Download Hydrocarbons - New York Science Teacher

Hydrocarbons
Aliphatic Series
Chains or Branched Chains
Kenneth E. Schnobrich
What Makes Carbon Special?
• Note the electron configuration of
carbon in the ground state, 2-4.
• Using Lewis Dot Structures we can
examine several arrangements for the
electrons
Case 1
Case 2
Case 3
Case 4
C
C
C
C
4 single
bonds
2 single
bonds &
1 double
bond
2 double
bonds
1 single
Bond &
1 triple bond
Carbon Special cont.
• Case #1 - atoms tend to bond in a tetrahedral fashion
around carbon. If they are identical atoms the
molecule is nonpolar.
• Case #2 - atoms tend to bond in a trigonal planar
fashion around carbon. These molecules tend to be
polar.
• Case #3 - atoms tend to bond in a linear fashion
around the carbon. If the bonding atoms are identical
the molecule will be nonpolar.
• Case #4 - atoms tend to bond in a linear fashion
around the carbon. These molecules tend to be
polar.
The Alkane Series
• Members of the Alkane series all have names
that end in “ane”.
• They are saturated hydrocarbons - all single
bonds between carbon atoms.
• They are all members of a homologous series
- they each differ by a -CH2 group.
• They all follow the general formula
CnH2n+2
• They undergo substitution reactions
iso-Butane
2 methyl Butane
C4H10
Methane
CH4
Ethane
C2H6
n-Pentane
C5H12
Propane
C3H8
n-Butane
C4H10
iso-Pentane
2 methyl Butane
C5H12
Isomers
• Notice that in Butane and Pentane the
molecular formula is the same but there
are different arrangements for the
atoms. This defines an isomer - same
formula, different arrangement.
• Look at Hexane on the next slide
Hexane & Isomers
n-Hexane
C6H14
2,3 dimethyl Butane
C6H14
2,2 dimethyl Butane
C6H14
Rules for Naming
• Locate the longest continuous chain of
carbon atoms (that is the base name)
• Number the carbons in the longest chain
starting from that end to which the attached
group (or groups) are closest
• If there is more than one of the same
attached group you must use a prefix like - di,
tri, tetra
• Identify the number of the carbon on the
longest chain to which the groups are each
attached
Let’s Use Hexane
Methyl group -CH3
1
2
4
3
Methyl group -CH3
- Notice there are four carbons in the longest
continuous chain (Butane)
-You can # from either end because of the
location of the attached “methyl” groups
- Since there are two “methyl” groups you
must use the prefix “di” (dimethyl)
- Notice that one is on carbon 2 and the
other on carbon 3
- So the final name would be
2,3 dimethyl Butane
Next Isomer of Hexane
both Methyl groups on carbon #2
Methyl group -CH3
Methyl group -CH3
2
4
1
3
- Notice there are four carbons in the longest
continuous chain (Butane)
-You must # from the left end because of the
location of the two attached “methyl” groups
- Since there are two “methyl” groups you
must use the prefix “di” (dimethyl)
- Notice that both “methyl” groups are on
carbon 2
- So the final name would be
2,2 dimethyl Butane
Isomers
• It should be noted that as the number of
carbons increases the number of
possible isomers increases
considerably.
• For example, Octane (C8H18), there are
18 possible isomers including a
continuous chain of 8 carbons.
The Alkene Series
• Members of the Alkene series all have names
that end in “ene”.
• The are unsaturated hydrocarbons - there is
one double bond between two carbon atoms.
• They are all members of a homologous series
- they differ by a -CH2 group
• They all follow the general formula CnH2n
• They undergo addition reactions
Alkene Series cont.
• Since the double bond can appear
anywhere in the longest chain you must
identify its location by numbering the
bond spaces.
• Always start from that end of the carbon
chain to which the double bond is
closest.
1
2
Note the double bond - since there are only two
bond spaces the name is simply Propene
2
1
Note the double bond - since there are only two
bond spaces the name is simply Propene
The double bond appears in bond position #1
so the compound is named Butene-1
3
2
1
The double bond appears in bond position #2
so the compound is named Butene-2 - it doesn’t
matter which end you number from, the double
bond appears in the second bond space
2
1
3
Note - as the number of carbons in the chain increases the number of
possible double bond locations increases
Alkyne Series
• The alkynes are hydrocarbons whose
names all end with “yne”.
• The alkynes are characterized by a
triple bond between two carbon atoms
somewhere in the structure.
• The alkynes are unsaturated and follow
the general formula CnH2n-2.
• Alkynes undergo addition reactions at
the triple bond.
Alkyne Series (cont.)
• The first member of the alkyne series is
ethyne (commonly called acetylene)
and its formula is C2H2.
Triple bond
• As the carbon chain grows longer (4 or
more carbons) it is necessary to locate
the triple bond in the name of the
compound.
Alkyne Series (cont.)
• Now you must number the bond spaces
(between the carbon atoms) starting
from that end of the chain to which the
triple bond is closest.
2
1
3
3
2
1
4
Triple bond
Triple bond
You can tell the triple bond by the
Shorter bond distance
Butyne-1 or 1-Butyne
Pentyne-2 or 2-Pentyne
General Comments
• Whether it is the alkane, alkene, or
alkyne series they are considered
homologous series because each
member differs by the same –CH2
grouping (or structure).
• In all of the series, the greater the
complexity of the structure the higher
the boiling point.
General Comments (cont.)
• Alkanes (saturated hydrocarbons)
undergo substitution reactions.
• Alkenes and Alkynes (unsaturated
hydrocarbons) undergo addition
reactions.
• Organic compounds generally have low
melting and boiling points (weak
intermolecular attractions).
Aromatic Hydrocarbons
• Aromatic hydrocarbons have typical,
sometimes unpleasant, odors.
• Benzene, the first member of the
Benzene series, has a unique ring
structure with alternating double bonds.
Double bond
Double bond
Just another way of representing Benzene
Double bond
Aromtic Hydrocarbons
• The second member of the Benzene
series is Toluene (foul smelling).
-CH3
• The general formula for the series is
CnH2n-6.