# How many isomers of C_4H_8Cl_2 are here? How do you tell if one structure is an isomer of another?

Jun 28, 2016

I count 13 isomers of ${\text{C"_4"H"_8"Cl}}_{2}$: 9 structural isomers and 4 optical isomers,

#### Explanation:

I find that the easiest way to tell if one structure is an isomer of another is to write their IUPAC names.

Each isomer will have a unique name.

We use a systematic procedure to generate the structures.

A. Base chain is 1-chlorobutane

1,1-Dichlorobutane

($R$)- and ($S$)-1,2-Dichlorobutane

($R$)- and ($S$)-1,3-Dichlorobutane

1,4-Dichlorobutane

B. Base chain is 2-chlorobutane

2,2-Dichlorobutane

(2R,3R)"-", (2S,3S)-, and ($2 R , 3 S$)-2,3-Dichlorobutane

C. Base is 1-chloro-2-methylpropane

1,1-dichloro-2-methylpropane

1,2-Dichloro-2-methylpropane

1,3-Dichloro-2-methylpropane