of straight chain alkanes (alkanes that do not branch) is
a straightforward process. To give an alkane a name, a prefix
indicating the number of carbons in the molecule is added
to the suffix ane, identifying both the kind of molecule
(an alkane) and how many carbons the molecule has (the prefix).
The name pentane, for example, tells you that the molecule
is an alkane (thus the ane ending) and that it has
five carbons (pent indicates five). Prefixes for alkanes that
have 1-4 carbons are rooted historically. These are methane,
ethane, propane, and butane, respectively. On the other hand,
for 5 carbons and up a prefix derived from greek is given.
(An easy way to remember the first four names is the anagram
Mary eats peanut butter, standing
for methane, ethane, propane, butane). Learning the prefixes
for up to twelve carbons is a good idea, and they are listed
in the figure below.
becomes more complex if the alkane branches. In such a case,
there are several rules that you must follow to give the
alkane the correct name.
the longest chain of carbons in the molecule. The number
of carbons in the longest chain becomes the parent name
(refer to the above table)
finding the parent chain, you number the parent chain starting
with the end nearest the first substituent (a substituent
is any fragment that juts off the main chain).
Next, determine the names of all substituents.
Substituents are named as if the piece were a separate molecule,
except that the suffix of yl is used rather than ane. Thus,
a two-carbon substituent would be an ethyl substituent (not
an ethane substituent).
the substituents in alphabetical order (ie. ethyl before
methyl) in front of the parent name.
Next, identify the positions of all substituents in the
name by placing the carbon number where the substituent
attaches to the parent chain in front of it. For example,
2-methylheptane indicates that a methyl substituent is attached
to the number 2 carbon.