topic 8. additions to alkenes and alkynes...

D.M. Collard 2007

TOPIC 8. ADDITIONS TO ALKENES AND ALKYNES (Chapter 8 and parts of chapters 7, 10 and 11)

L

OBJECTIVES

1. Describe mechanisms for addition reactions of alkenes and alkynes2. Predict the structure of the product(s) of addition reactions3. Understand the mechanisms which explain the regiochemical and

stereochemical outcome of addition reactions4. Use combination of substitution, elimination and addition chemistry to

propose synthetic routes to useful value-added compounds

D.M. Collard 2007

ADDITION REACTIONSAddition of H2- H2/Pd (alkene, alkyne)- H2/Lindlar catalyst (alkyne → cis alkene)- dissolving metal reduction (alkyne → trans alkene)

Addition of H-Hal- Markovnikov- anti-Markovnikov

Addition of H2O- H3O+ (regiochemistry)- Oxymercuration-demercuration (regiochemistry, stereochemistry)- Hydroboration-oxidation (regiochemistry, stereochemistry)- hydration of alkynes (regiochemistry)

Addition of Hal2- Hal2 (regiochemistry, stereochemistry)- Hal2/H2O (regiochemistry)

Generation and reaction of carbenesEpoxidationNucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)syn-HydroxylationOxidative cleavage of alkenes and alkynes- KMnO4- Ozonolysis

Radical Polymerization

~MAKE FLASHCARDS AFTER EACH LECTURE~

Lecture 1

Lecture 2

Lecture 3

Lecture 4

Lecture 5

HYDROGENATION OF ALKENESAND ALKYNES

Hydrogenation of Alkenes

CH3

CH3 H2Pd or Pt

Prob:7.40-42;

8.30e,g,i,37,45

S:7.12-7.14

D.M. Collard 2007

Hydrogenation of AlkynesComplete Hydrogenation

cis-Semihydrogenation

C CH2

Pt or Pd

C C

H2Pd/CaCO3

N

C C2Li, 2CH3OH

NH3 (solvent)

C C

Li

Li

Li

Dissolving Metal Reduction

D.M. Collard 2007

PREVIEW OF REACTIVITYAlkenes and Alkynes are Weakly _____ and Weakly

_____________

C C

E

C C E

H Br

S:8.1

ADDITION OF HYDROGEN HALIDESTO ALKENES AND ALKYNES

Overview

C CHC C

BrBrH

CH3CH3

I

C C C C ClH

H

Prob:8.27,28a,b,f,j,29b-g,35

S:8.2-8.3;18.19;

10.9

D.M. Collard 2007

Addition of H-Hal to AlkenesMechanism

C C H Br

Regiochemistry

Markovnikov’s Rule

In the addition of HX to an unsymmetrical alkene, the hydrogen adds to the

_____________ substituted carbon and the X groups adds to the

_____________ substituted carbon.

C CH2

H3C

H3CH Br

D.M. Collard 2007

The Basis of Markovnikov’s Rule: Stability of Carbocations

C C

HH

H

C CH2

H3C

H3CHBr

Mechanistic Restatement of Markovnikov’s RuleIn the ionic addition of HX to an unsymmetrical alkene, protonation gives the more stable carbocation as an intermediate.

The more substituted carbocation is formed. Remember hyperconjugation!

Stereochemistry of H–Hal Addition to Alkenes

Br

H Br

BrCH

D.M. Collard 2007

Anti-Markovnikov Addition of H-Hal to Alkenes

Mechanistic Rationale for Anti-Markovnikov Addition

C CH2

H

H3CH Br

Addition of H-Hal to Alkynes

R C C H

R C C R'

HClCCl4

D.M. Collard 2007

~ MAKE FLASHCARDS ~

HydrogenationDissolving metal reductionHydrogenation over Lindlar catalystMarkovnikov addition of H-HalAnti-Markovnikov addition of H-Hal

…..more next lecture








Lecture 1

Lecture 2

Lecture 3

Lecture 4

Lecture 5

D.M. Collard 2007

Addition of Water to Alkenes

C C

H OH2

H2O

H2SO4

SYNTHESIS OF ALCOHOLSBY HYDRATION OF ALKENES

L

Prob:8.27c,32,5811.33,35(a-g),38(a,d),

39,46,48

S:8.4-8.11

Proceeds via Markovnikov addition

D.M. Collard 2007

Rearrangements During Acid Catalyzed Hydration of Alkenes

Intermediate carbocations can rearrange.

