Vaniya was confused when she came to know about different structures of butane. Deduce the property behind it and give different structures of butane on the basis of this property.

Draw the structures of the isomers for bromobutane. 
 

Of the isomeric hexanes, the isomer which can give two mono chlorinated compounds is 

The following compounds $1$and  $2$ with the identical molecular formula, but different structures are called;

${\mathrm{C}}_5{\mathrm{H}}_{12}$