Bromonium ion mechanism Electrophilic addition Br: Br of bromine to give a cation is followed by cyclization to give a bromonium ion :Br · This bromonium ion is +B a reactive electrophile and bromide ion is a kood nucleophile gC Br+ Bromonium ion
Bromonium Ion Mechanism • Electrophilic addition of bromine to give a cation is followed by cyclization to give a bromonium ion • This bromoniun ion is a reactive electrophile and bromide ion is a good nucleophile
The reality of Bromonium lons Bromonium were postulated more than 60 years ago to expain the stereochemical course of the addition (to give the trans-dibromide from a cyclic alkene Olah showed that bromonium ions are stable in liquid SO, with SbFs and can be studied directly Br Br: HCN SbF C-C SbF \CH Liquid so HoC \CH3 H CH H Sb Bromonium ion (stable in SO solution) ◎ Thomson- Brooks cole
The Reality of Bromonium Ions • Bromonium were postulated more than 60 years ago to expain the stereochemical course of the addition (to give the trans-dibromide from a cyclic alkene • Olah showed that bromonium ions are stable in liquid SO2 with SbF5 and can be studied directly
4.6 Addition of ha to p96 Alkenes: Hydrogenation Addition of h-h across c=c Reduction in general is addition of h, or its equivalent Requires pt or pd as powders on carbon and H, Hydrogen is first adsorbed on catalyst Reaction is heterogeneous(process is not in solution) H ch? pi CH CH CH
4.6 Addition of H2 to Alkenes: Hydrogenation • Addition of H-H across C=C • Reduction in general is addition of H2 or its equivalent • Requires Pt or Pd as powders on carbon and H2 • Hydrogen is first adsorbed on catalyst • Reaction is heterogeneous (process is not in solution) p.96
Hydrogen Addition- Selectivity Selective for c=c no reaction with c=o. c=n Polyunsaturated liquid oils become solids If one side is blocked, hydrogen adds to other CH CH HC 人C=入 CHS H-H CH H
Hydrogen Addition- Selectivity • Selective for C=C. No reaction with C=O, C=N • Polyunsaturated liquid oils become solids • If one side is blocked, hydrogen adds to other
Mechanism of Catalytic Hydrogenation Heterogeneous-reaction between phases Addition of h-h is syn HH HH C-C Catalyst Hydrogen adsorbed Complex of alkene on catalyst surface to catalyst HH R enera Insertion of hyo rogen A⊥ kane product catalyst into carbon-carbon double bond g Thomson-Brooks Cole
Mechanism of Catalytic Hydrogenation • Heterogeneous – reaction between phases • Addition of H-H is syn