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LECTURE 6
Wednesday 1/25/17
THE SHAPE OF CYCLOALKANES
THE SHAPE OF CYCLOALKANES (continued)
NAMING CYCLOALKANES
• Cycloalkanes are alkanes containing rings of carbon atoms.
• The prefix __________- is used before the alkane name.
• When two or more substituents are attached to the
cycloalkanes, the ring numbering begins with the first group
alphabetically and proceeds to give lowest numbers possible.
Example:
CH2CH3
1
CH3
3
2
ISOMERISM & CYCLOALKANES
• Stereoisomers are compounds with the same structural
formula but different spatial arrangements of atoms.
• Geometric isomers are molecules with restricted rotation
around C-C bonds that differ in the three-dimensional
arrangements of their atoms in space and not in the order of
linkage of atoms.
• Rotation about C-C single bonds occurs in open-chain
compounds but not within rings.
ISOMERISM & CYCLOALKANES (continued)
• Two geometric isomers exist for 1,2-dimethylcyclopentane.
• _______-substituents are on the _______ side of the ring.
• _______-substituents are on the ________ sides of the ring.
PHYSICAL PROPERTIES OF ALKANES
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•
•
•
•
Non-polar molecules with weak intermolecular forces
Not soluble in water
Low density (less dense than water)
Melting points increase with molecular size
Boiling points increase with molecular size
PHYSICAL PROPERTIES OF ALKANES
(continued)
• A homologous series is a group of compounds with the
same functional class that differ by a –CH2– group.
PHYSICAL PROPERTIES OF ALKANES
(continued)
ALKANE REACTIONS
• Alkanes are the least reactive of all organic compounds.
• The most significant reaction of alkanes is combustion (rapid
oxidation).
• Many alkanes are used as fuels.
• Methane – natural gas
• Propane – used in gas grills
• Butane – lighters
• Gasoline – a mixture of hydrocarbons
ALKANE REACTIONS (continued)
• Complete Combustion (in the presence of adequate oxygen)
CH4 + 2O2 → CO2 + 2H2O + 212.8 kcal/mol
• Incomplete Combustion (not enough oxygen available)
2CH4 + 3O2 → 2CO + 4H2O
CH4 + O2 → C + 2H2O
CHAPTER 12
UNSATURATED HYDROCARBONS
UNSATURATED HYDROCARBONS
• Unsaturated hydrocarbons contain one or more carboncarbon multiple bonds.
• ______________ contain one or more carbon-carbon
double bonds
• _____________ contain one or more carbon-carbon triple
bonds
• _________ contain benzene rings.
NAMING ALKENES
• Step 1: Name the longest chain that contains the C=C bond.
Use the IUPAC root and the –ene ending.
• Step 2: Number the longest chain so the carbon atoms
joined in the C=C bond get the lowest number possible.
• Step 3: Locate the C=C bond with the lower-numbered
carbon.
Examples:
CH3-CH=CH-CH3
CH3-CH2-CH2-CH=CH-CH3
NAMING ALKENES (continued)
• Step 4: Locate and name attached groups.
• Step 5: Combine all the names.
NAMING ALKENES
WITH MULTIPLE DOUBLE BONDS
• Step 1: Follow the same naming instructions for alkenes with
one double bond, except use the endings –diene, – triene,
and the like to denote the number of double bonds.
• Step 2: Indicate the location of all the multiple bonds.
• EXAMPLES:
BONDING CHARACTERISTICS
ALKANES
THE GEOMETRY OF ALKENES
• In C=C bonds, sp2 hybrid orbitals are formed by the carbon
atoms, with one electron left in a 2p orbital. A representation
of sp2 hybridization of carbon:
THE GEOMETRY OF ALKENES (continued)
• During hybridization, two of the 2p orbitals mix with the single
2s orbital to produce three sp2 hybrid orbitals. One 2p orbital
is not hybridized and remains unchanged.
THE GEOMETRY OF ALKENES (continued)
• This gives a planar shape for the sp2 bonding orbitals with
the unhybridized p orbital perpendicular to the plane of the
three sp2 hybridized orbitals.
THE GEOMETRY OF ALKENES (continued)
THE GEOMETRY OF ALKENES (continued)
• Because there is no free rotation about the C=C bond,
_________________________ is possible.
• _______________________ have two similar or identical
groups on the same side of the double bond.
• _______________________ have two similar or identical
groups on opposite sides of the double bond.
THE GEOMETRY OF ALKENES (continued)
• Geometric isomers have different physical properties.
PHYSICAL PROPERTIES OF ALKENES
PHYSICAL PROPERTIES OF ALKENES