If C 12 H 24 reacts with HBr in an addition reaction, what is the molecular formula of the product? Alkenes undergo addition reactions; alkanes do not. Both burn. A polymer is as different from its monomer as a long strand of spaghetti is from a tiny speck of flour. For example, polyethylene, the familiar waxy material used to make plastic bags, is made from the monomer ethylene—a gas.
The bond lines extending at the ends in the formula of the product indicate that the structure extends for many units in each direction. Notice that all the atoms—two carbon atoms and four hydrogen atoms—of each monomer molecule are incorporated into the polymer structure.
Because displays such as the one above are cumbersome, the polymerization is often abbreviated as follows:. Many natural materials—such as proteins, cellulose and starch, and complex silicate minerals—are polymers. Artificial fibers, films, plastics, semisolid resins, and rubbers are also polymers. More than half the compounds produced by the chemical industry are synthetic polymers. Some common addition polymers are listed in Table 1.
Note that all the monomers have carbon-to-carbon double bonds. Many polymers are mundane e. An interesting use of polymers is the replacement of diseased, worn out, or missing parts in the body.
For example, about a , hip joints and , knees are replaced in US hospitals each year. The artificial ball-and-socket hip joints are made of a special steel the ball and plastic the socket. People crippled by arthritis or injuries gain freedom of movement and relief from pain. Patients with heart and circulatory problems can be helped by replacing worn out heart valves with parts based on synthetic polymers.
These are only a few of the many biomedical uses of polymers. Synthetic polymers are an important part of a hip joint replacement. The hip is much like a ball-and-socket joint, and total hip replacements mimic this with a metal ball that fits in a plastic cup. What is a monomer? What is a polymer? How do polymer molecules differ from the molecules we have discussed in earlier sections of this chapter?
What is addition polymerization? What structural feature usually characterizes molecules used as monomers in addition polymerization? Monomers are small molecules that can be assembled into giant molecules referred to as polymers, which are much larger than the molecules we discussed earlier in this chapter. In addition polymerization, the monomers add to one another in such a way that the polymer contains all the atoms of the starting monomers.
C H Cl Write the condensed structural formula of the monomer from which Saran is formed. The simplest alkyne—a hydrocarbon with carbon-to-carbon triple bond—has the molecular formula C 2 H 2 and is known by its common name—acetylene Figure 1. Acetylene is used in oxyacetylene torches for cutting and welding metals. The flame from such a torch can be very hot. Most acetylene, however, is converted to chemical intermediates that are used to make vinyl and acrylic plastics, fibers, resins, and a variety of other products.
Alkynes are similar to alkenes in both physical and chemical properties. For example, alkynes undergo many of the typical addition reactions of alkenes. The names of other alkynes are illustrated in the following exercises. Briefly identify the important differences between an alkene and an alkyne. How are they similar? Alkenes have double bonds; alkynes have triple bonds. Both undergo addition reactions. No; a triply bonded carbon atom can form only one other bond.
It would have to have two groups attached to show cis-trans isomerism. Next we consider a class of hydrocarbons with molecular formulas like those of unsaturated hydrocarbons, but which, unlike the alkenes, do not readily undergo addition reactions. These compounds comprise a distinct class, called aromatic hydrocarbons , with unique structures and properties. We start with the simplest of these compounds. The formula C 6 H 6 seems to indicate that benzene has a high degree of unsaturation.
Hexane, the saturated hydrocarbon with six carbon atoms has the formula C 6 H 14 —eight more hydrogen atoms than benzene. However, despite the seeming low level of saturation, benzene is rather unreactive. It does not, for example, react readily with bromine, which, as mentioned in Section 1. It is the aromatic hydrocarbon produced in the largest volume. It was formerly used to decaffeinate coffee and was a significant component of many consumer products, such as paint strippers, rubber cements, and home dry-cleaning spot removers.
