7-Reactions of Alkenes and Alkynes · 2016-07-06 · Alkene Reactions Unsymmetrical Addition Reactions • Markovnikov’s Rule • For double bonds that have unequal numbers of hydrogen

1

Fall, 2007 1

Chapter Objectives

�� Present reactions of alkenes and alkynesPresent reactions of alkenes and alkynes

�� Reactions related to those found in biologyReactions related to those found in biology

�� Must know reactionsMust know reactions

Fall, 2007 2

Preparation of Alkenes�� PrecursorsPrecursors

�� Alcohols (especially in biological chemistry)Alcohols (especially in biological chemistry)

�� Alkyl Halides (industrial chemistry)Alkyl Halides (industrial chemistry)

X

H

O H

H

s t r o n g b a s e

d e h y d r o h a l o g e n a t i o n

s t r o n g a c i d

d e h y d r a t i o n

Fall, 2007 3

Biological Dehydration�� Rarely done on free alcoholRarely done on free alcohol

�� Generally done on molecules containing carbonyl and Generally done on molecules containing carbonyl and hydroxyl groupshydroxyl groups

OHCO2

-

CO2-

O2C-

aconitase

H2O

CO2-

CO2-

O2C-

2

Fall, 2007 4

Reaction with X2�� HalogenationHalogenation

�� Reaction with ClReaction with Cl2 2 and Brand Br22

C l

C l

B r

B r

C l2

B r 2

Fall, 2007 5

Stereochemistry�� Reaction provides the trans productReaction provides the trans product

Fall, 2007 6

Explanation

�� Not a Not a carbocationcarbocationintermediate as shownintermediate as shown

�� BromoniumBromoniumion intermediate formsion intermediate forms

BrH H Br H

H Br+

Br-

3

Fall, 2007 7

Biological Halogenation

�� Marine organismsMarine organisms

�� HaloperoxidaseHaloperoxidase

�� HH22OO22 oxidizes oxidizes ClCl-- or Bror Br-- to Xto X++

C l

B rC l

B r

Fall, 2007 8

Reaction with X2 in H2O

�� ClCl22 in water yields HOin water yields HO--ClCl ((hypochloroushypochlorousacid)acid)

�� BrBr22 in water yields HOin water yields HO--Br (Br (hypobromoushypobromousacid)acid)

OH

Br

Br2/H2O

Fall, 2007 9

Hydration of Alkenes

�� Alkenes react with water to give alcoholsAlkenes react with water to give alcohols

�� Require high temperatures and pressuresRequire high temperatures and pressures

�� Does not work well in the laboratoryDoes not work well in the laboratory

H2OCH3CH2OH

4

Fall, 2007 10

Biological Hydration of Alkenes

�� Relatively rare reactionRelatively rare reaction

�� Cellular constraints are not present.Cellular constraints are not present.

O

O

O

O

OH

-OO-

fumarase-O

fumarate maleate

Fall, 2007 11

Cellular Constraints

�� Solvent is waterSolvent is water

�� Narrow pH rangeNarrow pH range

�� Fixed temperatureFixed temperature

�� Limited elemental choiceLimited elemental choice

Fall, 2007 12

Laboratory Hydration of AlkenesOxymercurationOxymercuration

Mercuric Acetate in THFMercuric Acetate in THF

MarkovnikovMarkovnikov ProductProduct

5

Fall, 2007 13

Laboratory Hydration of Alkenes

�� HydroborationHydroboration

�� NonNon--MarkovnikovMarkovnikovProductProduct

Fall, 2007 14

Mechanism of Hydroboration

�� BoraneBoraneis a Lewis acidis a Lewis acid

�� AlkeneAlkene is Lewis baseis Lewis base

�� Transition state involves Transition state involves anionic development on Banionic development on B

�� The components of BHThe components of BH33 add add across C=Cacross C=C

Fall, 2007 15

Reduction and Oxidation

�� Carbon always has 4 bondsCarbon always has 4 bonds

�� Oxidation changes are more difficult to seeOxidation changes are more difficult to see

�� Reduction:Reduction:

�� Increase in H contentIncrease in H content

�� Decrease in O contentDecrease in O content

�� Oxidation:Oxidation:

�� Decrease in H contentDecrease in H content

�� Increase in O contentIncrease in O content

6

Fall, 2007 16

Reduction of Alkenes: Hydrogenation

�� Addition of HAddition of H22

�� Requires Pt or Pd catalyst (or NR)Requires Pt or Pd catalyst (or NR)

�� Heterogeneous Reaction Heterogeneous Reaction

�� Process is not in solutionProcess is not in solution

Fall, 2007 17

Mechanism of Catalytic Hydrogenation�� Heterogeneous Heterogeneous –– reaction between phasesreaction between phases�� Addition of HAddition of H--H is H is synsyn

Fall, 2007 18

Biological Reductions�� Rare ReactionRare Reaction

�� Uses NADPH as reducing agentUses NADPH as reducing agent

ON

O

OH OH

O NH2

HH

OP

OP O

OH OPO2

N

N

N

N

NH2

O

O

O

O-2

--

Nicotinamide Adenine Dinucleotide Phosphate

7

Fall, 2007 19

Oxidation of Alkenes: Epoxides

�� Reaction with a Reaction with a peracidperacid

�� EpoxideEpoxideor or oxiraneoxirane

�� Cyclic etherCyclic ether

Cl

OOHO

O

H

mcpba

CH2Cl2

mcpba = peroxide

Fall, 2007 20

Epoxide Preparation

�� From From HalohydrinHalohydrin

OH

BrO

Br2/H2O base

bromohydrin

Fall, 2007 21

Biological Epoxidation

�� Present in variety of processesPresent in variety of processes

�� Does not involve Does not involve peracidsperacids

�� Peroxides formed by reaction with OPeroxides formed by reaction with O22

�� Very selective reaction (see Figure 7.8)Very selective reaction (see Figure 7.8)

8

Fall, 2007 22

Hydroxylation of Alkenes

�� DiolDiol formationformation

�� Laboratory and Biological ReactionLaboratory and Biological Reaction

�� Biological process useful for detoxificationBiological process useful for detoxification

OOH

OH

H3O+

Fall, 2007 23

Laboratory Hydroxylation�� Reaction with osmium Reaction with osmium tetroxidetetroxide

�� Stereochemistry of addition is Stereochemistry of addition is synsyn(product is (product is ciscis))

�� Product is a 1,2Product is a 1,2--dialcoholdialcoholor or dioldiol (also called a (also called a glycolglycol))

Fall, 2007 24

Reaction with Carbenes

�� HH22C:C:�� The The carbenecarbenefunctional groupfunctional group�� CarbenesCarbenesare electrically neutral with six electrons in the outer are electrically neutral with six electrons in the outer

shellshell�� They add symmetrically to double bonds giving They add symmetrically to double bonds giving cyclopropanescyclopropanes

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Fall, 2007 25

Formation of Dichlorocarbene

�� Base removes proton Base removes proton from chloroformfrom chloroform

�� Stabilized Stabilized carbanioncarbanionremainsremains

�� UnimolecularUnimolecularElimination of Elimination of ClCl--

gives electron gives electron deficient species, deficient species, dichlorocarbenedichlorocarbene

