Which is the condensed structure of a straight chain hydrocarbon

DDT was widely used to kill mosquitoes that spread malaria, and was also effective against the insects that spread sleeping sickness and typhus. Unfortunately, DDT persists in the environment for a long time, and its accumulation in wildlife lead to decreases in the populations of several bird species. It is used in some shampoos to kill lice and other ectoparasites. However, it is a suspected carcinogen, and is banned in California, and several countries.

Chlordane 3D Download 3D Chlordane was used as a pesticide on some crops, and was also used to kill termites. Because of concerns about its toxicity, it was banned by the EPA in Atkins, Molecules , 2nd ed. Cambridge: Cambridge University Press, , p. Paula Yurkanis Bruice, Organic Chemistry , 4th ed. Upper Saddle River: Prentice Hall, , p. Marye Anne Fox and James K. Whitesell, Organic Chemistry , 3rd ed. Sudbury: Jones and Bartlett Publishers, p.

Maitland Jones, Jr. New York: W. Richard J. Lewis, Sr. New York: Van Nostrand Reinhold, Marc Loudon, Organic Chemistry , 4th ed. New York: Oxford University Press, , p.

Englewood Cliffs: Prentice Hall, , p. Sharp, The Penguin Dictionary of Chemistry , 2nd ed. London: Penguin Books, Truman Schwartz, Diane M. Bunce, Robert G. Silberman, Conrad L. Stanitski, Wilmer J. Stratton, and Arden P. Dubuque: Wm. Brown Communicatiions, Inc. Wade, Jr. Martha Windholz ed. Number of Carbons Stem 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec-.

There are five structural isomers of C 6 H 14 : Using common or non-systematic names is not practical for molecules with a large number of carbon atoms, since it would be necessary to memorize unique names for each possible compound.

Table 1. This molecule is often found on traffic signs: well, maybe not Cyclononane C 9 H 18 3D Download 3D Cyclononane is a ring of nine carbon atoms. The oxygen atoms combine with oxygen molecules to make ozone: This ozone that is produced from this reaction absorbs ultraviolet light with wavelengths of nm or less, splitting into oxygen molecules and oxygen atoms, which then re-combine to form ozone, which can absorb another photon of ultraviolet light.

When a molecule of Freon drifts into the upper atmosphere, photons of high-energy light can strike it, causing it to release a chlorine atom: The chlorine atom has an unpaired electron, and is a highly reactive free radical , which reacts with ozone in the stratosphere, converting it to molecular oxygen: The chlorine atom is regenerated in this process, and behaves as a catalyst; one chlorine atom can destroy up to , ozone molecules. Bromochlorodifluoromethane Halon 3D Download 3D Bromochlorodifluoromethane Halon is an example of a halon , a haloalkane that has bromine atoms in addition to chlorine and fluorine atoms.

Navigation Bar. Molecule Gallery. Methane , CH 4. Download 3D. Ethane is an odorless, nontoxic, flammable gas, which has a boiling point of Propane is used as an industrial fuel, and in home heating and cooking. Butane , like propane, burns cleanly, and is used in LPG fuels liquefied petroleum gas for outdoor cooking. Butane is an unbranched or "normal" alkane. Pentane is a liquid at room temperature, having a boiling point of Hexane has a boiling point of Heptane has a boiling point of Octane has a boiling point of Isooctane is a structural isomer of octane both are C 8 H 18 , but is branched compare with butane and isobutane.

Nonane has a boiling point of Decane has a boiling point of Hexadecane is typical for the number of carbons in the hydrocarbons present in diesel fuel.

S ummary of the Straight-Chain Alkanes. Cyclopropane C 3 H 6. Because free rotation is not possible around the single bonds in a cycloalkane, when two methyl groups are added to cyclopropane, there are two possible arrangements: both methyl groups can be pointing to the same side of the ring cis , or to opposite sides of the ring trans :.

These molecules are not structural isomers of each other, because the order in which the atoms are connected is the same, but the two methyl groups are pointing in different directions in space, making them stereoisomers of each other. Cyclobutane C 4 H 8. Cyclopentane C 5 H Cyclohexane C 6 H With cyclohexane, ring chemistry gets even more interesting and complicated. There are still a number of C—H eclipsing interactions, however, and this is not the lowest-energy conformation which is possible.

