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Introduction to organic chemistry
AS Chemistry Introduction to organic chemistry
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Learning Objectives Candidates should be able:
to recall IGCSE work on crude oil and ‘cracking’. in a request for a structural formula, to give the minimal detail, using conventional groups, for an unambiguous structure. to draw and recognise displayed and skeletal formulae. to recognise the shape of the benzene ring when it is present in organic compounds. to interpret and use some of the terminology associated with organic chemistry.
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Starter activity
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Why carbon? Carbon can form strong covalent bonds with itself to give chains and rings of its atoms joined by C-C covalent bonds. This property is called catenation and leads to the limitless variety of organic compounds possible.
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Straight or branched?
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Benzene – C6H6 Best representations – bonds are intermediate between single and double.
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UK oil and gas fields Norway Netherlands
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Fractionating columns
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Fractional distillation
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Uses of each fraction Fuel gas Petrol / gasoline Naphtha Paraffin /
Kerosine Diesel fuel Fuel and lubricating oil Bitumen Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gas Fuel for cars and motorcycles, also used to make chemicals. Used to make chemicals. Fuel for greenhouse heaters and jet engines, manufacture of chemicals. Fuel for lorries, trains. Fuel for the heating systems of large buildings, fuel for ships, lubricating oil. Roofing, and road surfaces.
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Compounds in Crude Oil Alkanes Cycloalkanes Arenes (A2)
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The names and molecular formulae of the first 10 alkanes
methane CH4 hexane C6H14 ethane C2H6 heptane C7H16 propane C3H8 octane C8H18 butane C4H10 nonane C9H20 pentane C5H12 decane C10H22
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Some more alkanes……. 11 Undecane 22 Docosane 33 Tritriacontane
12 Dodecane 23 Tricosane 40 Tetracontane 13 Tridecane 24 Tetracosane 50 Pentacontane 14 Tetradecane 25 Pentacosane 60 Hexacontane 15 Pentadecane 26 Hexacosane 70 Heptacontane 16 Hexadecane 27 Heptacosane 80 Octacontane 17 Heptadecane 28 Octacosane 90 Nonacontane 18 Octadecane 29 Nonacosane 100 Hectane 19 Nonadecane 30 Triacontane 132 Dotriacontahectane 20 Icosane 31 Hentriacontane 21 Henicosane 32 Dotriacontane
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Key Terms Homologous series: a series or family of organic compounds with the same functional group, whose members differ only in the addition of a CH2 group. Functional group: the specific atom or group of atoms that confers a particular chemical property on a molecule, e.g. the –OH group in ethanol. Saturated: the molecule contains the maximum amount of hydrogen atoms possible, with no double or triple bonds between atoms.
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Structural Isomerism butane methylpropane
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Cycloalkanes
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Naming the alkanes 2-methylpentane pent counts 5 carbons
an tells you there aren't any double bonds 2-methyl tells you to add a methyl group on carbon 2 Finish by putting in the correct number of hydrogen atoms
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Naming the alkanes 2,2-dimethylbutane 2,3-dimethylbutane
3-ethyl-2-methylhexane
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Structural formulae Displayed formulae Skeletal formulae
3-dimensional structures
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“Stick” (skeletal) formulae
Penguinone Penguin real name: 3,4,4,5-tetramethylcyclohexa-2,5-dienone
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“Stick” (skeletal) formulae
butane cyclobutane brokenwindowpane windowpane
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“Stick” (skeletal) formulae
benzene mercedes benzene
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AS Chemistry Structural isomerism
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Learning Objectives Candidates should be able:
describe structural isomerism deduce the possible isomers for an organic molecule of known molecular formula.
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Chain isomerism
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Structural Isomerism What are isomers?
Isomers are molecules that have the same molecular formula, but have a different arrangement of the atoms in space. (That excludes any different arrangements which are simply due to the molecule rotating as a whole, or rotating about particular bonds.)
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TYPES OF ISOMERISM STRUCTURAL ISOMERISM
CHAIN ISOMERISM STRUCTURAL ISOMERISM POSITION ISOMERISM Same molecular formula but different structural formulae FUNCTIONAL GROUP ISOMERISM GEOMETRICAL ISOMERISM Occurs due to the restricted rotation of C=C double bonds... two forms… E and Z (CIS and TRANS) STEREOISOMERISM Same molecular formula but atoms occupy different positions in space. OPTICAL ISOMERISM Occurs when molecules have a chiral centre. Get two non- superimposable mirror images.
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What are Structural Isomers
In structural isomerism, the atoms are arranged in a completely different order.