Fall, 2007 26

Reaction of Dichlorocarbene

�� Addition of Addition of dichlorocarbenedichlorocarbeneis is stereospecificstereospecificciscis

Fall, 2007 27

Simmons-Smith Reaction�� Equivalent of addition of CHEquivalent of addition of CH22::�� Reaction of Reaction of diiodomethanediiodomethanewith zincwith zinc--copper alloy produces copper alloy produces

a a carbenoid carbenoid speciesspecies�� Forms Forms cyclopropanescyclopropanesby by cycloadditioncycloaddition

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Fall, 2007 28

Radical Reactions

�� Mechanism of addition of Mechanism of addition of HBrHBr was hotly debatedwas hotly debated�� NonNon--MarkovnikovMarkovnikovproduct was observedproduct was observed�� Peroxides form readily in starting materialPeroxides form readily in starting material

Br

BrBr

HBr

HBr

On occasion

+

Fall, 2007 29

Radical Reactions - HBr

�� If reaction is done with If reaction is done with HBrHBr/peroxides/peroxides

�� Get the nonGet the non--MarkovnikovMarkovnikovproductproduct

Br

HBr/peroxides

Fall, 2007 30

Radical Reactions: Polymer Formation

�� Polymer Polymer –– a very large molecule made of a very large molecule made of repeating units of smaller molecules repeating units of smaller molecules (monomers)(monomers)

�� Biological PolymersBiological Polymers�� StarchStarch�� CelluloseCellulose�� ProteinProtein�� Nucleic AcidNucleic Acid

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Fall, 2007 31

Polymers

�� AlkeneAlkenepolymerizationpolymerization

�� Initiator used generally is a radicalInitiator used generally is a radical

n

r e p e a t in gu n i t

Fall, 2007 32

Mechanism

�� InitiationInitiation

�� PropagationPropagation

�� TerminationTermination

�� See page 241 in text for detailsSee page 241 in text for details

�� High reactivity of radicals limits usefulnessHigh reactivity of radicals limits usefulness

�� Not true in biological chemistryNot true in biological chemistry

Fall, 2007 33

Biological Radical Reactions

�� Enzyme permits a single substrate at a time Enzyme permits a single substrate at a time at the active siteat the active site

�� Greater control over reactivityGreater control over reactivity

�� Radical reactions are commonRadical reactions are common

�� Example given on page 244 for biosynthesis Example given on page 244 for biosynthesis of the of the PGAsPGAs

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Fall, 2007 34

Dienes

�� Contain two double bondsContain two double bonds

�� NonNon--conjugatedconjugated

�� ConjugatedConjugated

Fall, 2007 35

Common Feature in Nature

Fall, 2007 36

Conjugation

�� Absorption of visible light produces colorAbsorption of visible light produces color

�� Conjugated hydrocarbon with many double Conjugated hydrocarbon with many double bonds are bonds are polyenes polyenes

�� LycopeneLycopene-- red color in tomatoesred color in tomatoes

�� CarroteneCarrotene–– orange colororange color

�� Extended conjugation in Extended conjugation in ketones ketones ((enonesenones) ) found in hormones such as progesteronefound in hormones such as progesterone

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Fall, 2007 37

Conjugated Dienes�� Chemistry is slightly differentChemistry is slightly different�� More stable than nonMore stable than non--conjugated conjugated dienesdienes�� Heat of hydrogenationHeat of hydrogenation

Fall, 2007 38

Greater Stability�� Why? Why?

�� Orbital Picture of Orbital Picture of alkenealkenebondingbonding

Fall, 2007 39

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Fall, 2007 40

�� Orbital picture of conjugated Orbital picture of conjugated dienediene

�� Electrons are delocalized (spreadElectrons are delocalized (spread--out) over out) over the entire pi frameworkthe entire pi framework

�� Impact upon the chemistryImpact upon the chemistry

Fall, 2007 41

Fall, 2007 42

Reactions

�� With With HBrHBr

�� Why?Why?

H

Br

H

BrHBr

(71%)

(29%)

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Fall, 2007 43

Mechanism

Fall, 2007 44

Allylic Cation

Fall, 2007 45

Some Data

X

H H

X

HX

1,2 product 1,4 product

Nucleophile 1,2 Product 1,4 Product Bromide 71% 29% Chloride 30% 70%

If HBr is added at 0 oC we see the above data.

If the reaction is done at 40 oC, we see 30% of the 1,2 product and 70% of the 1,4 product.

How do we explain these results?

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Fall, 2007 46

A B + C�� B forms faster than CB forms faster than C

�� Energy of activation is lower for B than CEnergy of activation is lower for B than C

�� C is more stable than BC is more stable than B

�� Constructing reaction energy diagramConstructing reaction energy diagram

energy

reaction progress

AB

C

Fall, 2007 47

Thermodynamic Control

�� Transition state leading to more stable species is Transition state leading to more stable species is higher in energy, therefore, it is easier to get to the higher in energy, therefore, it is easier to get to the less stable productless stable product

�� Reaction is Reaction is reversablereversable�� At high temperatures, sufficient E for both At high temperatures, sufficient E for both

reactions to occurreactions to occur�� A B (fast) and A C (slower)A B (fast) and A C (slower)�� or B A Cor B A C�� We see more stable product dominate.We see more stable product dominate.

Fall, 2007 48

Kinetic Control

�� At low temperaturesAt low temperatures

��Reaction is not Reaction is not reversablereversable

��Equilibrium is not reachedEquilibrium is not reached

�� Insufficient energy for A to CInsufficient energy for A to C

��Sufficient energy for A to BSufficient energy for A to B

��Less stable product dominates.Less stable product dominates.

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Fall, 2007 49

Reactions of Alkynes

�� Alkynes are rare in biological chemistryAlkynes are rare in biological chemistry

�� Chemistry is similar to alkenesChemistry is similar to alkenes

�� Generally less reactive than alkenesGenerally less reactive than alkenes

�� Reactions can be stopped at Reactions can be stopped at alkenealkenestage stage using one equivalent of the reagentusing one equivalent of the reagent

Fall, 2007 50

Reactions with HX

�� RegiochemistryRegiochemistryis is MarkovnikovMarkovnikov

Fall, 2007 51

Reactions with X2

�� Initial addition gives trans intermediateInitial addition gives trans intermediate

�� Product with excess reagent is tetraProduct with excess reagent is tetra--halidehalide

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Fall, 2007 52

Reactions with H2

�� Reduction using Pd or Pt does not stopReduction using Pd or Pt does not stop

�� AlkeneAlkeneis more reactive than is more reactive than alkynealkyne

Fall, 2007 53

Reactions with H2

�� Lindler’sLindler’s catalyst is poisonedcatalyst is poisoned�� Not as reactiveNot as reactive�� Stops at Stops at ciscis--alkenealkene

Fall, 2007 54

Reduction using dissolving metals

�� Anhydrous ammonia (NHAnhydrous ammonia (NH33) is a liquid below ) is a liquid below --33 33 ººCC�� Alkali metals dissolve in liquid ammoniaAlkali metals dissolve in liquid ammonia�� Provide a solution of eProvide a solution of e-- in NHin NH33

