CSUMB
ESSP 311 Organic Chemistry I
Ronald W. Rinehart, Ph.D.

Chapter 6 Reactions of Alkenes: Addition

for a reaction summary of all the goodies below, see
my "Big Wheel" of Alkene Addition Reactions
I also have a table summarizing alkene addition reactions
You might prefer the alkene reaction summary table by M. A. Schwartz at Florida State
http://www.chem.fsu.edu/schwartz/CHM2210/Reactions/alkenes/rxns.html
Or the alkenes reaction outline from Ron Rusay at Lawrence Livermore National Lab
http://education.llnl.gov/msds/orgchem/Chem226/alkenes-rxns.htm

or a nicer-looking PDF version of the same diagram from Clarkson University
[both apparently are taken from McMurry's organic text] at
http://www.clarkson.edu/~ochem/Fall01/CM241/AlkeneSummary.pdf
Or an older, but still nice, version from Yuzhuo Li at Clarkson University
http://people.clarkson.edu/~ligroup/f98241reaction1.pdf
Addition Reactions of Alkenes from Organic ChemistryOnLine
by Paul R.Young at the University of Illinois at Chicago
http://www.chem.uic.edu/web1/PDF/CH8.PDF
197 PowerPoint-type slides in PDF format
The Alkenes chapter in Exploring Organic Chemistry: An Electronic Textbook 
by Gary Trammell and Srinivas Vuppuluri at the University of Illinois at Springfield has lots of good stuff
http://people.uis.edu/gtram1/organic/alkenesmenu.htm 
Electrophilic Addition Mechanisms Menu by Jim Clark, Cornwall UK
http://www.chemguide.co.uk/mechanisms/eladdmenu.html#top
Virtual Textbook of Organic Chemistry by William Reusch at Michigan State University
Addition reactions of alkenes
http://www.cem.msu.edu/~reusch/VirtualText/addene1.htm#add1 
and
http://www.cem.msu.edu/~reusch/VirtualText/addene2.htm  
has it all -- and then some! a classy production!
 
 
Carey PowerPoint slides for chapter 6 from Columbia University
 [6.20, introduction to organic synthesis]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_20.html
 
 

Chapter 6:  Reactions of Alkenes.  Addition Reactions.

 I.  Reactions of Alkenes. 
            A.  Addition Reactions.
 
                        1. In addition reactions the alkene gains two  new groups:

                         2. A variety of reagents can add to the alkene. 
            B.  Reactions of Alkenes.
 
                        1.  Hydrogenation of Alkenes.
 

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.1 to 6.3, hydrogenation]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_01_03.html 

Details on catalytic hydrogenation by Gary Trammell at the University of Illinois at Springfield
http://people.uis.edu/gtram1/organic/alkenes/hydrogen.htm 
Gary Trammell's animation of catalytic hydrogenation
http://people.uis.edu/gtram1/organic/alkenes/hydrogenation.gif 

                                    a)   Overall reaction   

                                    b)  Catalysts:  Pt, Pd, Ni, Ru, Rh 
                                    c)   These are exothermic reactions, but react slowly without the above catalysts. 
                                    d)   Examples:                                              

                                     e)  Used in the production of margarines. 
                                    f)   Stereochemistry of hydrogenation.

                                        i)  Both H's add to the same face of C=C 
                                        ii)   This is referred to as syn addition. 
                                                 (From opposite sides would be called anti addition.)

                                        iii)   One cannot distinguish syn and anti addition with a reaction such as: 

                                                CH3CH=CHCH3  +  H2 / Pd   à   CH3CH2CH2CH3 

                                        iv)  Another stereochemical aspect of hydrogenation is stereoselectivity:
                                                       A reaction can theoretically yield two or more stereoisomers,
                                                       but one is more abundant than the other (or formed exclusively.)
 

                                        iv)  The bridge inhibits the approach  of  a-pinene to the catalyst surface
                                                by that side of the molecule. 
                                                 Only the 'underside' can approach the catalyst and be hydrogenated.
                                                 We say the reaction occurs on the "less hindered" side. 