H2SO4

H2OCH3 OH

CH3

H

CH3

OHHnot:

Oxymercuration-Demercuration of Alkenes

e.g.,

Step 1: Oxymercuration

Step 2: Demercuration

C C

(CH3CO2)2HgH2O

HO Hg OCH3

O

NaBH4NaOH

HO Hg OCH3

O

HO H

1. (CH3CO2)2Hg H2O

2. NaBH4, NaOH

OH

D.M. Collard 2007

Mechanism

O Hg O

OO

O Hg

O

H2O

Hydroboration-Oxidation: Anti-MarkovnikovHydration of Alkenes

e.g.,

Step 1: Hydroboration

Step 2: Oxidation

C CB2H6

H BH2

H2O2NaOH

H BH2 H OH

CH3 CH3H

OH

1. B2H6

2. H2O2 NaOH

D.M. Collard 2007

Mechanism: Regiochemistry

BH

HB

H2O2NaOH, H2O

B2H6 BH3

Stereochemistry

CH3CH3

H

B

CH3H

OH

D.M. Collard 2007

R C C HR

C CH

H2O

Hg++, H2SO4

H

HO

Hydration of Alkynes (covered in 16.5B)

SYNTHETIC STRATEGIES Prob:7.24

CN

Problem: Synthesize cis-1-cyano-2-methylcyclohexane (shown below) using any hydrocarbon.

D.M. Collard 2007

Problem: Female houseflies attract males with a pheromone which has been shown to be Z-9-tricosene (C23H46). Synthesize this compound starting with organic compounds containing 13 or less carbon atoms.

H Hn-C8H17 n-C13H27








Lecture 1

Lecture 2

Lecture 3

Lecture 4

Lecture 5

D.M. Collard 2007

ADDITION OF BROMINE AND CHLORINETO ALKENES AND ALKYNES

Overview C C Cl Cl

Br

Br

Br

Br50% S,S trans 50% R,R trans

+HCCl3

CCl4

C C Cl ClClCl

CCl4

Cl2

Br2

2 Cl2

L

Prob:8.30(c,d),

31,54

S:8.12-8.14;8.18

Addition of Hal2 to AlkenesStereochemistry

CH3H3CHH

HH3CCH3H

H3CH

Br

Br

CH3H

Br

Br

CH3

H3C

H

H

Br

Br

H

H3C

CH3

H

Br2

Br2 H3CH

Br

Br

HCH3

D.M. Collard 2007

Mechanism

CH3H3CHH

Br Br

Formation of Halohydrins

C C Cl OHCl2

H2O

CH3 CH3OH

Br

Br2H2O

D.M. Collard 2007

Mechanism

H

CH3

H

H

Cl2H2O

Cl Cl

Addition of Hal2 to Alkynes

R C C H

R C C R'

Br2

HCCl3

D.M. Collard 2007








Lecture 1

Lecture 2

Lecture 3

Lecture 4

Lecture 5

ADDITION OF CARBENES TO ALKENES

What is a Carbene?

What is a Carbenoid?

H2C N N

ClCCl

Cl HK OtBu

CH2

I CH2 I I CH2 Zn I

L29 S:8.15

D.M. Collard 2007

Additions to Alkenes

Mechanism

CH3H3CHH

CH2

C CCH2N2

orCH2I2, Zn

CH2

CCl2

HCH3HCHCl3

KOtBu

Synthesis

EPOXIDES

O

O

O

R O O HRCO3H

(peroxyacid)

RCO3H(peroxyacid)

OO

O

O OOHOOH

Cl

Mg2

2

mCPBAMMPP

Prob:11.43,44

S:11.13-11.15

D.M. Collard 2007

Nucleophilic Ring-opening

O OHHO

H3O+

orHO-, H2O

OOH

OH

Stereochemistry

O OHRO

RO

ORHO

ROH, H+O

Regiochemistry

D.M. Collard 2007

O OH

O OHC C R

NC

CC

R

O OHRHN

NH2R

C N

H2O

liquid NH3

CH3OH

excess

Addition of Other Nucleophiles

OXIDATION OF ALKENESAND ALKYNES

Syn-Hydroxylation of Alkenes

C C HO OH

OH

OH

1. OsO42. NaHSO3

orKMnO4,

NaOH, H2Ocold

KMnO4, NaOH, H2O

cold

Prob:8.27(k,n),30

(j,k),46,47

S:8.16-8.17,8.20

D.M. Collard 2007

Oxidative Cleavage of AlkenesPermanganate Oxidation

1. KMnO4NaOH, H2O, Δ

2. H3O+

1. KMnO4NaOH, H2O, Δ

2. H3O+

O

OHO

O

OH

CO2

+

+

1. O3, –78 °C2. Zn, CH3CO2H O

HO

H

OO

O OO

O

Ozonolysis

D.M. Collard 2007

Oxidative Cleavage of Alkynes

Problem: Compound X (C10H18) gave pentanoic acid upon reaction with basic potassium permanganate followed by acidification. What is the structure of compound X?