It was removed from many product formulations in the s, but others continued to use benzene in products until the s when it was associated with leukemia deaths. Benzene is still important in industry as a precursor in the production of plastics such as Styrofoam and nylon , drugs, detergents, synthetic rubber, pesticides, and dyes.
It is used as a solvent for such things as cleaning and maintaining printing equipment and for adhesives such as those used to attach soles to shoes.
Benzene is a natural constituent of petroleum products, but because it is a known carcinogen, its use as an additive in gasoline is now limited. To explain the surprising properties of benzene, chemists suppose the molecule has a cyclic, hexagonal, planar structure of six carbon atoms with one hydrogen atom bonded to each. We can write a structure with alternate single and double bonds, either as a full structural formula or as a line-angle formula:.
However, these structures do not explain the unique properties of benzene. Furthermore, experimental evidence indicates that all the carbon-to-carbon bonds in benzene are equivalent, and the molecule is unusually stable. Chemists often represent benzene as a hexagon with an inscribed circle:. The inner circle indicates that the valence electrons are shared equally by all six carbon atoms that is, the electrons are delocalized , or spread out, over all the carbon atoms.
It is understood that each corner of the hexagon is occupied by one carbon atom, and each carbon atom has one hydrogen atom attached to it. Any other atom or groups of atoms substituted for a hydrogen atom must be shown bonded to a particular corner of the hexagon.
We use this modern symbolism, but many scientists still use the earlier structure with alternate double and single bonds.
Most of the benzene used commercially comes from petroleum. It is employed as a starting material for the production of detergents, drugs, dyes, insecticides, and plastics. Once widely used as an organic solvent, benzene is now known to have both short- and long-term toxic effects.
The inhalation of large concentrations can cause nausea and even death due to respiratory or heart failure, while repeated exposure leads to a progressive disease in which the ability of the bone marrow to make new blood cells is eventually destroyed.
This results in a condition called aplastic anemia , in which there is a decrease in the numbers of both the red and white blood cells.
How do the typical reactions of benzene differ from those of the alkenes? Benzene is rather unreactive toward addition reactions compared to an alkene. Valence electrons are shared equally by all six carbon atoms that is, the electrons are delocalized. The six electrons are shared equally by all six carbon atoms. Draw the structure of benzene as if it had alternate single and double bonds. Draw the structure of benzene as chemists usually represent it today.
Historically, benzene-like substances were called aromatic hydrocarbons because they had distinctive aromas. Today, an aromatic compound is any compound that contains a benzene ring or has certain benzene-like properties but not necessarily a strong aroma. You can recognize the aromatic compounds in this text by the presence of one or more benzene rings in their structure. Some representative aromatic compounds and their uses are listed in Table 1.
In these structures, it is immaterial whether the single substituent is written at the top, side, or bottom of the ring: a hexagon is symmetrical, and therefore all positions are equivalent. These compounds are named in the usual way with the group that replaces a hydrogen atom named as a substituent group: Cl as chloro, Br as bromo, I as iodo, NO 2 as nitro, and CH 3 CH 2 as ethyl. Although some compounds are referred to exclusively by IUPAC names, some are more frequently denoted by common names, as is indicated in Table 1.
When there is more than one substituent, the corners of the hexagon are no longer equivalent, so we must designate the relative positions. There are three possible disubstituted benzenes, and we can use numbers to distinguish them Figure 1. We start numbering at the carbon atom to which one of the groups is attached and count toward the carbon atom that bears the other substituent group by the shortest path. In Figure 1. The substituent names are listed in alphabetical order.
The first substituent is given the lowest number. When a common name is used, the carbon atom that bears the group responsible for the name is given the number The nitro NO 2 group is a common substituent in aromatic compounds. Many nitro compounds are explosive, most notably 2,4,6-trinitrotoluene TNT.
Sometimes an aromatic group is found as a substituent bonded to a nonaromatic entity or to another aromatic ring. The group of atoms remaining when a hydrogen atom is removed from an aromatic compound is called an aryl group.
