有机化学英文课件：CH3-alkene2-addition.pptVIP

Bromine and Cyclohexene Br2 Br2 Relative Rate of Bromination 1 61 5,400 920,000 Br Br Br Br + - Bromonium Ion - + Cyclic Bromonium Ion Intermediate Br - Br- ? Cl- Anion goes to more stable cation center What Reagent? Br2 H2O Reactions of Alkenes Chapter 3 XY Hydrogenation H2 Pt Add H2 across double bond Pd on Carbon HYDROGEN ADSORBS ON THE SURFACE OF THE CATALYST n H2 + Pt Pt(H )2n H H H . Hydrogen Adsorbed on Catalyst Surface . . finely-divided particles dispersed in solution Pt Pt Pt Pt Pt . H . H Pt . H Pt Pt Pt Pt Pt . . H . H . H . H . H . H . H H H CATALYST MECHANISM OF HYDROGENATION . H . H . H . H . H . H . H . H . H HYDROGEN ADSORBS MECHANISM OF HYDROGENATION . H . H . H . H . H . H . H . H R R R R . . . H ALKENE APPROACHES MECHANISM OF HYDROGENATION . H . H . H . H . H . H . H . H . H R R R R . . ALKENE PICKS UP TWO HYDROGENS MECHANISM OF HYDROGENATION . H . H . H . H . H . H . H R R R R . . H . . H ALKANE IS FORMED MECHANISM OF HYDROGENATION H2 Pt + HEAT Measure heat of hydrogenation Heat of Hydrogenation 115 KJ/mole 119 KJ/mole 126 KJ/mole Addition of HX HCl, HBr, H2O and H2SO4 The Russian chemist Markovnikov in 1869 summarized his findings in a statement known as Markovnikov’s rule: In ionic addition of HX to unsymmetrical alkenes, the positive hydrogen of the hydrogen halide adds to the double-bond carbon with fewer alkyl substitutents, and the negative halide ion adds to the carbon with more alkyl substituents. Mechanism of Electrophilic Addition H + H + H+ H Cl Cl- more stable cation Add H+ to form the more stable carbocation The stability of carbocation: C C H .. H H + R R H+ + Cl- Br- H2O The addition of the HX to an alkene is believed to be a two-step process: (1)?? The hydrogen ion attacks the π electrons of the alkene, forming a C-H bond and a carbocation. (slow step) (2) The negatively charged species X- attacks the carbocation from the side opposite the C-H bond to form a new C-X bond. Peroxide effect ROOR Anti-Mar