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.
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.
Fractionating columns
Fuel gas
Petrol / gasoline
Naphtha
Paraffin / Kerosine
Diesel fuel
Fuel and lubricating oilBitumen
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.
Uses of each fraction
methane
CH4 hexane C6H14
ethane C2H6 heptane C7H16
propane C3H8 octane C8H18
butane C4H10 nonane C9H20
pentane C5H12 decane C10H22
The names and molecular formulae of the first 10 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
Some more alkanes…….
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.
Key Terms
Naming the alkanes
2-methylpentane
pent counts 5 carbons
2-methyl tells you to add a methyl group on carbon 2
an tells you there aren't any double bonds
Finish by putting in the correct number of hydrogen atoms
Learning Objectives
Candidates should be able:
describe structural isomerism
deduce the possible isomers for an organic molecule of known molecular formula.
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.)
TYPES OF ISOMERISM
Occurs due to the restricted rotation of C=C double bonds... two forms… E and Z (CIS and TRANS)
STRUCTURAL ISOMERISM
STEREOISOMERISM
GEOMETRICAL ISOMERISM
OPTICAL ISOMERISM
CHAIN ISOMERISM
Same molecular formula but different structural formulae
Occurs when molecules have a chiral centre. Get two non-superimposable mirror images.
Same molecular formula but atoms occupy different positions in space.
POSITION ISOMERISM
FUNCTIONAL GROUP ISOMERISM
In structural isomerism, the atoms are arranged in a completely different order.
What are Structural Isomers
STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULABUT DIFFERENT STRUCTURAL FORMULA
Chain different arrangements of the carbon skeletonsimilar chemical propertiesslightly different physical propertiesmore branching = lower boiling point
STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULABUT DIFFERENT STRUCTURAL FORMULA
Chain different arrangements of the carbon skeletonsimilar chemical propertiesslightly different physical propertiesmore branching = lower boiling point
Positional same carbon skeletonsame functional groupfunctional group is in a different positionsimilar chemical properties - slightly different physical properties
STRUCTURAL ISOMERISM - INTRODUCTION
COMPOUNDS HAVE THE SAME MOLECULAR FORMULABUT DIFFERENT STRUCTURAL FORMULA
Chain different arrangements of the carbon skeletonsimilar chemical propertiesslightly different physical propertiesmore branching = lower boiling point
Positional same carbon skeletonsame functional groupfunctional group is in a different positionsimilar chemical properties - slightly different physical properties
Functional Group different functional groupdifferent chemical propertiesdifferent 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
caused by different arrangements of the carbon skeletonsimilar chemical propertiesslightly different physical propertiesmore 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.
BUTANEstraight chain
2-METHYLPROPANEbranched
C4H10
STRUCTURAL ISOMERISM - CHAIN
STRUCTURAL ISOMERISM - CHAIN
DIFFERENCES BETWEEN CHAIN ISOMERS
Chemical Isomers show similar chemical properties becausethe 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 onesthe greater the degree of branching the lower the boiling pointbranching decreases the effectiveness of intermolecular forcesless energy has to be put in to separate the molecules
- 0.5°Cstraight chain
- 11.7°Cbranched
greater branching = lower boiling point
POSITION OF A DOUBLE BOND IN ALKENES
PENT-1-ENEdouble bond between carbons 1 and 2
PENT-2-ENEdouble bond between carbons 2 and 3
1 2 2 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.
