How many different ways are there to build each of the following compounds; CH4, C2H6, C3H8?

Question

I am just confused on this concept. I know you can represent these hydrocarbons with the ball and stick model, the molecular formula, structural formula, ect. But what does it mean different ways to build each compound and how many ways there are? Could someone explain how this works and how to answer this question? Thanks!

Answer 1

Basically you are being asked how many isomers exist for each of these molecular formulas.  The answer for each is 1.  Things start to get more interesting with C₄H₁₀.  There are two ways to connect the four carbons:  n-butane (4 carbons in linear chain) and 2-methylpropane (three carbons connected to one carbon).  The number of isomers increases with carbon number.

 

Carbons .   # isomers

1.                          1

2 .                         1

3.                          1

4.                          2

5.                          3

6 .                         5