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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 C 6 H 6 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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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. Uses of each fraction

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Alkanes Cycloalkanes Arenes (A2)

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methaneCH 4 hexaneC 6 H 14 ethaneC2H6C2H6 heptaneC 7 H 16 propaneC3H8C3H8 octaneC 8 H 18 butaneC 4 H 10 nonaneC 9 H 20 pentaneC 5 H 12 decaneC 10 H 22 The names and molecular formulae of the first 10 alkanes

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11 Undecane22 Docosane33 Tritriacontane 12 Dodecane23 Tricosane40 Tetracontane 13 Tridecane24 Tetracosane50 Pentacontane 14 Tetradecane25 Pentacosane60 Hexacontane 15 Pentadecane26 Hexacosane70 Heptacontane 16 Hexadecane27 Heptacosane80 Octacontane 17 Heptadecane28 Octacosane90 Nonacontane 18 Octadecane29 Nonacosane100 Hectane 19 Nonadecane30 Triacontane132 Dotriacontahectane 20 Icosane31 Hentriacontane 21 Henicosane32 Dotriacontane Some more alkanes.

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Homologous series: a series or family of organic compounds with the same functional group, whose members differ only in the addition of a CH 2 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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butanemethylpropane

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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

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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 3-dimensional structures Skeletal formulae

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real name: 3,4,4,5-tetramethylcyclohexa-2,5-dienone Stick (skeletal) formulae PenguinonePenguin

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windowpane brokenwindowpane butanecyclobutane

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benzene mercedes benzene

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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 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

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In structural isomerism, the atoms are arranged in a completely different order. What are Structural Isomers

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STRUCTURAL ISOMERISM - INTRODUCTION COMPOUNDS HAVE THE SAME MOLECULAR FORMULA BUT DIFFERENT STRUCTURAL FORMULA Chaindifferent 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 Chaindifferent arrangements of the carbon skeleton similar chemical properties slightly different physical properties more branching = lower boiling point Positionalsame 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 Chaindifferent arrangements of the carbon skeleton similar chemical properties slightly different physical properties more branching = lower boiling point Positionalsame carbon skeleton same functional group functional group is in a different position similar chemical properties - slightly different physical properties Functional Groupdifferent 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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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 C 4 H 10. 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 C 4 H 10 STRUCTURAL ISOMERISM - CHAIN

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DIFFERENCES BETWEEN CHAIN ISOMERS ChemicalIsomers show similar chemical properties because the same functional group is present. PhysicalProperties such as density and boiling point show trends according to the of the degree of branching Boiling Pointstraight 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 - 0.5C straight chain - 11.7C branched greater branching = lower boiling point

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POSITION OF A DOUBLE BOND IN ALKENES PENT-1-ENE double bond between carbons 1 and 2 PENT-2-ENE double bond between carbons 2 and 3 1223 There are no other isomers with five Cs 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 skeleton molecule has the same same functional group... BUT the functional group is in a different position have similar chemical properties / different physical properties

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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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1-CHLOROBUTANE halogen 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 C 4 H 9 Cl but they have a longest chain of 3 2-CHLOROBUTANE halogen on carbon 2 BUT is NOT 3-CHLOROBUTANE 2 POSITION OF A HALOGEN IN A HALOALKANEExample 2 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

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STRUCTURAL ISOMERISM - POSITIONAL 1,3-DICHLOROBENZENE meta dichlorobenzene 1,2-DICHLOROBENZENE ortho dichlorobenzene 1,4-DICHLOROBENZENE para dichlorobenzene RELATIVE POSITIONS ON A BENZENE RING Example 3 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

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Complete task 3,4 and 5 in your hand out..

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Chain and position isomers of C 4 H 9 OH butan-1-ol 2-methylpropan-1-ol butan-2-ol2-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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ALCOHOLS and ETHERS Name ETHANOL METHOXYMETHANE Classification ALCOHOL ETHER Functional Group R-OH R-O-R Physical propertiespolar 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 propertiesLewis base Inert Wide range of reactions STRUCTURAL ISOMERISM FUNCTIONAL GROUP

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ALDEHYDES and KETONES Name PROPANAL PROPANONE Classification ALDEHYDE KETONE Functional Group R-CHO R-CO-R Physical propertiespolar C=O bond gives polar C=O bond gives dipole-dipole interaction dipole-dipole interaction Chemical propertieseasily oxidised to acids of undergo oxidation under same number of carbons extreme conditions only reduced to 1 alcohols reduced to 2 alcohols STRUCTURAL ISOMERISM FUNCTIONAL GROUP

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CARBOXYLIC ACIDS and ESTERS Name PROPANOIC ACID METHYL ETHANOATE Classification CARBOXYLIC ACID ESTER Functional Group R-COOH R-COOR Physical propertiesO-H bond gives rise No hydrogen bonding to hydrogen bonding. insoluble in water get higher boiling point and solubility in water Chemical propertiesacidic fairly unreactive react with alcohols hydrolysed to acids STRUCTURAL ISOMERISM FUNCTIONAL GROUP

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What about benzene rings?

