Do you mean between #"a glycol"#, and #"glyoxal"#?
Explanation:
#"Glyoxal"# is dialdehyde, #H(O=)C-C(=O)H#...the which is commonly used as a precursor for organic synthesis...
On the other hand #"a glycol"# is a dialcohol...i.e. #"ethylene glycol"##-=##HOH_2C-CH_2OH#...here the carbon oxidation state is #-I#, whereas in glyoxal the carbon oxidation state is #+I#.