10-12 - SN2 = Substitution Nucleophilic 2nd Order Nu C X...

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1 Nucleophilic Substitution Reactions 29 continued rate = k Nu CX Nu transition state Ʃ G ± S N 2= S ubstitution N ucleophilic 2 nd Order 30 Nu + E R Ʃ G ° C Nu X + = - RT ln K eq Factors affecting S N 2 reaction rate Nu 1. basicity (nucleophilicity) of the nucleophile. Ʃ G ± 31 Nu + E R C Nu X + Nu 1. basicity (nucleophilicity) of the nucleophile. Ʃ G ± If we destabilize the nucleophile, the rate will: a) increase b) decrease 32 E R C Nu X + + Nu c) stay the same Factors affecting S N 2 reaction rate Nu 1. basicity (nucleophilicity) of the nucleophile. Ʃ G ± 33 E R C Nu X + a more basic nucleophile is less stable and will react faster + Nu Nucleophilicity OH CH 3 C O O HO H O basicity 34 pK a = 16 4.75 -1.72 H CH 3 COH H H
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2 Nucleophilicity OH CH 3 C O O HO H nucleophilicity basicity 35 + CC l H H H + Cl C HO H H H Ac O l H H HC AcO H H H Cl ++ + l H H H + Cl C H 2 O H H H H rate of reaction Which S N 2 reaction is faster? + CH 3 CO 2 Na Br O O A stronger base 36 + Br Br + H 2 O OH + HBr B Why? stronger conjugate acid weaker base weaker conjugate acid If the atom type (row of periodic table) changes, then nucleophilicity may not be determined by basicity. CH 3 C O O H basicity nucleophilicity 37 SH pK a = 16 7 H H CH 3 C O O H basicity nucleophilicity If the atom type (row of periodic table) changes, then nucleophilicity may not be determined by basicity. 38 basicity nucleophilicity Why are some species, such as H-S \ and I \ weak bases and strong nucleophiles?
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This note was uploaded on 12/25/2009 for the course CHE 320 taught by Professor Ff during the Spring '09 term at SUNY Stony Brook.

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10-12 - SN2 = Substitution Nucleophilic 2nd Order Nu C X...

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