  (English) In this lecture I discuss recent progress in the understanding of
the chemical evolution of protoplanetary disks that resemble our Solar system
during the first ten million years. At the verge of planet formation, strong
variations of temperature, density, and radiation intensities in these disks
lead to a layered chemical structure. In hot, dilute and heavily irradiated
atmosphere only simple radicals, atoms, and atomic ions can survive, formed and
destroyed by gas-phase processes. Beneath the atmosphere a partly UV-shielded,
warm molecular layer is located, where high-energy radiation drives rich
chemistry, both in the gas phase and on dust surfaces. In a cold, dense, dark
disk midplane many molecules are frozen out, forming thick icy mantles where
surface chemistry is active and where complex (organic) species are
synthesized.
