Chapter 20
Chemistry of Carbon


  1. Abundance and Importance of Carbon
    carbon found in all living matter
    found in fuels

    1. Structure and Bonding of Carbon
      mostly nonmetallic properties
      normal electron configuration v sp3 hybridization
      normally shares four electrons which are equal in energy

      Figure 20-1 page 625, Orbital models of carbon

      double bonds using sp2 hyrbidization

      Figure 20-2 page 626 Orbitals for double and triple bonds in carbon

      carbon atoms in the same plane for this type of hybridization as in C2H4 and C4H8.

      Triple bonds are linear because of the sp hybrid orbitals e.g. C2H2 and C6H10.

    2. Allotropes of Carbon
      Allotropes - definition

      1. Diamond
        hardest material known
        most dense form of carbon
        extremely high mp (3500oC)
        all due to structure

        Figure 20-3 page 626 Diamond structure

        covalent network crystal
        each atom in the center of a tetrahedron
        used for cutting, drilling, and grinding
        industrial diamonds are not gem quality diamonds

        conducts heat better than silver or copper because of its ability to use vibrational motion to transfer the heat

        does not conduct electricity because it has no free electrons that can move

      2. Graphite
        softness
        feels greasy and crumbles easily
        due to structure

        figure 20-4 page 627, structure of graphite

        layered structure with hexagons in each layer; hexagons involve strong covalent bonds while the layers are held together by weak London dispersion forces and thus can slide over one another

        lubricant and lead for pencils

        within the layer, each carbon is bonded to only three other carbons and so each has a free electron and so graphite conducts electricity; also the bonds within the layers are resonance hybrids

        delocalized electrons - definition

        high melting point (3652oC) because the delocalized electrons helps form a strong covalent network within the layers

        graphite fibers used in sporting goods; the bonds within layer create a situation that makes it difficult to pull apart the graphite in the direction parallel to the surface of the layers

      3. Fullerenes
        discovered in 1980

        class of compounds; part of the soot that forms when carbon compounds are burned with a limited amount of oxygen

        structure is almost spherical cages of carbon atoms; most stable is C60, formed by 60 carbon atoms arranged in interconnected five and six membered rings

        figure 20-5 page 628, geodesic dome and fullerenes structure

        C60 is called buckminsterfullerenes; structure also resembles a soccer ball

        Homework 20-1

    3. Organic Compounds
      All organic compounds contain some carbon but not all carbon compounds are considered organic e.g. Na2CO3, CO, CO2.

      organic compounds - definition

      Figure 20-6 page 629 examples of organic compounds

      1. Carbon Bonding and the diversity or Organic Compounds

        carbon electron configuration allows it to form chains and rings; it can also combine with other element, itself, and it can do so using single, double, or triple bonds

        1. Carbon Carbon Bonding

          the bonding that allows carbon to form long chains and rings is called catenation

          catenation - definition

          not only can you have chains but you can have branched chains and also rings

          figure 20-7 page 630 chains v rings

        2. Carbon Bonding to Other Elements

          carbon atoms can bind to elements with similar electronegativities

          hydrocarbons - definition

          some compounds contain a hydrocarbon backbone and other elements are attached to the backbone; these elements can include O, N, S, and the halogens

          Figure 20-8 page 630

        3. Arrangement of Atoms

          Some molecules of carbon can have the same atoms as other molecules of carbon but have different properties because the atoms are arranged differently

          e.g. C2H6O can be either ethanol or dimethyl ether

          Isomers - definition

          The more carbon atoms in a formula, the greater the number of isomers that are possible. e.g. For C8H18 there are 18 isomers; for C9H20 there are 35 isomers; for C10H22 there are 75 isomers.

          To distinguish one isomer from another for a particular compound, you need to know more than the molecular formula.

      2. Structural Formulas
        Organic chemists use structural formulas because of things like isomers.

        Structural formula - definition

        example of structural formula for C4H10 p 630




        Figure 20-9 p 631

        Condensed structural formula:



        Actual three-dimensional appearance of ethanol in figure 20-9


      3. Isomers
        Can have same molecular formula but different structural formula; also can have structural and geometric isomers.

        1. Structural Isomers
          structural isomers - definition

          Two structural isomers for the compound C4H10



          Butane on the left is a continuous chain of four carbon atoms;
          the methylpropane has a continuous chain of three carbon atoms and a methyl group attached to the center carbon.

          Structural isomers can have different physical and chemical properties e.g. table 20-1 page 632

        2. Geometric Isomers
          Geometric Isomers - definition

          e.g. 1,2-dichloroethene has a cis and trans isomer - page 632




          The two chlorines on the same side of the double bond make the left side molecule a cis molecule; when they are on different sides of the double bond they are trans molecules.

          The bonding order is the same i.e. each carbon in the double bond is bonded to a hydrogen and a chlorine.

