Reactions of the Alkenes and Alkynes
                                     Markinikov's Rule:
When a substitution is made across a C=C or triple bond the H will be added to the carbon that already has the most H's on it.  When a dehydration occurs across a C=C or triple bond then the H removed will be from the C that has the most H's on it.



5. Addition of Hydrogen
    This is an addition or saturation reaction.

         unsaturated                                    saturated
        hydrocarbon                                  hydrocarbon

eg.  pent-2-ene being changed into pentane


eg, 2 ethyne (acetylene) being converted into ethane



6.   Halogenation
        The addition of a halogen also called chlorination, bromination or iodination, etc). Trans addition is preferred over cis addition.

eg.  2-methyl-propene is halogenated with bromine to 1,2-dibromo-2-methyl-propane

As the halogen adds it prefers a trans addition.   This becomes very important if you need to halogenate an alkyne to an alkene. Remember that only alkenes can have a cis and trans isomer.


7.  Dehalogenation
      The opposite of the above reaction.  This reaction strips a pair of halogens off of a molecule leaving a double bond behind.

X can be any halogen. Either reagent combination can be used. Powdered metallic Zn and acetic acid (ethanoic acid) or powdered Mg and petroleum ether can be used to pull the halogens from the alkane. The bonding electrons are then free to join up with each other forming a double bond.

eg.  5,6-diiodo-decane becomes either trans-dec-5-ene or cis-dec-5-ene plus MgI2




8.   Hydrohalogenation
The addition of a H and a halogen. It is beneficial to add both the H and the halogen in one reagent so one of the binary halogen acids is usually used like HI, HBr, HCl, or HF.

HX can be any halogen acid. (HF, HCl, HBr, HI)
eg.   propene is hydrohalogenated with hydrobromic acid to create 2-bromo-propane



9.  Addition of Cyanide to an Alkene
This reaction is a necessary step in the creation of nitrogen compounds such as amines.  It can also be used to create a carboxylic acid with one more carbon from the original starting material.

eg. 3-methyl-but-1-ene is converted to 1-cyano-3-methyl-butane


10.  Hydration
This reaction involves the addition of water in the presence of a weak acid. Strong acids tend to draw water away from molecules. Weak acids only stimulate double bonds (Pi bonds) into breaking. Water is ionized slightly in weak acids and can then move into take their proper place in the broken alkene bonds.

eg.  2-methyl-propene is hydrated to 2-methyl-propan-2-ol



11.   Halohydrogenation
The addition of an OH and a halogen using bromine or chlorine water. When a halogen is mixed with water it forms a halogen hydroxide compound which is stable for a short period of time. (ie. as long as the halogen gas stays dissolved in the water)

               X2 + H2O ---> XOH + HX      (X can be any halogen)


eg.  propene is halohydrogenated with chlorine water to form 2-chloro-propan-1-ol and 1-chloro-propan-2-ol



12.  Halogen Substitution
        This reaction converts a haloalkane into an alcohol.

eg.  2-bromo-hexane is converted into hexan-2-ol



13.  Oxidation
The use of cold KMnO4 causes diol (double alcohol) formation.

eg.    but-1-ene is oxidized in buta-1,2-diol



14.   Ozonolysis
Ozonolysis means to cleave or break (to lyse) with oxygen, specifically ozone. There are actually three ways to achieve this type of reaction; with ozone, O3, with Zn and water, and with hot KMnO4.

 You must be very careful about this type of reaction. You are actually taking a single molecule with a single double bond and breaking it up into two new molecules. Depending upon the side chains you can get ketones, aldehydes and carboxylic acids formed as products.
eg. 2-methyl-pent-2-ene is ozonolyed into propan-2-one and propanal

Here is a 2nd possibility  2,3-dimethyl-pent-2-ene is ozonolyed into propan-2-one and butan-2-one



15.  Epoxide Formation
An epoxide is an normal oxygen found between two adjoining C's who are also covalently joined.

eg.  2-methyl-pent-2-ene is formed into 2-methyl-2-propyl-epoxide with concentrated acetic acid



16.   Cis Addition and AntiMarkinikov Hydration
Anytime an alcohol is needed from an alkene but the reverse of Markinikov is needed. The Cis addition is not important unless you do this to an alkyne and make an alkene out of it. If it is an alkene then you make an alkane which is free to rotate about the bond. Either of two reagents can be used. Diborane or hydrogen peroxide are both good at causing this reaction to take place.

eg. 2-methyl-propene is converted into 2-methyl-propanol.  This is antimarkinikov because Markinikov says that the product should be butan-2-ol


17.  Oxidation of an Alkyne
The term oxidation has many meanings. In organic chemistry oxidation means the addition of oxygen to a molecule. This definition is not the definitive meaning but in the context of this unit it is good enough. The reagent used is a mixture of mercury(II) sulphate and sulphuric acid.

Due to the position of the alkyne bond there is only one product possible in the example below.
eg.   propyne is oxidized into propan-2-one

In the next example there are two possible products above because the position of the alkyne bond in the pent-2-yne molecule. You will have to watch out for this situation. If you go to apply Markinikov's Rule and there are no hydrogens to help you make up your mind then there is probably more than one product.
eg. 2      pent-2-yne is oxidized into penta-3-one and penta-2-one


18.  Ozonolysis of an Alkyne
When an alkyne is subjected to ozonolysis it will always produce two carboxylic acids.

This ozonolysis reaction is identical to the others already demonstrated above. It is the starting material that determines what the products are.
eg.       5-methyl-hepta-3-yne is lysed with hot KMnO4 into 2-methyl-butanoic acid and propanoic acid