The most common aryl group is derived from benzene C 6 H 6 by removing one hydrogen atom C 6 H 5 and is called a phenyl group, from pheno , an old name for benzene. Some common aromatic hydrocarbons consist of fused benzene rings—rings that share a common side.
These compounds are called polycyclic aromatic hydrocarbons PAHs. The three examples shown here are colorless, crystalline solids generally obtained from coal tar.
Naphthalene has a pungent odor and is used in mothballs. Anthracene is used in the manufacture of certain dyes. Steroids, a large group of naturally occurring substances, contain the phenanthrene structure. For more information about steroids, see Chapter 7 "Lipids", Section 7.
The intense heating required for distilling coal tar results in the formation of PAHs. For many years, it has been known that workers in coal-tar refineries are susceptible to a type of skin cancer known as tar cancer.
Investigations have shown that a number of PAHs are carcinogens. One of the most active carcinogenic compounds, benzopyrene, occurs in coal tar and has also been isolated from cigarette smoke, automobile exhaust gases, and charcoal-broiled steaks.
It is estimated that more than 1, t of benzopyrene are emitted into the air over the United States each year. Only a few milligrams of benzopyrene per kilogram of body weight are required to induce cancer in experimental animals. Substances containing the benzene ring are common in both animals and plants, although they are more abundant in the latter.
Plants can synthesize the benzene ring from carbon dioxide, water, and inorganic materials. Animals cannot synthesize it, but they are dependent on certain aromatic compounds for survival and therefore must obtain them from food.
Phenylalanine, tyrosine, and tryptophan essential amino acids and vitamins K, B 2 riboflavin , and B 9 folic acid all contain the benzene ring. For more information about vitamins, see Chapter 9 "Proteins, and Enzymes", Section 9. Many important drugs, a few of which are shown in Table 1. So far we have studied only aromatic compounds with carbon-containing rings. However, many cyclic compounds have an element other than carbon atoms in the ring. These compounds, called heterocyclic compounds , are discussed in Chapter 5 "Amines and Amides", Section 5.
Some of these are heterocyclic aromatic compounds. Briefly identify the important characteristics of an aromatic compound. What is meant by the prefixes meta , ortho , or para? Give the name and draw the structure for a compound that illustrates each. What is a phenyl group? Give the structure for 3-phenyloctane. An aromatic compound is any compound that contains a benzene ring or has certain benzene-like properties.
To ensure that you understand the material in this unit, you should review the meanings of the bold terms in the following summary and ask yourself how they relate to the topics in the unit. Any hydrocarbon containing either a double or triple bond is an unsaturated hydrocarbon. Alkenes have a carbon-to-carbon double bond. The general formula for alkenes with one double bond is C n H 2 n. Alkenes can be straight chain, branched chain, or cyclic. Simple alkenes often have common names, but all alkenes can be named by the system of the International Union of Pure and Applied Chemistry.
Cis-trans isomers or geometric isomers are characterized by molecules that differ only in their configuration around a rigid part of the structure, such as a carbon—to-carbon double bond or a ring. The molecule having two identical or closely related atoms or groups on the same side is the cis isomer ; the one having the two groups on opposite sides is the trans isomer.
The physical properties of alkenes are quite similar to those of alkanes. Like other hydrocarbons, alkenes are insoluble in water but soluble in organic solvents.
More reactive than alkanes, alkenes undergo addition reactions across the double bond:. Alkenes also undergo addition polymerization , molecules joining together to form long-chain molecules.
The reactant units are monomers , and the product is a polymer. Alkynes have a carbon-to-carbon triple bond. The properties of alkynes are quite similar to those of alkenes. They are named much like alkenes but with the ending - yne. The cyclic hydrocarbon benzene C 6 H 6 has a ring of carbon atoms. The molecule seems to be unsaturated, but it does not undergo the typical reactions expected of alkenes.
