all of the structural isomers of C6H14.
First you draw the main straight chain.
Since you have six carbons in the formula,
this is hexane. This is your straight
chain isomer, with no branches. Now you
need to think about drawing the branched
To do that, you draw the main chain minus
one carbon. Since your main chain is 6
carbons long, you subtract one carbon
to give you five (pentane). You now have
to add a one-carbon unit (a methyl group)
to the pentane and make as many isomers
as you can, being careful not to duplicate
A general rule is that you don't want
to add groups to the ends of the chains,
because you will end up duplicating a
structure you have already drawn. In the
structure above, for example, don't add
the methyl to the 1 or the 5 carbon. Doing
so in this case would duplicate the straight
chain hexane isomer we have already drawn
in step 1.
In our five-carbon chain, you want to
look what positions to add the methyl
group. Since you don't want to add it
to the ends of the chains, there are three
spots available to add it to -- the 2,
3, and 4 carbons. However, if you draw
one isomer with a methyl group at the
two carbon, drawing another with the methyl
at the 4 carbon would give the same exact
molecule. You don't want to duplicate
structures, so you should just draw one
However, if you didn't recognize that,
and on an exam did draw the same structure
twice, that is okay, since you have a
check in step 5 to make sure each of your
structures are unique.
that you''ve done it for the six and the
five carbon chains, do it for the four.
With four you've subtracted two carbons
from the main chain, so you have to either
add two one carbon methyl groups, or one
two carbon ethyl group, to a butane.
In this case, adding a two-carbon unit
to either the number two or number three
carbon gives an identical structure to
one previously drawn. So try adding the
methyls. To your four-carbon chain you
need to add two methyl groups. You can
add both methyls to the number two carbon
(or both to the three carbon--they will
be the same molecule), or you can add
one methyl to the 2 and one to the three.
Again, you don't add to the end of the
chains. This gives you two more isomers
with the four carbon chain.
You have now drawn out the six, five,
and four carbon chains. Now, you could
try to go to three carbons, and then add
three methyl groups. But in this case,
doing so turns out to only repeat structures
that you have already drawn. (That is
probably not obvious. On an exam,
you would just have to keep going until
you found you were only drawing repeats.)
Now you want to make sure that you didn't
accidentally draw the same compound twice.
To check that, you name each of theisomers
using IUPAC nomenclature.
each one has a different name, all of these
are different isomers.