CHE 3331 Chapter Notes - Chapter 17: Steric Effects, Methoxy Group, Aniline
Document Summary
Sigma complex: resonance stabilized carbocation formed during electrophilic aromatic substitution: not aromatic because of the sp3 hybridized carbon interrupts the ring of p orbitals. Can regain aromaticity by a reversal of its formation (equilibrium) or by loss of a hydrogen on the tetrahedral carbon. Overall reaction: substitution of an electrophile (e+) for a proton (h+) Reagents: br2 and a lewis acid (albr3 or febr3) Bromine reacts with the lewis acid to generate a better electrophile, which is then attacked by one of benzene"s double bonds. Rate limiting step = formation of sigma complex. Similar to brominating, but uses alcl3 or fecl3. Requires an acidic oxidizing agents like hno3. First step: sulfuric acid reacts with nitric acid to form the nitronium ion (+no2) One of benzene"s bonds then attacks the nitronium ion, forming a sigma complex. Uses zn, sn or fe with hcl. Using fuming sulfuring acid (concentrated h2so4 with 7% so3) Sulfur trioxide (so3) is the electrophile in the reaction.