                                    g)  Heats of hydrogenation can be used to  compare the stability of alkenes in a similar manner
                                        as with heats of  combustion data.                                              

reaction

C4H8  +  H2/cat  à  C410

isomer

1-butene

cis-2-butene

trans-2-butene

DHohyd, kJ/mol

-126

-119

-115

C=C type

terminal
(monosubstituted)

cis-disubstituted

trans-disubstituted

conclusion

least stable

 

most stable

                                      i)  The stability of alkenes with  different number of C's [but same # of C=C] can be compared to
                                                   each other using heats of hydrogenation but not with heats of combustion.  Why?

                         2. Addition of Hydrogen Halides 

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.4 to 6.7, electrophilic addition of HX, Markovnikov's rule, carbocation rearrangements]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/PDF/06_04_07.pdf

Addition reactions by Gary Trammell and Srinivas Vuppuluri at the University of Illinois at Springfield
http://people.uis.edu/gtram1/organic/alkenes/react.htm 

Markovnikov addition by Gary Trammell and Srinivas Vuppuluri at the University of Illinois at Springfield
http://people.uis.edu/gtram1/organic/alkenes/markovnikov.htm 

                                    a)   Overall reaction    

                                     b) Order of reactivity of HX:      HI  >  HBr  >  HCl  >  HF
                                                i)  HI is the strongest acid of the series; HF is weakest.
                                                ii)  Electrophilic Addition, since H+ (an electrophile) first adds to the alkene.    
                                    c)  Solvents:  pentane, benzene, CH2Cl2, glacial acetic acid, CHCl3
                                    d)   Examples.

                                     e)  The reaction is regioselective:  In unsymmetrical alkenes the hydrogen goes to the carbon
                                                already bearing the greater number of hydrogens (of the two pi bonded  carbons): 
                                                            This is Markovnikov's Rule    THE RICH GET RICHER!!!
                                              In texts using the older German transliteration, you may see the spelling Markownikoff

                                    f)  Complete these reactions, showing both major and minor products. Label the major product. 

                                                i)   CH3CH=CH2  +  HCl  à   

                                                ii)               +  HBr  à

                                                                                                                                  

                                    g)  Mechanism:     

                                    h) Reason for Markovnikov's Rule:  The “rich getting richer” results in the formation of the more
                                                             stable (higher substituted and easier to form) carbocation. 
                                    i)  Exercise:  Complete the following reaction and then show the mechanism for the reaction,
                                             showing the carbocations leading to both major and minor products.

                                                            CH3CH2CH=CH3  + HCl  à 

                        3.  Addition of concentrated H2SO4

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.8 to 6.9, free radical addition of HBr; addition of H2SO4]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_08_09.html

 

                                    a)  This reaction works for ethene, monosubstituted alkenes, and vic disubstituted alkenes
                                             (RCH=CHR').
                                    b)    This reaction follows Markovnikov's Rule (complete and show the mechanism):

                         4.   Hydration:  Addition of Water (dilute H2SO4)    

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.10 to 6.13, acid-catalyzed hydration; hydroboration-oxidation]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_10_13.html

                                    a)  Overall reaction.

                                    b)  The reaction follows Markovnikov's Rule.
                                    c)  Complete the following reactions:

 

                                               

                                               

 

                                   

 

                                    d)   Show the mechanism:

 

                        5.   Addition of Halogens

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.14 to 6.17, halogen addition; halohydrin formation]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_14_17.html

Addition of Halogens by Gary Trammell and Srinivas Vuppuluri at the University of Illinois at Springfield
http://people.uis.edu/gtram1/organic/alkenes/bromine.htm 

                                    a)  Overall reaction.

                                     b)   X2 = Cl2, Br2   solvents used include CCl4, CH2Cl2, CH3CO2H
                                    c)   F2 is explosive
                                    d)  Vicinal diiodides lose I2 and revert to the alkene.     
                                    e)  Anti addition:  The halonium ion.

                                     f)  Mechanism:

                         6.   Addition of Hypohalous Acids:  Formation of Halohydrins 

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.14 to 6.17, halogen addition; halohydrin formation]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_14_17.html

                                    a)   Overall reaction and mechanism.

