Organic Chemistry

Chapter 25Alkanes and alkenes

125.1 Introduction to Organic ChemistryOrganic Chemistry is the study of all organic compounds that contain _________ & ______________.Organic compound may contain elements such as O, N or a halogen.A lot of things we use like plastics, rubber, detergents, insecticides, most medicines are organic compounds.carbonhydrogenOrganic chemistryWhat is it?This is a very complex branch of chemistry because

Organic chemistryChains and rings

Organic chemistry Single and multiple bonding

25.2 Classifying Organic Compounds

Homologous series

25.2 Functional GroupsThe compounds in each homologous series, except for alkanes, have special group of atoms called the functional group. all alkENEs contain C=C group. E.g. ethene, C2H4Alcohols have the OH group. E.g. ethanol, C2H5OHThe functional group is responsible for the chemical properties of a compound

General characteristics of an homologous seriesThey have the same general formula/ the same functional groupThey have similar chemical properties/undergo the same chemical reactionsThe formula of each member differs from the next by a CH2 groupThe physical properties show a gradual change as the number of carbon atoms in the molecules increases

1. The diagram shows the structures of four organic molecules.

Which two are members of the same homologous series?P and RP and SQ and RR and S2. The diagram shows the structure of a compound X. How is X classified? A. as an acid and as an alcoholB. as an alkene and as an acidC. as an alkene and as an alcoholD. as an alkane and as ester

3 Which statement about members of a homologous series is correct?A. they contain the same number of bonds per molecule B. they have the same empirical formulaC. they have the same number of carbon atoms per moleculeD. they undergo similar reactions

4. Which diagram represents a molecule of an alkane?

Exercises: pg 438 Q 1 -21 a) Which families of organic compounds are hydrocarbons?b) Which family of hydrocarbonsHas a functional group,Does not have a functional group?2. The compounds ethene and propene are both alkenes. What will the formula of both compounds contain?Alkanes and alkenesalkenesalkanesBoth will contain a carbon-carbon double bond Organic ChemistryPrefixThe number of Carbon AtomPrefixThe number of Carbon atomMeth-1Hex-6Eth-2Hept-7Prop-3Oct-8But-4Non-9Pent-5Dec-10Organic ChemistryAlkaneMade up of single bonds onlySuffix -ane

AlkeneContains a double bondSuffix -ene

Organic ChemistryAlcoholContains OH bond in the moleculeSuffix -anol

Carboxylic AcidContain COOH bond in the moleculeOrganic AcidSuffix -anoic acid

Organic ChemistryMethaneHas 1 carbon atomCombined with 4 hydrogen atoms by using single covalent bondImages of methane (Structural Formula)

Steps of naming an organic compound

Alkanes What are they?

25.3 AlkanesFuels produced from petroleum, such as diesel and petrol, are mixtures of alkanesThe names of all alkanes end with aneThe formula of one alkane differs from the formula of the next by a CH2 group of atoms.The carbon atoms are joined by single covalent bondsThey are saturated hydrocarbons as they contain the maximum number of hydrogen atoms

1. Complete the table below: Relative molecular mass of C = 12.00, H = 1.00Boiling point (oC)Relative molecular massAt room temperatureMethane, CH4-16216Gas__________, C2H6-89GasPropane, __________-42Gas__________, C4H100GasPentane, __________36LiquidEthaneButaneC3H8C5H1230445872Alkane structures

CH4 CH3CH3 CH3CH2CH3Condensed structural formula

Alkane structures

Alkane structures

25.3 Alkanes Physical PropertiesThere is a gradual change in physical properties as the number of carbon atoms in the molecules increases.Boiling point increases as carbon number increases

Solubility insoluble in water, soluble in organic solvents e.g. tetrachloromethaneDensity increases as carbon number increasesViscosity more viscous as carbon number increases.Flammability less flammable as carbon number increases. This is because the molecules evaporate less easily

Some properties of alkanes

Solubility insoluble in water, soluble in organic solventsDensity Greater number of C atoms = higher density25.3 Alkanes Reactions of AlkanesAll alkanes have similar chemical because they belong to the same homologous series.Alkanes are UNREACTIVE; they do not react with most chemicals.There are 2 reactions:CombustionReaction with ChlorineAlkanes - CombustionAlkanes burn in air to form carbon dioxide & water.

