1. Addition of Hydrogen Halides to Alkynes

2. HBr Br (60%) Alkynes are slightly less reactive than alkenes CH 3 (CH 2 ) 3 C CH CH 2 Follows Markovnikov's Rule

3. CH..Br H :.. RC..Br H :.. Observed rate law: rate = k[alkyne][HX] 2 Termolecular Rate-Determining Step

4. (76%) CH 3 CH 2 C CCH 2 CH 3 2 HF F F C CHH CH 3 CH 2 CH 2 CH 3 Two Molar Equivalents of Hydrogen Halide

5. Hydration of Alkynes

6. expected reaction: enol observed reaction: RCH 2 CR' O H+H+H+H+RC CR' H2OH2OH2OH2O + H+H+H+H+RCCR' H2OH2OH2OH2O + OHRCHCR' ketone Hydration of Alkynes

7. enols are regioisomers of ketones, and exist in equilibrium with them keto-enol equilibration is rapid in acidic media ketones are more stable than enols and predominate at equilibrium enol OHRCHCR' RCH 2 CR' O ketone Enols

8. OHC C H + O H H :.. : Mechanism of conversion of enol to ketone

9. O H C C H + O H H :..:

10. O H C C H + O H H :.. : :

11. O H C C H H O ::H +.. :

12. O H C CHH O : : H +.. :

13. O H C C H H O : H +.. :

14. Carbocation is stabilized by electron delocalization (resonance) H O C C H..H + Key Carbocation Intermediate O C C H +..:

15. H 2 O, H + (89%) via CH 3 (CH 2 ) 2 C C(CH 2 ) 2 CH 3 Hg 2+ O CH 3 (CH 2 ) 2 CH 2 C(CH 2 ) 2 CH 3 OH CH 3 (CH 2 ) 2 CH C(CH 2 ) 2 CH 3 Example of Alkyne Hydration

16. H 2 O, H 2 SO 4 HgSO 4 CH 3 (CH 2 ) 5 CCH 3 (91%) via Markovnikov's rule followed in formation of enol CH 3 (CH 2 ) 5 C CH 2 OH CH 3 (CH 2 ) 5 C CH ORegioselectivity

17. Addition of Halogens to Alkynes

18. + 2 Cl 2 ClCl (63%) C Cl 2 CH CH 3 HC CCH 3 Example

19. Br 2 CH 3 CH 2 CH 2 CH 3 Br Br (90%) CH 3 CH 2 C CCH 2 CH 3 C C Addition is anti