R C C R'

1. O32. CH3CO2H

or1. KMnO4, NaOH2. H3O+

R R'HOOH

O O








Lecture 1

Lecture 2

Lecture 3

Lecture 4

Lecture 5

D.M. Collard 2007

R OO

O RO

RADICAL POLYMERIZATION OFALKENES (CHAIN-GROWTH POLYMERS)

About 60 x 109 pounds of ethylene are manufactured and used each year, primarily to make polyethylene

Roll of Radical Initiator (Chain Initiation)

H2C CH2radical

initiatorE (CH2CH2)n E

n~40,000E = end group

L S:10.10

Chain-Growth (Chain Propagation)

End of Growth (Chain Termination)

H2C CH2+ R CH2CH2 (CH2CH2)n CH2CH2(n+1)

H2C CH2R

R CH2CH2

2 Polymer CH2CH2

combination

disproportionationPolymer CH

Polymer CH2CH3

CH2

Polymer CH2CH2 CH2CH2 Polymer

D.M. Collard 2007

Common Chain-Growth Polymers

H2C CH2

Monomer Polymer Name(s)

polyethylene

polypropylene

(CH2 CH2)n

(CH2 CH)n

CH3

poly(vinyl chloride), PVC(CH2 CH)n

Cl

polyacrylonitrile, "Orlon"(CH2 CH)n

CN

poly(methyl methacrylate)Lucite, Plexiglass

(CH2 C)n

CH3

CO2CH3

Cl

CN

CO2CH3

SYNTHETIC STRATEGIES

Add to your chart of organic reactions

No more reactions! For now!!!

C CH

Br

C CH

OHC C

C CH

H

SubstnSubstn

Br, hν

Zn, HBr

substitutions

subs

titutio

nsElimn

Elimn

C C

BrBr

Elimn

Elimn

Addn

Additions

Addn

Additions

Addn

H2/Pt

Add n

Addn

H2/Pt

Prob:8.21-

8.26,44

S:8.21

D.M. Collard 2007

DESIGNING SYNTHESESOne Step SynthesesThis is just the opposite of learning reactions - just think backwards. Although one step syntheses are relatively easy, they are harder than learning reactions.

Two Step SynthesesThis is involves considerable imagination and is quite different than “just the opposite of learning reactions”. You must be able to conceive of the intermediate. However, there is a direct link between the intermediate and both the product and the starting material. Think “retro” (retrosynthesis) -how do you synthesize the product from anything? Can you then synthesize your proposed synthetic intermediate from the starting material?

Starting material(s) Productstep 1 step 2reaction

intermediate

? ?

Three Step SynthesesThree design of three-step organic syntheses requires a little more imagination and can be a little more difficult than two-step syntheses. You must be able to conceive of two intermediates. In this case there may not be a clear link between intermediate one and the product or intermediate two and the starting material. Again “think retro”. Can you think of ANY compounds that could be converted to the product by chemistry you know? Can you then think of one or more compounds that could be converted to these proposed intermediates by chemistry you know? Can any of these second proposed intermediates be synthesized from the starting material?

Starting material(s) Productstep 1 step 3step 2reaction

intermediate 1reactionintermediate 2

Productinterm. A

interm. B

interm. C

interm. Dinterm. E

interm. F

interm. G

Potential

starting

material(s)

D.M. Collard 2007

Problem: Solomons 8.31(b). Show how 1-butyne could be synthesized from each of the following: (b) 1-chlorobutane

Cl

Problem:Br From any alkane

D.M. Collard 2007

Problem:

From

Br

Problem:From

BrHO

Br

D.M. Collard 2007

Problem: Propose a synthesis of 1-methyl-1,2-cyclopentanediol (with the two hydroxy groups trans to one another) from methylcyclopentane.

CH3 OH

OH

CH3

Prob:11.30,35,37,38,46

Problem: An insect physiologist required 4Z-hexen-2-ol for the study of insect pheromones. Propose a synthesis of 4Z-hexen-2-ol from propene.

OH

D.M. Collard 2007

TOPIC 8 ON EXAM 4

Types of Questions- Describe addition reaction mechanisms- Predict the products of addition reactionsThe problems in the book are good examples of the types of problems on the exam.

Preparing for Exam 4:- Work as many problems as possible. - Work in groups.- Do the “Learning Group Problem” at the end of the chapter.- Work through the practice exam

topic 8. additions to alkenes and alkynes...

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