          Figure 20-10 p 632

          Another example at the bottom of page 632 shows two molecules that are not geometric isomers. Geometric isomers have to have a rigid structure and each carbon has to have two different groups attached




          .

          Geometric isomers differ in both physical and chemical properties.

          Some geometric isomers are known to differ in physiological behavior e.g. pheromones.

          Figure 20-11 page 633 shows the European corn borer.

          Homework 20.2

    4. Saturated Hydrocarbons
      Hydrocarbons are grouped by the type of bonding.
      Saturated hydrocarbons - definition

      1. Alkanes
        Alkanes - definition

        table 20-2 page 635 - Alkanes with one to four carbon atoms

        Pattern -CH2-

        Page 634 homologous series - member differences




        Homologous series - definition

        Such series have a generalized formula. For the alkanes it is CnH2n+2.

        For an alkane with 30 carbons the formula would be C30H62.

        Alkanes with four or more carbon atoms can have straight or branched chains and so they can have structural isomers. One to three carbon atoms gives only straight chains and so no structural isomers

      2. Cycloalkanes
        Cycloalkanes - definition

        Simple form leaves out carbons and hydrogens such as at the top of page 636






        When there is a closed chain or ring structure, there are two fewer hydrogens as compared to a similar alkane. e.g. butane and cyclobutane on page 636






        The general formula for cycloalkanes is CnH2n.

      3. Systematic Names of Alkanes
        IUPAC

        name of longest carbon chain or parent hydrocarbon in the molecule

        table 20-3 page 636 - Carbon atom chain prefixes

        from five carbons on up, the prefixes are Latin or Greek prefixes

        1. Unbranched Chain Alkane Nomenclature
          Need the prefix to describe the number of carbons in the parent chain; add suffix -ane

          e.g. heptane page 636





        2. Branched Chain Alkane Nomenclature
          Alkyl groups - definition

          replace suffix -ane of the corresponding alkane with suffix -yl

          Table 20-4 page 637

          Example - page 637






          name groups attached to parent chain







          write them in alpha order

          use prefix to indicate more than one of a particular group

          number where groups attach to parent chain using lowest possible numbers

          hyphens separate numbers from names

          commas separate numbers

          Example p 638




          names of alkyl groups and numbering of alkyl group positions on parent chain

          ethyl methyloctane


          3-ethyl-2,4,5-trimethyloctane


          alkane nomenclature - page 639

          Sample Problem 20-1 page 639





















          Sample Problem 20-2 page 640











          Do practice problems on p 641

        3. Cycloalkane Nomenclature




          One alkyl group attached needs no number to identify its location; if more than one alkyl group, number the carbon atoms in the ring to provide the lowest possible numbers to locate the alkyl groups.





          cycloalkane nomenclature p 642

          propane example p 642


          Examples at bottom of p 642



      4. Properties and Uses of Alkanes
        Table 20-5 p 643

        Structure of alkanes: carbon-hydrogen bonds are nonpolar, thus the only forces of attraction are weak intermolecular forces, or London dispersion forces which increases as the mass of a molecule increases.

        1. Physical States
          Table 20-5 p 643

          Those with one to four carbons are gases at room temperature.

          Natural gas - definition

          Larger alkanes are liquids.

          Gasoline and kerosene - mostly liquid alkanes. Stronger London dispersion forces because of larger molecules.

          Alkanes with a very high molecular mass are solids - even greater London dispersion forces. Paraffin wax.

          Figure 20-12 p 643

        2. Boiling Points
          Table 20-5

          increase with increasing molecular mass

          greater molecular mass - greater London dispersion forces

          Petroleum - definition

          Molecules in petroleum contain from one to more than fifty carbon atoms.

          Table 20-6 p 644

          Fractional Distillation - definition

          Figure 20-13a p 644
          Figure 20-13b

          Read description.

        3. Combustion
          Alkanes are less reactive than other hydrocarbons because of their stable single bonds.

          They undergo combustion to form carbon dioxide and water.

          Greenhouse effect because of carbon dioxide.

          Internal combustion engine - knocking caused by spontaneous igniting of fuel before it is reached by the flame front - loss of power. Straight chain HC’s are more likely to do this.

          Octane rating - definition

          Based on mixtures of 2,2,4-trimethylpentane, a highly branched alkane, and heptane, a straight chain alkane.

          The term octane comes from the common name of 2,2,4-trimethypentane (isooctane). Pure isooctane is very resistant to knocking and is assigned an octane number of 100. Pure heptane has an octane number of zero and burns with a lot of knocking. Increasing the percentage of branched chain alkanes in gasoline is one way to increase octane rating.

          Figure 20-14 p 645 - Octane ratings on gasoline pumps.

