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Chem 2A2B Term 4 Notes A 2011 1 Coghlan Chemistry 2A2B – Term 4 Notes A Contain H and C only Hydrocarbons Open chain Closed rings Aliphatic Benzene ring based Alicyclic Aromatic Homologous series Alkanes Alkenes Alkynes Bonding in C compounds Electron __________ of C is usually 1s2 2s2 2px1 2py1. However when it reacts, it __________ some __________ and one of the 2s __________ is __________ and the configuration becomes 1s2 2s1 2px1 2py1 2pz1. So C can form __________ __________ bonds in organic compounds. So C can form a total of 4 covalent bonds with either itself or other species. Chem 2A2B Term 4 Notes A 2011 2 Coghlan Formulae of organic compounds Organic compounds can be represented by molecular formulae, __________ dot formulae or __________ formulae. Molecular formula tells the __________ of atoms of each __________ present. e.g. CH4, C2H6 Electron dot formula shows the __________ and non-bonding __________. e.g. Structural formula shows the relative __________ of the atoms in the molecule. Each straight line represents one __________ bond (one shared pair of electrons). The molecules themselves are three dimensional. e.g. Crude oil to petrol The number of C atoms on earth is __________. The C __________ summarises the various __________ that occur. Chem 2A2B Term 4 Notes A 2011 3 Coghlan http://www.windows.ucar.edu/earth/climate/carbon_cycle.html Hydrocarbons as Fuels The ____________ gas (a ____________ fuel) found on the north-west shelf consists mainly of ____________ (piped to Perth and used for ____________, ____________ etc.), with some ____________ (used in the ____________ industry to make plastics etc.), propane and butane (liquefied to form ____________ and exported), carbon dioxide, nitrogen and hydrogen sulfide. ____________ (a fossil fuel) is liquid and consists of alkanes in the C5 to C40 range. ____________ distillation is used to separate the different ____________ of the petroleum. http://www.geomore.com/Oil%20and%20Gas%20Traps.htm Coal and oil shale are also fossil fuels. All fossil fuels ultimately result from the ____________ reaction of ____________. The ____________ provides the ____________ energy source. The natural gas we have results from the ____________ ____________ of marine ____________ sediment. The gas from this decomposition is trapped between ____________ layers of rock in ____________ rock (sandstone or limestone). Chem 2A2B Term 4 Notes A 2011 4 Coghlan Petrol http://www.howstuffworks.com/oil-refining4.htm Petrol obtained from ____________ distillation causes engines to ____________ (not run ____________). The octane ____________ describes the burning ____________ of the petrol mix – a high octane number of 100 burns very ____________ while a low octane number burns ____________. A petrol with an octane number of 94 indicates a mixture that burns with the same characteristics as a mixture of 94 parts heptane and 7 parts 2, 2, 4 – trimethylpentane. Typical petrol has an octane number of 92. Aliphatic Hydrocarbons All aliphatic hydrocarbons are either __________ chain or branched chain hydrocarbons. They form three homologous __________ in which one member differs from the next by an __________ of CH2. The three homologous series are the __________, the __________ and the __________. Alkanes http://www.chemguide.co.uk/organicprops/alkanes/background.html#top The alkanes are all __________ hydrocarbons – they do not have any __________ bonds between the carbon atoms. e.g. The alkanes form an homologous series and differ from member to member by the CH 2 increment. Chem 2A2B Term 4 Notes A 2011 5 Coghlan Name Molecular Formula State Methane CH4 Gas Ethane C2H6 Gas Structural formula Propane Butane Pentane Liquid Hexane Heptane Octane Nonane Decane Solids after C18 General formula for the alkanes: CnH2n+2 The m.p., b.p. and density all __________with __________molecular mass due to the increasing __________forces acting. Structural isomers Chem 2A2B Term 4 Notes A 2011 6 Coghlan Because of the way that C can form 4 covalent bonds, there are a variety of ways in which most of the alkanes can be structured. Molecules that have the same __________formula but different __________formulae are called __________isomers. e.g. Structural isomers of pentane, C5H12. IUPAC Naming rules 1. Identify the longest C chain - this forms the stem name of the compound. 2. Identify any substituent groups branching off the main chain - this forms the front part of the name. Alkyl groups Name Formula Methyl CH3 - Ethyl Propyl Butyl Structure Chem 2A2B Term 4 Notes A 2011 7 Coghlan Pentyl Hexyl Heptyl 3. Number the branching groups so that they have the lowest possible number then finally name using alphabetical order for the branching chains. Note: Non-hydrocarbon attachments also occur and are called Name Formula Fluoro F- Chloro Bromo Iodo Nitro Amino Hydroxy Chem 2A2B Term 4 Notes A 2011 8 Coghlan Exercise 1. Write names for http://www.quia.com/custom/3962gate.html EC Set 32 Alkane Reactions Alkanes are relatively inert but do show two main types of reactions, combustion and substitution. 1. Combustion In excess oxygen Chem 2A2B Term 4 Notes A 2011 9 Coghlan In limited oxygen 2. Substitution Using suitable catalysts (e.g. concentrated H2SO4), the Hs can be removed from the C chain and substituted with another species.
