hydrogen halide addition

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Hydrogen Halide Addition. The addition of a hydrogen halide to an alkyne follows Markovnikov’s rule because a secondary vinylic cation is more stable than a primary vinylic cation. Hydrogen Halide Addition. When excess hydrogen halide is present, a second equivalent is added - PowerPoint PPT Presentation

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  • Hydrogen Halide Addition The addition of a hydrogen halide to an alkyne follows Markovnikovs rule because a secondary vinylic cation is more stable than a primary vinylic cation

    Chapter 5

  • Hydrogen Halide Addition When excess hydrogen halide is present, a second equivalent is addedMarkovnikovs Rule also is followed for the second addition, forming a geminal dihalide

    Chapter 5

  • Hydrogen Halide Addition in the presence of Peroxide Hydrogen peroxide has same effect on hydrogen bromide addition to an alkyne as to an alkene

    Chapter 5

  • Halogen Addition to AlkynesHalogens add to alkynes as well as to alkenesExcess halogen leads to the addition of a second equivalent

    Chapter 5

  • Addition of Water to AlkynesWater adds to alkynes in the presence of acid to yield an enol

    Chapter 5

  • Addition of Water to AlkynesHowever the initially formed enol reacts further to produce a ketoneSuch isomers, differing only in the placement of a hydrogen atom, are called tautomers

    Chapter 5

  • Mercuric-Ion-Catalyzed Addition of Water to Alkynes

    Chapter 5

  • HydroborationOxidationHydroboration of an internal alkyne leads to a ketone

    Chapter 5

  • Addition of Water to an Alkyne

    Chapter 5

  • Addition of Hydrogen to an Alkyne

    Chapter 5

  • Addition of Hydrogen to an Alkyne

    Chapter 5

  • Acidity of a Hydrogen Bonded to an sp CarbonThe acidities of hydrocarbons can be compared with the acidities of compounds having hydrogen attached to other second-row elements

    Chapter 5

  • Acidity of a Hydrogen Bonded to an sp CarbonThe conjugate bases have the following relative base strength because the stronger the acid, the weaker the conjugate base

    Chapter 5

  • Acidity of a Hydrogen Bonded to an sp CarbonRelative electronegativities of carbonsp > sp2 > sp3The amide ion is strong enough to remove the proton from an sp carbon

    Chapter 5

  • Acidity of a Hydrogen Bonded to an sp CarbonHydroxide ion is too weak to remove a proton from an sp carbon

    Chapter 5

  • Syntheses Using Acetylide IonsAlkylation reactions work best with primary alkyl halides and methyl halides

    Chapter 5

  • Introduction to Multistep SynthesisStarting with 1-butyne, how would you prepare the following ketone? At this point the only way we know to form a ketone is to add water to an alkyne in the presence of a catalyst

    Chapter 5

  • Introduction to Multistep SynthesisIf the alkyne used has identical substituents on both sp carbons, only one ketone will result3-Hexyne can be obtained from the starting material by removing the hydrogen bonded to the sp carbon and reacting with an alkyl halide

    Chapter 5

  • Introduction to Multistep SynthesisOverall we have a two-step synthesis

    Chapter 5

  • Introduction to Multistep SynthesisIn designing a synthesis it is best to start from the product and work backwards as we did in this example

    Chapter 5

  • Introduction to Multistep SynthesisThe thought process is known as retrosynthetic analysis and is indicated by using open arrows

    Chapter 5