Chapter 9 Lectures

Chapter 9 Lectures - Chapter 9 Recall that organic...

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Chapter 9
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Recall that organic compounds in which an sp 3 hybridized carbon is bonded to a halide leaving group can undergo the two types of reactions shown below: leaving group Y R X H R substitution Y + X (chapter 8) R elimination + H Y + X (chapter 9) We discussed substitution reactions last chapter. In this chapter we discuss elimination reactions .
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Two Types of Elimination Reactions – E2 and E1 There are two important mechanisms for the elimination reaction: X Y + H Y + X + X E2 (concerted, bimolecular) transition state + H Y H slow X fast H k 1 Y k 1 H Y + X E1 (stepwise, unimolecular) carbocation intermediate δ δ δ + δ + X H Key Features Reaction Kinetics Stereochemistry Relative Rates E2 Rate = k 1 [R-X][Y ] Stereospecific 3° > 2° > 1° E1 Rate = k 1 [R-X] Not Stereospecific 3° > 2° > 1° Regiochemistry * Zaitsev's Rule *Dependent on several factors. Often follows Zaitsev's Rule, but there are exceptions (see below).
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R–X R–X + Y Rxn Coord Rxn Coord + Y E + HY + X alkene + HY + X + X rate-determining step + Y fast step E2 Reaction E alkene + H E1 Reaction X H Y δ δ δ + δ +
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The E2 Reaction Br OH H 2 O Br E2 elimination is sometimes referred to as dehydrohalogenation or β -elimination . second order kinetics: rate depends on concentration of both reactants. mechanism:
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Chapter 9 Lectures - Chapter 9 Recall that organic...

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