�� Alkynes are reduced to trans alkenes with sodium or lithium in Alkynes are reduced to trans alkenes with sodium or lithium in liquid ammonialiquid ammonia

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Fall, 2007 55

Hydration of Alkynes�� Hydration (HgHydration (Hg+2+2) of terminal alkynes provides methyl ) of terminal alkynes provides methyl ketonesketones

�� Hydration (BHHydration (BH33) of terminal alkynes provides ) of terminal alkynes provides aldehydesaldehydes

Fall, 2007 56

Alkyne Acidity: Acetylide Anion

�� Terminal alkynes are weak Terminal alkynes are weak BrBrøønstednstedacidsacids�� pKpKaa is approximately 25is approximately 25�� alkenes and alkenes and alkanesalkanesare much less acidicare much less acidic�� Reaction of strong anhydrous bases with a Reaction of strong anhydrous bases with a

terminal acetylene produces an terminal acetylene produces an acetylideacetylide ionion

Fall, 2007 57

Alkylation of Acetylide Anions

�� AcetylideAcetylide ions are ions are nucleophiles nucleophiles �� AcetylideAcetylide ions are basesions are bases�� React with a primary alkyl halidesReact with a primary alkyl halides

PROBLEMS ON ALKENE CHEMISTRY ©2004 OCHeM.com

1

1. Answer the following questions concerning the three alkenes shown below. Your answer should

use words and illustrations.

CH3 O CH3 CF3

A B C

1 2 3 4 5 6

a) Which alkene would be most reactive with H+ ? Why?

b) Which alkene would be least reactive with H+ ? Why?

c) Which alkene would be most reactive under conditions of catalytic hydrogenation? Why?

d) Will all three alkenes undergo Markovnikov addition of HBr? If not, which alkene or alkenes

won’t and why?


2

2. Provide a mechanism for the following reaction. Then, predict the reaction energy diagram for the

entire reaction in the space provided. In your diagram, you must indicate the ΔH of the reaction,

label the activation energy (Ea) of the rate-determining step, and clearly identify all intermediates

and products of the reaction.

H Br

Br

En

erg

y

Reaction Coordinate


3

3. What starting materials & reagents are needed to produce the following compound?

Br Br 4. Draw the major product of each of the following reactions. Be sure to include stereochemistry in

your answers where appropriate.

CH3

CH3

CH3

CH3 Br2

H Cl

Cl2

CH3CH2OH

d)

a)

b)

c)1) Hg(OAc)2 / H2O

2) NaBH4

1) BH3•THF

2) H2O2 , NaOH

1

Alkene Reactions

• Addition Reactions - only one product

• 1. Hydrogenation (H2): Alkene + Hydrogen --> Alkane

• 2. Halogenation (X2):Alkene + diatomic halogen --> Dihaloalkane

• 3. Halgenation (HX):Alkene + HX --> Haloalkane

• 4. Hydration (HOH):Alkene + HOH --> alcohol

• 5. Polymerization:Many alkenes add together into a long alkane chain

Alkene Reactions

1. Hydrogenation Reaction

• Alkene + Hydrogen --> Alkane

• Hydrogen molecule adds to carbons with double bond.

CH2

HC

H3C + H2

C

HC

H3CH

H

H HH H

CH3

H2C

H3C

CC

H3C

H

H H

H

H

CC

2

Alkene Reactions

Alkene Reactions

2. Halogenation Reaction

• Alkene + Halogen --> Dihaloalkane

• Halogen molecule adds to carbons with double bond.

CH2

HC

H3C

C

HC

H3CH

H

CC

+ Br2

Br Br

CH2CH

H3C

Br

Br

CC

H3C

H

Br Br

H

H

3

Alkene Reactions

Unsymmetrical Addition Reactions

• Markovnikov’s Rule• For double bonds that have unequal numbers of

hydrogen atoms attached.• For unsymmetrical reactants such as HX and HOH

• The hydrogen of the reactant goes to the carbon of the double bond that already has the most hydrogen atoms. “the rich get richer”

• The -X or the -OH go the other carbon (the one with the least amount of hydrogen

3. Halogenation Reaction

• Alkene + HX --> haloalkane

• HCl molecule adds to carbons with double bond.

CH2

HC

H3C

C

HC

H3CH

H

CC

+ HCl

HCl

H3C

CH CH3

Cl

CC

H3C

H

H

H

H

ClMark's Rule

4

Alkene Reactions

4. Hydration Reaction

• Alkene + HOH� --> alcohol

• HOH molecule adds to carbons with double bond.

CH2

HC

H3C

C

HC

H3CH

H

CC

Mark's Rule

+ HOH

HOH

H3C

CH CH3

HO

CC

H3C

H

H

H

H

OH

Alkene Reactions

5

5. Polymerization Reaction

• Alkene + Alkene + Alkene --> long chain of carbons

• Double bonds convert to single bonds

C C

H

H

H

H

C C

H

H

H

H

C C

H

H

H

H

C C

H

H

H

H

C C

H

H

H

H

C C

H

H

H

H

CH2

H2C

CH2

H2C

CH2

H2C

C C

H

H

H

H

C C

H

H

H

H

C C

H

H

H

H

.... . .

Alkene Reactions

What is the structure for

Alkene Reactions

6

Alkene Reactions

Alkene Reactions

1. In the reaction shown below, only one product is formed. Why?

2. Consider the following reaction.

a. What is the IUPAC name for the starting material in this reaction? What is the stereochemistry of the starting material (if there is any)?

b. What is the IUPAC name for the product in this reaction? 3. Draw the major organic product formed (showing stereochemistry where applicable) for the

reaction of the following alkene under each of the reaction conditions listed below.

a)

b)

c)

+ H2OH2SO4

OH

C C

H

HH3C

H3C

Br2

Br

CH3H3C

H

Br

H

CCl4

CH3 C

CH3

CH3

CH CH2

HBr

H2O

H+

Cl2

CCl4

Br2

H2O

1. Hg(OAc)2, H2O

2. NaBH4

HBr

peroxides

4. Draw the major organic product formed (showing stereochemistry where applicable) for the reaction of the following cycloalkene under each of the reaction conditions listed below.

d)

e)

f)

g)

h)

i)

CH3

HBr

H2O

H+

Cl2

CCl4

Br2

H2O

1. Hg(OAc)2, H2O

2. NaBH4

1. BH3 THF

2. H2O2/NaOH

1. OsO4

2. H2O2

1. O3

2. (CH3)2S

H2

metal catalyst

HBr

peroxides

Alkenes II 1 Copyright, Arizona State University

Copyright, Arizona State University

Alkenes II Introduction to Synthesis (more...)

1 Additional Reactions of Alkenes • here are a series of mainly oxidation reactions that we need to complete our survey of alkene chemistry • some are not "pretty", i.e. with complex mechanisms, some that are not fully known... • Some of the stuff here you will just have to "know", i.e. here is some of the "bad bit" of Organic

1.1 Formation of cis-Diols (more) • TWO sets of reagents will accomplish this reaction The reaction

OR

OH OH

OsO4 / H2O2

syn-addition

(same side)

cold KMnO4/-OH/H2O

The mechanisms

OMn

O

O

OO O

MnO O

OHHO OH

+ MnO2

syn-addition!