The main use of alkanes is in combustion to produce energy e.g. cooking, fuels for vehicles.Greater number of C atoms = less flammable, more sooty flameSometimes, incomplete combustion happens instead and carbon monoxide & soot are produced. Higher alkanes will burn less completely and gives a more sooty flame

Alkanes Reaction with ChlorineAlkanes react with chlorine/bromine in the presence of LIGHT.The reaction is known as SUBSTITUTION REACTION.

The substitution of alkanes WILL NOT take place in darkness. The light energy is used to break the covalent bond in the chlorine molecule to produce chlorine atoms.

chloromethanedichloromethanetrichloromethanetetrachloromethaneOptional________CH4+ ________ O2 ________ CO2 + ________ H2O________ C2H6+ ________ O2 ________ CO2 + ________ H2O________ C3H8+ ________ O2 ________ CO2 + ________ H2O________ C4H10+ ________ O2 ________ CO2 + ________ H2O

222746534213810Exercises: pg 443 Q 1 -21 Look at the structure of the ethane moleculea) How many C C bonds does it have?b) How many C H bonds does it have?c) Draw an electron diagram for the molecule. Use outer shells only1 C C bond6 C H bond

Exercises: pg 443 Q 1 -22. Petrol is a mixture of alkane molecules.Approximately how many carbon atoms do molecules in petrol have? Write the molecular formulae for some of these alkanes.

What is the approximate range of boiling points of petrol? Explain why it does not have a single boiling point.

Predict the approximate density of petrol?Molecules in petrol have approximately 5 to 10 carbon atoms. Some of these alkanes have the molecular formula of C5H12 and C10H22.Petrol has an approximate boiling point range of 35OC to 75 OC. Petrol is a mixture of compounds and so boils over a range of temperaturesAround 0.7 g/cm3. (Refer to pg 440 of the textbook)

Alkenes What are they?

25.4 AlkENEsobtained from petroleum through cracking of alkanes.The general formula ______. Names of alkENEs end in ENE.They differ by CH2 group.Like alkane, melting points, boiling points, densities & viscosities increases while flammability decreases as carbon number increase.They all contain C = C bonds and are said to be unsaturated hydrocarbons

Alkene structures

1. Complete the table below: Relative molecular mass of C = 12.00, H = 1.00Boiling point (oC)

Relative molecular massAt room temperature__________, C2H4-89GasPropene, __________-42Gas__________, C4H80GasPentene, __________36LiquidEtheneButeneC3H6C5H1028425670AlkENEs ReactionsAs alkenes contain same functional group ______, they have similar chemical properties.The presence of the double bond makes the alkenes MORE REACTIVE than alkanes.There are two main reactions:CombustionAddition Reactions two or more molecules react to form a single productAddition of hydrogen (hydrogenation)Addition of bromine (used as a test for alkenes)Addition of water alcoholsPolymerisation poly(ethene)C = CAlkENEs CombustionAlkENEs burn in air like alkANEs.Hence they burn in air to produce: _____ & _______Carbon monoxide & soot (carbon) are produced if the combustion is ______________.In practice, alkenes produce more soot than alkanes when they burn in air.________ C2H4+ ________ O2 ________ CO2 + ________ H2O

CO2H2Oincomplete322Addition reactionAlkene + hydrogen (Hydrogenation)

Conditions:Nickel catalyst200OC

Alkanes and alkenesHow can you tell them apart?

Addition reactionsAlkene + Bromine (Bromination)

No catalystAddition reactionsAlkene + steam(hydration)No catalyst

Conditions:Phosphoric acid catalyst300OC60-70 atm

Polymerisation

Exercises: pg 447 Q 1 -4Draw electron diagrams for ethene and propene (use outer shells only)

Write the molecular formula of the products when butene reacts withbrominewater. hydrogenC4H8Br2C4H9OHC4H10

Exercises: pg 447 Q 1 -43 Limonene is an alkene found in orange peel oil. What would you expect to observe if an aqueous solution of bromine is shaken with a few drops of orange peel oil?

