10: Electrophilic Reactions
- Page ID
- 242293
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- 10.1: Prelude to Electrophilic Reactions
- In this chapter, we will learn about a class of organic reaction that is central to the biosynthesis of ergot alkaloids in Claviceps. The key first step in the biosynthetic pathway is a reaction unlike any we have yet seen.
- 10.2: Electrophilic Addition to Alkenes
- The simplest type of electrophilic reaction to visualize is the addition of a haloacid such as \(HBr\) to an isolated alkene. It is not a biological reaction, but nonetheless can serve as a convenient model to introduce some of the most important ideas about electrophilic reactions.
- 10.3: Elimination by the E1 Mechanism
- The reverse of electrophilic addition is called E1 elimination. We will begin by looking at some non-biochemical E1 reactions, as the E1 mechanisms is actually somewhat unusual in biochemical pathways.
- 10.4: Electrophilic Isomerization
- Electrophilic reactions in biochemistry are not limited to addition to alkene double bonds. The position of a double bond in an alkene can also be shifted through an electrophilic, carbocation-intermediate reaction. An electrophilic alkene isomerization occurs when an initial \(\pi \) bond protonation event (step 1 below) is followed by deprotonation of an adjacent carbon to re-form the \(\pi \) bond in a different location.
- 10.5: Electrophilic Substitution
- Until now, have already been introduced to electrophilic addition and electrophilic isomerization - now, let's move to the third variation on the electrophilic theme, that of electrophilic substitution. In an electrophilic substitution reaction, a pair of \(\pi\)-bonded electrons first attacks an electrophile - usually a carbocation species - and a proton is then abstracted from an adjacent carbon to reestablish the double bond, either in the original position or with isomerization.
- 10.6: Carbocation Rearrangements
- Earlier in this chapter we introduced the so-called 'Markovnikov rule', which can be used to predict the favored regiochemical outcome of electrophilic additions to asymmetric alkenes. According to what we have learned, addition of HBr to 3-methyl-1-butene should result in a secondary bromoalkane.