There Are Several Families of Hydrocarbons Among Which Are Alkanes

Affiliate xx. Organic Chemistry

20.ane Hydrocarbons

Learning Objectives

By the stop of this department, you will be able to:

• Explain the importance of hydrocarbons and the reason for their diversity
• Name saturated and unsaturated hydrocarbons, and molecules derived from them
• Describe the reactions feature of saturated and unsaturated hydrocarbons
• Identify structural and geometric isomers of hydrocarbons

The largest database^[i] of organic compounds lists about 10 million substances, which include compounds originating from living organisms and those synthesized past chemists. The number of potential organic compounds has been estimated^[2] at ten⁶⁰—an astronomically high number. The beingness of so many organic molecules is a event of the ability of carbon atoms to course upwards to four strong bonds to other carbon atoms, resulting in chains and rings of many different sizes, shapes, and complexities.

The simplest organic compounds contain only the elements carbon and hydrogen, and are chosen hydrocarbons. Fifty-fifty though they are equanimous of merely ii types of atoms, in that location is a wide diverseness of hydrocarbons because they may consist of varying lengths of chains, branched chains, and rings of carbon atoms, or combinations of these structures. In addition, hydrocarbons may differ in the types of carbon-carbon bonds nowadays in their molecules. Many hydrocarbons are found in plants, animals, and their fossils; other hydrocarbons accept been prepared in the laboratory. We use hydrocarbons every day, mainly equally fuels, such as natural gas, acetylene, propane, butane, and the principal components of gasoline, diesel fuel, and heating oil. The familiar plastics polyethylene, polypropylene, and polystyrene are also hydrocarbons. We can distinguish several types of hydrocarbons by differences in the bonding between carbon atoms. This leads to differences in geometries and in the hybridization of the carbon orbitals.

Alkanes

Alkanes, or saturated hydrocarbons, contain merely single covalent bonds betwixt carbon atoms. Each of the carbon atoms in an alkane series has sp ^three hybrid orbitals and is bonded to 4 other atoms, each of which is either carbon or hydrogen. The Lewis structures and models of marsh gas, ethane, and pentane are illustrated in Figure ane. Carbon bondage are normally fatigued as directly lines in Lewis structures, but ane has to remember that Lewis structures are not intended to indicate the geometry of molecules. Notice that the carbon atoms in the structural models (the ball-and-stick and space-filling models) of the pentane molecule do not prevarication in a direct line. Considering of the sp ⁱⁱⁱ hybridization, the bond angles in carbon bondage are close to 109.five°, giving such chains in an alkane a zigzag shape.

The structures of alkanes and other organic molecules may also exist represented in a less detailed fashion by condensed structural formulas (or only, condensed formulas). Instead of the usual format for chemical formulas in which each chemical element symbol appears just once, a condensed formula is written to propose the bonding in the molecule. These formulas have the advent of a Lewis structure from which about or all of the bail symbols have been removed. Condensed structural formulas for ethane and pentane are shown at the lesser of Figure 1, and several boosted examples are provided in the exercises at the end of this affiliate.

Figure 1. Pictured are the Lewis structures, ball-and-stick models, and infinite-filling models for molecules of methyl hydride, ethane, and pentane.

A mutual method used by organic chemists to simplify the drawings of larger molecules is to employ a skeletal structure (as well called a line-angle structure). In this blazon of structure, carbon atoms are not symbolized with a C, but represented past each cease of a line or curve in a line. Hydrogen atoms are non fatigued if they are attached to a carbon. Other atoms besides carbon and hydrogen are represented by their elemental symbols. Figure 2 shows three different ways to draw the same structure.

Figure 2. The same structure can be represented iii dissimilar ways: an expanded formula, a condensed formula, and a skeletal structure.

Case 1

Drawing Skeletal Structures
Describe the skeletal structures for these two molecules:

Solution
Each carbon cantlet is converted into the end of a line or the place where lines intersect. All hydrogen atoms attached to the carbon atoms are left out of the structure (although we even so need to recognize they are at that place):

Cheque Your Learning
Describe the skeletal structures for these two molecules:

Answer:

Example 2

Interpreting Skeletal Structures
Identify the chemical formula of the molecule represented here:

Solution
There are 8 places where lines intersect or end, meaning that there are 8 carbon atoms in the molecule. Since we know that carbon atoms tend to make four bonds, each carbon cantlet will have the number of hydrogen atoms that are required for 4 bonds. This compound contains 16 hydrogen atoms for a molecular formula of C_eightH₁₆.

Location of the hydrogen atoms:

Check Your Learning
Identify the chemical formula of the molecule represented here:

All alkanes are equanimous of carbon and hydrogen atoms, and have similar bonds, structures, and formulas; noncyclic alkanes all take a formula of C_nH_2n+2. The number of carbon atoms present in an paraffin has no limit. Greater numbers of atoms in the molecules will lead to stronger intermolecular attractions (dispersion forces) and correspondingly different physical properties of the molecules. Properties such as melting betoken and humid point (Table ane) usually alter smoothly and predictably as the number of carbon and hydrogen atoms in the molecules change.

