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Unformatted text preview: of the fo llowing four types: Addit io n of H2 Addit io n of X2 (hydrogenation) (halogenat ion) Addit io n of H2O Addit io n of HX (hydration) (hydrohalogenation) Symmetrical addit io n Unsymmetrical addit io n Addition of H2 H H C C H H C C B r H H C C H H C 3 1 at m C B r Pt, 25 C C H CH + H 3
2 H H H C 3 H O H CH 3 Addition of X2 H H C 3 H C C CH + Br 3 2 H C 3 CH 3 Addition of H2O H H C 3 H C C CH + 3 H O 2 +
H H C 3 CH 3 Addition of HX H H C 3 H C C H 7 H C 3 C C H CH + HC l 3 H Cl CH 3 Chemistry 52 Chapter 20 MARKOVNIKOV’S RULE
· When an unsymmetrical mo lecule such as HCl is added to an alkene, two products are theoretically possible. For example, when HCl adds to propene, 1chloropropane and 2 chloropropane are possible.
H C 3 H C H3 C H C CH 2 Cl H (about 100% yield) CH + HCl 2 H C CH 2 H H C 3 Cl (trace ) · Experimentally, however, we only find one product formed (2chloropropane).
· The reason for this selectiveness lies in the reaction mechanism, the pathway by which a reaction occurs. Addit ion of HCl to alkenes fo llows the fo llowing mechanism: Step 1: H3C 3 H C 2 CH2 + HCl 1 H3C H C CH2 + Cl H isopropy l carbocation Step 2: H3C H C H H3C H C CH2 Cl CH2 + Cl H 2chloropropane 8 Chemistry 52 Chapter 20 MARKOVNIKOV’S R...
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