1. Alkynes. CnH2n-2 C2H2 H:C:::C:H H—C  C—H sp => linear, 180o
acetylene
ethyne
C3H CH3CCH methylacetylene
propyne

2. nomenclature:
common names: “alkylacetylene”
IUPAC: parent chain = longest continuous carbon chain that contains the triple bond.
alkane drop –ane add -yne
prefix locant for the triple bond, etc.
CH3CH2CCCH pentyne
ethylmethylacetylene

3. “terminal” alkynes have the triple bond at the end of the chain:
CH3CH2CCH HCCCHCH2CH3
1-butyne methyl-1-pentyne
ethylacetylene sec-butylacetylene

4. physical properties:
weakly or non-polar, no H-bonding
relatively low mp/bp
water insoluble

5. Synthesis, alkynes:
dehydrohalogenation of vicinal dihalides
H H H
| | |
— C — C — + KOH  — C = C — KX + H2O
| | |
X X X H |
— C = C — NaNH2  — C  C — + NaX + NH3 X

6. H H
| |
— C — C — KOH  — C  C — KX + H2O
| | heat
X X
CH3CH2CHCH KOH; then NaNH2  CH3CH2CCH
Br Br
“ KOH, heat

7. X2
1. KOH
alkene
vicinal dihalide
alkyne
2. NaNH2
CH3CH=CH CH3CHCH CH3CCH
Br Br
Br2
KOH
NaNH2

9. coupling of metal acetylides with 1o/CH3 alkyl halides
R-CC-Na R´X  R-CC-R´ + NaX
SN2
R´X must be 1o or CH3X
CH3CC-Li CH3CH2-Br  CH3CCCH2CH3

10. note: R-X must be 1o or CH3 to get SN2!

11.   some alkynes acids bases terminal only metals oxid. reduct.
halogens 
 some
terminal only

12. Reactions, alkynes:
addition of H2 (reduction)
addition of X2
addition of HX
addition of H2O, H+
as acids
Ag+
oxidation

13. Addition of H2
H H
| |
— C  C — H2, Ni  — C — C —
alkane
requires catalyst (Ni, Pt or Pd)

14. HCCH H2, Pt  CH3CH3
[ HCCH + one mole H2, Pt  CH3CH CH2=CH2 + HCCH ] H
\ /
Na or Li C = C anti-
NH3(liq) / \
— C  C —
\ /
H2, Pd-C C = C syn-
Lindlar catalyst / \
H H

15. CH3 H
\ /
Na or Li C = C anti-
NH3(liq) / \
H CH3
trans-2-butene
CH3CCCH3
H H
H2, Pd-C C = C syn-
Lindlar catalyst / \
CH3 CH3
cis-2-butene

16. Addition of X2
X X X
| | |
— C C— X2  — C = C — + X2  — C — C —
| | |
X X X
Br Br Br
CH3CCH Br2  CH3C=CH Br2  CH3-C-CH
Br Br Br

17. Addition of hydrogen halides:
H H X
| | |
— C C— HX  — C = C — + HX  — C — C —
| | |
X H X
HX = HI, HBr, HCl
Markovnikov orientation Cl
CH3CCH HCl  CH3C=CH HCl  CH3CCH3
Cl Cl

18. Addition of water. Hydration.
— C  C — H2O, H+, HgO  — CH2 — C—
H OH
— C = C —
“enol” keto-enol tautomerism
Markovnikov orientation.

19. CH3CH2CCH H2O, H2SO4, HgO 
1-butyne O
CH3CH2CCH3
2-butanone

20. As acids. terminal alkynes only!
with active metals
CH3CCH Na  CH3CC-Na+ + ½ H2 
with bases
CH3CCH CH3MgBr  CH CH3C CMgBr
SA SB WA WB

21. acid strength:
CH4 < NH3 < HCCH < ROH < H2O < HF
HC CH NaOH  NR ( H2O = stronger acid! )
CH3CH2CCH LiNH2  NH CH3CH2CC-Li+
SA WA

22. Ag+ terminal alkynes only!
CH3CH2CCH AgNO3  CH3CH2CC-Ag+ 
CH3CCCH AgNO3  NR (not terminal)
formation of a precipitate is a test for terminal alkynes.

23. Oxidation
KMnO4
R-CC-R´ hot KMnO4 RCOOH + HOOCR´
carboxylic acids
O3; then Zn, H2O

24. CH3CH2CCCH KMnO4 
CH3CCH hot KMnO4 
CH3CCCH O3; then Zn, H2O 
CH3CH2COOH HOOCCH3
CH3COOH CO2
2 CH3COOH

25. Alkynes
Nomenclature
Syntheses
1. dehydrohalogenation of vicinal dihalide
2. coupling of metal acetylides with 1o/CH3X

26. Reactions, alkynes:
addition of H2 (reduction)
addition of X2
addition of HX
addition of H2O, H+
as acids
Ag+
oxidation