-OH

O O

Mn

–O O–

–O O

MnO O–

HOHO

addition/elimination mechanism

-OH

–O O–

+ MnO2(OH)2

–O O

Mn

–O O–

HO OH

aqueousworkup

radicalreduction

don't need to know!!

• although this is obviously complex, the important part is that the MnO4 ion starts the reaction by adding to both ends of the alkene at the same side, which is why a cis-diol must be formed • note that in mechanisms involving metal atoms, the metal has enough electrons and empty orbitals to give and take electrons on its own, almost at will (almost like cheating to an organic chemist!!)

OOs

O

O

O O O

OsO O

H2O2

HO OH+ OsO4

catalyst

regenerated!

don't need to know.....

• syn-addition!

H2O2


why TWO reagents? KMnO4 - inexpensive, used for large scale reactions, variable yields OsO4 - expensive, good yields, used in small scale syntheses • This illustrates the principle that in general there will always be more than one reagent to accomplish any transformation even if we only discuss one in this course Examples

H

HO

H

OH

cold KMnO4/-OH/H2Ocis-diol

H3C

C C

CH3

H H

OsO4 / H2O2 C C

HO OH

H HH3C CH3

meso- diol

H3C

C C

H

H CH3

OsO4 / H2O2

(±)

H3C

C C

CH3H

HO

OHH

HO

OH

(±)

=

1.2 Formation of Epoxides and trans-Diols (more) New reagent

R C

O

O R O OOHperoxideperoxy acid

R C

O

OH

carboxylic acid

R C

O

O OH

Cl

meta-chloroperbenzoic acid (MCPBA)

Mechanism

C

C

OH O

CO R

C

C

O

CO R

H

O +

epoxide carboxylic acid • concerted mechanism - all bonds made and broken at the same time • no chance for bond rotation "in the middle" - stereospecific reaction! Examples

MCPBA O cis-epoxide formedcis-alkene

• reaction is STEREOSPECIFIC

Synthesis of a trans-Diol

H3C

C C

CH3

H H

MCPBA

C

HO

C

OHHCH3

HCH3

(±)

ANTI-addition

C

O

C

OHH CH3

HCH3H

H OH H

O

C C

H H

H3C CH3

H

O

C C

H H

H3C CH3

OH H

H3O+

O

H

H

H

backside attack!

cis-alkene

LB/BB

LA/BA

LB

LA

LB/BB

LA/BA


• when H3O+ is a reagent, this means aqueous acid (e.g. HCl or H2SO4 in water)

• the intermediate is an oxonium ion (onium means more than usual valence, in this case 3 for oxygen), compare with bromonium etc., • this reaction sequence makes a trans-diol as opposed to the cis-diols we saw above, so........

H

HO H

OH

trans-diol

(±) racemic mixture

1. MCPBA

2. H3O+OsO4

H2O2 cis-diol

H

HO OH

H

meso compound!

1.3 Oxidative Cleavage of Alkenes: Ozonolysis (more) New reagent

O OOozone = O3 =

OOO

• has separated charges and more non-bonding electrons, much more reactive than molecular oxygen Mechanism

CH3C CH3

CH3CO

OO

CH3C CH3

CH3C O

O O

HH

O OO

C

H3C CH3

C

H3C HC

H3C

H3CO +

Me2S

CH3C

HO

moloxide ozonide

ketone aldehyde(reducing agent)

C

CH3 H3C

CH3C

OO

O

HS

Me

MeS

Me

Me

O

don't need to know!!

+

• the ozonide is the primary product, but it is never isolated • in the presence of Me2S it is reduced to (in this case) are an aldehyde and ketone • if Me2S is replaced by the oxidizing hydrogen peroxide, different products result.....

C

H3C CH3

C

H3C H

1. O3

2. Me2SC

H3C

H3CO +

CH3C

HO

ketone aldehyde

CH3C

H3CO +

CH3C

OHO

ketone carboxylic acid

1. O32. H2O2


Examples

1. O32. Me2S

HO

O

OH

O

HO

H

O

O

O

H

O

O1. O3

2. Me2S

1. O3

2. H2O2

2 Synthesis of Alkenes

2.1 From Alkyl Halides (seen before, review) • i.e. reactions of alkyl halides that have alkenes as the products • in useful reactions we want avoid carbocations, thus we want to do E2 elimination

H3C CH3

CH

Br

H3C CH2

CHbase

Which base to use to ensure elimination versus SN2???? Remember...... • E2 reaction is favored for 3Y halides • For 2

Y halides, E2 can be forced over SN2 by using a bulky base, see below

• For 3Y halides, a bulky base is not necessary, the product will be the Saytzeff product

• For 3Y halides, a bulky base will give the least substituted alkene, for steric reasons

Examples of bulky bases

NH O

N

diisopropylamine (i-Pr2NH) t-butoxide (t-BuO–) dimethylpyridine

Example Reactions

Br

t-BuO– +

K

acetone • 2Y halide, use bulky base to ensure no SN2, get Saytzeff alkene product

Br

Na+ –

OMe

acetone


• 3Y halide, use NON-bulky base (no SN2 not possible), get Saytzeff alkene product

Br

t-BuO– +K

acetone

• 3Y halide, use BULKY base and get Non-Saytzeff (Hoffmann) alkene product Bottom line • for 2

Y halides, use t-BuO

– to ensure no SN2 and to obtain Saytzeff product

• for 3Y halides, use CH3O

– to obtain Saytzeff product and t-BuO

– to obtain Hoffman product

2.2 From Alcohols (E1 and E2 elimination in a new context) The reaction

H

C C

OH conc. H2SO4

heatC C + H2O

• note a special kind of SOLVENT EFFECT here! In an aqueous medium, acid catalyzes water ADDITION to the alkene to make an alcohol. In conc. sulfuric acid medium, the acid helps to REMOVE water from an alcohol to make an alkene (the sulfuric acid DEHYDRATES the alcohol) Mechanism: you already know it - either an E1 or an E2 elimination! • in the mechanism, H2O is the leaving group,

–OH is a poor leaving group (this is an important general principle

that we will return to again later....)

