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Chapter 20.3 : Saturated and Unsaturated Hydrocarbons

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Chapter 20.3 : Saturated and Unsaturated Hydrocarbons

  1. 1. Chapter 20.3 and 4<br />Saturated and Unsaturated Hydrocarbons<br />
  2. 2. Objectives:<br />Distinguish among the structures of alkanes, alkenes, alkynes, and aromatic hydrocarbons<br />Write structural formulas and names for alkanes, alkenes, and alkynes<br />Relate properties of different types of hydrocarbons to their structures.<br />
  3. 3. Hydrocarbons<br />Compounds that contain only carbon and hydrogen<br />Simplest class of organic compounds.<br />All other organic compounds can be viewed as<br />hydrocarbons in which one or more hydrogen atoms have been replaced by other atoms or other groups of atoms<br />Saturated hydrocarbons<br />Each carbon atom in the molecule forms four single covalent bonds with other atoms<br />Alkanes<br />Hydrocarbons that contain only single bonds <br />
  4. 4. Straight-chain alkanes differ from one another by one carbon atom and two hydrogen atoms, a –CH2– group<br />homologous series<br />General molecular formula <br />Same for all members of a homologous series<br />Straight-chain alkanes, <br />the general formula CnH2n+2<br />Propane<br />
  5. 5. Alkanes<br />butane<br />
  6. 6. alkanes in which the carbon atoms are arranged in a ring, or cyclic, structure<br />Cycloalkanes<br />Skeletal representation<br />
  7. 7. General formula – cycloalkanes<br />CnH2n<br />2 <br />fewer hydrogen atoms than noncyclic alkanes<br />Cycloalkanes have no free ends where a carbon atom is attached to three hydrogen atoms<br />pentane<br />
  8. 8. Historically, the names were derived from the sources in which they were found<br />A systematic naming method for organic compounds became necessary because of the many organic compounds that are possible<br />IUPAC - International Union of Pure and Applied Chemistry<br />Systematic naming, tells what the structure of an organic compound is by looking at its name<br />Systematic Names of Alkanes<br />hexane<br />
  9. 9. Use the prefix that corresponds to the number of carbon atoms<br />add the suffix –ane<br />Unbranched-chain alkane nomenclature<br />C<br />C<br />C<br />C<br />C<br />pentane<br />
  10. 10. All Prefixes<br />
  11. 11.
  12. 12. Branched-chain alkane nomenclature<br />Alkyl groups<br />Groups of atoms that are formed when one hydrogen atom is removed from an alkane molecule<br />Small carbon chains<br />Naming an alkyl group<br />Replacing the suffix -aneof the parent alkane with the suffix -yl<br />
  13. 13. first locate the parent hydrocarbon <br />the longest continuous chain that contains the most straight-chain branches<br />Do not be tricked by the way the molecule is drawn: the longest chain with the most straight-chain branches may be shown bent:<br />not:<br />
  14. 14. name the parent hydrocarbon<br />add the suffix -ane to the correct prefix<br />OCTANE<br />Now identify and name the alkyl groups<br />The three –CH3 groups are methyl groups. <br />The –CH2–CH3 group is an ethyl group<br />Arrange the names in alphabetical order in front of the name of the parent hydrocarbon<br />ethyl methyloctane<br />
  15. 15. To show that there are three methyl groups present, attach the prefix tri- to the name methyl to form trimethyl<br />ethyl trimethyloctane<br />show the locations of the alkyl groups on the parent hydrocarbon<br />Number the octane chain so that the alkyl groups have the lowest numbers possible<br />not:<br />
  16. 16. Place the location numbers of each of the alkyl groups in front of its name. Separate the numbers from the names of the alkyl groups with hyphens<br />The ethyl group is on carbon 3. Because there are three methyl groups, there will be three numbers, separated by commas, in front of trimethyl<br />3-ethyl-2,4,5-trimethyloctane<br />
  17. 17. Properties and uses of Alkanes<br />Alkane molecules are nonpolar<br />Forces of attraction between nonpolar molecules<br />weak London dispersion forces<br />stronger when the molecules are larger<br />So, physical states of alkanes are a function of their molecular size<br />lowest mass—those with 1 to 4 carbon atoms<br />EX: Natural Gas<br />Larger alkanes --- are liquids<br />EX: Gasoline and Kerosene<br />Very high molecular mass --- are solids<br />EX: Paraffin wax<br />
  18. 18. Boiling points of alkanes <br />increase with molecular mass<br />As London dispersion forces increase<br />more energy is required to pull the molecules apart<br />This property is used in the separation of petroleum, a major source of alkanes<br />Petroleum<br />complex mixture of different hydrocarbons that varies greatly in composition<br />Hydrocarbon molecules in petroleum <br />contain from 1 to more than 50 carbon atoms<br />This range allows the separation of petroleum into different portions using different boiling point ranges<br />Fractional distillation<br />components of a mixture are separated on the basis of boiling point, by condensation of vapor in a fractionating column.<br />
  19. 19. How Stuff Works!!<br />
  20. 20. Alkanes – less reactive than other hydrocarbons<br />Stability of single bonds<br />Combustion is main reaction of alkanes<br />CH4 + O2 CO2 + H2O<br />Possible Contribution to Greenhouse effect<br /> Global Warming<br />Powers engines<br />Octane Rating – measure of its burning efficiency and its antiknock properties<br />2,2,4 – trimethylpentane ---- 100 (Very resistant)<br />Heptane ---- 0 (Lots of knocking)<br />Combustion<br />
  21. 21. Unsaturated hydrocarbons<br />Hydrocarbons that do not contain the maximum amount of hydrogen<br />NOT all carbon atoms have four single covalent bonds<br />One or more double bonds or triple bonds between carbon atoms<br />Alkenes<br />hydrocarbons that contain double covalent bonds<br />General formula for alkenes with one double bond is<br />CnH2n<br />
  22. 22. Systematic Names of Alkenes<br />Rules similar to naming alkanes<br />parent hydrocarbon <br />longest continuous chain of carbon atoms that contains the double bond<br />Number so the double bond has the lowest number<br />not:<br />1-pentene<br />
  23. 23. Name alkyl groups – same as alkanes<br /> 2-ethyl-1-pentene<br />More than one double bond<br />the suffix of the name is modified to indicate the number of bonds: <br />2 = -adiene, 3 = -atriene, and so on<br />Name this alkene:<br />
  24. 24. Properties of Alkenes<br />Alkenes are nonpolar <br />show trends in properties similar to those of alkanes in boiling points and physical states.<br />EX:<br />α-farnesene, a solid at room temperature, is found in the natural wax covering of apples<br />
  25. 25. Alkynes<br />Hydrocarbons with triple covalent bonds<br />The simplest alkyne<br />ethyne, more commonly known as acetylene<br />C2H2<br />General formula for an alkyne with one triple bond<br />CnH2n–2<br />Alkyne nomenclature <br />Almost the same as alkene<br />Only difference<br />-enesuffix of the corresponding alkene is replaced with -yne<br />
  26. 26. Aromatic Hydrocarbons<br />hydrocarbons that have six-membered carbon rings and delocalized electrons.<br />Benzene is the primary aromatic hydrocarbon.<br />Molecular formula of benzene is C6H6<br />Benzene does not behave chemically like an alkene<br />Structure of the benzene ring<br />Allows electrons to be spread through delocalized p-orbitals over the whole ring<br />
  27. 27. The structural and skeletal formulas of benzene<br />

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