The electrons that might be fixed in three double bonds are instead delocalized over all six carbon atoms. A hydrocarbon containing one or more benzene rings or other similarly stable electron arrangements is an aromatic hydrocarbon , and any related substance is an aromatic compound.
One or more of the hydrogen atoms on a benzene ring can be replaced by other atoms. When two hydrogen atoms are replaced, the product name is based on the relative position of the replacement atoms or atom groups.
A 1,2-disubstituted benzene is designated as an ortho o - isomer; 1,3-, a meta m - isomer; and 1,4-, a para p - isomer. An aromatic group as a substituent is called an aryl group. A polycyclic aromatic hydrocarbon PAH has fused benzene rings sharing a common side. When three isomeric pentenes—X, Y, and Z—are hydrogenated, all three form 2-methylbutane. The addition of Cl 2 to Y gives 1,2-dichloromethylbutane, and the addition of Cl 2 to Z gives 1,2-dichloromethylbutane.
Draw the original structures for X, Y, and Z. Pentane and 1-pentene are both colorless, low-boiling liquids. Describe a simple test that distinguishes the two compounds. Indicate what you would observe. Draw and name all the alkene cis-trans isomers corresponding to the molecular formula C 5 H Hint: there are only two. Balance the equation.
What mass, in grams, of carbon dioxide is formed by the complete combustion of Draw the structure and give the correct name for each compound. Following are line-angle formulas for three compounds. Draw the structure and give the name for each. Following are ball-and-stick molecular models for three compounds blue balls represent H atoms; red balls are C atoms. Write the condensed structural formula and give the name for each.
Add bromine solution reddish-brown to each. Pentane will not react, and the reddish-brown color persists; 1-pentene will react, leaving a colorless solution. It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge.
If you continue with this browser, you may see unexpected results. Ball, John W. Hill, and Rhonda J. How to print this page To print this page: Click on the printer icon at the bottom of the screen Is your printout incomplete? Opening Essay Hydrocarbons are the simplest organic compounds, but they have interesting physiological effects.
Note The word organic has different meanings. Concept Review Exercises Classify each compound as organic or inorganic. Answers organic inorganic inorganic organic. Key Takeaway Organic chemistry is the study of carbon compounds, nearly all of which also contain hydrogen atoms.
Exercises Classify each compound as organic or inorganic. Classify each compound as organic or inorganic. Which member of each pair has a higher melting point? Concept Review Exercises In the homologous series of alkanes, what is the molecular formula for the member just above C 8 H 18? Answers C 9 H Key Takeaway Simple alkanes exist as a homologous series, in which adjacent members differ by a CH 2 unit.
Exercises What compounds contain fewer carbon atoms than C 3 H 8 and are its homologs? Note A continuous unbranched chain of carbon atoms is often called a straight chain even though the tetrahedral arrangement about each carbon gives it a zigzag shape.
Concept Review Exercises In alkanes, can there be a two-carbon branch off the second carbon atom of a four-carbon chain? Answers No; the branch would make the longest continuous chain of five carbon atoms. No; both are five-carbon continuous chains. Key Takeaway Alkanes with four or more carbon atoms can exist in isomeric forms. Exercises Briefly identify the important distinctions between a straight-chain alkane and a branched-chain alkane. Write the structural formula for each compound. Draw line-angle formulas given structural formulas.
Note Parentheses in condensed structural formulas indicate that the enclosed grouping of atoms is attached to the adjacent carbon atom. Key Takeaways Condensed chemical formulas show the hydrogen atoms or other atoms or groups right next to the carbon atoms to which they are attached. Line-angle formulas imply a carbon atom at the corners and ends of lines. Exercises Write the condensed structural formula for each structural formula. Stem Number meth- 1 eth- 2 prop- 3 but- 4 pent- 5 hex- 6 hept- 7 oct- 8 non- 9 dec- Example 1 Name each compound.
