Organic Chemistry I

Addition of Alcohol to Alkenes
With the presence of acid, an alcohol can be added to the alkene in the same way that water does, and ether formed
as product. For example:
Figure 10.3d Example of addition of Alcohol to Alkenes
Examples:
Show the mechanism for above addition reaction of methanol to 2-methyl-1-butene.
Refer to the hydration mechanism.
Solutions:
Mechanism:
addition of methanol to 2-methyl-1-butene
Step 1:
Electrophilic attack of H
3
O
+
to the alkene, carbocation intermediate formed
Step 2:
Methanol reacts with the carbocation
Step 3:
Deprotonation to get neutral product
334 | 10.3 Reactions of Alkenes: Addition of Water (or Alcohol) to Alkenes

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Note:
Please keep in mind that for the reaction that involves carbocation intermediate, the rearrangement of
carbocation is always an option. Therefore the addition of water/alcohol to alkenes may involve carbocation
rearrangement if possible.
Exercises 10.3
Show major product(s) for the following reactions.
10.3 Reactions of Alkenes: Addition of Water (or Alcohol) to Alkenes | 335

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Answers to Practice Questions Chapter 10
336 | 10.3 Reactions of Alkenes: Addition of Water (or Alcohol) to Alkenes

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10.4 Reactions of Alkenes: Addition of Bromine and
Chlorine to Alkenes
Addition reaction also occur easily between halogens (Br
2
and Cl
2
) and alkenes. In the presence of aprotic solvent, the
product is a vicinal dihalide, as shown here for the addition of chlorine to propene.
Figure 10.4a Addition reaction
The reaction between C=C double bond and bromine (Br
2
) can be used as a test for the presence of alkene in an unknown
sample. The bromine reagent is in reddish color, and the product vicinal dibromide is colorless. When bromine is added
to the sample, if the reddish color disappear, that means the sample does contain an alkene. The addition reaction
occurs to get reddish bromine consumed and colorless product formed, so color fades off.