H

C C

OH

X

H

C C

OH2

H+

H

C C

H

C C

OH

H2O

does not happen!

good nucleophile but

poor leaving group

poor nucleophile but

good leaving group

• in general, small neutral molecules such as water make excellent leaving groups, since they tend to contain low energy electrons Example

OHconc. H2SO4

heat

H OSO2OH

OH2

HOSO2OH

major

LA/BA

LB/BB

LA/BALB/BB

E1

• 3Y and 2Y alcohols almost certainly E1 mechanism • carbocation intermediates means rearrangements • the sulfuric acid is the initial acid, the bisulfate anion is a likely base to deprotonate, recovering the acid catalyst


Example

OH

H OSO2OH LA/BA

OH2

H

OSO2OH LB/BB

LB/BB

LA/BA H OSO2OH

LA/BA

HH

LB/BB

OSO2OH LB/BB

conc. H2SO4

heat

E2 LA/BA

• Almost certainly an E2 mechanism with a 1Y alcohol, but the first alkene product must get protonated, it is in conc. sulfuric acid after all, resulting in overall formation of a more substituted alkene • the final product is the SAME as if the mechanism was E1 followed by carbocation rearrangement

3 Synthesis of Alkyl Halides

3.1 From Alkanes (seen before, review)

Br2

h

Br

Br2

hBr

• actually, this is a pretty poor reaction since it is unselective, but it is the only one we have for alkanes! • use only if all hydrogens are identical (first example) or there is an obvious 3

Y hydrogen (second example)

3.2 From Alkenes (seen before, review)

NBS

h

Br

• we already learned that NBS is the best reagent to use for allylic bromination, don't use Br2 • to be safe, you CAN USE NBS and light for ALL RADICAL BROMINATIONS, including ALKANES

HBr

Br

HBr

ROOR Br

• Markivnokov and anti-Markovnikov addition to an alkene also forms an alkyl halide


4 Summary of Reactions (more) • all of them so far!! (non-bonding electrons are not shown in this summary for simplicity)

Br2, h

Br

NBS, h

Br

(±)

Br Na+ –

CN

acetone

CNSN2

(and analogues)

Br

Ph

Ph

Na+ –

O-t-Bu

DMF Ph

Ph

E2

conc. H2SO4

heatOH

HBr

CCl4

Br

(±)

H2O

H2SO4

(±)

OH

rearranged!

1. Hg(OAc)2/H2O

2. NaBH4

(±)

OH

1. Hg(OAc)2/EtOH

2. NaBH4

(±)

H

OEt

Br2

CCl4

Br

Br

(±)

Br2

CH3OH

Br

OCH3

(±)

1. BH3.THF

2. –OH/H2O2

(±)

D H OH

D


HBr

ROOR Br

H2

Pd/C

H

H

dil. KMnO4/–OH

or

OH

(±)OsO4/H2O2

OH

MCPBAO

1. MCPBA

HO2. H3O

+ OH (±)

OH

OO

1. O3

2. H2O2

1. O3

2. Me2S

H

OO

• looks like a lot, actually not (there will be more next semester!!) • do not attempt to memorize these, to learn them WORK THE PROBLEMS. After you have worked the problems and understood the mechanisms you will realize that you actually know most of them or can work them out. After working the problems you might like to test yourself on the reactions above to make sure that you have all the details about reagents and conditions correct



Alkenes II PROBLEMS Reaction Practice Provide the missing major organic product(s), reagents/conditions or reactant structure

as required.

1 (standard)

OOHO

O

OH

O+

Answer Correct Y / N

2 (standard)

OHconc. H2SO4

heat


3 (standard)

2. NaOH

1. HBr


4 (standard)

2. Me2S

1. O3


5 (challenging)

OHOH

OH

(ignorestereochemistry)


6 (challenging)

O

O

OH


REMEMBER, doing problems is the ONLY WAY that you will learn organic chemistry. Keep track of exactly what problems you get correct and which incorrect. Keep coming back until you get them ALL correct.


5 Synthesis • a large part of organic chemistry involves building larger or more complex molecules from smaller ones using a designed sequence of reactions, i.e. chemical synthesis • this involves putting a series of reactions together in sequence • here we will look at some simple example to practice this, later we will learn a more systematic method for solving complex synthesis problems, retrosynthesis • to do these problems you need to know the reactions, and PRACTICE, practice, practice, practice...... Example Problems: make the molecule on the right from the one on the left. this can not be done in one reaction. Give reagents and conditions and the intermediate molecules at each step.

Br

NBS, h Na+ –

OCH3

acetone

???

• brominate to get a functional group onto the alkene, then E2, which is the standard way to make an alkene

???

NBS, h

Na+ –

OMe

acetone

NBS, h

Br

Br

• brominate to get a functional group onto the alkene, then E2, which is the standard way to make an alkene, then brominate again (note that I changed this example from the one that was originally in he notes, next semester you will see why)

need to add –Br and –OCH3

???Br

OCH3

Br2 CH3OH

(±)

Br t-BuO– +

K

DMF

NBS, h

• need to add Br AND -OMe, we know how to do that from an ALKENE, thus make the alkene first as usual

???

Brt-BuO

– +K

DMF

NBS, h

Br NBS, hX

HBr

X

HBr ROOR


• need to add Br at a position that is not possible by direct bromination, the obvious way is by addition of HBr to an alkene Anti-Markovnikov, so first, make an alkene as usual

Br Br

OCH3???

NBS, h

t-BuO– +

K

DMF

HBr

ROOR

H3CO– +

K DMF

• can't add -OMe to an alkane, so we need to a a functional group, a LEAVING group at that carbon, once we recognize this then the strategy is same as previous problem

???OH

OH

conc. H2SO4, heat

H2SO4/H2O

• we have two ways to make an alcohol, SN2 or water addition to an alkene, the best thing to "do" with the starting alcohol is make an alkene, which decides for us which alcohol synthesis method to use



Alkenes II PROBLEMS Cumulative Problems Provide a synthesis of the target molecule on the right from the starting molecule on the

left. This cannot be done in one reaction. Give reagents, conditions and intermediate molecules at each step. Do not show any mechanisms or transient intermediates

1 (easier)


2 (easier)

CN


3 (easier)

OH

Br


4 (easier)

OHBr


5 (easier)

OCH3


6 (standard)

OH


7 (standard)

Br


8 (standard)

OH


9 (standard)

H H

O O


10 (standard)

HO

OH


See also the RETROSYNTHESIS Web Pages

REMEMBER, doing problems is the ONLY WAY that you will learn organic chemistry. Keep track of exactly what problems you get correct and which incorrect. Keep coming back until you get them ALL correct.

ALKENES AND ALKYNES – REACTIONS

A STUDENT WHO HAS MASTERED THE MATERIAL IN THIS SECTION SHOULD BEABLE TO:

1. Given the starting materials and reaction conditions, predict the products of the followingreactions of alkenes and alkynes.

Markovnikov addition of acids to alkenes and alkynes, including the acid-catalyzed additionof water (hydration). Rearrangement is possible in the additions to alkenes;tautomerization occurs in the hydration of alkynes.

Anti-Markovnikov addition of HBr.Addition of halogens (and halohydrin formation). These reactions are anti additions. In

halohydrin formation, the OH goes to the more substituted carbon.Epoxidation, and the hydrolysis of the resulting epoxides to glycols (overall anti addition).Glycol formation using either KMnO4 (cold) or OsO4 (these are syn additions).Degradation of alkenes and alkynes using either ozonolysis or KMnO4 (hot)Addition of carbenes to alkenes

2. Using any of the above reactions, propose syntheses of compounds that can be made usingalkenes as starting materials or intermediates. As always, synthesis problems may requireany reaction that you have studied in the course so far.

3. Propose mechanisms, and predict and explain experimental results using your knowledge ofmechanism. Important reactions include:

Markovnikov additions (which proceed by protonation of the alkene to give a carbocation).Addition of bromine and bromohydrin formation (by formation of the bromonium ion).Hydrolysis of epoxides (under acid conditions the oxygen is protonated first).

