Organic Chemistry

1. Like alkenes, but endingLike alkenes, but ending -ene-ene turns intoturns into –yne.–yne.
HC CHHC CH
EthyneEthyne
55
44
33
22
11
1-Pentyne1-Pentyne
BrBr
11
22
33
44
55
66
5-Bromo-2-hexyne5-Bromo-2-hexyne
-ol -yne-ol -yne>> OHOH
11
22
33
2-Propyn-1-ol2-Propyn-1-ol
Alkynes: The C CAlkynes: The C C
Triple BondTriple Bond
NamesNames
Priority:Priority:

2. When the alkyne contains also double bonds, itWhen the alkyne contains also double bonds, it
is called anis called an enyne.enyne. However, despite being anHowever, despite being an
“yne”, numbering begins closest to either group:“yne”, numbering begins closest to either group:
11
22
33 44
55
66
3-Hexen-1-yne3-Hexen-1-yne
1-Penten-4-yne1-Penten-4-yne
11
22
33
44
55
When double and triple bond are equidistant fromWhen double and triple bond are equidistant from
each terminus:each terminus: Ene firstEne first (alphabetical)(alphabetical)
11
22
33
44
55
66
77
1-Hepten-4-yne1-Hepten-4-yne

3. Substituents:Substituents:
EthynylEthynyl 2-Propynyl2-Propynyl
(or propargyl)(or propargyl)
Rings:Rings: Naming follows hydrocarbon rule:Naming follows hydrocarbon rule:
Smaller R is a substituent to larger R (ignoreSmaller R is a substituent to larger R (ignore
function)function)
3-Cyclobutyl-1-hexyne3-Cyclobutyl-1-hexyne EthynylcyclohexaneEthynylcyclohexane
11
22

4. Two perpendicularTwo perpendicular ππ bonds;bonds; spsp hybridshybrids RR CC CC RR
EthyneEthyne

6. The Triple Bond isThe Triple Bond is
EnergeticEnergetic
Kcal molKcal mol-1-1
Heat of hydrogenationHeat of hydrogenation:: MoreMore than Two Alkenethan Two Alkene ππ BondsBonds
(which would be ~ -60 kcal mol(which would be ~ -60 kcal mol-1-1
))
DDHH ° HC CH H° HC CH H22C CHC CH22 HH33C CHC CH33
229229 173173 9090

7. Acetylene TorchAcetylene Torch

8. Hydrogens get more acidicHydrogens get more acidic (blue)(blue)
Acidity:Acidity: RC CRC C HH ++ BB R CR C CC ++ HHBB
-- --
:: ::
ppKKaa ~ 25!~ 25! cf. CHcf. CH22 CHCH22 44, CH44, CH33 CHCH33 5050
Why?Why? 50% s-character50% s-character
KK

9. ++ LiLi oror
LiLi LiLi
++-- ++
++ CHCH33MgBrMgBr MgBrMgBr ++ CHCH44
ppKKaa 2525 ppKKaa 5050
H H + Na NHH H + Na NH22
++ ::
::
HH
NaNa C CC C:::: ----
NHNH33++
NaNHNaNH22
NaNa
++ ++
ppKKaa 3333
1 equiv.1 equiv.
::--
Synthetic Use ofSynthetic Use of
AcidityAcidity
--

10. 11
H NMR:H NMR: RC CRC C HH δδ = 1.7-3.1 != 1.7-3.1 !
Recall:Recall: RCH CHRCH CH22 δδ = 4.6-6 ppm= 4.6-6 ppm

11. AlkAlkeneene hydrogens:hydrogens:
deshieldeddeshielded
Why?Why? Cylindrical electron currentCylindrical electron current
shields alkynyl hydrogenshields alkynyl hydrogen
AlkAlkyneyne hydrogens:hydrogens:
shieldedshielded
Recall alkene NMRRecall alkene NMR

12. Long range:Long range: RCRCHH22 C CC C HH JJ = 2-4 Hz= 2-4 Hz
RCRCHH22 C C CC C CHH22 R’R’ JJ = 2-3 Hz= 2-3 Hz
Coupling:Coupling:

