Alkene Addition Reactions: A Complete Guide To Predicting The Products With Correct Stereochemistry.

1. Hydrohalogenation


The reagent for this reaction is HX, where X is either Cl, Br or I.


Product: Turn double bond into single and add X (halogen) to the MOST substituted carbon from the double bond (Markovnikov rule). Warning: Rearrangements are possible!

hydrohalogenation predict the product
hydrohalogenation predict the product

The reaction is also called addition of hydrogen halides to alkenes.


2. Acid Catalyzed Hydration Of Alkenes

The reagent is H2O with any catalytic acid such as H2SO4. Examples are: H2O/H2SO4, H3O+


Product:Turn double bond into single and add OH to the MOST substituted carbon from the double bond (Markovnikov rule). Warning: Rearrangements are possible!

acid catalyzed hydration predict the product
acid catalyzed hydration predict the product

3. Hydroalkoxylation

This reaction is an addition of alcohol with an acid catalyst to an alkene. It is similar to the acid catalyzed hydration described above except that instead of OH, OR group will be added.


The reagent is ROH with a catalytic acid.

Product: Turn double bond into single and add OR to the MOST substituted carbon from the double bond carbons.

hydroxyalkylation predict the product
hydroxyalkylation predict the product

4. Halogenation

The reagent is Br2 or Cl2 with a solvent such as (CH2Cl2).


Product: Turn double bond into single and add two bromines (or chlorines) one on each carbon from the double bond. Stereochemistry: ANTI ( one is on a wedge and another is on a dash).

alkene halogenation predict the product
alkene halogenation predict the product

The reaction is also called addition of halogens to alkenes.


5. Halogenation Of Alkenes In the Presence Of Water/ Formation of Halohydrins


The reagent is Br2 or Cl2 with H2O.


Product: Turn double bond into single and add OH to the most substituted carbon from the double bond and Br (or Cl) to the less substituted carbon from the double bond. Stereochemistry: TRANS

halogenation of alkenes in the presence of water predict the product
halogenation of alkenes in the presence of water predict the product

6. Oxymercuration

The reagent is 1.Hg(OAc)2, H2O 2.NaBH4


Product: Turn double bond into single and add OH to the most substituted carbon from the double bond. The other carbon gets the hydrogen. No Rearrangements!

This reaction is very useful. Both acid catalyzed alkene hydration and oxymercuration give the same product, but the difference is that oxymercuration can not have any rearrangements. Therefore, for synthesis, it might be a better choice for the reagent.

oxymercuration predict the product
oxymercuration predict the product

7. Alcoxymercuration

The reagent is 1.Hg(OAc)2, ROH 2.NaBH4


Product: Turn double bond into single and add OR to the most substituted carbon from the double bond. The other carbon gets the hydrogen. No Rearrangements!

alcoxymercuration predict the product
alcoxymercuration predict the product


8. Hydroboration


The reagent is 1.BH3, THF 2. H2O2, NaOH or 1.B2H6,diglyme 2.H2O2, NaOH


Product: Turn double bond into single and add OH to the LEAST substituted carbon from the double bond (Anti Markovnikov Rule) and hydrogen on the most substituted carbon from the double bond. OH and H add syn (same side, both are dash or wedge)


Hydroboration is a very useful reaction because it is rare for reactions to go the anti Markovnikov way.

If we notice OH on the less substituted carbon in the product in a synthesis problem, hydroboration most likely led to that product.


hydroboration predict the product
hydroboration predict the product

9. Syn Hydroxylation


The reagent is 1.OsO4 2.H2O2 OR 1.KMnO4 2. H2O, OH- (cold, dilute)


Product: Turn double bond into single and add two OHs, one on each carbon from the double bond. Stereochemistry: syn (same side, both wedge or both dash).


syn hydroxylation predict the product
syn hydroxylation predict the product

10. Catalytic Hydrogenation Of Alkenes


The reagent is H2 with a metal catalyst such as Pt, Pd, or Ni


Product: Turn double bond into single by adding 2 hydrogens ,one on each carbon from the double bond. Hydrogen add syn (both wedge or both dash)


hydrogenation predict the product
hydrogenation predict the product


11. Ozonolysis With Reductive Workup

The reagent is 1.O3 2. (CH3)2S (also called DMS) OR Zn, H2O


Product: Break the double bond in two and add two oxygens, one on each end of the double bond broken.

oxonolysis with reductive workup predict the product
ozonolysis with reductive workup predict the product


12. Ozonolysis With Oxidative Workup


The reagent is 1.O3 2.H2O2


Product: Break the double bond in two and add two oxygens, one on each end of the double bond broken. If you made an aldehyde (C=O connected to H), you have to change H into OH to make carboxylic acid.

ozonolysis with oxidative workup predict the product
ozonolysis with oxidative workup predict the product

This product can be also achieves with KMnO4 (warm, concentrated)


13. Epoxidation


The reagent is RCO3H (peroxyacid). Popular reagents include CF3CO3H and mCPBA


Product: Turn double bond into a single bond and attach the two carbons that had a double bond to an oxygen, making an epoxide. The epoxide can on a wedge (both carbons attached to the oxygen on a wedge) or dashed.


epoxidation predict the products
epoxidation predict the products

14. Radical Addition Of HBr


The reagent is HBr, ROOR (peroxide)


Product: Turn double bond into a single bond and attach Br to the LEAST substituted carbon from the double bond carbons (Anti Markovnikov).


radical addition of HBr predict the product
radical addition of HBr predict the product

The reaction is also called Free-Radical Addition of HBr


15.The Simmons-Smith Reaction


The reagent is CH2I2 with Zn,CuCl

Product: Turn double bond into single bond and attach the two carbons from the double bond to another carbon making a cyclopropane (triangle).

the Simmons-Smith reaction predict the product
the Simmons-Smith reaction predict the product


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