Organic Chemistry Help!  
Organic Chemistry Help
Organic Chemistry Help!     
Organic Chemistry Help!





































































 site navigation

site info

site search






drawing isomers1 > organic chemistry tutorials > home      

Drawing isomers from a molecular formula


Draw all of the structural isomers of C6H14.

Here goes.

  1. 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 isomers.

  2. 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 structures.

    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 of them.

    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.

  3. Now 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.

  4. 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.)

  5. 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.

Since each one has a different name, all of these are different isomers.

 See other tutorials

Home || email: ||