CH 221 1st Edition Lecture 21 Outline of Last Lecture I. Formation of a Second Asymmetric CenterII. Syn and Anti AdditionIII. Hydroboration-OxidationIV. AlkynesOutline of Current Lecture V. Alkynes’ Addition ReactionsVI. π- ComplexVII. Internal AlkynesCurrent LectureV. Alkynes undergo electrophile addition reactions- Alkynes are less stable and less reactive than alkenes - The addition of an electrophile to an alkyl forms a vinylic cation- Relative carbocation stability- Most stable tertiary> secondary> secondary vinylic = primary> primary vinylic = methyl cation least stableVI. Evidence for the formation of the π-complex- 2-butyne combined with HCl and anti addition form (Z)-2-chloro-2-butene- A primary vinylic cation is less stable than a primary alkyl cation- A second addition reaction can occur that forms a germinal dihalide- The addition to a terminal alkyne is regioselective- The second electrophile addition reaction is also regioselective- Second electrophile addition reaction is slower which explains why if only one equivalent of HCl used, the reaction stops at the halo-substituated alkeneVII. An asymmetrical internal alkyne forms two products- A symmetrical internal alkyne forms only one productThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- The acid-catalyzed addition of water to an alkene is the same process for an
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