                                     b)   X2 = Cl2, Br2   in water   
                                    c)   Important Facts Concerning Addition of "HOX".
                                                i)  Follows Markovnikov's Rule.  (X goes to the carbon richer in H's; OH to the other.)
                                                the results appear as if:  1)  X2 + H2O
à HOX + X  2) HOX     HO + X+

                                                ii)  Anti addition is observed.  
                                                iii) Reaction mechanism involves the halonium ion.
                                    d)   Mechanism:                                                        

                                    e)  Examples:

 

                                                ii)  Consider the mechanism for this reaction in order to understand which product is preferred:

                                                iii) Notice that the water molecule attacks the more substituted carbon of the halonium ion
                                                        since it carries greater positive character than the less substituted carbon.

 

                                    f)   Halohydrins are converted by base to epoxides [see # 10]

 

 

                        7.  Oxymercuration-Demercuration. Synthesis of Alcohols. 
                                               
[not in the text, but you should know it anyway!]
                                    a)   Overall reaction.
 

                                     b)   Important Facts Concerning Oxymercuration/Demercuration:
                                                i)   Follows Markovnikov's Rule
                                                ii)  No rearrangements occur even though a carbocation intermediate is involved in
                                                         the mechanism (the carbocation is stabilized by Hg).
                                                iii)  A water/tetrahydrofuran (THF) mixture is used as solvent: 
                                                        good solvent for organics and water.     
                                                iv)   Mechanism for the 2nd step of the reaction (demercuration) is uncertain: 
                                                        free radicals have been suggested.

                                    c)  Example:

                                     d)  Mechanism:

         + 2CH3CO2  + Hg0 + BO43 

                         8.  Free Radical Addition of HBr.  Anti-Markovnikov Addition 

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.8 to 6.9, free radical addition of HBr; addition of H2SO4]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_08_09.html

                                    a)  Recall the normal addition of HBr to an alkene:

                                                            H2C=CHCH3 + HBr à CH3-CHBrCH3        2-bromopropane           

                                                 i)  Markovnikov Addition is observed.                            

                                    b)  BUT in the presence of peroxides [in nonpolar solvents]: 

                                                H2C=CHCH3  +  HBr  +RO-OR  à   BrCH2CH2CH3    1-bromopropane

                                                 i)  Anti-Markovnikov addition  is observed.
                                                            [also called counter-Markovnikov or Kharasch addition]  

                                    c)   Mechanism:

1)    alkoxy radicals

2) 

3)  

4)  

                                     d)  Complete the following reactions:

 

                                    e)  Synthesize the following compounds, using methods which will give maximum yields of product:                                                                         

i)

ii)

 

 

                                    f)  Solutions: 

                                                i)  CH3CH2CH2CH=CH2  +  HBr à 

 

                                                ii)  CH3CH2CH2CH=CH2  +  HBr  + peroxides  à

 

                        9.   Hydroboration-Oxidation:  Synthesis of Alcohols from Alkenes. 

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.10 to 6.13, acid-catalyzed hydration; hydroboration-oxidation]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_10_13.html

 

                                    a)   Some important observations concerning hydroboration:

                                                i)  Anti-Markovnikov addition.    [hydration]
                                                ii)  Syn addition.
                                                iii) No rearrangements.
                                                iv)  Solvents: 


Diglyme 
(diethylene glycol dimethyl ether)

THF 
(tetrahydrofuran, oxolane)

                                                 v)  Retention of configuration is observed in the oxidation step.

                                     b)  Example:  

                                                CH3CH=CH2   à { 1. BH3, diglyme   2. H2O2, OH-   } à          CH3CH2CH2OH

                                     c)  Mechanism:                                                                             

                                     d)  Reason for regioselectivity: 

                                                i)   The C-B bond that forms is the one favoring the more stable transition state
                                                                        (so that the positive character is on the more substituted C).  

                                                ii)  Steric Factors:  The bulky BH3  group is attracted to the less hindered (less substituted) carbon.

                        10.  Epoxidation 

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.18 to 6.19, epoxidation; ozonolysis]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_18_19.html

Epoxides by Gary Trammell and Srinivas Vuppuluri at the University of Illinois at Springfield
http://people.uis.edu/gtram1/organic/alkenes/epoxides.htm 

                                    a)  Epoxidation is achieved directly by the reaction between an alkene and a peroxy acid
                                                            (and indirectly by forming a halohydrin, then treating with base  [6f].)