          Homework 20.3


  2. Unsaturated Hydrocarbons
    unsaturated hydrocarbons - definition

    1. Alkenes
      alkenes - definition

      Table 20-7 p 647

      simplest has to have two carbons because of double bond




      general formula is CnH2n

      can have geometric isomers

      e.g. butene p 648




      1. Systematic Names of Alkenes

        similar to rules for alkanes

        parent chain must contain the double bond

        suffix -ene is used with carbon chain prefix

        e.g. pentene p 648




        number indicating the position of the double bond is placed before the name of the hydrocarbon chain and separated by a hyphen

        1-pentene

        position and name of alkyl group are placed in front of the double bond position number

        2-ethyl-1-pentene
        If there is more than one double bond, the suffix is as follows: 2 double bonds: -adiene; 3 double bonds: -atriene, etc.

        e.g. 1,4-pentadiene p 648




        if numbering from both ends gives equivalent positions for the double bonds in an alkene with two double bonds, then the chain is numbered from the end nearest the first alkyl group

        e.g. 2-methy,-1,3-butadiene p 648



        Alkene Nomenclature p 649

        Figure 20-15 p 650

        Figure 20-16 p 651

        Sample Problem 20-3 p 649















      2. Properties and Uses of Alkenes
        Read

    2. Alkynes
      alkynes - definition

      simplest one has two carbons

      general formula: CnH2n-2

      1. Systematic Naming of Alkynes
        suffix is -yne
        similar to alkenes

        Alkyne Nomenclature p 651 and Alkyne Nomenclature p 652

        1-pentyne and 3-methyl-1-butyne p 652





        figure 20-17 p 652


      2. Properties and Uses of Alkynes
        Read

    3. Aromatic Hydrocarbons
      aromatic hydrocarbons - definition

      benzene, C6H6 - the primary aromatic hydrocarbon

      structure of benzene p 652

      not chemically like an alkene

      all of the carbon-carbon bonds are the same

      delocalized electrons

      molecule is in the same plane

      figure 20-18 p 653

      condensed form of benzene p 653

      simplest aromatic hydrocarbons have one benzene ring as in methylbenzene p 653

      1. Systematic Names of Aromatic Hydrocarbons
        simplest named as alkyl substituted benzenes

        alkyl group added to word benzene

        No need to specify which carbon of the ring if there is only one alkyl group

        If more than one, number the carbons to give all of the alkyl groups the lowest possible numbers

        e.g. propylbenzene and 1,3-dimethylbenzene p 653

        Simple Aromatic Hydrocarbon Nomenclature p 653 and p654

        Sample Problem 20-4 p 654







      2. Properties and Uses of Aromatic Hydrocarbons
        Read


        Homework 20.4

        end of notes

        An alkyl group is a group of atoms that are formed when one hydrogen atom is removed from an alkane molecule. back

      3. Alkanes are hydrocarbons that contain only single bonds. back

        Allotropes are two or more forms of an element that have different structures. back

        fullerenes are dark colored solids made of spherically networked carbon atom cages. back

        Delocalized electrons are electrons shred by more than two atoms. back

        Organic compounds are covalently bonded compounds containing carbon, excluding carbonates and oxides. back

        Catenation is the covalent binding of an element to itself to form chains or rings. back

        Hydrocarbons are composed of only carbon and hydrogen; they are the simplest organic compounds. back

        Isomers are compounds that have the same molecular formula but different structures. back

        A structural formula indicates the number and types of atoms present in a molecule and also sows the bonding arrangement of the atoms. back

        Structural isomers are isomers in which the atoms are bonded together in different orders. back

        Geometric isomers are isomers in which the order of atom bonding is the same but the arrangement of atoms in space is different. back

        Saturated hydrocarbons are hydrocarbons in which each carbon atom in the molecule forms four single covalent bonds with other atoms. back

        A homologous series is one in which adjacent members differ by a constant unit. back

        Cycloalkanes are alkanes in which the carbon atoms are arranged in a ring, or cyclic structure. back

        Alkyl groups are groups of atoms that are formed when on hydrogen atom is removed from an alkane molecule. back

        Natural gas is a fossil fuel composed primarily of alkanes containing one to four carbon atoms. back

        Petroleum is a complex mixture of different hydrocarbons that varies greatly in composition. back

        Fractional distillation involves the separation of the components of a mixture on the basis of boiling points by condensation of vapor in a fractionating column. back

        Octane rating of a fuel is a measure of its burning efficiency and its antiknock properties. back

        Unsaturated hydrocarbons are hydrocarbons in which not all carbon atoms have four single covalent bonds. back

        Alkenes are hydrocarbons that contain double covalent bonds. back

        Alkynes are hydrocarbons with triple covalent bonds. back

        Aromatic hydrocarbons are hydrocarbons with six membered carbon rings and delocalized electrons. back

        Benzene is the primary aromatic hydrocarbon. back