Alkane	Molecular Formula	Melting Point (°C)	Humid Betoken (°C)	Phase at STP[iii]	Number of Structural Isomers
marsh gas	CH4	–182.5	–161.v	gas	ane
ethane	C2H6	–183.three	–88.6	gas	one
propane	C3Height	–187.7	–42.1	gas	i
butane	CivH10	–138.iii	–0.5	gas	two
pentane	C5H12	–129.seven	36.1	liquid	3
hexane	C6H14	–95.three	68.7	liquid	five
heptane	CviiH16	–ninety.6	98.4	liquid	nine
octane	C8H18	–56.viii	125.7	liquid	18
nonane	C9H20	–53.6	150.8	liquid	35
decane	C10H22	–29.7	174.0	liquid	75
tetradecane	C14Hxxx	five.9	253.five	solid	1858
octadecane	C18H38	28.two	316.1	solid	60,523
Table 1. Properties of Some Alkanes[4]

Hydrocarbons with the aforementioned formula, including alkanes, can have unlike structures. For example, two alkanes have the formula C_fourH₁₀: They are chosen n-butane and 2-methylpropane (or isobutane), and have the post-obit Lewis structures:

The compounds n-butane and 2-methylpropane are structural isomers (the term constitutional isomers is besides commonly used). Constitutional isomers have the aforementioned molecular formula but different spatial arrangements of the atoms in their molecules. The n-butane molecule contains an unbranched concatenation, meaning that no carbon atom is bonded to more than 2 other carbon atoms. We employ the term normal, or the prefix n, to refer to a chain of carbon atoms without branching. The compound ii–methylpropane has a branched chain (the carbon atom in the center of the Lewis structure is bonded to three other carbon atoms)

Identifying isomers from Lewis structures is not every bit like shooting fish in a barrel every bit it looks. Lewis structures that look different may actually correspond the same isomers. For example, the iii structures in Figure 3 all represent the aforementioned molecule, due north-butane, and hence are non different isomers. They are identical because each contains an unbranched chain of iv carbon atoms.

Figure 3. These three representations of the construction of n-butane are not isomers because they all contain the same organization of atoms and bonds.

The Basics of Organic Classification: Naming Alkanes

The International Union of Pure and Applied Chemistry (IUPAC) has devised a system of nomenclature that begins with the names of the alkanes and can exist adjusted from at that place to account for more complicated structures. The nomenclature for alkanes is based on 2 rules:

1. To proper noun an alkane, first identify the longest chain of carbon atoms in its construction. A two-carbon chain is chosen ethane; a three-carbon chain, propane; and a 4-carbon concatenation, butane. Longer chains are named as follows: pentane (five-carbon chain), hexane (half dozen), heptane (seven), octane (8), nonane (ix), and decane (x). These prefixes tin be seen in the names of the alkanes described in Table 1.
2. Add prefixes to the name of the longest chain to indicate the positions and names of substituents. Substituents are branches or functional groups that supersede hydrogen atoms on a chain. The position of a substituent or branch is identified by the number of the carbon atom it is bonded to in the chain. Nosotros number the carbon atoms in the chain past counting from the stop of the chain nearest the substituents. Multiple substituents are named individually and placed in alphabetical order at the front of the proper noun.

When more than than one substituent is present, either on the same carbon atom or on unlike carbon atoms, the substituents are listed alphabetically. Because the carbon cantlet numbering begins at the finish closest to a substituent, the longest chain of carbon atoms is numbered in such a mode every bit to produce the lowest number for the substituents. The ending -o replaces -ide at the end of the name of an electronegative substituent (in ionic compounds, the negatively charged ion ends with -ide like chloride; in organic compounds, such atoms are treated as substituents and the -o ending is used). The number of substituents of the same type is indicated by the prefixes di- (two), tri- (three), tetra- (four), and so on (for example, difluoro- indicates 2 fluoride substituents).

Example 3

Naming Halogen-substituted Alkanes
Proper name the molecule whose construction is shown here:

Solution

The four-carbon concatenation is numbered from the terminate with the chlorine cantlet. This puts the substituents on positions 1 and two (numbering from the other end would put the substituents on positions 3 and 4). Four carbon atoms means that the base of operations proper name of this chemical compound will be butane. The bromine at position 2 will be described past adding 2-bromo-; this volition come at the beginning of the name, since bromo- comes before chloro- alphabetically. The chlorine at position 1 will be described by adding 1-chloro-, resulting in the proper name of the molecule beingness 2-bromo-one-chlorobutane.

Bank check Your Learning
Proper noun the post-obit molecule:

Answer:

three,3-dibromo-2-iodopentane

We call a substituent that contains i less hydrogen than the corresponding alkane series an alkyl group. The name of an alkyl group is obtained by dropping the suffix -ane of the alkane series name and adding -yl:

The open up bonds in the methyl and ethyl groups betoken that these alkyl groups are bonded to another atom.

