Hydrocarbon Nomenclature
The carbon is at the
center of a tetrahedron
formed by 4 hydrogens
General Formula for Alkanes: CnH2n+2
1) Full Structure
2)
No hydrogens
3) Condensed Formula
4)
Short Form

Imagine a carbon at the end of each line!
Octane C8H18
CH3CH2CH2CH2CH3
Pentane C5H12
Decane C10H22
CH3(CH2)5CH3
Heptane C7H16
Octane C8H18
1)
For each hydrocarbon, write a condensed
formula and a line drawing
Propane
2)
Nonane
3)
Hexane
4)
Pentane


Draw this hydrocarbon: (add enough bonds
or “sticks” so that each C makes 4 bonds)
C
|




C–C|
-C-C–C–C–C–C-C
|
|
C
C–C–C
We now have several new nomenclature
issues!
C
C–C–
|
|
-C-C–C–C–C–C-C
|
|
C
C–C–C
1) Find the longest continuous C chain –
lets circle it in red. This is the PARENT
CHAIN
2) Find all of the branches or substituents –
circle them in green
3) Number the carbons of the parent chain
from the end of the chain that gives the
substituents the lowest numbers. If two
or more side chains are in equivalent
positions, assign the lowest number to
the one which will come first in the
name.
In our hydrocarbon, start numbering from the
left because the first branch occurs from the
second C (while it would be the fourth C if you
started from the right)




If the same substituent occurs more than once, the location of each
point on which the substituent occurs is given. In addition, the number
of times the substituent group occurs is indicated by a prefix (di, tri,
tetra, etc.).
If there are two or more different substituents they are listed in
alphabetical order using the base name (ignore the prefixes). The only
prefix which is used when putting the substituents in alphabetical order
is iso as in isopropyl or isobutyl. The prefixes sec- and tert- are not
used in determining alphabetical order except when compared with each
other.
If chains of equal length are competing for selection as the parent chain,
then the choice goes in series to:
a) the chain which has the greatest number of side chains.
b) the chain whose substituents have the lowest- numbers.
c) the chain having the greatest number of carbon atoms in the smaller
side chain.
d)the chain having the least branched side chains.
A cyclic (ring) hydrocarbon is designated by the prefix cyclo- which
appears directly in front of the base name.