6.2-1

Alkenes II-continuedAlkenes II-continued1. Types of Rxn.: elimination, addition, substitution2. Mechanisms: How rxn’s of molecules occur.3. Electrophilic (Markovnikov) addition A. Addition of HX, regioselective

R3C+ > R2HC+ > RH2C+ > H3C+

B. Hydration H+/H2O C. Rearrangements D. Bromonium ions, (anti addition) E. Halohydrin formation, (anti) F. H+ - hydration , Hg+2-hydration - (anti)4. Hydroboration (syn addition)5. Oxidation (syn)6. Reduction (syn), olefin and diene stability 7. Reactions relative to stereocenters

X

For PRACTICE (“worksheet”) problems go to the home pageWork/Study Sheet 6 due in recitation 3/26 or 3/27

R Br

H+

R

H

HRBr

H

HH

HH

HH

H

H

Br

HgOAc

SS! 28 19

6.2-2

Chapter 6

H3C

CH3

H

H OH

CH

H3C F

HO

CH

H3CF

O

CO

H3C

H

OH

O

CO

H3C

OH

H

+

+

XH

H2 / M

Cl

IC

H

H3C D

NC

CH

H3CD

(-):CN:

CH2

OH O

HCH3

CH3

H

Br Mg CH3

δ+ δ−

LiCu

2

reaction typesolefin additions

mechanismsenergy

progress of rx

specific additionsand reactions

6.2-3

Chapter 6 hydrationrearrangements

halogenationhalohydration

mercury hydration

hydroborationother additionsstereochemistry

6.2-4F. Alternative “Hydration” of Alkenes Oxymercuration/Reduction

H2OC

CH

H

H

R R CC

H H

H OH

HHg(OAc)2

NaBH4 + Hgo +HOAc

R = H, alkyl, Ph, etc.

2 rx sequence

6.2-5

Br BrBr

Br

Last lecture:

Br

Br

Br Br

OR

Br

6.2-6

Last lecture:

3o>2o

Hg OAcHg

O

OAc

H2O(XS)

HH

OAc

HgOAc

OHH

-H+

etc.

OR

Hg OAc

OAc HgOAc

6.2-7

E(+)E(+)

E [(+) or (++)]OR

EE(+)

E

NuNu:

Nu:[(0) or (-)]

“general” antiaddition

6.2-10

HgAcO OAc

OH

+

NaBH4

H2O1

2

HgAcO

HgAcO

OH

H

HgAcO

OH

H

HgAcO

O H

H:(-)

Issues: no rearrangement regiochemistrystereochemistry

6.2-11

HgAcO

OH

H

δ+

HgAcO

OH H

δ+

Issues: rearrangement regiochemistrystereochemistry

6.2-12

H

OH

+ Hg

OAc

AcO[1]

[2]

Hg

AcO

OH

NaBH4

HgAcO OAc

O H

H

Hg

AcO

O H

H

~[ :H(-)]

Na H B H

H

HIssues:

rearrangement regiochemistrystereochemistry

6.2-136.4 HYDROBORATION [ BH3 or B2H6 ]

CH3

H

H2B H

CH3

H

δδ+B H

H

H

δ

(+)

CH3H

H

H HB

mechanism: syn addition

H moves with2 electrons [H:](-)

6.2-14

[ts] synchronous B & H addition

B HH

H

CH3

HB

H

HH

CH3H

HBHH

rx

H CH3

BH3

6.4 HYDROBORATION [BH3 or B2H6]

6.2-156.4 HYDROBORATION /

synchronous B & H addition

CH3

HB

H

HH

rx

H CH3

BH3

OXIDATIONCH3

HHO

HH2O2

NaOH

B HH

H

H CH3

B HH

H

CH3H

HBHH

ts

6.2-166.4 HYDROBORATION /CH3

HB

H

HH

rx

H CH3

BH3

OXIDATIONCH3

HHO

HH2O2

NaOH

OO

H

CH3

HB

H

HH O O

H

CH3

HB

H

HH

O

O H

H

HO

OH O H+ H

OO O H+ H

Na Na

6.2-17

C C H

H

H

R

OHH

Note regioselectivity

C CH

H

H

R

BH3

ether C C H

H

H

R

BH2H

C C H

H

H

R

OHH

NaOH

H2O2

H+

H2O

C CH

H

H

R

Hg(OAc)2

H2O

NaBH4

6.2-18Hydroxylation [O] of olefins

RC C

H

H

H

+ OsO4

tBuOOHH2O

RC C

H

H

H OH OH(cat.)

tBuOOH =H3C

C

H3C

H3CO

OH

tBuOOH

OsO4 OsO3

hydroxylation

Note: cold KMnO4/(-)OH = OsO4/ROOH/H2O

6.2-19

R

C C

H

H

H

OOs

O

OO

R

C C H

H

H

OOs

O

O O

R

C C H

H

H

O OH HO

H

H

OsO

O

O OH

H

OsO O

O O

HH

OMn

O

O O K

isoelectronic

mechanism: syn addition of O’s

cold/basic/H2O

H2OROOH

6.2-21

note!

