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Chapter 20.3 : Saturated and Unsaturated Hydrocarbons
 

Chapter 20.3 : Saturated and Unsaturated Hydrocarbons

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  • praciou, consider the C=C double bonds in alkenes. Compare it to the definition of saturated hydrocarbon in the slide.
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    Chapter 20.3 : Saturated and Unsaturated Hydrocarbons Chapter 20.3 : Saturated and Unsaturated Hydrocarbons Presentation Transcript

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      hydrocarbons in which one or more hydrogen atoms have been replaced by other atoms or other groups of atoms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