Chapter 10 Additions to Carbon-Carbon Double and Triple Bonds

Chapter 10 Additions to Carbon-Carbon Double and Triple Bonds

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1 Chapter 10 Additions to Carbon-Carbon Double and Triple Bonds 10.2 General addition reactions of C=C double bonds General expressions: Z 2 = H 2 , Br 2 , Cl 2 C C + Z Z add.reaction C C Z Z C C + Z Y add.reaction C C Z Y Z-Y = HI, HBr, HCl, H 3 O, H 2 SO 4 , RCOOH, HOX (X 2 /H 2 O) + sym. reagent unsym. reagent
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2 10.3 Addition of HX to alkenes elimination (E1 or E2) C C + H X add.reaction C C H X 1. Rregioselectivity of the addition by ionic mechanism Reactivity: HI > HBr > HCl C-C-C-C Cl X H H X or + X C-C=C-C + H-X or X-H
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3 CH 2 CHCH 3 + H 2 C CHCH 3 HCl 2-chloropropane AcOH C-C-C Cl H C C C C C + AcOH tert-butylchloride Markovnikov’s rule : In the ionic addition of HX, the proton always adds to the C atom of the carbon-carbon double bond which has more H atoms.
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4 Markovnikov’s addition slow rate determining C C H + ¨’ X - C C + H X δ + δ - Step 1 Step 2 + - C C H ¨’ X fast C C H X
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2. Stereoselectivity of the ionic addition to an olefin R C C R ' H R'' + H R ' C R CH 2 R'' C CH 2 R" R R' X : - C X CH 2 R" R R' C X R"CH 2 R R ' X : - + + a racemer 3. Regioselectivity of the free radical addition of HBr C C C + Br H ROOR or h υ C-C-C-Br H
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6 the addition reaction via a free radical mechanism: step 1 step 2 step 3 C C C + Br . a b a b HBr C-C-C . Br C-C-C Br H +Br . C-C-C-Br HBr C-C-C Br H + Br . . RO OR 2RO . RO . + H Br ROH + Br . anti-Markovnikov’s addition The order of stability of carbon free radicals: 3°C . > 2°C . > 1°C . > . CH 3 Notice: Under the same conditions HF, HCl and HI do not react with olefins in a free radical mechanism.
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7 10.4 Addition of Br 2 and Cl 2 to olefins in non- polar solvents r.t. in the dark CCl 4 C C Br Br Br 2 + C C Reactivity: F 2 >> Cl 2 > Br 2 > I 2 Stereoselectivity: + Br 2 in the dark CCl 4 H Br Br H + anti-addition H Br Br H trans-vic-dibromide
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8 mechanism: step 1 H H Br Br δ - δ + H H + + bromonium ion C C H H Br δ + δ + δ + C C H H Br step 2 H H C C H H Br + Br a b a b Br CH 2 H 2 C Br
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9 Br - R R C C H H Br Br a b a b C C Br Br H H R R + a b C C H H R R cis-olefin Br Br R H C C Br Br R H e.g. C C H H R R trans-olefin Br Br C C Br Br H H R R mesomer
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10 The common rule for the addition of a symmetric reagent Z 2 to a C=C bond: a mesomer a racemer C C X X Y Y syn-addition of Z 2 anti-addition of Z 2 C C X X Y Y syn-addition of Z 2 anti-addition of Z 2 a mesomer a racemer cis trans
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11 10.5 Addition of X 2
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This note was uploaded on 10/16/2010 for the course CHEM 60280 taught by Professor Ryu during the Spring '09 term at TCU.

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Chapter 10 Additions to Carbon-Carbon Double and Triple Bonds

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