This is drastically oversimplified, of course; the chair and boat conformation represent the extremes of a large number of possible intermediate conformations, and the energetics of the ring system change a great deal when substituents are added to the ring. Cycloheptane C 7 H There is a slight amount of strain energy in cycloheptane and larger cycloalkanes, since it is difficult for them to adopt bond angles of Cyclooctane C 8 H Cyclooctane is a ring of eight carbon atoms.

This molecule is often found on traffic signs: well, maybe not. Cyclononane C 9 H Cyclodecane C 10 H Decalin C 10 H Decalin , or bicyclo[4. Norbornane , bicyclo[2. 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:.

Toluene and xylene are important solvents and raw materials in the chemical industry. Styrene is used to produce the polymer polystyrene. Structure of Aromatic Hydrocarbons One possible isomer created by a substitution reaction that replaces a hydrogen atom attached to the aromatic ring of toluene with a chlorine atom is shown here.

Draw two other possible isomers in which the chlorine atom replaces a different hydrogen atom attached to the aromatic ring:. Solution Since the six-carbon ring with alternating double bonds is necessary for the molecule to be classified as aromatic, appropriate isomers can be produced only by changing the positions of the chloro-substituent relative to the methyl-substituent:.

Check Your Learning Draw three isomers of a six-membered aromatic ring compound substituted with two bromines. Strong, stable bonds between carbon atoms produce complex molecules containing chains, branches, and rings. The chemistry of these compounds is called organic chemistry. Hydrocarbons are organic compounds composed of only carbon and hydrogen. The alkanes are saturated hydrocarbons—that is, hydrocarbons that contain only single bonds. Alkenes contain one or more carbon-carbon double bonds.

Alkynes contain one or more carbon-carbon triple bonds. Draw Lewis structures for these compounds, with resonance structures as appropriate, and determine the hybridization of the carbon atoms in each.

Write the formula of the compound showing the acetylide ion. How many kilograms of ethylene is produced by the pyrolysis of 1. Both reactions result in bromine being incorporated into the structure of the product. The difference is the way in which that incorporation takes place. In the saturated hydrocarbon, an existing C—H bond is broken, and a bond between the C and the Br can then be formed.

Note that the bonds dashes can be shown or not; sometimes they are needed for spacing. What is a CH 3 group called when it is attached to a chain of carbon atoms—a substituent or a functional group? Briefly identify the important distinctions between an alkane and an alkyl group.

What is a substituent? An alkane is a molecule; an alkyl group is not an independent molecule but rather a part of a molecule that we consider as a unit. Common names are widely used but not very systematic; IUPAC names identify a parent compound and name other groups as substituents. Because alkanes have relatively predictable physical properties and undergo relatively few chemical reactions other than combustion, they serve as a basis of comparison for the properties of many other organic compound families.

Because alkane molecules are nonpolar, they are insoluble in water, which is a polar solvent, but are soluble in nonpolar and slightly polar solvents. Consequently, alkanes themselves are commonly used as solvents for organic substances of low polarity, such as fats, oils, and waxes. Nearly all alkanes have densities less than 1. These properties explain why oil and grease do not mix with water but rather float on its surface.

Gas densities are at 1 atm pressure. The leak was a mile below the surface, making it difficult to estimate the size of the spill. One liter of oil can create a slick 2. Natural gas is composed chiefly of methane, which has a density of about 0.

The density of air is about 1. Because natural gas is less dense than air, it rises. When a natural-gas leak is detected and shut off in a room, the gas can be removed by opening an upper window. On the other hand, bottled gas can be either propane density 1. Both are much heavier than air density 1. If bottled gas escapes into a building, it collects near the floor. This presents a much more serious fire hazard than a natural-gas leak because it is more difficult to rid the room of the heavier gas.

As shown in Table 1. This general rule holds true for the straight-chain homologs of all organic compound families. Larger molecules have greater surface areas and consequently interact more strongly; more energy is therefore required to separate them. For a given molar mass, the boiling points of alkanes are relatively low because these nonpolar molecules have only weak dispersion forces to hold them together in the liquid state. 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.

This understanding is also vital because it is the basis for describing the properties of other organic and biological compound families. For example, large portions of the structures of lipids consist of nonpolar alkyl groups.

Lipids include the dietary fats and fatlike compounds called phospholipids and sphingolipids that serve as structural components of living tissues.