                                       b)  Nomenclature:
                                                i)   Epoxides can be named as epoxy derivatives of alkanes: 



epoxyethane

1,2-epoxypropane

4-methyl-2,3-epoxyhexane

(ethylene oxide)

(propylene oxide)

-------

oxirane

2-methyloxirane

2-sec-butyl-3-methyloxirane

                                                 ii)  Simple epoxides can also be named as oxiranes, where oxirane is the parent name of the simplest
                                                             epoxide.  Number 1 = O on the ring.  See bottom row in table just above.  

                                    b)   Complete the following reactions and name the product: 

 

  

                                      5,5-dimethyl-3,4-epoxyheptane                                      2-methyl-2,3-epoxyhexane

                                     c)  Mechanism: 

 

                        11.  Ozonolysis:  (1) Ozonation followed by (2) hydrolysis. 
                                   
[not in the text, but you should know it anyway!]

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.18 to 6.19, epoxidation; ozonolysis]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_18_19.html

Ozonolysis by Gary Trammell and Srinivas Vuppuluri at the University of Illinois at Springfield
http://people.uis.edu/gtram1/organic/alkenes/ozonolysis.htm 

                                    a)  Overall reaction. “Snip & cap”

                                                           

                                    b)  Zn is a reducing agent, added to prevent the oxidation of aldehydes to carboxylic   acids.  

                                    c) Ozonolysis is used to deduce the structure of alkenes by analyzing the structure of the resulting
                                                 carbonyl compounds. 

                                    d)  Examples for two isomers of C5H10:

                             12.   Permanganate Cleavage of Alkenes. [not in the text, but you should know it anyway!]

                                     a)  This reaction is an alternative to ozonolysis.        

                                    b)  Carboxylic acids are formed in place of  aldehydes.

 

                                    c)   Examples.  (Complete the reactions):

                         13.  Acid-catalyzed Polymerization:  Alkenes + Alkenes. 

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.21, polymerization]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_21.html

                                    a)  Overall reaction.

                                    b)  Occurs when 3o carbocations can form [e.g., from R2C=CH2, R2C=CHR, R2C=CR2 with H+]. 
                                    c)  Mechanism: (Cationic Polymerization).

                         14.  Free-Radical Polymerization. 

Carey PowerPoint slides for chapter 6 from Columbia University
 [6.21, polymerization]
http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/06_21.html

Polymers page from my CHEM 30B course at MPC

                                    a)  Overall reaction [for ethylene].                                                                            

                                                                                                                                               

                                    b)  n can equal thousands!  
                                    c)   Mechanism:

1)    alkoxy radicals
 

The linear “high-density” polyethylene generally has superior physical properties to the branched “low-density” form, and thus is far more useful. But, since 2o radicals are more stable than 1o radicals, the less desirable branched product is more likely to be formed. Special catalysts [such as mixtures of Et3Al and TiCl4,
a  “Ziegler-Natta catalyst”] are required for the exclusive formation of the linear polymer. Karl Ziegler and Giulio Natta won the Nobel Prize in 1963 for their work in developing these catalysts for stereospecific polymerizations.

                                      d)   Some common monomers/polymers:  [See my 30B polymers page]

Monomer

Polymer

CH2=CH2

ethylene

polyethylene

CH3CH=CH2

propylene

polypropylene

CH2=CHCl

vinyl chloride

polyvinylchloride (PVC)

CH2=CHPh

styrene

polystyrene

CH2=CCl2

vinylidene chloride

Saran

F2C=CF2

tetrafluoroethylene

Teflon

 

            15.  Syn hydroxylation [not in the text, but you should know it anyway!]

                                    a)  overall reaction

                                    b)  Reagent alternatives

                                                            i)  OsO4  osmium tetroxide [+ H2O2]:  expensive, quite toxic, gives better yields
                                                            ii)  cold, dilute KMnO4  potassium permanganate:  cheaper, less hazardous

                                    c)  Mechanism involves cyclic intermediate; both OH groups introduced syn

 

Many thanks to Rod Oka of MPC for generously sharing his "Lecture Companion" outline,
reproduced here in extensively modified form by permission, with web references and other goodies added by me.
Structures drawn using  MDL IsisDraw™ , CS ChemOffice ChemDraw™, and ACDLabs ChemSketch™.
"It's all good!"