Very good

1. Alkynes. CnH2n-2
C2H2 H:C:::C:H H—C  C—H sp => linear, 180o
acetylene
ethyne
C3H4 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CCH3 2-pentyne
ethylmethylacetylene

3. “terminal” alkynes have the triple bond at the end of the
chain:
CH3
CH3CH2CCH HCCCHCH2CH3
1-butyne 3-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:
1. 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 — + 2 KOH  — C  C — + KX + H2O
| | heat
X X
CH3CH2CHCH2 + KOH; then NaNH2  CH3CH2CCH
Br Br
“ + 2 KOH, heat

7. alkene vicinal dihalide alkyne
X2 1. KOH
2. NaNH2
CH3CH=CH2 CH3CHCH2 CH3CCH
Br Br
Br2 1. KOH
2. NaNH2

8. Synthesis of propyne from propane
CH3CH2CH3
Br2, heat
CH3CH2CH2-Br + CH3CHCH3
Br
KOH(alc)
CH3CH=CH2
Br2
CH3CHCH2
Br Br
KOH
CH3CH CH
Br
NaNH2
CH3C CH

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

10. CH3C C Na + CH3CCH3
CH3
Br
CH3C CH
+
CH3C CH2
CH3
3o alkyl halide
E2 elimination!
note: R-X must be 1o or CH3 to get SN2!

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

12. Reactions, alkynes:
1. addition of H2 (reduction)
2. addition of X2
3. addition of HX
4. addition of H2O, H+
5. as acids
6. Ag+
7. oxidation

13. 1. Addition of H2
H H
| |
— C  C — + 2 H2, Ni  — C — C —
| |
H H
alkane
requires catalyst (Ni, Pt or Pd)

14. HCCH + 2 H2, Pt  CH3CH3
[ HCCH + one mole H2, Pt  CH3CH3 + CH2=CH2 + HCCH
]
H
/
Na or Li C = C anti-
NH3(liq) /
H
— 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. 2. 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. 3. Addition of hydrogen halides:
H H X
| | |
— C C— + HX  — C = C — + HX  — C — C —
| | |
X H X
a) HX = HI, HBr, HCl
b) Markovnikov orientation
Cl
CH3CCH + HCl  CH3C=CH2 + HCl  CH3CCH3
Cl Cl

18. 4. Addition of water. Hydration.
O
— 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. 5. As acids. terminal alkynes only!
a) with active metals
CH3CCH + Na  CH3CC-Na+ + ½ H2 
b) with bases
CH3CCH + CH3MgBr  CH4 + 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  NH3 + CH3CH2CC-Li+
SA WA

22. 6. Ag+ terminal alkynes only!
CH3CH2CCH + AgNO3  CH3CH2CC-Ag+ 
CH3CCCH3 + AgNO3  NR (not terminal)
formation of a precipitate is a test for terminal alkynes.

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

24. CH3CH2CCCH3 + KMnO4 
CH3CCH + hot KMnO4 
CH3CCCH3 + 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:
1. addition of H2 (reduction)
2. addition of X2
3. addition of HX
4. addition of H2O, H+
5. as acids
6. Ag+
7. oxidation