For more information about lipids, see Chapter 7 "Lipids". These compounds have both polar and nonpolar groups, enabling them to bridge the gap between water-soluble and water-insoluble phases. This characteristic is essential for the selective permeability of cell membranes.

Tripalmitin a , a typical fat molecule, has long hydrocarbon chains typical of most lipids. Compare these chains to hexadecane b , an alkane with 16 carbon atoms. Without referring to a table, predict which has a higher boiling point—hexane or octane.

If 25 mL of hexane were added to mL of water in a beaker, which of the following would you expect to happen? Hexane would not dissolve in water and would sink to the bottom of the container. Without referring to a table or other reference, predict which member of each pair has the higher boiling point. Alkane molecules are nonpolar and therefore generally do not react with ionic compounds such as most laboratory acids, bases, oxidizing agents, or reducing agents.

Consider butane as an example:. Neither positive ions nor negative ions are attracted to a nonpolar molecule. Two important reactions that the alkanes do undergo are combustion and halogenation. Nothing happens when alkanes are merely mixed with oxygen O 2 at room temperature, but when a flame or spark provides the activation energy, a highly exothermic combustion reaction proceeds vigorously.

For methane CH 4 , the reaction is as follows:. If the reactants are adequately mixed and there is sufficient oxygen, the only products are carbon dioxide CO 2 , water H 2 O , and heat—heat for cooking foods, heating homes, and drying clothes. Because conditions are rarely ideal, however, other products are frequently formed.

When the oxygen supply is limited, carbon monoxide CO is a by-product:. This reaction is responsible for dozens of deaths each year from unventilated or improperly adjusted gas heaters. Similar reactions with similar results occur with kerosene heaters. Alkanes also react with the halogens chlorine Cl 2 and bromine Br 2 in the presence of ultraviolet light or at high temperatures to yield chlorinated and brominated alkanes.

Fluorine F 2 , the lightest halogen, combines explosively with most hydrocarbons. Iodine I 2 is relatively unreactive. Fluorinated and iodinated alkanes are produced by indirect methods. We will discuss the names and uses of halogenated hydrocarbons in Section 1. Which halogen reacts most readily with alkanes?

Which reacts least readily? Alkanes do not react with many common chemicals. Why do alkanes usually not react with ionic compounds such as most laboratory acids, bases, oxidizing agents, or reducing agents? Write an equation for the complete combustion of methane CH 4 , the main component of natural gas. Name some substances other than oxygen that react readily with alkanes. Many organic compounds are closely related to the alkanes.

As we noted in Section 1. Even more closely related are the cycloalkanes, compounds in which the carbon atoms are joined in a ring, or cyclic fashion. The reactions of alkanes with halogens produce halogenated hydrocarbons , compounds in which one or more hydrogen atoms of a hydrocarbon have been replaced by halogen atoms:.

The replacement of only one hydrogen atom gives an alkyl halide or haloalkane. The common names of alkyl halides consist of two parts: the name of the alkyl group plus the stem of the name of the halogen, with the ending -ide. The prefixes are fluoro -, chloro -, bromo-, and iodo -. Alkyl halides with simple alkyl groups one to four carbon atoms are often called by common names. A wide variety of interesting and often useful compounds have one or more halogen atoms per molecule.

For example, methane CH 4 can react with chlorine Cl 2 , replacing one, two, three, or all four hydrogen atoms with Cl atoms. Once widely used in consumer products, many chlorinated hydrocarbons are suspected carcinogens cancer-causing substances and also are known to cause severe liver damage.

An example is carbon tetrachloride CCl 4 , once used as a dry-cleaning solvent and in fire extinguishers but no longer recommended for either use. Even in small amounts, its vapor can cause serious illness if exposure is prolonged. Moreover, it reacts with water at high temperatures to form deadly phosgene COCl 2 gas, which makes the use of CCl 4 in fire extinguishers particularly dangerous.

Ethyl chloride, in contrast, is used as an external local anesthetic. When sprayed on the skin, it evaporates quickly, cooling the area enough to make it insensitive to pain. It can also be used as an emergency general anesthetic. Bromine-containing compounds are widely used in fire extinguishers and as fire retardants on clothing and other materials.

Because they too are toxic and have adverse effects on the environment, scientists are engaged in designing safer substitutes for them, as for many other halogenated compounds. 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.

