No. of possible monochlorinated product (only structural isomers) of iso-octane 

Iso-octane is 2,2,4-trimethylpentane, its skeletal structure is:

To count the number of possible monochlorinated structural isomers of iso-octane, consider the distinct types of hydrogen atoms that can be replaced by chlorine.

Types of hydrogens:

1. On primary carbons (methyl groups): The three types of methyls are:
   • Two equivalent methyls at C-2 (two attached methyl groups on the same carbon),
   • One methyl at C-4,
   • One methyl at C-1 (terminal).
2. On secondary carbons (CH):
3. On tertiary carbons (C with three alkyl groups).

Counting distinct positions:

• Cl substitution on each unique type of hydrogen gives different isomers.

By considering symmetry and positions, the number of distinct monochlorinated structural isomers of iso-octane is 9.