Ch_322b_16.04

Ch_322b_16.04 - Chapter 16.4 lecture note

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Nucleophilic Addition to the Carbon-Oxygen Double Bond The reactivity of the carbon-oxygen double bond is determined by the polarization : C = O : !" ! + Because of the permanent dipole, nucleophiles add to the electropositive carbon and electrophiles add to the electronegative oxygen. Two General Mechanisms (1) When the reagent is a strong nucleophile ( Nu: - ) such as an organometallic or metal hydride reagent, addition usually occurs first to the carbon center forming an oxide ion. Electrophilic addition then occurs to the oxide.
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C = O : Nu: - sp 2 -hybridized carbon trigonal planar C O: R R' Nu R R' - sp 3 -hybridized carbon tetrahedral E + C O- E Nu R R' addition product tetrahedral In these additions, E + is often a proton or metal ion.
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(2) A second general mechanism is acid-catalyzed nucleophilic addition . This mechanism often involves weaker oxygen nucleophiles adding to the carbonyl group in the presence of catalytic amounts of acid. C
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Ch_322b_16.04 - Chapter 16.4 lecture note

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