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. synthesis but first …… nomenclature - structure, classification
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. synthesis nomenclature - structure, classification
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. Structure - two general types
acetylene, ethyne C H
Structure - two general types
(1) internal - R and R’ = alkyl, Aryl, etc. C R R'
(2) terminal - R = alkyl, Aryl, etc.
<-- creates additional
chemistry
8,28

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

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

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

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

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

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

15. Alkylation of Acetylides

16. Alkylation of Acetylides
Acetylide anions - 2° and 3° halides:
-eliminates (strong base, reverse of addition)
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. NOTE! alkenes are sources of diBrs
Preparation: Dehydrohalogenation (-2 HX)
NOTE! alkenes are sources of diBrs
two -eliminations
2 arrangements of diBrs => same acetylene

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

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

30. regiochemistry

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

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

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

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

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

36. How could the vinyl bromide be converted into the Z-olefin
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/∆

37. convert 2-bromopropene
to 2-hexanone

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

39. compare carbon skeleton
functional groups

40. other
way?