first three chapters established some fundamental principles concerning the structure of organic molecules. In this chapter we begin our discussion of organic chemical reactions by directing attention to alcohols and alkyl halides. These two rank among the most useful classes of organic compounds because they often serve as starting materials for the preparation of numerous other families

drogen peroxide is formed in the cells of plants and animals but is toxic to them. neemen Consequently, living systems hav developed mechanisms to rid themselves of hydrogen peroxide, usually by enzyme-catalyzed reduction to water. An under- standing of how reactions take place, be they reactions in living systems or reactions in

Ikenes are hydrocarbons that contain a carbon-carbon double bond. A car- bon-carbon double bond is both an important structural unit and an important functional group in organic chemistry. The shape of an organic molecule is influ- enced by the presence of this bond, and the double bond is the site of most of the chem- ical reactions that alkenes undergo. Some representative alkenes include isobutylene(an industrial chemical), a-pinene (a fragrant liquid obtained from pine trees), and farnesene (a naturally occurring alkene with three double bonds

he Greek word stereos means\solid, \and stereochemistry refers to chemistry in three dimensions. The foundations of organic stereochemistry were laid by Jacobus van't Hoff* and Joseph Achille Le Bel in 1874. Independently of each other, van't Hoff and Le Bel proposed that the four bonds to carbon were directed toward the cor- ners of a tetrahedron. One consequence of a tetrahedral arrangement of bonds to carbon

H ydrocarbons that contain carbon-carbon triple bond are called alkynes. Non- cyclic alkynes have the molecular formula C, H2n-2. Acetylene (HCCH) is th simplest alkyne. We call compounds that have their triple bond at the end of a carbon chain(RC=CH) monosubstituted, or terminal, alkynes. Disubstituted alkynes (RCCR') are said to have internal triple bonds. You will see in this chapter that a car- bon-carbon triple bond is a functional group, reacting with many of the same reagents

this chapter and the next we extend our coverage of conjugated systems to include arenes. Arenes are hydrocarbons based on the benzene ring as a structural unit. Ben- are zene, toluene, and naphthalene, for example, are arenes

ntil the second half of the twentieth century, the structure of a substance-a newly discovered natural product, for example-was determined using information obtained from chemical reactions. This information included the identification of functional groups by chemical tests, along with the results of experiments in which the substance was broken down into smaller, more readily identifiable fragments. Typical of this approach is the demonstration of the presence of a double bond in an alkene by cat- nd subsequent

he next several chapters deal with the chemistry of various oxygen-containing functional groups. The interplay of these important classes of compounds-alco- hols, ethers, aldehydes, ketones, carboxylic acids, and derivatives of carboxylic acids-is fundamental to organic chemistry and biochemistry

ADDITION TO THE CARBONYL GROUP Idehydes and ketones contain an acyl group RC-bonded either to hydrogen or to another carbon

arboxylic acids, compounds of the type RCOH, constitute one of the most fre- quently encountered classes of organic compounds Countless natural products are carboxylic acids or are derived from them. Some carboxylic acids, such as acetic acid, have been known for centuries. Others, such as the prostaglandins, which are pow erful regulators of numerous biological processes remained unknown until relatively