Pentamethylene and hexamethylene glycols over a catalyst consisting of iron, silicon, chromium and potassium oxides undergo intramolecular condensation at about 640 K, but considerably different products are obtained: 2,3-dihydropyran and cyclopentanone, respectively. Above 650 K, both glycols undergo intermolecular condensation forming corresponding 5-nonanone and 6-undecanone. Reactions were carried out in a standard flow system under atmospheric pressure in the gas phase.