Skill-Building Exercise Name each compound. Example 2 Draw the structure for each compound. The parent chain is butane, indicating four carbon atoms in the LCC. Skill-Building Exercise Draw the structure for each compound. Concept Review Exercises What is a CH 3 group called when it is attached to a chain of carbon atoms—a substituent or a functional group? Answers substituent. Exercises Briefly identify the important distinctions between an alkane and an alkyl group.
How many carbon atoms are present in each molecule? Draw the structure for each compound. Answers 1. Looking Closer: An Alkane Basis for Properties of Other Compounds An understanding of the physical properties of the alkanes is important in that petroleum and natural gas and the many products derived from them—gasoline, bottled gas, solvents, plastics, and more—are composed primarily of alkanes.
Concept Review Exercises Without referring to a table, predict which has a higher boiling point—hexane or octane. Hexane would dissolve in water. Hexane would not dissolve in water and would float on top. Answers octane because of its greater molar mass. Key Takeaway Alkanes are nonpolar compounds that are low boiling and insoluble in water. Exercises Without referring to a table or other reference, predict which member of each pair has the higher boiling point.
For which member of each pair is hexane a good solvent? Concept Review Exercises Why are alkanes sometimes called paraffins? Answers Alkanes do not react with many common chemicals. Key Takeaway Alkanes react with oxygen combustion and with halogens halogenation. Exercises Why do alkanes usually not react with ionic compounds such as most laboratory acids, bases, oxidizing agents, or reducing agents?
What is the most important reaction of alkanes? The common name is therefore propyl bromide. For the IUPAC name, the prefix for bromine bromo is combined with the name for a three-carbon chain propane , preceded by a number identifying the carbon atom to which the Br atom is attached, so the IUPAC name is 1-bromopropane.
The alkyl group [ CH 3 2 CH—] has three carbon atoms, with a chlorine Cl atom attached to the middle carbon atom. The alkyl group is therefore isopropyl, and the common name of the compound is isopropyl chloride. For the IUPAC name, the Cl atom prefix chloro - attached to the middle second carbon atom of a propane chain results in 2-chloropropane. To Your Health: Halogenated Hydrocarbons Once widely used in consumer products, many chlorinated hydrocarbons are suspected carcinogens cancer-causing substances and also are known to cause severe liver damage.
To Your Health: Chlorofluorocarbons and the Ozone Layer Alkanes substituted with both fluorine F and chlorine Cl atoms have been used as the dispersing gases in aerosol cans, as foaming agents for plastics, and as refrigerants. Answers 1,1,1,2-tetrafluoroethane. Key Takeaway The replacement of an hydrogen atom on an alkane by a halogen atom—F, Cl, Br, or I—forms a halogenated compound.
Exercises Write the condensed structural formula for each compound. Example 5 Draw the structure for each compound. Concept Review Exercises What is the molecular formula of cyclooctane? Answers C 8 H Key Takeaway Many organic compounds have cyclic structures.
Exercises Draw the structure for each compound. What is the danger in swallowing a liquid alkane? Which pair of formulas represents isomers? Draw each structure. Which formula represents an alkyl halide?
Name the compound and write its condensed structural formula. Which formula represents a cyclic alkane? The main source of these liquid alkane fuels is crude oil, a complex mixture that is separated by fractional distillation. Fractional distillation takes advantage of differences in the boiling points of the components of the mixture see Figure 5. You may recall that boiling point is a function of intermolecular interactions, which was discussed in the chapter on solutions and colloids.
No carbon-carbon bonds are broken in these reactions, and the hybridization of the carbon atoms does not change. For example, the reaction between ethane and molecular chlorine depicted here is a substitution reaction:. The C—Cl portion of the chloroethane molecule is an example of a functional group , the part or moiety of a molecule that imparts a specific chemical reactivity.
