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ALKYNES - Chapter 7

ALKYNES - Chapter 7. nomenclature - ( chapt 5 ) , structure, classification acidity of terminal acetylenes - ( chapt 4 ) alkylation prep - dehydrohalogenation (-2HX) or double  -elimination reduction - H 2 /M (chapt 6) and chemical hydroboration (chapt 6) - protonation

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ALKYNES - Chapter 7

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  1. ALKYNES - Chapter 7 nomenclature - (chapt 5), structure, classification acidity of terminal acetylenes - (chapt 4) alkylation prep - dehydrohalogenation (-2HX) or double -elimination reduction - H2/M(chapt 6) and chemical hydroboration (chapt 6) - protonation - oxidation (hydration) enol-keto tautomerism addition of Hg++,HX, X2, H2O (chapt 6) synthesis (chapts 6) ss25 18 [blue- chemistry from previous chapters]

  2. Chapter 7 synthesis nomenclature - structure, classification acidity of terminal acetylenes ) alkylation -elimination reduction - H2/M & chemical hydroboration - protonation - oxidation enol-keto tautomerism addition: Hg++/H2O,HX, X2 synthesis but first ……

  3. Chapter 7 synthesis nomenclature - structure, classification acidity of terminal acetylenes ) alkylation -elimination reduction - H2/M & chemical hydroboration - protonation - oxidation enol-keto tautomerism addition: Hg++/H2O,HX, X2 synthesis

  4. H C C H R C C R' acetylene, ethyne Structure - two general types (1) internal - R and R’ = alkyl, Aryl, etc. (2) terminal - R = alkyl, Aryl, etc. <-- creates additional chemistry 8,28

  5. R C C R’ Alkyne Nomenclature Common: alkyl alkyl' acetylene

  6. Nomenclature: IUPAC - longest chain containing the most important functional group(s) = root #-alkyne 4-chloro-6-cyclohexyl-5-methyl-2-hexyne add substituents with #’s

  7. 90o angle  bond to  orbitals)ß C R C R’ Acetylene - linear geometry - sp hybridization 180o bond angles R-C-C-R’  -bond 180o bond angle

  8. Name: ______________ seat: ____ Write the product(s) of the following reactions.

  9. H H H H H C C C H > CH C > C C 3 CH 3 CH H 3 H H pKa = 50 pKa = 44 H-Csp3 H-Csp2 The more s-character,the moreacidic the C-H bond 50% 33% 25% Acidity of organic compounds pKa = 25 H-Csp Why ? recall chapter 4

  10. also -NH2 H-NH3 Relative basicity (acidity)

  11. Acid-Base reactions organometallic reagent (15)

  12. last Thursday: Acid-Base reactions R' = alkyl = D

  13. Alkylation of Acetylides Recall RX type: substitution acetylide anions undergo substitution rx with 1o alkyl halides form new C-C bonds termed “alkylation”

  14. How do we make the anions of acetylenes? Alkylation of Acetylides

  15. Alkylation of Acetylides

  16. Acetylide anions - 2°and3° halides: -eliminates (strong base, reverse of addition) Alkylation of Acetylides no alkylation 2°R-X

  17. Preparation: Dehydrohalogenation (-2 HX) two -eliminations 2 arrangements of diBrs => same acetylene

  18. Preparation: Dehydrohalogenation (-2 HX) two -eliminations 2 arrangements of diBrs => same acetylene

  19. Preparation: Dehydrohalogenation (-2 HX) two -eliminations 2 arrangements of diBrs => same acetylene

  20. two -eliminations NOTE! alkenes are sources of diBrs 2 arrangements of diBrs => same acetylene Preparation: Dehydrohalogenation (-2 HX)

  21. Reactions - several like C=C - additions A. Reduction - addition of hydrogen syn addition (2x)

  22. Reactions - several like C=C - additions A. Reduction - addition of hydrogen With choice of catalyst - stop at olefin (add 1 eq H2). [Lindlar cat.] syn addition (2x)

  23. H C H Nao 3 H C C C CH C C 3 3 NH3 (liq.) CH H 3 ether (cosolvent) “mechanism” -Na donates e’s, know rx as prep for trans olefins Chemical reduction of a triple bond. trans olefin for internal acetylenes

  24. Acetylene chemistry - recall olefin chemistry R = H, alkyl

  25. Hydroboration of an internal alkyne terminal

  26. Terminal acetylene hindered borane adds once di-sec-isoamylborane or HB(sia)2

  27. Terminal acetylene hindered borane adds once di-sec-isoamylborane or HB(sia)2 tautomerism H+ transfer (O to C)

  28. ketone R' BH R' R' 2 O C H O C BH 2 2 C 2 + C H C NaOH H C H R R R H keto enol internal with oxidation - ketone

  29. regiochemistry

  30. enol-keto tautomerism H+ transfer C  O from HB/[O] Hg+2/H2O other rxs mechanism e(-) arrows or

  31. Hydration of acetylenes terminal yne - HBR2/[O] aldehyde - Hg++/H2O  ketone internal yne - “either”  ketone(s)

  32. R' Br R' Br R' Br C Br C 2 C Br 2 1 eq. C 1 eq. C C Br or XS Br R R R Br R' R' R' X C C C X X X C C C R R X R X electrophilic additions Br2 / Cl2 Assume bromonium (chloronium) ion ( like alkene X2 addition ) Mechanism for 1st addition of X2

  33. R' Br R' Br R' HBr C HBr C C Br 1 eq. C 1 eq. C C H or XS H H H H H R' C 2o-vinyl R+ C H H addition of HX vinyl bromide

  34. R' R' Br Br R' C HBr HBr C C Br C 1 eq. 1 eq. C C H or XS H H H H H R' Br R' Br C C Br(-) C C H H H H H H H Br R' C 1o carbocation and no resonance! C H H addition of HX - second addition 2o carbocation with resonance

  35. How could the vinyl bromide be converted into the Z-olefin? Use any number of reactions but show all necessary reagents and expected products of each step. how? a. H2/Lindlar(cat.) how? Na+-NH2 or b. (1)BH3,(2)AcOH/∆

  36. convert 2-bromopropene to 2-hexanone

  37. compare carbon skeleton functional groups convert 2-bromopropene to 2-hexanone

  38. compare carbon skeleton functional groups

  39. other way?

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