|Using methane, CH4, as a starting point we can add more carbons, one at a time, and more hydrogens to fill out the bonds on the carbons. This first group is called the alkane series and it has the general formula:|
|Look at the list very carefully. Each successive
compound increases by only CH2. Also the molecular weight
only 14.03, that is CH2. It also seems that as
length of the carbon chain increases from 1 to 11 the melting point
as well as the boiling point.
|All of the above are straight-chain alkanes. That is, each
additional carbon is added to the end to form one long continuous chain
are only single bonds in the main chain of the molecule.
|Propane has three carbons in a main chain, hence, prop,
and there are only single bonds in this main chain therefore (ane).
Octane has eight C's in a main chain hence, oct, and again the main
chain has only single bonds between beach carbon therefore it is an
"ane". Both of the above are members of the alkane series. Draw
several more to verify for yourself how these compounds are put
|IUPAC Rules For Naming Organic Compounds.
(International Union of Pure and Applied Chemists)
|1. Find the longest continuous carbon chain. Count the
of carbons in it and determine the prefix.
|2. Check to make sure that all the bonds in this long
chain are single. The ending will be "ane"
|3. Put the prefix and ending together.
|Naming compounds with side chains|
|How do we name something like this?|
|First find the longest carbon chain. It has 11 carbons in
it therefore this compound is a "undec" something. Check to see if it
single bonds. It does, therefore it is an "ane" as well. The compound
a "undecane". What about the C-C group?
|Two carbons is "eth" and it has single bonds therefore it
is ethane but it is attached to the longer chain. Take the "ane" off
and add "yl". This is an ethyl group. If you count bonds it is not C2H6
but it is in fact C2H5-. The "-"
indicates the point of attachment to the long undecane chain. So this
ethylundecane. But where is the "ethyl" group attached. Start counting
from the end of the undecane. The ethyl group is either 5 from one end
6 from the other end. When this happens always choose the lowest
So we can name this as 5-ethylundecane. That is, an 11 carbon
called undecane with an ethyl group stuck on it at the 5th
from the end.
|IUPAC Rules For Naming Branched Compounds|
|1. Determine the longest continuous chain, this will be
the parent chain. Give the parent chain a prefix matching the number of
carbon's in it.
|2. Assign #'s to each C of the parent chain so that the
numbers of all attached side pieces add up to the smallest sum.
|3. Determine the correct name for each branch or other
atom or group.
|4. Attach the name of the alkyl group or other substituent
the name of the parent as a prefix. Place the location # in front and
separate from the name by a hyphen.
|Parent chain is 7 carbons long with all single bonds,
therefore heptane. Side group is one carbon, therefore "meth" and
because it is attached to the parent we add "yl" so we get methyl. The
methyl group is attached
to the parent chain at carbon number 3 not carbon number 5. Count for
yourself. Put it all together 3-methylheptane.
|5. When 2 or more groups are attached, name each, and
locate them by number. Always use hyphens to separate the #'s from each
|Ethyl comes before methyl alphabetically, it just happens
to come that way numerically in this example as well.
|In this example ethyl still comes first alphabetically
methyl. The numbers that locate their point of attachment go with them.
|6. When 2 or more of the substituents are identical, use special prefixes such as "di" for 2, "tri" for three and "tetra" for 4 and specify the location #'s of every group. eg.|
|7. When identical groups are on the same carbon in the
chain, repeat the number on the parent
|Add-on Substitution Groups
The following are substitution groups that can be added on to a main parent chain.
|In addition to the above there are the
F is fluoro
Cl is chloro
Br is bromo
and I is iodo
Go to Organic Worksheet #1 - Simple Chain Nomenclature