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STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULA BUT DIFFERENT STRUCTURAL FORMULA Chain different arrangements of the carbon skeleton similar chemical properties slightly different physical properties more branching = lower boiling point
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STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULA BUT DIFFERENT STRUCTURAL FORMULA Chain different arrangements of the carbon skeleton similar chemical properties slightly different physical properties more branching = lower boiling point Positional same carbon skeleton same functional group functional group is in a different position similar chemical properties - slightly different physical properties
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STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULA BUT DIFFERENT STRUCTURAL FORMULA Chain different arrangements of the carbon skeleton similar chemical properties slightly different physical properties more branching = lower boiling point Positional same carbon skeleton same functional group functional group is in a different position similar chemical properties - slightly different physical properties Functional Group different functional group different chemical properties different physical properties Sometimes more than one type of isomerism occurs in the same molecule. The more carbon atoms there are, the greater the number of possible isomers
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STRUCTURAL ISOMERISM - CHAIN
caused by different arrangements of the carbon skeleton similar chemical properties slightly different physical properties more branching = lower boiling point There are two structural isomers of C4H10. One is a straight chain molecule where all the carbon atoms are in a single row. The other is a branched molecule where three carbon atoms are in a row and one carbon atom sticks out of the main chain. BUTANE straight chain 2-METHYLPROPANE branched C4H10
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STRUCTURAL ISOMERISM - CHAIN
DIFFERENCES BETWEEN CHAIN ISOMERS Chemical Isomers show similar chemical properties because the same functional group is present. Physical Properties such as density and boiling point show trends according to the of the degree of branching Boiling Point “straight” chain isomers have higher values than branched ones the greater the degree of branching the lower the boiling point branching decreases the effectiveness of intermolecular forces less energy has to be put in to separate the molecules - 0.5°C straight chain - 11.7°C branched greater branching = lower boiling point
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STRUCTURAL ISOMERISM - POSITIONAL
molecule has the same carbon skeleton molecule has the same same functional group... BUT the functional group is in a different position have similar chemical properties / different physical properties Example 1 POSITION OF A DOUBLE BOND IN ALKENES 1 2 2 3 PENT-1-ENE double bond between carbons 1 and 2 PENT-2-ENE double bond between carbons 2 and 3 There are no other isomers with five C’s in the longest chain but there are three other structural isomers with a chain of four carbons plus one in a branch.
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Complete task 1 and task 2 in your hand out…..
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Chain isomerism – isomers of pentane
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STRUCTURAL ISOMERISM - POSITIONAL
molecule has the same carbon skeleton molecule has the same same functional group... BUT the functional group is in a different position have similar chemical properties / different physical properties Example 2 POSITION OF A HALOGEN IN A HALOALKANE BUT 1 2 2 1-CHLOROBUTANE halogen on carbon 1 2-CHLOROBUTANE halogen on carbon 2 is NOT 3-CHLOROBUTANE Moving the chlorine along the chain makes new isomers; the position is measured from the end nearest the functional group... the third example is 2- NOT 3-chlorobutane. There are 2 more structural isomers of C4H9Cl but they have a longest chain of 3
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STRUCTURAL ISOMERISM - POSITIONAL
molecule has the same carbon skeleton molecule has the same same functional group... BUT the functional group is in a different position have similar chemical properties / different physical properties RELATIVE POSITIONS ON A BENZENE RING Example 3 1,2-DICHLOROBENZENE ortho dichlorobenzene 1,3-DICHLOROBENZENE meta dichlorobenzene 1,4-DICHLOROBENZENE para dichlorobenzene
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Complete task 3 ,4 and 5 in your hand out..
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Chain and position isomers of C4H9OH
2-methylpropan-1-ol butan-1-ol butan-2-ol 2-methylpropan-1-ol
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Chain isomerism – isomers of hexane
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Position isomerism
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STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
molecules have same molecular formula molecules have different functional groups molecules have different chemical properties molecules have different physical properties ALCOHOLS and ETHERS ALDEHYDES and KETONES ACIDS and ESTERS MORE DETAILS FOLLOW
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STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
ALCOHOLS and ETHERS Name ETHANOL METHOXYMETHANE Classification ALCOHOL ETHER Functional Group R-OH R-O-R Physical properties polar O-H bond gives rise No hydrogen bonding to hydrogen bonding low boiling point get higher boiling point insoluble in water and solubility in water Chemical properties Lewis base Inert Wide range of reactions
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STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
ALDEHYDES and KETONES Name PROPANAL PROPANONE Classification ALDEHYDE KETONE Functional Group R-CHO R-CO-R Physical properties polar C=O bond gives polar C=O bond gives dipole-dipole interaction dipole-dipole interaction Chemical properties easily oxidised to acids of undergo oxidation under same number of carbons extreme conditions only reduced to 1° alcohols reduced to 2° alcohols
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STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
CARBOXYLIC ACIDS and ESTERS Name PROPANOIC ACID METHYL ETHANOATE Classification CARBOXYLIC ACID ESTER Functional Group R-COOH R-COOR Physical properties O-H bond gives rise No hydrogen bonding to hydrogen bonding insoluble in water get higher boiling point and solubility in water Chemical properties acidic fairly unreactive react with alcohols hydrolysed to acids
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What about benzene rings?
