This is “Chemical Properties of Alkenes”, section 13.4 from the book Introduction to Chemistry: General, Organic, and Biological (v. 1.0).
This book is licensed under a Creative Commons by-nc-sa 3.0 license. See the license for more details, but that basically means you can share this book as long as you credit the author (but see below), don't make money from it, and do make it available to everyone else under the same terms.
This content was accessible as of December 29, 2012, and it was downloaded then by Andy Schmitz in an effort to preserve the availability of this book.
Normally, the author and publisher would be credited here. However, the publisher has asked for the customary Creative Commons attribution to the original publisher, authors, title, and book URI to be removed. Additionally, per the publisher's request, their name has been removed in some passages. More information is available on this project's attribution page.
For more information on the source of this book, or why it is available for free, please see the project's home page. You can browse or download additional books there. You may also download a PDF copy of this book (72 MB) or just this chapter (3 MB), suitable for printing or most e-readers, or a .zip file containing this book's HTML files (for use in a web browser offline).
Alkenes are valued mainly for addition reactionsA reaction in which substituent groups join to hydrocarbon molecules at points of unsaturation—the double or triple bonds., in which one of the bonds in the double bond is broken. Each of the carbon atoms in the bond can then attach another atom or group while remaining joined to each other by a single bond.
Perhaps the simplest addition reaction is hydrogenationA reaction in which hydrogen gas reacts at a carbon-to-carbon double or triple bond or a carbon-to-oxygen double bond to add hydrogen atoms to carbon atoms.—a reaction with hydrogen (H2) in the presence of a catalyst such as nickel (Ni) or platinum (Pt).
The product is an alkane having the same carbon skeleton as the alkene. (The use of hydrogenation to convert unsaturated vegetable oils to saturated fats is discussed in Chapter 17 "Lipids", Section 17.2 "Fats and Oils".)
Alkenes also readily undergo halogenationA reaction in which a halogen reacts at a carbon-to-carbon double or triple bond to add halogen atoms to carbon atoms.—the addition of halogens. Indeed, the reaction with bromine (Br2) can be used to test for alkenes. Bromine solutions are brownish red. When we add a Br2 solution to an alkene, the color of the solution disappears because the alkene reacts with the bromine:
Another important addition reaction is that between an alkene and water to form an alcohol. This reaction, called hydrationThe addition of water to a substance; in organic chemistry, the addition of water across the carbon-to-carbon double bond of an alkene or the carbon-to-oxygen double bond of an aldehyde or ketone., requires a catalyst—usually a strong acid, such as sulfuric acid (H2SO4):
Write the equation for the reaction between CH3CH=CHCH3 and each substance.
In each reaction, the reagent adds across the double bond.
Write the equation for each reaction.
CH3CH2CH=CH2 with H2 (Ni catalyst)
CH3CH=CH2 with Cl2
CH3CH2CH=CHCH2CH3 with H2O (H2SO4 catalyst)
What is the principal difference in properties between alkenes and alkanes? How are they alike?
If C12H24 reacts with HBr in an addition reaction, what is the molecular formula of the product?
Alkenes undergo addition reactions; alkanes do not. Both burn.
Complete each equation.
Complete each equation.