This module aims to provide to the students a formation on the Hückel theory of and its application on delocalized systems, the creation and reactivity of various cations and other electron-deficient species, various anions and other electron-rich species. Concerning the application of the theory of Hückel on delocalized systems, the stress will be on the determination of the charge on various reactional sites of the system to determine which sites will be preferentially attacked and on the symmetry of molecular orbitals of these systems. ¶Concerning the various reactionnel species, a special attention ¶will be put on the concept of hard a soft of the base or acid to understanding the regioselectivity of these reagents. Concerning ¶ the concept of aromaticity, the stress will be on the structure, the energy of stabibility of the various aromatic systems. Concerning ¶the strategies of synthesis the module stresses on the protection and the deprotection of functional group and retrosynthetic analysis to establish a plan of synthesis. As for the organometallic compounds the stress will be on the utilisation of transition metals in organic synthesis.