Example 1
STRUCTURAL ISOMERISM - POSITIONAL
molecule has the same carbon skeletonmolecule has the same same functional group... BUTthe functional group is in a different positionhave similar chemical properties / different physical properties
1-CHLOROBUTANEhalogen on carbon 1
1 2
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
2-CHLOROBUTANEhalogen on carbon 2
BUT
is NOT3-CHLOROBUTANE
2
POSITION OF A HALOGEN IN A HALOALKANEExample 2
STRUCTURAL ISOMERISM - POSITIONAL
molecule has the same carbon skeletonmolecule has the same same functional group... BUTthe functional group is in a different positionhave similar chemical properties / different physical properties
STRUCTURAL ISOMERISM - POSITIONAL
1,3-DICHLOROBENZENEmeta dichlorobenzene
1,2-DICHLOROBENZENEortho dichlorobenzene
1,4-DICHLOROBENZENEpara dichlorobenzene
RELATIVE POSITIONS ON A BENZENE RING
Example 3
molecule has the same carbon skeletonmolecule has the same same functional group... BUTthe functional group is in a different positionhave similar chemical properties / different physical properties
STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
molecules have same molecular formulamolecules have different functional groupsmolecules have different chemical propertiesmolecules have different physical properties
ALCOHOLS and ETHERS
ALDEHYDES and KETONES
ACIDS and ESTERS
MORE DETAILS FOLLOW
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 bondingto hydrogen bonding. low boiling pointget higher boiling point insoluble in waterand solubility in water
Chemical properties Lewis base InertWide range of reactions
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 undersame number of carbons extreme conditions only
reduced to 1° alcohols reduced to 2° alcohols
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 bondingto hydrogen bonding. insoluble in waterget higher boiling pointand solubility in water
Chemical properties acidic fairly unreactivereact with alcohols hydrolysed to acids
STRUCTURAL ISOMERISM – FUNCTIONAL GROUP
Functional group isomerism
A molecular formula C3H6O could be either propanal (an aldehyde) or propanone (a ketone).
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
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
Combustion of alkanes
Alasken
plan on nor
clues pinhole
police shelter
fans rap if
activation
exothermic
reaction
combustion
stable
vacation it
cheer mix it
acne riot
cubism onto
bleats
Alkanes
non-polar
nucleophiles
electrophiles
paraffins
C6H14 + 9½O2 6CO2 + 7H2O
Combustion of hydrocarbons
As chain length increases:
• More oxygen is needed for complete combustion
• The reactions become more exothermic
Incomplete combustion
CH4 + 2O2 CO2 + 2H2O
CH4 + 1½O2 CO + 2H2O
CH4 + O2 C + 2H2O
Often the flame is yellow and luminous
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.
Carbon monoxide poisoning
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.
Emission Source Chemical equation (where appropriate)
Problems associated with this emission
CO2
Complete combustion of fuel
CxHy + O2 xCO2 + H2OGreenhouse gas; major contributor to global warming.
CO
Complete combustion of fuel
CxHy + O2 xCO2 + 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.
NON2 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.
2
y
2
y
2
y
2
1y
Catalytic converters
These help to promote the following reactions:
2CO + 2NO N2 + 2CO2
CO and CxHx are also oxidised by the air:
CO + O2 CO2
e.g. C7H16 + O2 7CO2 + 8H2O
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.
CH4 + Cl2 CH3Cl + HCl
Overall reaction equation
Conditions
ultra violet lightexcess methane
i.e. homolytic breaking of covalent bonds
to reduce further substitution
Free radical substitutionchlorination of methane
CH4 + Cl CH3 + HCl
Cl2 Cl + Cl
CH3 + Cl2 CH3Cl + Cl
CH3ClCH3 + Cl
initiation step
two propagation steps
termination step
ultra-violet
CH3CH3CH3 + CH3
minor termination step
Free radical substitution mechanism
CH3Cl + Cl2 CH2Cl2 + HCl
Overall reaction equations
Conditions ultra-violet light
CH2Cl2 + Cl2 CHCl3 + HCl
CHCl3 + Cl2 CCl4 + HCl
excess chlorine
Further free radical substitutions
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.
FractionthApproximate %
Crude oil Demand
Gases 2 4Petrol and naphtha
16 27
Kerosene 13 8Gas oil 19 23Residue 50 38
Why crack?
• Produces a high proportion of alkenes• Temperatures range from 400-900oC • Pressures up to 7000kPa
Thermal cracking
• Produces a large proportion of branched alkanes, cycloalkanes and aromatic hydrocarbons
• Uses zeolite (crystalline aluminosilicate) catalysts• Temperature around 450oC• Pressure just above atmospheric
Catalytic cracking
Catalytic cracking
Zeolite catalyst
‘Cat’ cracker
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