CH3C

CH3

CH3C

H

+ O3

CH3C

CH3

O

CH3CO

OH

+

H2O2

oxidizing reagent

S(CH3)2

reducing agent

OCH3C

H

CH3C

CH3

O+

Ozonolysis

(or Zn:)

H oxidized to OH

mechanism: syn addition,ignore

6.2-24

Ozonolysis

H

H

O3

Zn:

H

H

O

O

H

O3

HOOHO

O

O+

H

OO

H

+

??

H

O3

Zn:

6.2-25

metal surface

Catalytic addition of H2 to bonds

break one C-C bond, gain two C-H bonds

How?

RR

R

H H

RC C

H H

R

R

R

RC C

H2

H3C CH3H3C CH3H H

H2cat.

metal catalyst Pd (Pd/C) Pt Ni

R

R

R

HH

RC C

6.2-26

H2

6.2-27

Catalytic addition of H2 to bonds

C

H

H

H2

Pt

C

HH

HH

C

H

H

D2

Pt

C

HH

DD

other double bonds

OH2

Pt

OH

H

NH2

NiN

HH

CH3CH3

6.2-28

RC C

H H

H+ H2

metalcat.

RC C

H H

H

H H+

H

CC

H

HH

< CC

HH

RH

<

CC

HR

RR

<

CC

RR

RR

<

CC

HH

RR

CC

HR

RH

CC

RH

RH

stability of olefins(based on energy released)

6.2-29Conjugated Dienes - similar to simple olefins but resonance makes them special.

Classification:

conjugated

isolated

resonance energy

~56.5 kcal

H2

cat.

~60.6 kcal

H2

cat.

60.6 kcal-56.5 kcal

4.1 kcal

6.2-30

Reaction: conjugated vs unconjugated

1 equivalentBr2

1 equivalentBr2

13

14

Br-Br

Br-Br

Br

BrH

14

BrH

BrH

14 +

Br(+)

Br(-)

"1" Br

Br"4"

“1,4-addition” vs “1,2-addition”

6.2-32Stereochemistry of Reactions

regio

stereo

selective specific

constitutional isomers

stereoisomers

excess of product X over Y only product X, no Y (product X’s, no Y’s)

6.2-33

Regioselective rx - of 2 possible constitutional isomers, rx forms 1 > other (Markovnikov addition).

Stereochemistry of Reactions

Regiospecific rx - of 2 possible constitutional isomers, rx forms 1 (Markovnikov addition).

H-Cl

Cl

Cl

100% 0%

30 | 70

H

Br

H-Br

Br

H

+ + "other products"

6.2-34

Stereospecific rxstereoisomers stereoisomers products

D D

D

D

H2

M

H2

M

D DH H

S S

D DH H

R R+

D

D

H

H

D

DH H

R S S R+

6.2-35

HH

Stereoselective rx: Rx stereoisomer [B] > [C]

major

HH

HH

HH

HH

HH

DCH3

HH

CH3

H

D

H

CH3

H

H

D

+H-H

H

H H

HPd/C

C

H

HH

HDH

6.2-36

Rx forming stereogenic center - ionic addition: H3CH2C

CH

C H

H

H3CH2CC

HC H

H

H

+ Br

regiospecific not stereo-selective or -specific

H3CH2CC

H

C HH

HBr

"R"

H3CH2C

CH C HH

H

Br

"S"

equal opportunity either side

7

Review

6.2-37Review:

No RR

H3CC

H3CCH3

C C

H

H

H

Br

OH

No RR

H3CC

H3CCH3

C C

H

H

H

HgOAc

OHH3C

CH3C

CH3

C C

H

H

H

H

OH

NaBH4

H3CC

H3CCH3

CC

H

H

H Br2

Br- No RR

H3CC

H3CCH3

C C

H

H

HBr

Br

H3CC

H3CCH3

CC

H

H

H Br2

xs H2O

H3CC

H3CCH3

CC

H

H

HBr

H3CC

H3CCH3

CC

H

H

HBr

H3CC

H3CCH3

CC

H

H

HHg(OAc)2

H2O/H+

H3CC

H3CCH3

CC

H

H

HHgOAc

Br2, Cl2, I2, Hg++ - anti addition

7

6.2-38

No RR

H3CC

H3CCH3

CC

H

H

H H+

-BrC

H3CCH3

CC

H

H

H

CH3H

OsO4, KMnO4, HBR2, H2 , O3 - syn addition

CH3C

CH3

CC

H

H

H

CH3HBr

ionic addition - carbocations - possible RR

7

H3CC

H3C CH3

CC

H

H

H

HB

H

H

δ-

δ+H3C

CH3C CH3

CC

H

H

H

HB H

H H3CC

H3C CH3

CC

H

H

H

H BH2

CH3C CH3

CC

H

H

H

H3C H

C

H3C CH3

C C

H

HH

H Br

H3C racemic