How do you determine the number of isomers an organic compound can form?

Answer 1

With any hyrdrocarbon there is a way to narrow down your possible isomers. I always use this formula to start a problem of this kind. This formula is used to find the unsaturation of the molecule which in turn can help you figure out how many rings, double or triple bonds are in the structure.

(2C+2-H-X+N)/2

You just multiply the number of Carbons by 2 add 2 subtract the number of hydrogens and halides (X= Cl, I, Br) and add the number of nitrogens. Divide all of that by 2. NOTE: the number of oxygens does not factor into the unsaturation

Here's an example of how to find unsaturation:

C6H9Cl

(2(6) + 2 - 9 - 1)/2 = 2

How to interpret your results:

An unsaturation of o indicates no unsaturation and therefore the molecule has no rings, or double or triple bonds

An unsaturation of 1 indicates that there is either a ring or a double bond

An unsaturation of 2 indicates there is either a ring and a double bond, 2 double bonds or a triple bond

etc...

We now know that the example will have isomers with 1 triple bond, 2 double bonds, and ones with a ring and a double bond.

This formula is very useful and a great tool for organic chemistry.

Answer 2

No of sterioisomers = 2n

Answer 3

You can not calculate this in general. There is no rule or law for that issue.

Compensate lack of knowledge and experienced insight by lots of trial and error work.

Answer 4

C(number) H(2xnumber +2)

Example, if a molecule has 12 carbon, it will have (12 x 2 +2) = 26 hydrogen

Answer 5

2n