(1) Compounds containing two or more -OH or O groups attached adjacent carbon atoms upon treatment with periodic acid HIO₄ undergo oxidation with cleavage of carbon-carbon bonds. -CHO group is oxidised to formic acid, -CH₂OH to formaldehyde, >CHOH to aldehyde or formic acid according to the positions of the groups. The reagent does not react with 1, 3 diols or 1, 4 diols or carbonyl compounds. HIO₄ is reduced to HIO₃. The oxidation is useful in determining the structure. For the same bond cleavage, we can use Lead tetra acetate (CH3COO)₄Pb. The two reagents HIO₄ and (CH₃COO)₄Pb are complementary since periodic acid is best used in water and lead tetra acetate in organic solvents. Similar cleavage is undergone by other compounds that contain oxygens and nitrogens on adjacent carbons beta-aminoalcohols, alpha-hydroxyaldehydes and ketones, alpha-Diketones, aldehydes Glyoxals.   By HIO₄ we can convert epoxides into aldehydes. Alpha hydroxy acids and alpha keto acids are not cleaved by HIO4 but are cleaved by lead tetra acetate. alpha-hydroxyacids give aldehydes or ketones and alpha-ketoacids give carboxylic acids.