Hydrocarbons

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Hydrocarbons

• L. Scheffler
• IB Chemistry 3-4.
• Lincoln H.S.

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Hydrocarbons

• Hydrocarbons are organic compounds that contain
  only hydrogen and carbon
• Types of hydrocarbons include
• Alkanes
• Alkenes
• Alkynes
• Aromatic

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Alkanes

• Alkanes have only carbon to carbon single bonds
• Every carbon has four chemical bonds either to
  hydrogen or another carbon atom

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Alkane Structures

• Alkanes have only carbon to carbon single bonds.
• Each time a carbon atom is added to the chain
  there are also two hydrogen atoms added.

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Alkane Structures

• With carbon chains that are four carbon atoms or
  longer there are multiple ways to arrange the
  carbon chains.

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Alkane Structures

• Compounds that have the same molecular formula
  but different structural formulas are called
  Structural Isomers. The carbon chain may be
  consecutive or branched

Straight chain
Straight chain
Double Branched chain
Branched chain
Branched chain
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Alkenes

• Alkenes have one (or more) carbon to carbon
  double bonds
• Since there are fewer hydrogen atoms in alkenes
  as a result of the double bond, alkenes are
  referred to as unsaturated.
• Alkanes on the other hand have the maximum number
  of hydrogen atoms. They are referred to as
  saturated.

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Alkene Structures

• Like alkanes, alkenes can have branched or
  consecutive chains. In the larger alkenes there
  are also multiple locations for the CC. Hence
  multiple structural isomers are possible.

Straight chain. The double bond is between the
second and third carbon
Branched chain
Straight chain. The double bond is between the
first and second carbon
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Alkynes

• Alkynes have one (or more) carbon to carbon
  triple bonds
• Since there are fewer hydrogen atoms in alkynes
  as a result of the triple bond, alkynes like
  alkenes are referred to as unsaturated.

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Alkyne Structures

• Like alkanes and alkenes, alkynes can have
  branched or consecutive chains. In the larger
  alkenes there are also multiple locations for the
  CC. Multiple structural isomers are possible.
  The branch cannot originate on one of the carbons
  making up the triple bond

Branched chain. The triple bond can occur in one
of the branches but branches cannot be attached
to any carbon in the triple bond
Straight chain. The triple bond is between the
second and third carbon
Straight chain. The triple bond is between the
first and second carbon
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Ring Structures

• Hydrocarbons that exist in chains are known as
  aliphatic hydrocarbons
• The ends of a chain may be joined to form a ring
  structure.
• These compounds are known as cyclic structures

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Saturated Cyclic Hydrocarbons

• A number of the smaller alkanes exist as cyclic
  structures including
• Cyclopropane
• Cyclobutane
• Cyclopentane
• Cyclohexane

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Saturated Cyclic Hydrocarbons

• Cyclic alkanes have the general formula
• CnH2n. The additional C-C bond results in the
  loss of two hydrogen atoms

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Unsaturated Cyclic Hydrocarbons

• A few cyclic hydrocarbons may contain CC double
  bonds. Two of the most common are cyclopentene
  and cyclohexene shown in the diagram at the left

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Cyclic Hydrocarbons Condensed structures

• Writing structural formulas for cyclic
  hydrocarbons can be tedious. These short form
  structures are commonly used.
• Each vertex represents a carbon atom and it is
  implied that there are enough H atoms on each
  vertex to make four bonds

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Aromatic Structures

• The benzene ring is a common structure in organic
  molecules
• It consists of 6 carbon atoms and 6 hydrogen
  atoms.
• One would predict that there should also be 3 CC
  bonds in a benzene ring

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Aromatic Structures

• Further investigation reveals that the double
  bonds are not distinct in benzene. Rather it is
  a resonance hybrid.
• Either of these structures could be used to
  represent benzene.

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Aromatic Structures

• Research shows that there are no differences in
  the C to C bonds in benzene.
• The current view of benzene holds that there are
  6 C-C single bonds and 3 pairs or 6 delocalized
  electrons

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Aromatic Structures

• The structure of benzene is shown as either of
  these two structures, or as a circle in a hexagon
  which depicts that the electrons are delocalized

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Fused Aromatic Structures

• Aromatic hydrocarbons are not limited to a single
  ring
• The fused ring structure shown is Naphthalene

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Reactions of Hydrocarbons

• Hydrocarbons tend to be very unreactive compounds
  when compared to other organic molecules.
• Most hydrocarbons are flammable. They burn in
  the presence of oxygen to form carbon dioxide and
  water vapor.
• Examples

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Reactions of Hydrocarbons

• Most Hydrocarbons undergo substitution reactions
  in the presence of ultraviolet light
• Examples

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Reactions of Alkenes

• Hydrocarbons that have CC- undergo addition
  reactions.

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Petroleum

• Crude oil is a mixture of hydrocarbons formed
  over along period of time from the slow decay of
  plant and animal matter
• It is separated by distillation into a variety of
  fractions

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Petroleum

• Crude

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Gasoline

• Gasoline is a mixture of hydrocarbons.
• The grade of a gasoline is based on a system
  known as an octane rating.
• Isooctane is a major component in gasoline that
  burns evenly. It has octane rating of 100
• Heptane burns with small explosions and tends to
  cause engines to knock
• The octane rating is the percentage
• of isooctane in the gasoline mixture
• For an example Gasoline with an
• octane rating of 87 isooctane
• and 13 heptane.

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Natural Gas

• Natural gas is about 85 methane

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Halogenoalkanes or Alkyl Halides

• Halogenoalkanes are compounds in which one or
  more hydrogen atoms in an alkane have been
  replaced by halogen atoms (fluorine, chlorine,
  bromine or iodine).
• Halogenoalkanes are commonly known as alkyl
  halides

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Halogenoalkanes or Alkyl Halides

• Depending on the location of the halogen atom,
  halogenoalkanes may be primary secondary or
  tertiary

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Boiling Points of Halogenoalkanes

• The boiling point depends on the halide
• Cl lt Br lt I
• The boiling points increase as the chain length
  increases

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Solubility of Halogenoalkanes

• The halogenoalkanes are only very slightly
  soluble in water.
• The attractions between the halogenoalkane
  molecules (van der Waals dispersion and
  dipole-dipole interactions) are relatively strong
• Halogenoalkanes are only slightly polar and do
  not effectively break the hydrogen bonds between
  water molecules.
• Halogenoalkanes are soluble in non polar or less
  polar organic solvents such as alcohol, ether,
  and benzene .

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