The types of functional groups present in an organic molecule are major determinants of its chemical properties and are used as a means of classifying organic compounds as detailed in the remaining sections of this chapter. Want more practice naming alkanes? Watch this brief video tutorial to review the nomenclature process. Organic compounds that contain one or more double or triple bonds between carbon atoms are described as unsaturated.
You have likely heard of unsaturated fats. These are complex organic molecules with long chains of carbon atoms, which contain at least one double bond between carbon atoms. Unsaturated hydrocarbon molecules that contain one or more double bonds are called alkenes. Double and triple bonds give rise to a different geometry around the carbon atom that participates in them, leading to important differences in molecular shape and properties. The differing geometries are responsible for the different properties of unsaturated versus saturated fats.
Ethene, C 2 H 4 , is the simplest alkene. Each carbon atom in ethene, commonly called ethylene, has a trigonal planar structure. The second member of the series is propene propylene Figure 6 ; the butene isomers follow in the series.
Four carbon atoms in the chain of butene allows for the formation of isomers based on the position of the double bond, as well as a new form of isomerism. Ethylene the common industrial name for ethene is a basic raw material in the production of polyethylene and other important compounds.
Over million tons of ethylene were produced worldwide in for use in the polymer, petrochemical, and plastic industries. Ethylene is produced industrially in a process called cracking, in which the long hydrocarbon chains in a petroleum mixture are broken into smaller molecules.
Polymers can be natural starch is a polymer of sugar residues and proteins are polymers of amino acids or synthetic [like polyethylene, polyvinyl chloride PVC , and polystyrene].
The variety of structures of polymers translates into a broad range of properties and uses that make them integral parts of our everyday lives. Adding functional groups to the structure of a polymer can result in significantly different properties see the discussion about Kevlar later in this chapter. An example of a polymerization reaction is shown in Figure 7. The monomer ethylene C 2 H 4 is a gas at room temperature, but when polymerized, using a transition metal catalyst, it is transformed into a solid material made up of long chains of —CH 2 — units called polyethylene.
Polyethylene is a commodity plastic used primarily for packaging bags and films. Polyethylene is a member of one subset of synthetic polymers classified as plastics. Plastics are synthetic organic solids that can be molded; they are typically organic polymers with high molecular masses. Most of the monomers that go into common plastics ethylene, propylene, vinyl chloride, styrene, and ethylene terephthalate are derived from petrochemicals and are not very biodegradable, making them candidate materials for recycling.
Recycling plastics helps minimize the need for using more of the petrochemical supplies and also minimizes the environmental damage caused by throwing away these nonbiodegradable materials. Plastic recycling is the process of recovering waste, scrap, or used plastics, and reprocessing the material into useful products. For example, polyethylene terephthalate soft drink bottles can be melted down and used for plastic furniture, in carpets, or for other applications. Other plastics, like polyethylene bags and polypropylene cups, plastic food containers , can be recycled or reprocessed to be used again.
Many areas of the country have recycling programs that focus on one or more of the commodity plastics that have been assigned a recycling code see Figure 8. These operations have been in effect since the s and have made the production of some plastics among the most efficient industrial operations today. The name of an alkene is derived from the name of the alkane with the same number of carbon atoms. The presence of the double bond is signified by replacing the suffix -ane with the suffix -ene.
The location of the double bond is identified by naming the smaller of the numbers of the carbon atoms participating in the double bond:. Molecules of 1-butene and 2-butene are structural isomers; the arrangement of the atoms in these two molecules differs. As an example of arrangement differences, the first carbon atom in 1-butene is bonded to two hydrogen atoms; the first carbon atom in 2-butene is bonded to three hydrogen atoms.
The compound 2-butene and some other alkenes also form a second type of isomer called a geometric isomer. In a set of geometric isomers, the same types of atoms are attached to each other in the same order, but the geometries of the two molecules differ. Carbon atoms are free to rotate around a single bond but not around a double bond; a double bond is rigid. This makes it possible to have two isomers of 2-butene, one with both methyl groups on the same side of the double bond and one with the methyl groups on opposite sides.