4. Identify unknown alkenes and alkynes when given either the products of ozonolysis or ofKMnO4 degradation. You will not be called on to distinguish between cis and transisomers; these methods do not give that information. (Further information can be obtainedfrom the index of hydrogen deficiency).

5. Use the results of simple chemical tests in identifying unknown compounds. Data from IRspectra may also be used. Important tests include:

Solubility in concentrated sulfuric acid (compounds containing only alkanes, halogens, andaromatic rings do not dissolve)

Bromine in carbon tetrachloride (alkenes and alkynes give an immediate reaction,decolorizing the reddish-brown bromine solution)

Potassium permanganate (cold, dilute) (alkenes and alkynes give an immediate brownprecipitate; other compounds leave the permanganate solution purple)

Silver nitrate in alcohol solution (gives a white precipitate with alkyl chlorides, a tan ppt.with alkyl bromides, a brown ppt. with alkyl iodides, no reaction when the halogen isattached to an sp2 carbon, and no reaction with other materials)

Silver nitrate in ammonia (gives a white ppt. with terminal alkynes)

96

A STUDENT WHO HAS MASTERED THE OBJECTIVES ON THE PREVIOUS PAGESHOULD BE ABLE TO SOLVE THE FOLLOWING PROBLEMS AND RELATED ONES:

1.1 Predict the major organic product or products of each of the following reactions.

a) (CH3)2CHCH=CH2 + HCl ----->

no peroxidesb) CH3CH2CH2CH=CH2 + HBr ------------------>

peroxidesc) CH3CH2CH2CH=CH2 + HBr --------------->

(cold, dilute)+ KMnO4 ----------------->d)

KOC(CH3)3

----------------> CHCl3

e)

CCl4+ Br2 -------->f)

+ Cl2 + H2O ----->g)

OH , H2O, heat+ KMnO4 -------------------->h)

H3O--------->

COOHHOOC

H H

CCl4+ Br2 -------->i) C C

CH2I2/Zn(Cu)------------------> ether

j)

97

1.2 For each of the following compounds, compare the reaction products from the addition ofHBr in the presence of peroxides with the addition of HBr in the absence of peroxides.

CH3 |

CH3—CH—CH=CH2a)

b)H

CH=CH2

2. Propose a synthesis of each of these compounds, from the given starting material and anyneeded inorganic reagent and/or solvent.

a)CH3

Br

CH3 from

b) CH3CH2CHBr2 from CH3C≡CH

c)OH

fromOH

d)OH

fromOH Br

98

2.2 Propose a synthesis of each of these compounds from the given starting materials(s) andany needed inorganic reagents or solvents.

a)CH3

Br

CH3 from

b) CH3CH2CH2CH2Br from HC≡CH and CH3CH2I

c) (CH3)3CBr from (CH3)2CHCH2OH

d)OH

fromOH

CH3 CH3

H H

e) C C

CH3

CH3H

H

C C from

f) (CH3)2CHCH2CH2CH3 from (CH3)2C=CH2 and H-C≡CNa

99

3. Propose a mechanism for each of the reactions shown.

OHa)

H3O+ H2O ---------->

OHO

b) (CH3)2CHCH=CH2 + HCl -----> (CH3)2CClCH2CH3

c) H3O

+ H2O ---------->

CH2CH3

CH=CH2 OH

d) CH3CH2CH=CH2 + Br2 + I– -----> CH3CH2CH—CH2 + Br– | | I Br

e)

CH2

H3O+ H2O ---------->

CH3HO

f) H3O (trace)------------------->

CH2 CH3

100

4.1 Identify each of these unknowns from the information given.

a) O3 Zn

C6H12 ----> ------> H2O

O | |

CH3CH2C-H+

O | |CH3C-CH3

b) O3 Zn

C9H16 ----> ------> H2O

O | |

CH3CH2C-HO +

c) KMnO4, OH

C6H10 -------------------> heat

O O | | | |HO-C-CH2CH2CH2C-CH3

H3O --------->

d) KMnO4, OH

C10H16 -------------------> heat

H3O --------->

O

CH2CH2CH2COOH

4.2 Predict the products of the following reactions.

a) O3 Zn----> ------> H2O

CH2

b) KMnO4, OH-------------------> heat

H3O --------->

CH=CHCH3

5.1 Match each set of test results with one of the compounds shown.

CH3CH2CH2CH2BrOH

CH3CH2CH2C C-H

A C EDB

a) Decolorizes Br2 in CCl4 Soluble in H2SO4 No reaction with AgNO3 in ammonia

b) No reaction with cold dilute KMnO4 No reaction with AgNO3 in alcohol Soluble in conc. H2SO4

101

5.1 Unknowns, continued. The possibilities are:

CH3CH2CH2CH2BrOH

CH3CH2CH2C C-H

A C EDB

c) Gives a brown precipitate with cold dilute KMnO4 Gives a white precipitate with AgNO3 in ammonia Soluble in conc. H2SO4

d) No reaction with cold dilute KMnO4 No reaction with alcoholic AgNO3 Insoluble in conc. H2SO4

5.2 Describe simple chemical tests that can distinguish between:

a) cyclohexene and cyclohexyl bromideb) 1-hexene and 1-hexynec) tert-butyl alcohol and tert-butyl bromided) pentane and 1-pentenee) ethanol and 2-pentyne

102

ANSWERS TO THE PROBLEMS:

1.1 Predict the major organic product or products of each of the following reactions.

a) (CH3)2CHCH=CH2 + HCl -----> (CH3)2CClCH2CH3

no peroxidesb) CH3CH2CH2CH=CH2 + HBr ------------------> CH3CH2CH2CHBrCH3

peroxidesc) CH3CH2CH2CH=CH2 + HBr ---------------> CH3CH2CH2CH2CH2Br

(cold, dilute)+ KMnO4 ----------------->d)

OH

OH

KOC(CH3)3

----------------> CHCl3

e)Cl

Cl

CCl4+ Br2 -------->f)

Br

Br+ enantiomer

+ Cl2 + H2O ----->g)Cl

OH

+ HCl+ enantiomer

OH , H2O, heat+ KMnO4 -------------------->h)

H3O--------->

COOH

COOH

Br BrH H

COOHHOOC

H H

CCl4+ Br2 -------->i) C C

COOHHOOC

C C + enantiomer

CH2I2/Zn(Cu)------------------> ether

j)

103

1.2 Compare the addition of HBr in the presence and in the absence of peroxides to each of thefollowing compounds. (Hint: Predict the products.)