Two of the best known of these chlorofluorocarbons CFCs are listed in Table 1. Chlorofluorocarbons contribute to the greenhouse effect in the lower atmosphere.

They also diffuse into the stratosphere, where they are broken down by ultraviolet UV radiation to release Cl atoms. These in turn break down the ozone O 3 molecules that protect Earth from harmful UV radiation. Worldwide action has reduced the use of CFCs and related compounds. The CFCs and other Cl- or bromine Br -containing ozone-destroying compounds are being replaced with more benign substances. HCFC molecules break down more readily in the troposphere, and fewer ozone-destroying molecules reach the stratosphere.

They occur mainly over Antarctica from late August through early October and fill in about mid-November. Ozone depletion has also been noted over the Arctic regions. The largest ozone hole ever observed occurred on 24 September Hint: you must use a number to indicate the location of each substituent F atom. Write the condensed structural formula for each compound. Write the condensed structural formulas for the two isomers that have the molecular formula C 3 H 7 Br.

Write the condensed structural formulas for the four isomers that have the molecular formula C 4 H 9 Br. What is a CFC? How are CFCs involved in the destruction of the ozone layer? Explain why each compound is less destructive to the ozone layer than are CFCs. The hydrocarbons we have encountered so far have been composed of molecules with open-ended chains of carbon atoms.

When a chain contains three or more carbon atoms, the atoms can join to form ring or cyclic structures. The simplest of these cyclic hydrocarbons has the formula C 3 H 6. Each carbon atom has two hydrogen atoms attached Figure 1. It is also a potent, quick-acting anesthetic with few undesirable side effects in the body. It is no longer used in surgery, however, because it forms explosive mixtures with air at nearly all concentrations.

The cycloalkanes —cyclic hydrocarbons with only single bonds—are named by adding the prefix cyclo- to the name of the open-chain compound having the same number of carbon atoms as there are in the ring. Thus the name for the cyclic compound C 4 H 8 is cyclobutane. The carbon atoms in cyclic compounds can be represented by line-angle formulas that result in regular geometric figures.

Keep in mind, however, that each corner of the geometric figure represents a carbon atom plus as many hydrogen atoms as needed to give each carbon atom four bonds. Some cyclic compounds have substituent groups attached. Example 5 interprets the name of a cycloalkane with a single substituent group. The name cyclopentane indicates a cyclic cyclo alkane with five pent- carbon atoms. It can be represented as a pentagon.

The name methylcyclobutane indicates a cyclic alkane with four but- carbon atoms in the cyclic part. It can be represented as a square with a CH 3 group attached. The properties of cyclic hydrocarbons are generally quite similar to those of the corresponding open-chain compounds. So cycloalkanes with the exception of cyclopropane, which has a highly strained ring act very much like noncyclic alkanes.

Cyclic structures containing five or six carbon atoms, such as cyclopentane and cyclohexane, are particularly stable. We will see in Chapter 6 "Carbohydrates" that some carbohydrates sugars form five- or six-membered rings in solution. This strain is readily evident when you try to build a ball-and-stick model of cyclopropane; see Figure 1. Cyclopentane and cyclohexane rings have little strain because the C—C—C angles are near the preferred angles.

Cycloalkyl groups can be derived from cycloalkanes in the same way that alkyl groups are derived from alkanes. These groups are named as cyclopropyl, cyclobutyl, and so on.

Name each cycloalkyl halide. As with alkyl derivatives, monosubstituted derivatives need no number to indicate the position of the halogen. To name disubstituted derivatives, the carbon atoms are numbered starting at the position of one substituent C1 and proceeding to the second substituted atom by the shortest route. Name each compound. To ensure that you understand the material in this unit, you should review the meanings of the following bold terms in the summary and ask yourself how they relate to the topics in the unit.

Organic chemistry is the chemistry of carbon compounds, and inorganic chemistry is the chemistry of all the other elements. Carbon atoms can form stable covalent bonds with other carbon atoms and with atoms of other elements, and this property allows the formation the tens of millions of organic compounds. Hydrocarbons contain only hydrogen and carbon atoms. Hydrocarbons in which each carbon atom is bonded to four other atoms are called alkanes or saturated hydrocarbons.

