1. Acid-Catalyzed Hydration of Alkenes19

2. Acid-Catalyzed Hydration of AlkenesOH C H +
H—OH
reaction is acid catalyzed; typical hydration medium is 50% H2SO4-50% H2O
Follows Markovnikov's Rule 2

3. Hydration – Thermodynamics
Hydrohalogenation & hydration reactions are at equilibrium.

4. Hydration – Thermodynamics
How could Le Châtelier’s principle be used to shift the equilibrium to the right or left?
SEE: CONCEPTUAL CHECKPOINT 9.11.

5. Hydration – Thermodynamics
Similar to hydrohalogenation, the stereochemistry of hydration reactions is controlled by the geometry of the carbocation. Draw the complete mechanism for the reaction above to show WHY a racemic mixture is formed. SEE: SKILLBUILDER 9.3.

6. Markovnikov's Rule H3C H 50% H2SO4 CH3 CH2CH3 C C 50% H2O CH3 OH (90%)

7. Follows Markovnikov's RuleOH
CH3
50% H2SO4
50% H2O
CH2
(80%) 4

8. involves a carbocation intermediate
Mechanism
involves a carbocation intermediate
is the reverse of acid-catalyzed dehydration of alcohols to alkenes OH C
CH3
H3C C
CH2 H+
+ H2O 5

9. Addition of Water to Alkene
(alcohols)

10. Addition of Water to Alkenes
(alcohols)

11. Question
Which alkene will undergo acid-catalyzed hydrolysis at the fastest rate?
A) B)
C) D)

12. Principle of Microscopic ReversibilityOH C
CH3
H3C C
CH2 H+
+ H2O
In an equilibrium process, the same intermediates and transition states are encountered in the forward direction and the reverse, but in the opposite order. 11

13. H2O addition: Markovnikov's Rule3

14. Question
The product isolated from the acid-catalyzed hydration of (Z)-3-methyl-2-pentene is:
A) 2-ethyl-2-butanol
B) 2-ethyl-1-butanol
C) 3-methyl-2-pentanol
D) 3-methyl-3-pentanol

15. Question
The product isolated from the acid-catalyzed hydration of (E)-3-methyl-2-pentene is:
A) chiral
B) achiral

16. Oxymercuration-Demercuration
Because rearrangements often produce a mixture of products, the synthetic utility of Markovnikov hydration reactions is somewhat limited. OXYMERCURATION-DEMERCURATION is an alternative process that can yield Markovnikov products avoiding rearrangements

17. Oxymercuration-Demercuration
OXYMERCURATION begins with mercuric acetate.
How would you classify the mercuric cation?
As a nucleophile or an electrophile?
As a Lewis acid or Lewis base?

18. Oxymercuration-Demercuration
Similar to how we saw the alkene attack a proton previously, it can also attack the mercuric cation. Resonance stabilizes the mercurinium ion. Can you draw a reasonable resonance hybrid?

19. Oxymercuration-Demercuration
The mercurinium ion is also a good electrophile, and it can easily be attacked by a nucleophile, even a weak nucleophile such as water. NaBH4 is generally used to replace the –HgOAc group with a –H group via a free radical mechanism.

20. Addition of Alcohol to Alkenes
(ethers)

21. Stereochemistry of Addition to Alkenes+
E—Y E Y
Regiochemistry withstanding, in order to understand the
stereochemistry of the product, you must consider two things:
(1) Stereochemistry of the starting alkene (cis or trans; Z or E)
(2) Stereochemistry of the addition (syn or anti) 2

22. Stereochemistry of Addition to Alkenes+
E—Y E Y
Optically inactive reactants produce optically inactive products.
(Racemic mixtures are optically inactive)
The correlary is that an optically active starting material
MAY produce an
optically active product depending on the mechanism. 2

23. Question
The product isolated from the acid-catalyzed hydration of (E)- or (Z)-3-methyl-2-pentene is:
A) optically active
B) an optically inactive racemic mixture
C) an optically inactive enantiomer

24. Hydroboration-Oxidation of Alkenes19

25. Hydroboration-Oxidation
To achieve anti-Markovnikov hydration, hydroboration-oxidation is often used. Note that the process occurs in two steps.

