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Solutions_Manual_for_Organic_Chemistry_6th_Ed 136

Solutions_Manual_for_Organic_Chemistry_6th_Ed 136 - 6-70...

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6-70 The problem is how to explain this reaction: facts Et2N: : NEt2 I HO- I H2C - CH - CH2CH3 H2C - CH - CH2CH3 + Cl- I I 1) second order, but several thousand times faster than similar second order reactions without the NEt2 group Solution Cl OH 1 2 2) NEt2 group migrates Clearly, the NEt2 group is involved. The nitrogen is a nucleophile and can do an internal nucleophilic substitution (SNi), a very fast reaction for entropy reasons because two different molecules do not have to come together. very fast 3 The slower step is attack of HO- on intermediate 3; the N is a good leaving group because it has a positive charge. Where will HO- attack 3? On the less substituted carbon, in typical SN2 fashion. :NEt2 I H2C - CH - CH2CH3 I OH 2 This overall reaction is fast because of the neighboring group assistance
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