14. 1313
C NMR:C NMR: δδ = 65-85 ppm: Also= 65-85 ppm: Also shielded.shielded.
Compare alkenes:Compare alkenes:
120-150ppm.120-150ppm.
HC CCHHC CCH22CHCH22CHCH22CHCH33
14-3114-316969 8484
IR spectra:IR spectra: diagnostic peaks for triple bonddiagnostic peaks for triple bond
and its attached H.and its attached H.
υυ (R(RC CC CR’) =R’) = 2120 cm2120 cm-1-1
;; υυ (RC(RC C HC H) =) = 3300 cm3300 cm-1-1~~
strongstrong
~~

16. Stability of Alkynes:Stability of Alkynes:
Heats of HydrogenationHeats of Hydrogenation
RevisitedRevisited
CHCHHCHC ++ HH22
Special cat.Special cat.
CHCH22 CHCH22
ΔΔHH ° = -44.9° = -44.9
kcal molkcal mol-1-1
CHCH22 CHCH22 ++ HH22
Cat.Cat.
CHCH33 CHCH33
ΔΔHH ° = -32.7° = -32.7
kcal molkcal mol-1-1
FirstFirst ΠΠ bond has more “heat content”, isbond has more “heat content”, is
also more reactive. Allows for:also more reactive. Allows for:
RR11
CC CC RR22
++ A BA B
AA
CC CC
RR22
RR11
BB
AA
CC CC
BB
RR11
RR22
++
Stereoselective alkene synthesisStereoselective alkene synthesis

17. InternalInternal alkynes arealkynes are more stablemore stable thanthan
terminal onesterminal ones
++ HH22
cat.cat.
++ HH22
cat.cat.
ΔΔHH ° = -69.9 kcal mol° = -69.9 kcal mol-1-1
ΔΔHH ° = -65.1 kcal mol° = -65.1 kcal mol-1-1
Parallels the behavior of alkenes.Parallels the behavior of alkenes.
Same reason:Same reason: hyperconjugationhyperconjugation..

18. PreparationPreparation
1.1. Elimination E2 of DihaloalkanesElimination E2 of Dihaloalkanes
CC CC
HH HH
XX XX
CC CC CC CC
BrBr
BrBr NaNa
B:B:-- HH
XX
B:B:--
NaNHNaNH22
excessexcess
NHNH33 liq.liq.
HH++
, H, H22OO
work upwork up
75%75%

19. Application in synthesis:Application in synthesis:
RCH CHR R C C RRCH CHR R C C R
BrBr
BrBrBrBr
BrBr
BrBr22
NaNHNaNH22
NHNH33 liqliq
1,5-Hexadiyne1,5-Hexadiyne

20. 2. Alkylation of Alkynyl Metals2. Alkylation of Alkynyl Metals
SSNN2 rules2 rules
LiLi
THFTHF
LiLi
II
∆∆
90%90%
BestBest: RI, THF, ∆. RBr or RCl need: RI, THF, ∆. RBr or RCl need
“coordinating”“coordinating” additives: e.g. ;additives: e.g. ;
or HMPA. Remember: Grignardsor HMPA. Remember: Grignards don’t workdon’t work
for RX, but O.K. for orfor RX, but O.K. for or carbonyls.carbonyls.
HH22NN NHNH22
OO

21. + CH+ CH33MgBrMgBr
MgBrMgBr
CHCH22 OO
OHOH
++ LiNHLiNH22 (l equiv)(l equiv) LiLi
OO
OHOH
+ 2 CH+ 2 CH33MgBrMgBr MgBrMgBrBrMgBrMg
HOHOOHOH
LiLi++
LiLi
OO
CHCH33
OHOH
CHCH33CHCH
OO

22. ReactionReaction
ss
1. Reductions1. Reductions a. Complete hydrogenationa. Complete hydrogenation
HH22, Pt, Pt
100%100%
b. Partial hydrogenation:b. Partial hydrogenation: “Poisoned”“Poisoned” Lindlar’sLindlar’s
catalyst:catalyst: Cis!Cis!
Pd-CaCOPd-CaCO33, Pb(OCCH, Pb(OCCH33))22, quinoline, quinoline
OO
NN
HH22,, LindlarLindlar
100%100%
HHHH
CisCis-3-heptene-3-heptene
c. Na reduction:c. Na reduction: Trans!Trans! Via stepwise 2e transferVia stepwise 2e transfer
+ Na°+ Na°
NNHH33 liq.liq.
86%86%
HH
HH
TransTrans-3--3-
hepteneheptene

23. Equilibrates between
cis and trans (more stable) LipshutzLipshutz
Mechanism:Mechanism:
HolidayHoliday
Na dissolves in liquid ammonia, makes “solvated” electronsNa dissolves in liquid ammonia, makes “solvated” electrons

