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Electrophilic addition to alkynes

(read sections 6.1-6.4 on your own). Electrophilic addition to alkynes. why addition to alkynes is slower than for alkenes: vinylic carbocations high in energy. regioselectivity of second addition:. addition of halogens. addition of water: forms ketone!. (we’ll learn mechanism in Ch 18).

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Electrophilic addition to alkynes

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  1. (read sections 6.1-6.4 on your own) Electrophilic addition to alkynes

  2. why addition to alkynes is slower than for alkenes: vinylic carbocations high in energy

  3. regioselectivity of second addition:

  4. addition of halogens

  5. addition of water: forms ketone!

  6. (we’ll learn mechanism in Ch 18)

  7. terminal alkynes require HgSO4 catalyst

  8. hydroboration-oxidation

  9. diasoamylborane used to convert terminal alkynes to aldehydes bulky isoamyl group prevents 2nd and 3rd reactions with alkene

  10. regiochemical control:

  11. catalytic hydrogenation

  12. stopping at cis-alkene stage

  13. alkyne to trans-alkene: (don’t worry about mechanism – radical intermediates

  14. acidity of terminal alkybes

  15. making a useful carbon nucleophile pKa ~ 35 pKa ~ 25 strong base needed!

  16. hydroxide not strong enough base pKa ~ 25 pKa 15.7

  17. new carbon-carbon bond!

  18. Organic synthesis

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