# Question #b418c

Dec 30, 2014

You can't. You need a structural formula to identify a peroxy group.

Consider the molecular formula C₂H₄O₃.

This could represent either hydroxyacetic acid

or peroxyacetic acid

or methyl peroxyformate

H-C(=O)-O-OCH₃

The latter two structures contain peroxy groups, but you need more information than the molecular formula to decide which compound you have.