Working through this chapter of the study guide will enable you to:

1. Understand the importance of organic chemicals in your everyday life.
2. Understand the bonding structure of molecules in organic compounds.
3. Describe the various types of common hydrocarbons and some of the derivatives of hydrocarbons.
4. Explain what constitutional isomers are and how they are constructed.
5. Identify the benzene ring and tell how this relates to the formation of aromatic hydrocarbons.
6. Depict the basic structures of gasoline, soap, alcohol, and many other common hydrocarbons and derivatives of hydrocarbons.

Discussion

Organic compounds make up a large percentage of the chemicals that we encounter in our everyday lives. Organic compounds were originally defined as those having an animal or plant origin, but that definition has now been expanded to include all compounds that contain carbon. Carbon is the basic constituent of complex molecules such as proteins, fats, and carbohydrates, as well as many synthetic fibers, drugs, and detergents. That makes the study of organic chemistry a keystone for many modern advancements that we now take for granted.

Organic compounds are formed by covalent bonding and can form into any structure that does not violate the octet bonding rules. This is the reason that millions of organic compounds have already been identified and that more are being found, or made synthetically, every day. Because hydrogen is easily bonded to carbon, many of the complex compounds formed in organic chemistry are hydrocarbons, and even when other elements are involved in the formation of organic compounds, these substances are treated as derivatives of hydrocarbons.

We will study several different types of hydrocarbons in this chapter, including aromatic hydrocarbons and aliphatic hydrocarbons. Some of the names used for subgroups of these hydrocarbon classes are quite similar, so you will have to pay close attention to the terms presented in this chapter and learn their definitions right away. Once you understand the terminology used in organic chemistry, the information presented in this chapter will explain the composition and structure of many of the materials that you encounter and deal with each day.

Look carefully at the common names for the various hydrocarbons discussed in this chapter and you may be surprised by how many of them you recognize. Examples are butane, which is used as a fuel in lighters, gasoline and kerosene, which are made up of various alkanes such as octane and pentane, mothballs and model airplane glue, which are composed of benzene ring structures, and so on. It should be clear to you by now that organic chemistry really is an important part of our modern lifestyle.


Section  14.1Bonding in Organic Compounds

The most common elements that make up organic molecules are all nonmetals, so the covalent bond is very important in the formation of organic materials. Carbon and nitrogen can form single, double, or triple covalent bonds, and oxygen can form single or double covalent bonds. This variety in electron-pair sharing leads to a large number of diverse compounds, many of which are made up of long molecular chains.


Section  14.2Aromatic Hydrocarbons

Hydrocarbons are the simplest of the organic compounds because they are made up of only two elements, hydrogen and carbon. One complex form of bonding in hydrocarbons involves the formation of benzene rings. When one or more benzene rings are present in a hydrocarbon, the compound is classified as an aromatic hydrocarbon. The old theory of benzene ring formation involved alternating single and double bonds among the six carbon atoms forming the basic ring structure. This has been replaced by a revised model in which six electrons are shared by all of the atoms in the benzene ring. This complex sharing of electrons provides an especially stable structure for members of this class of hydrocarbons.


Section  14.3Aliphatic Hydrocarbons

The hydrocarbons that do not contain benzene rings are called aliphatic hydrocarbons. These compounds can be further broken down into the following categories.

Alkanes	Only single bonding between carbon atoms
Cycloalkanes	Only single bonding between carbon atoms but with ring formation
Alkenes	Double bonding between two carbon atoms
Alkynes	Triple bonding between two carbon atoms

Both alkanes and cycloalkanes are considered saturated hydrocarbons because they have the maximum number of hydrogen atoms that can bond with the number of carbon atoms present. Constitutional isomers, compounds that have the same molecular formulas but different structural formulas, can exist for all but the simplest hydrocarbons. That is because the simple continuous chain of carbon atoms, sometimes called a straight-chain, can usually be replaced with one or more branching-chain structures, thus producing compounds with different structural formulas.


Section  14.4Derivatives of Hydrocarbons

When atoms of other elements are added to basic hydrocarbon structures to replace one or more of the usual hydrogen atoms, compounds known as derivatives of hydrocarbons are formed. The following classes of compounds are examples:

Alkyl halides	Contain halogen atoms (F, Cl, Br, I)
Alcohols	Contain hydroxyl groups, —OH
Amines	Contain amino groups, —NH2
Carboxylic acids	Contain carboxyl groups, —COOH
Esters	Have the structure RCOOR'
Amides	Have the structure RCONHR'

Esters are formed from the reaction of carboxylic acids with alcohols. Amides are formed from the reaction of carboxylic acids with amines. In both cases, water is the other product formed.


Section  14.5Synthetic Polymers

The production of natural compounds from elements and other available compounds has long been the function of chemists. In organic chemistry, this process has been extended to the formation of molecules that have no duplicate in nature. Such molecules are called synthetic compounds. Synthetic compounds are produced by substituting replacement atoms into existing organic molecules, or by extending the structure of simple compounds called monomers into long chains called polymers.

The first synthetic compound developed in the laboratory was Bakelite. This was soon followed by synthetic rubber and then by other polymers that can be molded and hardened, which are known collectively as plastics. These compounds often have properties that far exceed those of naturally occurring materials in strength, heat dissipation, and ease of manufacturing. Plastics and other synthetics have become indispensable in our modern, technological world.

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