The 2-butene isomer in which the two methyl groups are on the same side is called a cis -isomer; the one in which the two methyl groups are on opposite sides is called a trans -isomer Figure 9. The different geometries produce different physical properties, such as boiling point, that may make separation of the isomers possible:.
This reaction is called an addition reaction. The hybridization of the carbon atoms in the double bond in an alkene changes from sp 2 to sp 3 during an addition reaction.
For example, halogens add to the double bond in an alkene instead of replacing hydrogen, as occurs in an alkane:. Solution The reactant is a five-carbon chain that contains a carbon-carbon double bond, so the base name will be pentene. We begin counting at the end of the chain closest to the double bond—in this case, from the left—the double bond spans carbons 2 and 3, so the name becomes 2-pentene.
Since there are two carbon-containing groups attached to the two carbon atoms in the double bond—and they are on the same side of the double bond—this molecule is the cis- isomer, making the name of the starting alkene cis pentene.
The product of the halogenation reaction will have two chlorine atoms attached to the carbon atoms that were a part of the carbon-carbon double bond:.
This molecule is now a substituted alkane and will be named as such. The base of the name will be pentane. We will count from the end that numbers the carbon atoms where the chlorine atoms are attached as 2 and 3, making the name of the product 2,3-dichloropentane. Check Your Learning Provide names for the reactant and product of the reaction shown:. Hydrocarbon molecules with one or more triple bonds are called alkynes ; they make up another series of unsaturated hydrocarbons.
The simplest member of the alkyne series is ethyne, C 2 H 2 , commonly called acetylene. The Lewis structure for ethyne, a linear molecule, is:. The IUPAC nomenclature for alkynes is similar to that for alkenes except that the suffix -yne is used to indicate a triple bond in the chain. Structure of Alkynes Describe the geometry and hybridization of the carbon atoms in the following molecule:. Solution Carbon atoms 1 and 4 have four single bonds and are thus tetrahedral with sp 3 hybridization.
Carbon atoms 2 and 3 are involved in the triple bond, so they have linear geometries and would be classified as sp hybrids. Check Your Learning Identify the hybridization and bond angles at the carbon atoms in the molecule shown:. Chemically, the alkynes are similar to the alkenes.
The reaction of acetylene with bromine is a typical example:. Acetylene and the other alkynes also burn readily. An acetylene torch takes advantage of the high heat of combustion for acetylene.
Benzene, C 6 H 6 , is the simplest member of a large family of hydrocarbons, called aromatic hydrocarbons. These compounds contain ring structures and exhibit bonding that must be described using the resonance hybrid concept of valence bond theory or the delocalization concept of molecular orbital theory.
To review these concepts, refer to the earlier chapters on chemical bonding. The resonance structures for benzene, C 6 H 6 , are:.
Valence bond theory describes the benzene molecule and other planar aromatic hydrocarbon molecules as hexagonal rings of sp 2 -hybridized carbon atoms with the unhybridized p orbital of each carbon atom perpendicular to the plane of the ring. Benzene does not, however, exhibit the characteristics typical of an alkene. To represent this unique bonding, structural formulas for benzene and its derivatives are typically drawn with single bonds between the carbon atoms and a circle within the ring as shown in Figure There are many derivatives of benzene.
The hydrogen atoms can be replaced by many different substituents. Aromatic compounds more readily undergo substitution reactions than addition reactions; replacement of one of the hydrogen atoms with another substituent will leave the delocalized double bonds intact. The following are typical examples of substituted benzene derivatives:. C8H14 4. Which formula represents an unsaturated hydrocarbon is a saturated hydrocarbon let Of these hydrocarbons does not have isomers which is a chemical which formula represents an unsaturated hydrocarbon of this?.
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