Question

Explain why this reaction takes place in anti markownikoff regiochemistry. ?
CF3CH=CH2+HCL give rise to CH3CH2CH2CL

Answer 1

Anti-markownikoff addition with unsymmetrical reagents e.g HCl or HBr or HI etc is possible in case of addition on alkene having electron withdrawing groups e.g CF3CH=CH2 (i.e Fluorine is a electron withdrawing group).Substituents with several bonds to electronegative atoms (e.g. -CF3) adjacent to the pi system are electron withdrawing groups (EWG) - they decreasing the electron density on the double through a inductive withdrawing effect. Here after first step (protonation), carbocation is formed on terminal carbon (away from electron withdrawing group) hence nucleophile (Cl) attacks on this terminal carbon (which has greater number of hydrogens).