This course is the continuity of study of organic reaction mechanisms (CHEM-6209) in which rest of the polar mechanism (redox, molecular rearrangements and pericyclic cyclization) are addressed. The chemistry of reactive intermediates (carbenes, nitrenes, arynes) are also focused in this course. This course is a foundation course for Organic Synthesis (CHEM-6240, Organic Chemistry major course of semester-VIII) and Advance Organic Synthesis (CHEM-7146) of MSc and MPhil, respectively, with organic chemistry specialization. The reaction mechanism of a chemical reaction is a step-bystep description of the course on which the starting materials are converted into the products. The course is described on a molecular level and contains information about the position of all atoms and electrons of the reactants (including the solvent, etc.) at each point of the reaction course (called reaction coordinate) and, thus, about all the shiftings and movements of electrons and atoms. At the end of this course the student’s shall be able to predict the mechanism of reaction and the synthetic methodologies of small organic molecules.