26. Suppose you wanted to prepare 1-decanol from 1-decene?
Synthesis
Suppose you wanted to prepare 1-decanol from 1-decene? OH
Needed: a method for hydration of alkenes with a regioselectivity opposite to Markovnikov's rule. 13

27. Synthesis
Two-step reaction sequence called hydroboration- oxidation converts alkenes to alcohols with a regiochemistry opposite to Markovnikov's rule.
1. hydroboration
2. oxidation OH 13

28. Hydroboration Step C H BH2 C + H—BH2
Hydroboration can be viewed as the addition of borane (BH3) to the double bond. But BH3 is not the reagent actually used. 14

29. Hydroboration reagents:
Hydroboration Step C H
BH2 C
+ H—BH2
Hydroboration reagents: H
Diborane (B2H6) normally used in an ether-like solvent called "diglyme"
H2B
BH2 H 14

30. Hydroboration reagents:
Hydroboration Step C H
BH2 C
+ H—BH2
Hydroboration reagents: + O
BH3 – ••
Borane-tetrahydrofuran complex (H3B-THF) 14

31. Oxidation Step H2O2, HO– H BH2 C H OH C
Organoborane formed in the hydroboration step is oxidized with hydrogen peroxide. 17

32. Example
1. B2H6, diglyme
2. H2O2, HO– OH
(93%) 13

33. Example H C
CH3 OH
H3C
CH3
1. H3B-THF
2. H2O2, HO– C
H3C H
(98%) 13

34. Features of Hydroboration-Oxidation
hydration of alkenes
regioselectivity opposite to Markovnikov's rule
no rearrangement
stereospecific syn addition 18

35. Example OH
1. B2H6, diglyme
2. H2O2, HO–
(82%) 13

36. Stereochemistry of Hydroboration-Oxidation19

37. Features of Hydroboration-Oxidation
hydration of alkenes
regioselectivity opposite to Markovnikov's rule
no rearrangement
stereospecific syn addition 18

38. only product is trans-2-methylcyclopentanol (86%) yield
syn Addition
H and OH become attached to same face of double bond H
CH3 HO
CH3 H
1. B2H6
2. H2O2, NaOH
only product is trans-2-methylcyclopentanol (86%) yield 20

41. Question
Hydroboration-oxidation of which one of the following yields a primary alcohol as the major product?
A) B)
C) D)

42. The product is optically active The product is a racemic mixture
Question H C
CH3 OH
H3C
CH3
1. H3B-THF
2. H2O2, HO– C
H3C H
The product is achiral
The product is optically active
The product is a racemic mixture
The product is a single enantiomer 13

43. Conversion of Alkenes to Vicinal Halohydrins20

44. in the Presence of Water
Addition of Halogens
in the Presence of Water
(halohydrins)

45. alkenes react with X2 to form vicinal dihalides

46. alkenes react with X2 to form vicinal dihalides
alkenes react with X2 in water to give vicinal halohydrins C C
+ X2
+ H2O X OH
+ H—X 2

47. anti addition: only product
Examples
H2O
H2C
CH2 +
Br2
BrCH2CH2OH
(70%) OH Cl H
Cl2 H
H2O
anti addition: only product 6

48. anti addition: only product
Examples
H2O
H2C
CH2 +
Br2
BrCH2CH2OH
(70%) OH Cl H
Cl2 H
H2O
anti addition: only product 6

49. Figure Number: UN
Title: 3-Bromo-2-butanol Isomers
Caption: Named perspective formulas and Fischer projections of the isomers of 3-bromo-2-butanol.
Notes: The first two structures on the left are enantiomers of each other. The last two structures on the right are also enantiomers. Each of the structures in the left pair is a diastereomer of each of the structures in the right pair.

50. Figure Number: UN-A
Title: Erythro and Threo Diastereomers
Caption: Erythro enantiomers are diastereomers of threo enantiomers.
Notes: Diastereomers are stereoisomers which are not mirror images of one another. Erythro enantiomers are stereoisomers with two adjacent chirality centers, which have two similar groups on the same side of the carbon chain, and threo enantiomers have the two similar groups on opposite sides of the carbon chain.

51. Perspective formula
Fischer projection

52. Regioselectivity CH3 OH C CH2Br H3C C CH2 Br2 H2O (77%)
Markovnikov's rule applied to halohydrin formation: the halogen adds to the carbon having the greater number of hydrogens. 32

53. Explanation H O .. H O .. H3C H3C H3C H3C C CH2 CH2 C : Br : : Br : 
transition state for attack of water on bromonium ion has carbocation character; more stable transition state (left) has positive charge on more highly substituted carbon 34

55. Question
What is the product (in addition to its enantiomer) of the following reaction?

56. Conversion of Alkenes to Vicinal Diols20

57. Syn Dihydroxylation
SYN dihydroxylation adds across the C=C double bond in ONE step.

58. SEE: CONCEPTUAL CHECKPOINT 9.33.
Syn Dihydroxylation
MnO41- is similar to OsO4 but more reactive.
SYN dihydroxylation occurs with KMnO4 only under mild conditions (cold temperatures).
Diols are commonly further oxidized by MnO41-, and in addition MnO41- is reactive toward many other functional groups as well. It is very useful in qualitative analysis due to a pronounced color change.
SEE: CONCEPTUAL CHECKPOINT 9.33.