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8: Substitution and Elimination Reactions

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    • 8.1: Prelude to Nucleophilic Substitution Reactions
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    • 8.2: Two Mechanistic Models for Nucleophilic Substitution
      As we begin our study of nucleophilic substitution reactions, we will focus at first on simple alkyl halide compounds. While the specific reactions we'll initially consider do not occur in living things, it is nonetheless useful to start with alkyl halides as a model to illustrate some fundamental ideas that we must cover. Later, we will move on to apply what we have earned about alkyl halides to the larger and more complex biomolecules that are undergoing nucleophilic substitution in cells.
    • 8.3: Nucleophiles
      A nucleophile is an atom or functional group with a pair of electrons (usually a non-bonding, or lone pair) that can be shared. The same, however, can be said about a base: in fact, bases can act as nucleophiles, and nucleophiles can act as bases. What, then, is the difference between a base and a nucleophile?
    • 8.4: Electrophiles
      Next, we turn to electrophiles. In the vast majority of the nucleophilic substitution reactions you will see in this and other organic chemistry texts, the electrophilic atom is a carbon bonded to an electronegative atom, usually oxygen, nitrogen, sulfur, or a halogen.
    • 8.5: Leaving Groups
      In our general discussion of nucleophilic substitution reactions, we have until now been using chloride ion as our common leaving group. Alkyl chlorides are indeed common reactants in laboratory nucleophilic substitution reactions, as are alkyl bromides and alkyl iodides.
    • 8.6: Regiochemistry of SN1 Reactions with Allylic Electrophiles
      SN1 reactions with allylic electrophiles can often lead to more than one possible regiochemical outcome - resonance delocalization of the carbocation intermediate means that more than one carbon is electrophilic. For example, hydrolysis of this allylic alkyl bromide leads to a mixture of primary and secondary allylic alcohols.
    • 8.7: SN1 or SN2? Predicting the Mechanism
      While many nucleophilic substitution reactions can be described as proceeding through 'pure' SN1 or SN2 pathways, other reactions - in particular some important biochemical reactions we'll see later - lie somewhere in the continuum between the SN1 and the SN2 model (more on this later).
    • 8.8: The E2 Reaction
      The conditions used for substitution reactions by the SN2 mechanism very often lead to elimination.
    • 8.9: The E1 Reaction
      Many secondary and tertiary halides undergo E1 elimination in competition with the SN1 reaction in neutral or acidic solutions. The SN1 and E1 reactions have a common rate-determining step, namely, slow ionization of the halide.
    • 8.10: Biological Nucleophilic Substitution Reactions
      The nucleophilic substitution reactions we have seen so far have all been laboratory reactions, rather than biochemical ones. Now, finally, let's take a look at a few examples of nucleophilic substitutions in a biological context. All of the principles we have learned so far still apply to these biochemical reactions, but in addition we need to consider the roles of the enzyme catalysts.
    • 8.11: Nucleophilic substitution in the Lab
      Synthetic organic chemists often make use of a reaction that is conceptually very similar to the SAM-dependent methylation reactions we saw earlier. The 'Williamson ether synthesis' is named for Alexander William Williamson, who developed the reaction in 1850.
    • 8.12: Nucleophilic Substitution Reactions (Exercises)
    • 8.13: Nucleophilic Substitution and Elimination Reactions (Exercises)
      These are the homework exercises to accompany Chapter 8 of the Textmap for Basic Principles of Organic Chemistry (Roberts and Caserio).
    • 8.14: Nucleophilic Substitution Reactions (Summary)