4. A closed flask A contains a hydrocarbon with the formula C3H6. Another closed flask B contains a hydrocarbon with the formula C4H10. A little bromine solution is added to each flask, and the flask is shaken. What would you expect to see in each flask.The reddish brown colour of bromine solution would be decolourisedFlask A contains C3H6 which is an unsaturated alkene and will decolourise aqueous bromine. Flask B contains C4H10 which is a saturated alkane and will not have any effect on the bromine solution.25.5 Isomerism in Alkanes & AlkenesIsomers are different compounds with the same molecular formula.

They have different structural formulae & different boiling points.Exercises: pg 450 Q 1 -2The structural formula of pentane is:

Write the structural formula of two other hydrocarbons that are isomers of pentane

2. Write the structural formulae of two isomers with molecular formula C2H4Br2

Exercises: pg 451 Q 1 -2Suggest how you would attempt to test a vegetable oil to find out if it is unsaturated.

What type of reaction is the conversion of vegetable oil into margarine?

Shake the vegetable oil with bromine solution. If the vegetable oil is unsaturated, the reddish brown colour of bromine would be decolourised.Addition reactionCrackingWhat happens?Large hydrocarbons are vaporised (turned into gas)The vapors are passed over a hot catalystBonds are broken and smaller molecules are madeThermal decomposition (breaking up by heating) takes placeCatalysts help speed up reactions

CrackingWhat happens?Many different hydrocarbons are produced because the molecules can break down in different ways

CrackingWhy is it done?Production of fuel for motor carsProduction of alkenesProduction of hydrogen1. Write down the equations to show examples of cracking. Which alkane is produced?a) cracking of decane (C10H22) to obtain ethene and an alkane.C10H22 b) cracking octane (C8H18) to obtain propene and an alkane.C8H18 c) cracking ethane to obtain ethene and a gas.C2H6

C2H4 + C8H18C3H6 + C5H12C2H4 + H2OctanepentanehydrogenExercises: pg 453 Q 1 -3Suggest the names of two other petroleum fractions that can be manufactured from the cracking of the lubricating oil fraction. Why is this important?

The following equation shows a cracking reaction. C14H30 C12H24 + compound XWhat is the name and formula of compound X?

Petrol and diesel are manufactured from the cracking of lubricating oil fractions. This provides more of these fuels as there are not enough petrol and diesel in petroleum to meet the demand for them.Compound X is Ethane, C2H6Exercises: pg 453 Q 1 -33. Write a balanced chemical equation in each case to show the cracking of C16H34 to produceOne alkane molecule with six carbon atoms and one alkene molecule andC16H34 Four ethene molecules and one other moleculeC16H34 C6H14 + C10H206C2H4 + C8H18Organic ChemistrySkeletal FormulaEach end of the line represent a carbon atomExample

Contains 6 carbon, can be written as

Structural FormulaOrganic Chemistry5 Carbon Atoms= Pent-Single Bond= -aneName of the compound = Pentane

Organic Chemistry5 Carbon Atoms= Pent-Double Bond= -eneName of the compound = Pentene

Organic Chemistry5 Carbon Atoms= Pent--OH bond= -anolName of the compound = Pentanol

Organic Chemistry6 Carbon Atoms= Hex-Carboxylic Acid= -anoic acidName of the compound = Hexanoic Acid

Organic Chemistry2 Carbon Atoms=Eth -Carboxylic Acid= -anoic acidName of the compound = Ethanoic Acid

Organic Chemistry

6 Carbon Atoms= Hex-Single Bond= -aneName of the compound = HexaneOrganic Chemistry4 Carbon Atoms= But-Double Bond= -anoic AcidName of the compound = Butanoic Acid

Organic Chemistry8 Carbon Atoms= Oct-Double Bond Bond= -eneName of the compound = Octene

Draw the structural formula of ButeneSkeletal Formula of Butene

Organic Chemistry