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Functional group isomerism A molecular formula C 3 H 6 O could be either propanal (an aldehyde) or propanone (a ketone).

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All three compounds are aromatic. Aspirin is also a carboxylic acid ( CO 2 H) and an ester ( CO 2 CH 3 ). Tylenol is also an alcohol ( O H) and an amide ( CONH ). Ibuprofen contains alkane substituents and a carboxylic acid functional group

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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 activation exothermic reaction combustion stable vacation it cheer mix it acne riot cubism onto bleats Alkanes non-polar nucleophiles electrophiles paraffins

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C 6 H 14 + 9O 2 6CO 2 + 7H 2 O Combustion of hydrocarbons As chain length increases: More oxygen is needed for complete combustion The reactions become more exothermic

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Incomplete combustion CH 4 + 2O 2 CO 2 + 2H 2 O CH 4 + 1 O 2 CO + 2H 2 O CH 4 + O 2 C + 2H 2 O Often the flame is yellow and luminous

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Bunsen Burner

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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

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Carbon monoxide, CO, poisons the body by combining with hemoglobin some 250 times more tightly than O 2, thus hindering the transport of O 2 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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EmissionSourceChemical equation (where appropriate) Problems associated with this emission CO 2 Complete combustion of fuel C x H y + O 2 xCO 2 + H 2 O Greenhouse gas; major contributor to global warming. CO Complete combustion of fuel C x H y + O 2 xCO 2 + H 2 O Toxic gas; combines with haemoglobin and prevents O 2 transport. Leads to photochemical smog. CxHyCxHy Unburnt hydrocarbon fuel - Some (especially benzene) are toxic and carcinogenic. Leads to photochemical smog. NO N 2 and O 2 react under high T conditions of car engine N 2 + O 2 2NO Contributes to formation of acid rain and photochemical smog. Linked to respiratory problems. NO x 2 o pollutant formed from oxidation of NO 2NO + O 2 2NO 2 SO 2 Combustion of S impurities in fossil fuels S + O 2 SO 2 Choking gas; major contributor to formation of acid rain.

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Catalytic converters These help to promote the following reactions: 2CO + 2NO N 2 + 2CO 2 CO and C x H x are also oxidised by the air: CO + O 2 CO 2 e.g. C 7 H 16 + O 2 7CO 2 + 8H 2 O

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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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CH 4 + Cl 2 CH 3 Cl + HCl Overall reaction equation Conditions ultra violet light excess methane i.e. homolytic breaking of covalent bonds to reduce further substitution Free radical substitution chlorination of methane

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CH 4 + ClCH 3 + HCl Cl 2 Cl + Cl CH 3 + Cl 2 CH 3 Cl + Cl CH 3 ClCH 3 + Cl initiation step two propagation steps termination step ultra-violet CH 3 CH 3 + CH 3 minor termination step Free radical substitution mechanism

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CH 3 Cl + Cl 2 CH 2 Cl 2 + HCl Overall reaction equations Conditionsultra-violet light CH 2 Cl 2 + Cl 2 CHCl 3 + HCl CHCl 3 + Cl 2 CCl 4 + HCl excess chlorine Further free radical substitutions

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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 M r from larger hydrocarbon molecules.

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Starter activity

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Fractionth Approximate % Crude oilDemand Gases24 Petrol and naphtha1627 Kerosene138 Gas oil1923 Residue5038 Why crack?

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One example of a cracking reaction?

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Produces a high proportion of alkenes Temperatures range from 400-900 o C Pressures up to 7000kPa Thermal cracking

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Produces a large proportion of branched alkanes, cycloalkanes and aromatic hydrocarbons Uses zeolite (crystalline aluminosilicate) catalysts Temperature around 450 o C Pressure just above atmospheric Catalytic cracking

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Zeolite catalyst Cat cracker

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Catalytic cracker