Question

How do you draw and name all isomers of `C_3H_4Cl_2`?

Answer 1

You first draw the parent compound propene `C_3H_6`

Explanation:

There is a double bond in it: `CH_2=CH-CH_3`

Now replace two of the `H`'s with `Cl`. You can do this in 5 ways. (remember the double bond always has the lowest number)

`C Cl_2=CH-CH_3` 1,1-dichloropropene

`CHCl=C Cl-CH_3` 1,2-dichloropropene

`CHCl=CH-CH_2Cl` 1,3-dichloropropene

`CH_2=C Cl-CH_2Cl` 2,3-dichloropropene

`CH_2=CH-CHCl_2` 3,3-dichloropropene

Then there's another parent compound `C_3H_6` called cyclopropane , where the `C`'s form a triangle of `CH_2`'s

Here there are only two possibilities to replace two `H`'s:

Both on the same `C` 1,1-dichlorocyclopropane

On two neighbouring `C`'s 1.2-dichlorocyclopropane