1. Aliphatic Series Chains or Branched Chains
Hydrocarbons
Aliphatic Series
Chains or Branched Chains
Kenneth E. Schnobrich

2. 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
2 single
bonds &
1 double
bond
2 double
bonds
1 single
Bond &
1 triple bond
4 single
bonds

3. 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.

4. 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

5. iso-Butane
2 methyl Butane
C4H10
Methane
CH4
Ethane
C2H6
n-Pentane
C5H12
Propane
C3H8
iso-Pentane
2 methyl Butane
C5H12
n-Butane
C4H10

6. 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

7. Hexane & Isomers n-Hexane C6H14 2,3 dimethyl Butane

8. 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

9. Let’s Use Hexane
Methyl group -CH3 1
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 2 4 3
Methyl group -CH3

10. Next Isomer of Hexane
both Methyl groups on carbon #2
Methyl group -CH3
Methyl group -CH3
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 2 1 4 3

11. 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.

12. 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

13. 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.

14. Note the double bond - since there are only two 1
Note the double bond - since there are only two
bond spaces the name is simply Propene 2 2 1
Note the double bond - since there are only two
bond spaces the name is simply Propene

15. 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

16. 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.

17. Alkyne Series (cont.)
The first member of the alkyne series is ethyne (commonly called acetylene) and its formula is C2H2.
As the carbon chain grows longer (4 or more carbons) it is necessary to locate the triple bond in the name of the compound.
Triple bond

18. You can tell the triple bond by the
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.
Triple bond
You can tell the triple bond by the
Shorter bond distance
Butyne-1 or 1-Butyne
Pentyne-2 or 2-Pentyne 1 2 3 4

19. 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.

20. 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).

21. 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

22. Aromtic Hydrocarbons
The second member of the Benzene series is Toluene (foul smelling).
The general formula for the series is CnH2n-6.
-CH3