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Functional group isomerism
A molecular formula C3H6O could be either propanal (an aldehyde) or propanone (a ketone).
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All three compounds are aromatic
All three compounds are aromatic. Aspirin is also a carboxylic acid ( CO2H) and an ester ( CO2CH3). Tylenol is also an alcohol ( OH) and an amide ( CONH ). Ibuprofen contains alkane substituents and a carboxylic acid functional group
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AS Chemistry Combustion
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Learning Objectives Candidates should be able:
describe the combustion chemistry of alkanes and how these reactions lead to their use as fuels in industry, in the home and in transport recognise the environmental consequences of: carbon monoxide, oxides of nitrogen and unburnt hydrocarbons arising from the internal combustion engine and of their catalytic removal gases that contribute to the enhanced greenhouse effect
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Starter activity
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Combustion of alkanes Alasken plan on nor clues pinhole police shelter
fans rap if Alkanes non-polar nucleophiles electrophiles paraffins vacation it cheer mix it acne riot cubism onto bleats activation exothermic reaction combustion stable
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Combustion of hydrocarbons
C6H ½O CO H2O As chain length increases: More oxygen is needed for complete combustion The reactions become more exothermic
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Incomplete combustion
Often the flame is yellow and luminous CH O2 CO H2O CH ½O2 CO H2O CH O2 C H2O
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Bunsen Burner
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Bunsen Burner
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Carbon monoxide poisoning
Two children who died on Corfu were killed by carbon monoxide poisoning, Greek officials have confirmed. A pathologist said very high levels of the gas were found in the bodies of Christianne Shepherd, seven and her brother Robert, six.
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Carbon monoxide poisoning
Carbon monoxide, CO, poisons the body by combining with hemoglobin some 250 times more tightly than O2, thus hindering the transport of O2 to the body's tissues.
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Air pollution Can you complete the table?
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Acid Rain
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- Emission Source Chemical equation (where appropriate)
Problems associated with this emission CO2 Complete combustion of fuel CxHy O2 xCO H2O Greenhouse gas; major contributor to global warming. CO CxHy O2 xCO H2O Toxic gas; combines with haemoglobin and prevents O2 transport. Leads to photochemical smog. CxHy Unburnt hydrocarbon fuel - Some (especially benzene) are toxic and carcinogenic. Leads to photochemical smog. NO N2 and O2 react under high T conditions of car engine N2 + O2 2NO Contributes to formation of acid rain and photochemical smog. Linked to respiratory problems. NOx 2o pollutant formed from oxidation of NO 2NO + O2 2NO2 SO2 Combustion of S impurities in fossil fuels S + O2 SO2 Choking gas; major contributor to formation of acid rain.
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Catalytic converters These help to promote the following reactions:
2CO NO N CO2 CO and CxHx are also oxidised by the air: CO O2 CO2 e.g. C7H O2 7CO H2O
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Free-radical substitution reactions of alkanes
AS Chemistry Free-radical substitution reactions of alkanes
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Learning Objectives Candidates should be able:
describe the mechanism of free-radical substitution at methyl groups with particular reference to the initiation, propagation and termination reactions. describe the substitution of alkanes by chlorine and bromine.
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Starter activity
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Free radical substitution
chlorination of methane i.e. homolytic breaking of covalent bonds Overall reaction equation CH4 + Cl2 CH3Cl + HCl Conditions ultra violet light excess methane to reduce further substitution
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Free radical substitution mechanism
ultra-violet Cl2 Cl + Cl initiation step two propagation steps CH4 + Cl CH3 + HCl CH3 + Cl2 CH3Cl + Cl termination step CH3 + Cl CH3Cl minor termination step CH3CH3 CH CH3
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Further free radical substitutions
Overall reaction equations CH3Cl + Cl2 CH2Cl2 + HCl CH2Cl2 + Cl2 CHCl3 + HCl CHCl3 + Cl2 CCl4 + HCl Conditions ultra-violet light excess chlorine
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AS Chemistry Cracking
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Learning Objectives Candidates should be able to suggest how ‘cracking’ can be used to obtain more useful alkanes and alkenes of lower Mr from larger hydrocarbon molecules.
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Starter activity
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Why crack? Fractionth Approximate % Crude oil Demand Gases 2 4
Petrol and naphtha 16 27 Kerosene 13 8 Gas oil 19 23 Residue 50 38
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One example of a cracking reaction?
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Thermal cracking Produces a high proportion of alkenes
Temperatures range from oC Pressures up to 7000kPa
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Catalytic cracking Produces a large proportion of branched alkanes, cycloalkanes and aromatic hydrocarbons Uses zeolite (crystalline aluminosilicate) catalysts Temperature around 450oC Pressure just above atmospheric
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Catalytic cracking Zeolite catalyst ‘Cat’ cracker
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Catalytic cracker
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