24. 2. Electrophilic additions.2. Electrophilic additions. Like alkenes.Like alkenes.
a. HX:a. HX:
RRRR ++ HH++
CC CC RR
RR
HH
++ XX
--
Anti toAnti to HH;;
pushes Rpushes R
transtrans
CC CC
RR
HH RR
XX
HH++
MarkovnikovMarkovnikov
CC
RR
XX
RCRCHH22
XX
--
RCRCHH22CCXX22RR
Geminal dihalideGeminal dihalide
CHCHRCRC
HXHX
CC CC
XX
RR HH
HH HXHX
RCXRCX22CHCH33
Markovnikov twiceMarkovnikov twice
spsp
++
spsp 22
Internal alkynesInternal alkynes
Resonance with XResonance with X

25. δ 13
C = 202.4 ppm
++
ν = 1987 cm -1~~
1.22 Å
Linear!Linear!
Angew. Chem.Angew. Chem. 20042004, 43, 43, 1543., 1543.

26. Examples:Examples:
HBrHBr
BrBr BrBr
HIHI
II II
II II++
HClHCl
ClCl ClCl
Note:Note:
BrBr22
BrBr
BrBr
NaNHNaNH22
NHNH33
HBrHBr
BrBr BrBr
VicinalVicinal GeminalGeminal

27. b. Xb. X22:: Anti additionAnti addition, as for alkenes, as for alkenes
CHCH33
BrBr22
BrBr CHCH33
BrBr
BrBr22
BrBr BrBr
BrBr BrBr
c.c. Cat.Cat. HgSOHgSO44, H, H22O hydrationO hydration, Markovnikov, Markovnikov
CRCRRCRC
Cat. HgSOCat. HgSO44
HH22OO CC CC
HH
RR OHOH
RR TautomerizationTautomerization
OO
HH++
oror OHOH
catalyzedcatalyzed
--
UnstableUnstable
RCHRCH22CRCR
No NaBH4
needed

28. OO
RR
Mechanism of tautomerizationMechanism of tautomerization
HH++
:: CC
OHOH
RCHRCH22
++ RR
CC
OO
RCHRCH22 HH++ RCHRCH22CRCR
OO
--HH++
OHOH :: RCHRCH22CRCR
OO
++HH++
CC CC
HH
RR OO
RR
CC CC
HH
RR
RR--
--
--
CC CC
HH
RR OOHH
RR
HH++
oror OHOH catalyzedcatalyzed
--

29. CHCHRCRC
HgSOHgSO44
HH22OO
cat.cat.
CC
HOHO
RR
CHCH22
RCCHRCCH33
OO
Methyl ketoneMethyl ketone
d. Radical HBr:d. Radical HBr: Anti-Markovnikov additionAnti-Markovnikov addition
HBrHBr
ROORROOR
BrBr BrBr
HBrHBr
-Br-Br
BrBr BrBr
HH
HH
MixturesMixtures
++

30. HaloalkenesHaloalkenes
No SNo SNN2:2:
No SNo SNN1:1:

31. But:But:
And, metal catalysts couple alkenyl halides to
alkenes in the Heck reaction:

33. A variant with alkynes: Sonogashira reactionA variant with alkynes: Sonogashira reaction
CC CC
RR
HH RR
XX
R’C CHR’C CH++ CC CC
RR
HH RR
R’R’

34. BBRR22
e. Hydroboration-Oxidatione. Hydroboration-Oxidation
Use RUse R22BH (R =BH (R = bulkybulky group) togroup) to protectprotect
alkenylborane: R =alkenylborane: R = cyclohexylcyclohexyl
CHCHRCRC ++ B-HB-H
22
CC CC
RR
HH
HH HH22OO22,, --
OHOH
OHOH
CC CC
RR
HH
HH TautomerizationTautomerization
RCHRCH22CHCH
OO
Aldehyde !Aldehyde !
Steric controlSteric control

35. 1.1. RR22BHBH
2.2. HH22OO22,,--
OHOH
1.1. HBRHBR22
2.2. HH22OO22,,--
OHOH
Therefore:Therefore:
HH
OO
butbut HgSOHgSO44
HH22OO
cat.cat. OO
RRRR RCCHRCCH22RR
OO
R = R : MixturesR = R : Mixtures