a very common problem type seen at the beginning of a course
in organic chemistry, and as such they have a sneaky way making
it onto exams. They are of the kind in which a question is
asked such as, "Draw as many of the structural isomers
of the formula CXHY as you can."
describe a systematic technique for drawing the isomers for
saturated hydrocarbons (the alkanes), which have the formula
CNHN+2. First I'll describe the technique, handled in five
steps, and then I'll apply it to a problem to show you how
to put it to practical use.
FIVE STEPS FOR DRAWING ISOMERS:
the main chain.
Draw the main chain minus 1 carbon, and add a methyl group
to as many positions as possible. Never add the methyl groups
to the end of the chain, and watch not to repeat structures
(it's okay if you accidentally repeat structures, for they
will be caught and discarded when you do step 5).
Draw the main chain minus 2 carbons, and add two one-carbon
groups (two methyls) or one 2-carbon group (an ethyl) to
as many positions possible, trying not to repeat structures.
Continue subtracting and adding groups in this fashion until
you run out of carbons or doing so only results in repeated
Give the IUPAC name to all the compounds you drew. If you
accidentally drew the same one twice, they will have identical
names, and you can cross one of them off.
an example problem