Chapter 20.3 : Saturated and Unsaturated Hydrocarbons
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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    hydrocarbons in which one or more hydrogen atoms have been replaced by other atoms or other groups of atoms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
    View slide
  • 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
    View slide
  • 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