Structure and Synthesis of Alkenes

Alkenes are hydrocarbons with carbon-carbon double bonds. Alkenes are sometimes called olefins, a term derived from olefiant gas, meaning oil-forming gas. This term originated with early experimentalists who noticed the oily appearance of alkene derivatives. Alkenes are among the most important industrial compounds (see Section 7-6), and many alkenes are also found in plants and animals. Ethylene is the largest-volume industrial organic compound, used to make polyethylene and a variety of other industrial and consumer chemicals. Pinene is a major component of turpentine, the paint solvent distilled from extracts of evergreen trees. Muscalure (cis-9-tricosene) is the sex attractant of the common housefly. 

The bond energy of a carbon-carbon double bond is about 611 kJ/mol (146 kcal/mol), compared with the single-bond energy of about 347 kJ/mol (83 kcal/mol). From these eneigies, we can calculate the approximate energy of a pi bond  

This value of 264 kJ/mol is much less than the sigma bond energy of 347 kJ/mol, showing that pi bonds should be more reactive than sigma bonds. 

Because a carbon-carbon double bond is relatively reactive, it is considered to be a junctional group, and its reactions are characteristic of alkenes. In previous chapters, we saw alkene synthesis by elimination reactions and we encountered a few reactions of alkenes. In this chapter, we study alkenes in more detail, concentrating on their properties and the ways they are synthesized. 

In a Lewis structure, the double bond of an alkene is represented by two pairs of electrons between the carbon atoms. The Pauli exclusion principle tells us that two pairs of electrons can go into one region of space between the carbon nuclei only if each pair has its own molecular orbital. Using ethylene as an example, let s consider how the electrons are distributed in the double bond. 

7-1 The number of elements of unsaturation in a hydrocarbon formula is given by  

7-3 Hundreds of examples of C4HgNOCl are possible. Yours may not match these, but all must contain two elements of unsaturation. 

Note to the student The lUPAC system of nomenclature is undergoing many changes, most notably in the placement of position numbers. The new system places the position number close to the functional group designation, which is what this Solutions Manual will attempt to follow however, you should be able to use and recognize names in either the old or the new style. Ask your instructor which system to use. 

5-chlorocyclohexa-l, 3-diene (positions of double bonds need 

Q Show how alkenes can be synthesized by eliminations from alkyl halides and alcohols. 

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