Reaction Mechanisms (see p. 310) A. Recognizing/Classifying as Radical, Cationic, or Anionic 1. Radical initiation requires both energy (either hv or and a weak, breakable ) heteroatom bond Cl-Cl, Br-Br, O-O (peroxide), N-Br, etc.. 2 Guides for That are Usually Reliable: hv radical mechanism peroxides radical mechanism 2. Anionic a strong anion/base appears in the recipe no strong should appear in the recipe mechanisms should involve anionic intermediates and reactants, not strongly cationic ones (except for do-nothing spectators like metal cations) The first step in the mechanism will involve the strong anion/base that appears in the recipe 3. Cationic a strong acid/electrophile appears in the recipe no strong anion/base should appear in the recipe mechanisms should involve cationic intermediates and reactants, not strongly anionic ones (except for do-nothing spectators like halide or hydrogen sulfate anions) The first step in the mechanism will involve the acid that appears in the recipe. The last step will often involve a deprotonation step. Often the main step occurs in between the proton-on and proton-off steps B. Miscellaneous Mechanism Tips Keep track of hydrogens on reacting carbons Each step in a mechanism must balance The types of intermediates involved (cation, anion, or radical) should be consistent with the reaction classification above If the reaction is cationic, don’t show anionic intermediates If the reaction is anionic, don’t show cationic intermediates Usually conditions are ionic. Use a reactive species, whether strong or an acid, to start the first step If acidic, first step will involve protonation of the organic If anionic, the step will involve the anion attacking the organic. it isn’t always easy to figure out what is a good mechanism, you should often be able to eliminate an unreasonable mechanism.
Reaction Mechanisms (see p. 310) A. Recognizing/Classifying as Radical, Cationic, or Anionic 1. Radical initiation requires both energy (either hv or ) and a weak, breakable bond Cl-Cl, Br-Br, O-O (peroxide), N-Br, etc.. 2 Guides for That are Usually Reliable: hv radical mechanism peroxides radical mechanism 2. Anionic a strong anion/base appears in the recipe no strong should appear in the recipe mechanisms should involve anionic intermediates and reactants, not strongly cationic ones (except for do-nothing spectators like metal cations) The first step in the mechanism will involve the strong anion/base that appears in the recipe 3. Cationic a strong acid/electrophile appears in the recipe no strong anion/base should appear in the recipe mechanisms should involve cationic intermediates and reactants, not strongly anionic ones (except for do-nothing spectators like halide or hydrogen sulfate anions) The first step in the mechanism will involve the acid that appears in the recipe. The last step will often involve a deprotonation step. Often the main step occurs in between the proton-on and proton-off steps B. Miscellaneous Mechanism Tips Keep track of hydrogens on reacting carbons Each step in a mechanism must balance The types of intermediates involved (cation, anion, or radical) should be consistent with the reaction classification above If the reaction is cationic, don’t show anionic intermediates If the reaction is anionic, don’t show cationic intermediates Usually conditions are ionic. Use a reactive species, whether strong or an acid, to start the first step If acidic, first step will involve protonation of the organic If anionic, the step will involve the anion attacking the organic. it isn’t always easy to figure out what is a good mechanism, you should often be able to eliminate an unreasonable mechanism. heteroatom
Review%20of%20Organic%20Chem%20II.docx