Number of structural isomers for ${\mathrm{C}}_3{\mathrm{H}}_6\mathrm{O}$

Structural isomerism happens when two or more compounds have the same chemical formulae but have different structures. 
Prop-1-en-1-ol, Prop-1-en-2-ol, Prop-2-en-1-ol, Methoxyethene, Propanal, Propanone, Cyclopropanol, Oxetane, Methyloxirane; this all adds up to 9 structural isomers.