Week_4.4_PurpleBook_Answers

Week_4.4_PurpleBook_Answers - 109 Nucleophilic Aromatic...

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NO 2 O H 3 CO Cl NO 2 O H 3 CO SCH 3 OH I O O O Nucleophilic Aromatic Substitution: Mechanisms NO 2 O H 3 CO SCH 3 Cl 1. Provide curved-arrow mechanisms for the following transformations: + H + (this structure is the anionic intermediate; it has many possible resonance structures!) O: (st rongbaseisind ica t iveo f benzyne mechanism) O :OtBu :OtBu I H tBuO—H O + Diels-Alder I I benzyne NaSCH 3 KO t Bu NaNH 2 :SCH 3
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Cl NO 2 Cl NO 2 CH 3 H 3 C NC Cl NO 2 CH 3 Cl CH 3 OH CH 3 OH In this resonance structure, the negative charge is next to the electron-withdrawing CN group. This is good. So this one will react faster. NO 2 CH 3 H 3 CO Cl faster Nucleophilic Aromatic Substitution: Direction 1. For each pair, choose the species which will react faster with NaOCH 3 , and explain your reasoning. (Resonance structures will be helpful!) vs. This is the "benzyne" mechanism! 2. Explain the unusual product mixture observed in the following reaction. Cl NO 2 CN faster vs. + NO 2 CN H 3 CO Cl NaOH, heat In this resonance structure, the negative charge is next to the electron-donating CH 3 group. This is bad. So the other one is faster; it never has a negative charge next to the methyl. H :OH can attack either carbon. CH 3 Cl CH 3 O: CH 3 O: :OH Week 4 110
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a) Although most hydrocarbons are fairly nonpolar, the following hydrocarbon has a significant dipole moment. (As part of your explanation, please indicate the direction of the dipole moment: which end is positive and which end is negative.)
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This note was uploaded on 05/01/2008 for the course CHEM 51 taught by Professor Gribble during the Spring '08 term at Dartmouth.

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Week_4.4_PurpleBook_Answers - 109 Nucleophilic Aromatic...

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