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GSU CHEM 3410 - Nucleophilic Aromatic Subsituition

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CHEM 3410 1st Edition Lecture 11Outline of Last LectureI. Table of RulesII. Directing Effects and ReactivityIII. Synthesis IV. Nucleophilic Aromatic SubstitutionOutline of CurrentI. Nucleophilic Aromatic SubsituitionA. Resonance Mechanism ReviewB. Introduction of Benzyl MechanismII. EAS vs NASIII. Reduction of BenzeneIV. Intramolecular/ Intermolecular Forms of FC AcylationV. Synthesis PracticeCurrent LectureI.Nucleophilic Aromatic Substitution A. Resonance Mechanism: Molecular Pop Gun/ MisenhymerResonance Withdrawing Group at Para PositionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Resonance Withdrawing group Ortho PositionWhen you have a resonance withdrawing group at the ortho or para position, you will only get a single product. You will get a single product because when the strong nucleophile attacks the ring the ring, it will attack at the carbon of the halide, forcing the pi electrons onto the neighboring carbon, forcing that leaving group off. Therefore, we only get replacement of the leaving group on the carbon it existed on, creating only one product.META WILL NOT WORK WITH THIS MECHANISM. It would be a BENZYL MechanismThere is no resonance mechanism that can be done here, so it is a benzyne mechanism. You cannot push the electrons into the nitro when it is the meta position. B. Introduction to the Benzyne Mechanismo When a nucleophile cannot behave as a nucleophile, it will behave as a base. Our OH or NH2 deprotonates the hydrogen on our ring and s. It is not E2, it is E2 - like.The benzyne mechanism creates multiple products That is because you have a benzyne intermediate:You had available Hydrogens on both sides of the leaving group, so you could form either of these benzyne intermediates, thus you have 3 possible products. You are destroying the delocalization of the electrons, and you have 4 pi electrons localized in these spots. Very reactive.Summary: - Benzyne mechanism occurs when resonance cannot occur. You will always have at least two products.o If you are trying to perform a benzyl mechanism and have R groups ortho to your halide, you will have no reaction. You need the H groups to deprotonate for the reaction to occur.o When a nucleophile cannot behave as a nucleophile, it will behave as a base. Our OH or NH2 deprotonates the hydrogen on our ring rather than the carbon, pushes the electrons into the ring, and kicks off the leaving group. It is not E2, it is E2 – like, thus itis concerted. - If you have a resonance withdrawing group ortho or para to your leaving group, you will always have only 1 product. Any other time, you do benzyne. If you have an resonance withdrawing group ortho or para to your leaving group, you do the RESONANCE MECHANISM. Any other time, do the benzyne mechanisms. How do we know this exists and is reactive?He treated benzene with strong base and a ton of heat, made the benzyne intermediate (or something very close to it), and said that, if he hit his target and the reaction was not complete crap, it should participate in Diels-alder. IT WORKED.Practice: Be able to label MisenhymervsBenzyne reactions and draw the products on an exam or quiz.II.Electrophilic Aromatic SubstitutionvsNucleophilicAromatic Substitution.- Electron withdrawing groups make benzene more reactive in nucleophilic aromatic substitution because benzene acts as the electrophile.- Electron donating groups make benzene less reactive in electrophilic aromatic substitution because benzene is your nucleophile.REGARDLESS OF MECHANISM (B vs M)EAS NASBenzene Benzene is your nucleophile Benzene is your electrophileSubstituent Favored by electron donating groupsFavored by electron withdrawing groupsIII. Reduction of BenzeneIV. Intra vs Intermolecular Rxns of FC AcylationIn the intramolecular reaction, the molecule reacts with itself.IV. Synthesis


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