Any given alkane differs from the next one in a series by a CH 2 unit. Any family of compounds in which adjacent members differ from each other by a definite factor is called a homologous series. Carbon atoms in alkanes can form straight chains or branched chains. Two or more compounds having the same molecular formula but different structural formulas are isomers of each other.

There are no isomeric forms for the three smallest alkanes; beginning with C 4 H 10 , all other alkanes have isomeric forms. A structural formula shows all the carbon and hydrogen atoms and how they are attached to one another. A condensed structural formula shows the hydrogen atoms right next to the carbon atoms to which they are attached. A line-angle formula is a formula in which carbon atoms are implied at the corners and ends of lines. Each carbon atom is understood to be attached to enough hydrogen atoms to give each carbon atom four bonds.

An alkyl group is a unit formed by removing one hydrogen atom from an alkane. The physical properties of alkanes reflect the fact that alkane molecules are nonpolar. Alkanes are insoluble in water and less dense than water.

Alkanes are generally unreactive toward laboratory acids, bases, oxidizing agents, and reducing agents. They do burn undergo combustion reactions. Alkanes react with halogens by substituting one or more halogen atoms for hydrogen atoms to form halogenated hydrocarbons. An alkyl halide haloalkane is a compound resulting from the replacement of a hydrogen atom of an alkane with a halogen atom.

Cycloalkanes are hydrocarbons whose molecules are closed rings rather than straight or branched chains. A cyclic hydrocarbon is a hydrocarbon with a ring of carbon atoms. It ignites readily and burns readily. The substance is insoluble in water and floats on the surface.

Is the substance likely to be organic or inorganic? Give the molecular formulas for methylcyclopentane, 2-methylpentane, and cyclohexane. Which are isomers? What is wrong with each name? Hint: first write the structure as if it were correct. Give the correct name for each compound.

Distinguish between lighter and heavier liquid alkanes in terms of their effects on the skin. Following is the line formula for an alkane. Draw its structure and give its name. Write equations for the complete combustion of each compound. The density of a gasoline sample is 0. On the basis of the complete combustion of octane, calculate the amount in grams of carbon dioxide CO 2 and water H 2 O formed per gallon 3.

Draw the structures for the five isomeric hexanes C 6 H Consider the line-angle formulas shown here and answer the questions. Two numbers are needed to indicate two substituents; 2,2-dimethylpropane. An ethyl substituent is not possible on the second carbon atom; 3,5-dimethylheptane.

A propyl substituent is not possible on the fifth carbon atom; 3,4,5-trimethyloctane. Our modern society is based to a large degree on the chemicals we discuss in this chapter. Most are made from petroleum. Earlier in this chapter we noted that alkanes—saturated hydrocarbons—have relatively few important chemical properties other than that they undergo combustion and react with halogens.

Unsaturated hydrocarbons—hydrocarbons with double or triple bonds—on the other hand, are quite reactive. In fact, they serve as building blocks for many familiar plastics—polyethylene, vinyl plastics, acrylics—and other important synthetic materials e. Aromatic hydrocarbons have formulas that can be drawn as cyclic alkenes, making them appear unsaturated, but their structure and properties are generally quite different, so they are not considered to be alkenes.

Aromatic compounds serve as the basis for many drugs, antiseptics, explosives, solvents, and plastics e. The two simplest unsaturated compounds—ethylene ethene and acetylene ethyne —were once used as anesthetics and were introduced to the medical field in However, it was discovered that acetylene forms explosive mixtures with air, so its medical use was abandoned in Ethylene was thought to be safer, but it too was implicated in numerous lethal fires and explosions during anesthesia.

Even so, it remained an important anesthetic into the s, when it was replaced by nonflammable anesthetics such as halothane CHBrClCF 3. Collectively, they are called unsaturated hydrocarbons because they have fewer hydrogen atoms than does an alkane with the same number of carbon atoms, as is indicated in the following general formulas:.

Some representative alkenes—their names, structures, and physical properties—are given in Table 1. We used only condensed structural formulas in Table 1. The double bond is shared by the two carbon atoms and does not involve the hydrogen atoms, although the condensed formula does not make this point obvious. Note that the molecular formula for ethene is C 2 H 4 , whereas that for ethane is C 2 H 6. The first two alkenes in Table 1.

