1. Alkynes. C n H 2n-2 C 2 H 2 H:C:::C:H H—C  C—H sp => linear, 180 o acetylene ethyne C 3 H 4 CH 3 C  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. CH 3 CH 2 C  CCH 3 2-pentyne ethylmethylacetylene

3. “terminal” alkynes have the triple bond at the end of the chain: CH 3 CH 3 CH 2 C  CHHC  CCHCH 2 CH 3 1-butyne 3-methyl-1-pentyne ethylacetylenesec-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 + H 2 O | | | X X X H | — C = C — + NaNH 2  — C  C — + NaX + NH 3 | X

6. H H | | — C — C — + 2 KOH  — C  C — + KX + H 2 O | | heat X X CH 3 CH 2 CHCH 2 + KOH; then NaNH 2  CH 3 CH 2 C  CH Br Br “ + 2 KOH, heat

7. alkenevicinal dihalidealkyne X2X2 1. KOH 2. NaNH 2 CH 3 CH=CH 2 CH 3 CHCH 2 CH 3 C  CH Br Br Br 2 1.KOH 2.NaNH 2

9. 2.coupling of metal acetylides with 1 o /CH 3 alkyl halides R-C  C - Na + + R´X  R-C  C-R´ + NaX a)S N 2 b)R´X must be 1 o or CH 3 X CH 3 C  C - Li + + CH 3 CH 2 -Br  CH 3 C  CCH 2 CH 3

10. note: R-X must be 1 o or CH 3 to get S N 2!

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

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

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

14. HC  CH + 2 H 2, Pt  CH 3 CH 3 [ HC  CH + one mole H 2, Pt  CH 3 CH 3 + CH 2 =CH 2 + HC  CH ] H \ / Na or Li C = C anti- NH 3 (liq) / \ H — C  C — \ / H 2, Pd-C C = C syn- Lindlar catalyst / \ H H

15. CH 3 H \ / Na or Li C = C anti- NH 3 (liq) / \ H CH 3 trans-2-butene CH 3 C  CCH 3 H H \ / H 2, Pd-C C = C syn- Lindlar catalyst / \ CH 3 CH 3 cis-2-butene

16. 2.Addition of X 2 X X X | | | — C  C— + X 2  — C = C — + X 2  — C — C — | | | X X X Br Br Br CH 3 C  CH + Br 2  CH 3 C=CH + Br 2  CH 3 -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 CH 3 C  CH + HCl  CH 3 C=CH 2 + HCl  CH 3 CCH 3 Cl Cl

18. 4.Addition of water. Hydration. O — C  C — + H 2 O, H +, HgO  — CH2 — C— H OH — C = C — “enol” keto-enol tautomerism Markovnikov orientation.

19. CH 3 CH 2 C  CH + H 2 O, H 2 SO 4, HgO  1-butyne O CH 3 CH 2 CCH 3 2-butanone

20. 5.As acids. terminal alkynes only! a)with active metals CH 3 C  CH + Na  CH 3 C  C - Na + + ½ H 2  b)with bases CH 3 C  CH + CH 3 MgBr  CH 4 + CH 3 C  CMgBr SA SB WA WB

21. acid strength: CH 4 < NH 3 < HC  CH < ROH < H 2 O < HF HC  CH + NaOH  NR ( H 2 O = stronger acid! ) CH 3 CH 2 C  CH + LiNH 2  NH 3 + CH 3 CH 2 C  C - Li + SA WA

22. 6.Ag + terminal alkynes only! CH 3 CH 2 C  CH + AgNO 3  CH 3 CH 2 C  C - Ag +  CH 3 C  CCH 3 + AgNO 3  NR (not terminal) formation of a precipitate is a test for terminal alkynes.

23. 7.Oxidation KMnO 4 R-C  C-R´ hot KMnO 4 RCOOH + HOOCR´ carboxylic acids O 3 ; then Zn, H 2 O

24. CH 3 CH 2 C  CCH 3 + KMnO 4  CH 3 C  CH + hot KMnO 4  CH 3 C  CCH 3 + O 3 ; then Zn, H 2 O  CH 3 CH 2 COOH + HOOCCH 3 CH 3 COOH + CO 2 2 CH 3 COOH

25. Alkynes Nomenclature Syntheses 1. dehydrohalogenation of vicinal dihalide 2. coupling of metal acetylides with 1 o /CH 3 X

26. Reactions, alkynes: 1.addition of H 2 (reduction) 2.addition of X 2 3.addition of HX 4.addition of H 2 O, H + 5.as acids 6.Ag + 7.oxidation