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Peroxyacids such as mCPBA convert alkenes to epoxides through a concerted, stereospecific process that retains the alkene’s relative geometry. Epoxides can then open under acidic conditions to form trans-diols. In contrast, OsO₄ with a co-oxidant or cold, dilute alkaline KMnO₄ gives syn-dihydroxylation and cis-diols. Further oxidation can cleave vicinal diols or alkenes: periodic acid cleaves diols, while ozonolysis produces carbonyl compounds under reductive work-up and can yield carboxylic acids under oxidative work-up. Hot, concentrated KMnO₄ is a stronger cleavage reagent. The lesson also introduces alkyne oxidation, epoxide ring-opening selectivity, the Baeyer test, and reagent-strength comparisons.