Ethylene is a major commercial chemical. The US chemical industry produces about 25 billion kilograms of ethylene annually, more than any other synthetic organic chemical. More than half of this ethylene goes into the manufacture of polyethylene, one of the most familiar plastics. For more information about polymers and plastics, see Section 1. Propylene is also an important industrial chemical.

It is converted to plastics, isopropyl alcohol, and a variety of other products. Although there is only one alkene with the formula C 2 H 4 ethene and only one with the formula C 3 H 6 propene , there are several alkenes with the formula C 4 H 8. Section 1. Substituent groups are named as with alkanes, and their position is indicated by a number. Note that the numbering of the parent chain is always done in such a way as to give the double bond the lowest number, even if that causes a substituent to have a higher number.

The double bond always has priority in numbering. Just as there are cycloalkanes, there are cycloalkenes. These compounds are named like alkenes, but with the prefix cyclo - attached to the beginning of the parent alkene name. Then add the double bond between the second and third carbon atoms:. Now place the methyl group on the third carbon atom and add enough hydrogen atoms to give each carbon atom a total of four bonds.

First, consider what each of the three parts of the name means. Cyclo means a ring compound, hex means 6 carbon atoms, and - ene means a double bond. Briefly identify the important distinctions between a saturated hydrocarbon and an unsaturated hydrocarbon. Briefly identify the important distinctions between an alkene and an alkane.

Classify each compound as saturated or unsaturated. Identify each as an alkane, an alkene, or an alkyne. Unsaturated hydrocarbons have double or triple bonds and are quite reactive; saturated hydrocarbons have only single bonds and are rather unreactive. An alkene has a double bond; an alkane has single bonds only.

As noted in earlier in this chapter, there is free rotation about the carbon-to-carbon single bonds C—C in alkanes. In contrast, the structure of alkenes requires that the carbon atoms of a double bond and the two atoms bonded to each carbon atom all lie in a single plane, and that each doubly bonded carbon atom lies in the center of a triangle. Look at the two chlorinated hydrocarbons in Figure 1.

In 1,2-dichloroethane a , free rotation about the C—C bond allows the two structures to be interconverted by a twist of one end relative to the other. In 1,2-dichloroethene b , restricted rotation about the double bond means that the relative positions of substituent groups above or below the double bond are significant. In 1,2-dichloroethane part a of Figure 1. The two models shown represent exactly the same molecule; they are not isomers.

You can draw structural formulas that look different, but if you bear in mind the possibility of this free rotation about single bonds, you should recognize that these two structures represent the same molecule:. In 1,2-dichloroethene part b of Figure 1. This leads to a special kind of isomerism. These two compounds are cis-trans isomers or geometric isomers , compounds that have different configurations groups permanently in different places in space because of the presence of a rigid structure in their molecule.

We could name it 2-butene, but there are actually two such compounds; the double bond results in cis-trans isomerism Figure 1.

Figure 1. Cis butene has both methyl groups on the same side of the molecule. Trans butene has the methyl groups on opposite sides of the molecule. Their structural formulas are as follows:. Note, however, that the presence of a double bond does not necessarily lead to cis-trans isomerism.

We can draw two seemingly different propenes:. However, these two structures are not really different from each other. If you could pick up either molecule from the page and flip it over top to bottom, you would see that the two formulas are identical. Thus there are two requirements for cis-trans isomerism:. In these propene structures, the second requirement for cis-trans isomerism is not fulfilled. One of the doubly bonded carbon atoms does have two different groups attached, but the rules require that both carbon atoms have two different groups.

In general, the following statements hold true in cis-trans isomerism:. Cis-trans isomerism also occurs in cyclic compounds. In ring structures, groups are unable to rotate about any of the ring carbon—carbon bonds. Therefore, groups can be either on the same side of the ring cis or on opposite sides of the ring trans.

For our purposes here, we represent all cycloalkanes as planar structures, and we indicate the positions of the groups, either above or below the plane of the ring. Which compounds can exist as cis-trans geometric isomers? Draw them.

All four structures have a double bond and thus meet rule 1 for cis-trans isomerism. This compound meets rule 2; it has two nonidentical groups on each carbon atom H and Cl on one and H and Br on the other. It exists as both cis and trans isomers:. This compound meets rule 2; it has two nonidentical groups on each carbon atom and exists as both cis and trans isomers:.

What are cis-trans geometric isomers?