HBr, no peroxides

HBr, peroxides

CH3 |

CH3—CH—CH=CH2a)

(CH3)2CBr—CH2CH3

(CH3)2CH—CH2CH2Br

Note that both of these problems involve rearrangements in the absence of peroxides.

b)H

CH=CH2

HBr, no peroxides

HBr, peroxides

Br

CH2CH3

H

CH2CH2Br

2.1 Synthesis problems. These answers are in shorthand (not balanced equation) form.

a)CH3

Br

CH3 HBr, peroxides-------------------->

2 HBr, peroxidesb) CH3C≡CH -----------------------> CH3CH2CHBr2

c) C6H5CO3H----------------> O

H2O, H3O----------------->

OH

OH

d) C6H5CO3H---------------->

H2O, H3O----------------->

OH

OH Br KOH, heat--------------->

(Last two steps as in c) above)

2.2 More synthesis:

a)CH3

Br

CH3 Br2, light-------------> CH3

Br HBr-------------> peroxides

KOH--------> heat

104

NaNH2 CH3CH2Ib) HC≡CH -----------> HC≡CNa --------------> HC≡CCH2CH3 and then

H2, Ni2B HBr HC≡CCH2CH3 ------------> H2C=CHCH2CH3 ------------> CH3CH2CH2CH2Br

peroxides

H2SO4, heat HBr, no peroxidesc) (CH3)2CHCH2OH ----------------> (CH3)2CH=CH2 ----------------------> (CH3)3CBr

d)

OH

Br2

------> light

OH Br KOH------> heat

C6H5CO3H--------------->

H3O---------> H2O

CH3 CH3

H H

e) C C

CH3

CH3H

H

C C

Br2

-------> CCl4

CH3CHBrCHBrCH3 NaNH2

---------> CH3C CCH3 then

CH3C CCH3 Li, NH3

----------->

HBr, peroxidesf) (CH3)2C=CH2 ---------------------> (CH3)2CHCH2Br, then:

H-C≡CNa (CH3)2CHCH2Br ---------------> (CH3)2CHCH2C≡CH, then:

2H2, Pt (CH3)2CHCH2C≡CH ----------> (CH3)2CHCH2CH2CH3

105

3) Mechanisms. Note that balanced equations are used throughout.

OHa)

H3O+ H2O ---------->

OHO

OH2

+ H3O ----->

OH

O + H2OO H

O H + H2O ----->

OH2

OH+ H2O ----->

OH

OH+ H3O

b) (CH3)2CHCH=CH2 + HCl -----> (CH3)2CClCH2CH3

(CH3)2CHCH=CH2 + HCl -----> (CH3)2CHCHCH3 + Cl

H |

(CH3)2C—CHCH3 -----> (CH3)2C—CH2CH3

(CH3)2C—CH2CH3 + Cl -----> (CH3)2CClCH2CH3

c) H3O

+ H2O ---------->CH=CH2

OH

CH2CH3

----->

CH=CH2

OH2

+ H3O ----->CHCH3

+ H2O

CHCH3 CH2CH3

CH2CH3

+ H2O ----->CH2CH3

OHOH2

CH2CH3

+ H2O ----->CH2CH3

+ H3O

H

106

3) Mechanisms, continued. Note again that balanced equations are used throughout.

d) CH3CH2CH=CH2 + Br2 + I– -----> CH3CH2CH—CH2 + Br– | | I Br

Br I

CH3CH2CH=CH2 + Br—Br -----> CH3CH2CH—CH2 + Br

CH3CH2CH—CH2

Br

+ I CH3CH2CH—CH2----->

Br

e)

CH2

H3O+ H2O ---------->

CH3HO

CH2

+ H2O

CH3HO

+ H3O ---------->

CH3

+ H2O

CH3

------>

OH2H3C

OH2H3C

+ H2O ------> + H3O

f) H3O (trace)------------------->

CH2 CH3

+ H2O

CH2

CH3

+ H3O ----->

CH3

+ H2O

CH3

-----> + H3OH

107

4.1 The unknowns are:

a) CH3CH2CH=C(CH3)2 b) CHCH2CH3

CH3c) d)

4.2 The products are:

a) O3 Zn----> ------> H2O

O

CHO

O O | | | |+ HCCH2CH

CH2

b) KMnO4, OH-------------------> heat

H3O --------->

CH=CHCH3

O

COOH+ CH3COOH

+ CO2

5.1 The unknowns are: a) B; b) A; c) E; d) C

5.2 Descriptions of simple chemical tests that can distinguish between the pairs. (Only oneanswer is required.)

a) Cyclohexene gives no reaction with alcoholic AgNO3, while cyclohexyl bromide gives awhite precipitate. Cyclohexene reacts with bromine in carbon tetrachloride and withcold dilute potassium permanganate, and dissolves in concentrated sulfuric acid;cyclohexyl bromide does none of these things.

b) 1-Hexene gives no reaction with AgNO3 in ammonia, while 1-hexyne gives a whiteprecipitate.

c) tert-Butyl alcohol dissolves in concentrated sulfuric acid, while tert-butyl bromide doesnot. The bromide gives a white precipitate with AgNO3 in alcohol, while the tert-butylalcohol does not react.

d) 1-Pentene decolorizes bromine in carbon tetrachloride, gives a brown precipitate withcold dilute potassium permanganate, and dissolves in conc. sulfuric acid. Pentane doesnot react with any of these reagents.

e) 2-Pentyne reacts with bromine in carbon tetrachloride and with cold dilute potassiumpermanganate; ethanol does neither of these things.

108

Name ___________________________________________________ Eighth Drill Test (Sample)Organic Chemistry 2210 DR Answer All Questions

1) Predict the major organic product or products the following reaction.

CH3CH2CH2CH=CH2 + C6H5CO3H ------>

2) Propose a synthesis of each of the following compounds from the given starting materialand any needed inorganic reagents or solvents.

a) fromOH

OH

b) fromBr

Br

c) (CH3)3COH from (CH3)2CHCH2OH

3) Propose a mechanism for each of the reactions shown. H3O+

a) CH3CH2CH=CH2 + H2O -------> CH3CH2CHOHCH3

+ Br2 + Cl ----> Br +Br

Clb)

4) Give the structures of these unknowns from the information given.

a)

C8H14b) KMnO4, base, heat acid------------------------> ------> + CH3CO2HO

C8H16 O3 Zn, H2O----> ----------->

O | |

2 CH3CH2CH2C-H

5) Which of these compounds gives a peak in the IR spectrum near 1640 cm-1, is soluble inconc. H2SO4, reacts with cold alkaline KMnO4, and gives no reaction with either silvernitrate in ethanol or Ag(NH3)2+?

A. CH3CH=CH2 B. CH3C≡C-H C. CH3CH2CH3 D. CH3CH2OH E. CH3CH2Cl

109

Name _________________________________________________ Eighth Drill Test (Sample B)Organic Chemistry 2210 DR Answer All Questions

1) Predict the major organic product of each of the following reactions.

a)

b)

H2SO4---------->CH3CH=CH2 + H2O

CH3 + HBr peroxides------------->

2) Propose a synthesis of each. You may use any needed inorganic reagents and solvents.a) (CH3)3CCl from (CH3)3COH

b) bicyclo[3.1.0]hexane from cyclopentene

c) trans-1,2-cyclohexanediol from bromocyclohexane

3) Propose a mechanism for each of the reactions shown. For problem a), first complete theequation by predicting the product.

a)

b) CH3CH=CH2 + Br2 + Cl ------>

+ H2OO H3O---------->

CH3CHClCH2Br + Br

4) Which of the compounds shown is soluble in conc. H2SO4, reacts with cold alkalineKMnO4, and gives no reaction with either AgNO3 in alcohol or Ag(NH3)2+?

A. CH3CH2Br B. CH3CH2OH C. CH3CH=CH2 D. CH3C≡C-H E. CH3CH2CH3

5) Give the structures of the unknowns from the information given.

