Chapter 7 Nucleophilic Substitution Reactions

Chapter 7 Nucleophilic Substitution Reactions - Chapter 7...

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1 Chapter 7 Nucleophilic Substitution Reactions 7.1~7.2 The general reaction The covalent bonds may break in 3 ways: heterolysis C ionic reaction homolysis C free radical reaction C free radical 7e carbocation 6e carbanion 8e A-B B + B : A : A + R 3 C . Z . R 3 C ¨’ Z : R 3 C : Z ¨’ A . B . + + + 1 2 3 1 2 3 R 3 C Z + + + intermediate
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2 7.4, 7.7 Nucleophilic substitution reactions Nu: + R 3 C-X δ + δ - R 3 C- Nu + X X= Cl,Br,I Nu: = any anions(OH - ,OR - NC RC C RCO 2 CH(CO 2 R) 2 , , ... ) , , - neutral molecules with unshared e-pairs: ROH, NH 3 , HNR 2 , PR 3 ... .. .. .. .. ) H 2 O, .. ( .. .. nucleophile
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3 2. Reaction rates and potential energy diagrams of S N 1and S N 2 reactions Two pathways: S N 2—bimolecular nucleophilic substitution reaction Nu: + RX Nu ... R R ... X δ - δ - Nu + X : rate [ Nu : ] [ ] RX [ Nu : ] [ ] = k rate transition state S N 2 mechanism:
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The potential energy curve of S N 2 reactions: E PE Nu ... R ... X δ - δ - Nu : + RX NuR + X : ¡÷ H reaction process the energy of activation 2S the heat of reaction
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R ¨’ + Nu: RNu fast R X R ¨’ + X slow S N 1—unimolecular nucleophilic substitution reaction (two or more than two steps, first order, via an intermediate of a carbocation) rate k [ ] RX rate [ ] RX S N 1 mechanism: carbocation step 1 step 2 rate-determining step
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6 The potential energy curve of S N 1 reactions: R ... X RX R ... Nu RNu + X - R + +X - + Nu : PE reaction process ¡÷ H E2 ¡÷ E1 ¡÷
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7.3, 7.5 Mechanism and stereochemistry of S N 2 reactions configuration inversion T Z C 2 H 5 Br CH 3 H + NaOH S N 2 C C 2 H 5 Br H H 3 C R HO C 2 H 5 CH 3 H C C 2 H 5 H HO CH 3 e.g. Nu : + C R 1 R 3 R 2 Nu C R 1 R 2 R 3 X Nu δ - δ - C X R 1 R 2 R 3 enantioselective
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8 + OH S N 2 Cl H 3 C H H H 3 C H H OH (1R,3S)-1-chloro-3-methyl cyclopentane (1S,3S)-3-methyl cyclopentanol 3S 1R 1S 3S
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7.8 Mechanism and stereochemistry of S N 1 reactions R 3 CX + Nu : R 3 CNu + X or (2') R 3 C ¨’ + H 2 O fast OH 2 R 3 C H + fast R 3 C OH (1) R 3 C X slow + X R 3 C ¨’ (2) R 3 C ¨’ + OH fast R 3 C OH +
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10 + R 1 R 2 R 3 Nu C Nu R 1 R 2 R 3 frontside: configuration retention backside: configuration inversion X Nu : X - slow C R 1 R 2 R 3 C R 1 R 2 R 3 back Nu : front fast + Racemization:
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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 7 Nucleophilic Substitution Reactions - Chapter 7...

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