8: Additions
- Page ID
- 451155
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- 8.1: Electrophilic Addition Reactions (EARs)
- Electrophilic addition reactions can occur in compounds containing pi bonds like the alkenes. Depending on the structure of the alkene and the specific reagents, the reactions can be regioselective and/or stereoselective.
- 8.2: Addition of Hydrogen Halides to Symmetrical Alkenes
- The regioselective reaction of the carbon-carbon double bond in alkenes with hydrohalogens (HX) is a controlled by carbocation stability. Consequently, the symmetry of the alkene must be considered for this mechanistic pathway.
- 8.3: Alkene Asymmetry and Markovnikov's Rule
- The regioselectivity of electrophilic addition reactions is determined by carbocation stability and is summarized by Markovnikov's Rule.
- 8.4: Hydration- Acid Catalyzed Addition of Water
- Electrophilic hydration is the act of adding electrophilic hydrogen from a non-nucleophilic strong acid (a reusable catalyst, examples of which include sulfuric and phosphoric acid) and applying appropriate temperatures to break the alkene's double bond. After a carbocation is formed, water bonds with the carbocation to form a 1º, 2º, or 3º alcohol on the alkane.
- 8.5: Addition of Halogens
- Halogens can act as electrophiles due to polarizability of their covalent bond and react with the pi bond of alkenes. This electrophilic addition mechanism is stereospecific. The orientation of the electrophile during a stereospecific electrophilic addition reaction will determine the stereochemistry of the product(s).
- 8.6: Formation of Halohydrins
- When the halogenation reaction of alkenes is performed in a nucleophilic solvent like water or alcohol, then the solvent becomes the nucleophile to give halohydrin or haloalkoxy products.
- 8.7: Stability of Alkenes
- Alkene hydrogenation is the syn-addition of hydrogen to an alkene, saturating the bond. The alkene reacts with hydrogen gas in the presence of a metal catalyst which allows the reaction to occur quickly. The energy released in this process, called the heat of hydrogenation, indicates the relative stability of the double bond in the molecule.
- 8.8: Reduction of Alkynes
- Reactions between alkynes and catalysts are a common source of alkene formation. Because alkynes differ from alkenes on account of their two procurable π bonds, alkynes are more susceptible to additions. Aside from turning them into alkenes, these catalysts affect the arrangement of substituents on the newly formed alkene molecule. Depending on which catalyst is used, the catalysts cause anti- or syn-addition of hydrogens. Alkynes can readily undergo additions because of their availability of tw