O| |

O| |

O| |

C7H12a)

b)

KMnO4, base, heat acid------------------------> ------>

C7H14

O| |

OHHO

O3 Zn, H2O----> -----------> +H

110

Type and definition of reaction: Example Reaction equation, structural formulas, names, conditions: 1. Substitution (pg. 1025) The replacement of one atom (or group) by another atom (or group). Note substitution is the only way to add a halogen to an alkane.

propane + Br2

C C C

H

H

H

H

H

H

H

H + Br Br C C C

(H)Br

H

(H)Br

H

H

H

H

H Br(H) H+

Product: 2-bromopropane or 1-bromopropane, also could be 1,2- or 1,3- or 1,1- or 2,2-dibromopropane)

2. Halogenation (pg. 1023) The addition of a halogen (group VII element) to a multiple bond (the halogen atoms add across a pi bond).

propene + Cl2

CH3

CH CH2 + Cl Cl

CH3

CH CH2

Cl Cl

1,2-dichloropropane 3. Hydrogenation (pg. 1023) The addition of H2 to a multiple bond (across a pi bond). (Hydrogenation, also known as saturation, is used commercially in the production of margarine).

1-butene + H2

CH2

CH CH2

CH3

+ H H

CH2

CH CH2

H H

CH3

butane 4. Hydrolysis (pg. 1023) The addition of a water molecule to a double bond.

propene + H2O

CH3

CH CH2 +

CH3

CH CH2

(HO)H OH(H)

OH2

2-propanol or 1-propanol 5. Elimination (pg.1027) The loss of a small molecule from a larger molecule. When the small molecule is H2O the process is also referred to as “condensation” or “dehydration”.

ethanol

C C

H

H

OH

H

HHOH

H

+

H

C C

H

H

H

ethene water

catalyst

heat, (pressure)

room temp.

catalyst

heat, pressure

heat

catalyst

acid catalyst

http://www.chalkbored.com/lessons/chemistry-12.htm

Type and definition of reaction: Example Reaction equation, structural formulas, names, conditions: 6. Esterification (pg. 1030) The condensation reaction that joins an alcohol with a carboxylic acid to produce an ester.

producing isopentyl acetate

CH3

CH CH2

CH2CH3 OH

+

OH

C

O

CH3

CH3

CH CH2

CH2CH3 O

C

O

CH3

+ OH2

3-methyl-1-butanol ethanoic acid 3-methylbutyl ethanoate water (isopentyl alcohol) (acetic acid) (isopentyl acetate)

7. Polymerization The conversion of “monomers” into “polymers”. I.e. the joining of small molecules to form large molecules with repeating units.

a) addition (pg. 1023)

eth(yl)ene monomer

CH2 CH2 ...

CH2

CH2

CH2

CH2

CH2

CH2

CH2

CH2

...n

polyeth(yl)ene b) condensation (pg. 1031) General Reaction

(for Dacron replace R1 with

-CH2-CH2- and R2 with benzene.

+R1OH OH OH C

O

R2 OHC

O

O C

O

R2 OC

O

R1... R1 ...

diol dicarboxylic acid polyester + H2O (ethylene glycol) (terephthalic acid) (Dacron)

8. Oxidation (pg. 1028) (More) oxygen atoms are placed on an organic molecule.

ethanal + K2Cr2O7

H C C

H

H

O

H + C C O

OH

H

H H

K2Cr2O7

+H2SO4

Cr2(SO4)3

K2SO4

H2O

ethanoic acid 1. Define addition reaction. Which of these reactions are addition reactions? Which reaction is the opposite of an addition reaction? 2. Define condensation reaction. Which of these reactions are condensation reactions? 3. Based on these reactions how could you make the following chemicals (draw reaction, showing reactants, products and conditions. Also

indicate the type of reaction): 1,2-dichlorocyclopentane, octane (using 4-octyne), 2,2,3,3-tetrabromopentane, 1-butene, propanoic acid, ethanol, ethyl propanoate.

H+

heat

room temp.

catalytic process

Unit 5 Review: Hydrocarbons1. Briefly define or explain the significance of the following terms:

a) acetylene b) acyclic c) addition reaction d) aliphatic e) alkane f) alkene g) alkyne

h) aromatic i) bond energy j) calorimeter k) cyclic l) endothermic m) exothermic n) fractionation

o) monomer p) organic chemistry q) petroleum r) polymer s) saturated hydrocarbon t) unsaturated hydrocarbon u) Wöhler

2. What general formula describes a) alkanes, b) alkenes, c) alkynes, d) cycloalkanes?

3. Draw the structural diagram for benzene.

4. For 3-methylpentane draw the a) complete structural diagram, b) condensed structural diagram, and c) line structural diagram

5. a) Write a balanced equation for the complete combustion of hexane. b) Write two possible balanced equations for the incomplete combustion of hexane.

6. Draw structures for these compounds: Name these structures: a) 2-methylbutane b) 4-propyl-3-heptene c) 5-ethyl-4,4,5-trimethyldecane d) cis-1,3-dimethylcyclohexane

7. Identify each pair as structural isomers, geometric isomers, or neither a) cyclopentane, pentane b) 1,1-dichloroethene, trans-1,2-dichloroethene c) cis-1,2-dichlorocyclopentane, trans-1,2-dichlorocyclopentane d) cis-1,2-dichlorocyclopentane, trans-1,3-dichlorocyclopentane

8. Using Br2(aq), how can you easily distinguish between ethane, ethene, and ethyne?

9. Using a table of bond energies calculate the heat of reaction when excess Br2 reacts with a) 1 mole of ethene, b) 1 mole of ethyne.

10. Differentiate the following terms with respect to definition, symbol, and units: a) heat capacity, b) specific heat capacity, c) heat of reaction, d) specific heat, e) molar heat of reaction

11. A forensics lab receives a small 0.16 g sample of metal. To identify the metal they heat it using exactly 3.0 J of energy. The temperature rises from 20°C to 98°C. What is the unknown metal (see pg. 568)?

12. 50.0 grams of butane is placed in a calorimeter. The 350 grams of water in the calorimeter rose from 19.7°C to 21.2°C. a) Calculate the heat released by the butane. b) Calculate the molar heat of reaction.

13. There is something wrong with each of the following names. Identify the error in each case (often the correct name can be determined by trying to draw the structure and then renaming it). a) 5-methyl-3-hexyne b) 3,3-dimethyl-3-hexyne

c) 1,2-dichlorocyclobutane d) 3-methyloctene

e) 2-ethyl-2-methylhexane f) 2,3-dimethyl-4-ethylnonane

e

CH

CH

CH

CH2

CH2

CH2

CH3

CH3 CH CH2 CH2 C CH3

CH3

CH2

CH3

CH3

e f

C C

Br H

C C

Br

H

Cl

H H Cl

f C C

Cl

Cl

H

H

CC

Cl

Cl

H

H

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Documents

7-Reactions of Alkenes and Alkynes · 2016-07-06 · Alkene Reactions Unsymmetrical Addition Reactions • Markovnikov’s Rule • For double bonds that have unequal numbers of hydrogen