols ?
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
Why should you never seal the end of the condenser in reflux?
As the build up of gas pressure could cause the apparatus to explode. This is true of any apparatus where volatile liquids are heated
Why are Anti-bumping granules added to the flask in both distillation and reflux ?
To prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles
What are the different ways to purify an organic liquid?
drying with an anhydrous salt
Solvent extraction
Distillation
Process of drying to purify organic liquid
• Put the distillate of impure product into a separating funnel
• wash product by adding either
sodium hydrogen carbonate solution , shaking and releasing the pressure from CO2 produced.
Saturated sodium chloride solution
•Allow the layers to separate in the funnel, and then run and discard the aqueous layer.
•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.
• Carefully decant the liquid into the distillation flask
•Distil to collect pure product
Drying agent should be
- be insoluble in the organic liquid
* not react with the organic liquid
Solvent Extraction for purifying organic liquids
Mix organic solvent and oil-water mixture in a separating funnel
Then separate the oil layer.
Distil to separate oil from organic solvent
Add anhydrous CaCl2 to clove oil to dry oil
Decant to remove CaCl2
How do we check the purity of an organic liquid ?
This can be done in a distillation set up or by simply boiling a tube of the sample in an heating oil bath.
not the most accurate method of identifying a substance as several substances may have the same boiling point.
