Wade Chapter 3 - 3 Structure and Stereochemistry of Alkanes...

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81 Structure and Stereochemistry of Alkanes 3 TABLE 3-1 Summary of Hydrocarbon Classification Compound Type Functional Group Example alkanes none (no double or triple bonds) propane alkenes propene alkynes triple bond propyne CH 2 CH 3 ethylbenzene C C C C C C benzene ring aromatics H ¬ C C ¬ CH 3 , ¬ C C ¬ CH 2 CH ¬ CH 3 , CC CH 3 ¬ CH 2 ¬ CH 3 , W henever possible, we will study organic chemistry using families of compounds to organize the material. The properties and reactions of the compounds in a family are similar, just as their structures are similar. By considering how the structural features of a class of compounds determine their prop- erties, we can predict the properties and reactions of similar new compounds. This organization elevates organic chemistry from a catalog of many individual com- pounds to a systematic study of a few types of compounds. Families of organic molecules are classified according to their reactive parts, called functional groups . We considered some of the common functional groups in Sections 2-12 through 2-14. An alkane is a hydrocarbon that contains only single bonds. The alkanes are the sim- plest and least reactive class of organic compounds because they contain only hydrogen and hybridized carbon, and they have no reactive functional groups. Although alkanes undergo reactions such as cracking and combustion at high temperatures, they are much less reactive than other classes of compounds having functional groups. sp 3 3-1 Classification of Hydrocarbons (Review) We classify hydrocarbons according to their bonding (Section 2-12), as shown in Table 3-1. Alkanes have only single bonds. A hydrocarbon with a carbon–carbon dou- ble bond (such as ethylene) is an alkene . If a hydrocarbon has a carbon–carbon triple bond (like acetylene), it is an alkyne . Hydrocarbons with aromatic rings (resembling benzene) are called aromatic hydrocarbons .
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82 Chapter 3: Structure and Stereochemistry of Alkanes A hydrocarbon with no double or triple bonds is said to be saturated because it has the maximum number of bonded hydrogens. Another way to describe alkanes , then, is as the class of saturated hydrocarbons . 3-2 Molecular Formulas of Alkanes Table 3-2 shows the structures and formulas of the first 20 unbranched alkanes. Any isomers of these compounds have the same molecular formulas even though their structures are different. Notice how the molecular formulas increase by two hydrogen atoms each time a carbon atom is added. The structures of the alkanes in Table 3-2 are purposely written as chains of groups ( methylene groups ), terminated at each end by a hydrogen atom. This is the general formula for the unbranched (straight-chain) alkanes. These alkanes differ only by the number of methylene groups in the chain. If the molecule contains n carbon atoms, it must contain hydrogen atoms.
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This note was uploaded on 04/29/2008 for the course CHM 2210 taught by Professor Reynolds during the Spring '01 term at University of Florida.

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Wade Chapter 3 - 3 Structure and Stereochemistry of Alkanes...

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