Case iv

Naming Substituted Alkanes
Name the molecule whose structure is shown here:

Solution
The longest carbon chain runs horizontally across the page and contains six carbon atoms (this makes the base of the name hexane, but we will besides need to contain the name of the branch). In this case, we want to number from correct to left (as shown by the blue numbers) and then the co-operative is connected to carbon iii (imagine the numbers from left to right—this would put the branch on carbon 4, violating our rules). The co-operative attached to position 3 of our chain contains two carbon atoms (numbered in scarlet)—so we accept our name for two carbons eth- and attach -yl at the end to signify nosotros are describing a branch. Putting all the pieces together, this molecule is 3-ethylhexane.

Check Your Learning
Name the following molecule:

Some hydrocarbons tin course more than 1 blazon of alkyl grouping when the hydrogen atoms that would be removed have different "environments" in the molecule. This diversity of possible alkyl groups tin can exist identified in the following manner: The iv hydrogen atoms in a methyl hydride molecule are equivalent; they all take the same surroundings. They are equivalent because each is bonded to a carbon atom (the same carbon cantlet) that is bonded to 3 hydrogen atoms. (It may be easier to see the equivalency in the ball and stick models in Figure 1. Removal of any one of the four hydrogen atoms from methane forms a methyl group. Too, the vi hydrogen atoms in ethane are equivalent (Figure i) and removing whatsoever ane of these hydrogen atoms produces an ethyl group. Each of the six hydrogen atoms is bonded to a carbon atom that is bonded to two other hydrogen atoms and a carbon cantlet. Withal, in both propane and 2–methylpropane, there are hydrogen atoms in two unlike environments, distinguished by the side by side atoms or groups of atoms:

Each of the 6 equivalent hydrogen atoms of the first type in propane and each of the 9 equivalent hydrogen atoms of that type in 2-methylpropane (all shown in black) are bonded to a carbon atom that is bonded to simply one other carbon atom. The two purple hydrogen atoms in propane are of a second blazon. They differ from the six hydrogen atoms of the outset type in that they are bonded to a carbon atom bonded to 2 other carbon atoms. The green hydrogen atom in 2-methylpropane differs from the other ix hydrogen atoms in that molecule and from the purple hydrogen atoms in propane. The light-green hydrogen cantlet in 2-methylpropane is bonded to a carbon atom bonded to three other carbon atoms. Two different alkyl groups can be formed from each of these molecules, depending on which hydrogen atom is removed. The names and structures of these and several other alkyl groups are listed in Figure 4.

Effigy 4. This listing gives the names and formulas for various alkyl groups formed by the removal of hydrogen atoms from dissimilar locations.

Note that alkyl groups practise not exist as stable independent entities. They are e'er a role of some larger molecule. The location of an alkyl grouping on a hydrocarbon concatenation is indicated in the aforementioned style as any other substituent:

Alkanes are relatively stable molecules, but rut or light volition activate reactions that involve the breaking of C–H or C–C unmarried bonds. Combustion is 1 such reaction:

[latex]\text{CH}_4(g)\;+\;two\text{O}_2(thou)\;{\longrightarrow}\;\text{CO}_2(g)\;+\;ii\text{H}_2\text{O}(one thousand)[/latex]

Alkanes burn in the presence of oxygen, a highly exothermic oxidation-reduction reaction that produces carbon dioxide and water. As a issue, alkanes are splendid fuels. For example, methane, CH₄, is the principal component of natural gas. Butane, C₄H₁₀, used in camping stoves and lighters is an alkane. Gasoline is a liquid mixture of continuous- and branched-chain alkanes, each containing from five to 9 carbon atoms, plus various additives to meliorate its operation equally a fuel. Kerosene, diesel oil, and fuel oil are primarily mixtures of alkanes with higher molecular masses. The master 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 Effigy five). You may recall that boiling point is a function of intermolecular interactions, which was discussed in the chapter on solutions and colloids.

Figure 5. In a cavalcade for the partial distillation of rough oil, oil heated to virtually 425 °C in the furnace vaporizes when it enters the base of operations of the tower. The vapors rise through bubble caps in a series of trays in the tower. Equally the vapors gradually absurd, fractions of higher, then of lower, humid points condense to liquids and are drawn off. (credit left: modification of work by Luigi Chiesa)

In a exchange reaction, some other typical reaction of alkanes, ane or more of the alkane's hydrogen atoms is replaced with a different cantlet or group of atoms. 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 commutation reaction:

The C–Cl portion of the chloroethane molecule is an case of a functional group, the role 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 backdrop and are used equally a means of classifying organic compounds as detailed in the remaining sections of this chapter.

Want more than practice naming alkanes? Watch this brief video tutorial to review the classification process.

Alkenes

Organic compounds that contain one or more than double or triple bonds betwixt carbon atoms are described every bit unsaturated. Yous take likely heard of unsaturated fats. These are complex organic molecules with long chains of carbon atoms, which incorporate at least one double bond betwixt carbon atoms. Unsaturated hydrocarbon molecules that contain one or more double bonds are chosen alkenes. Carbon atoms linked by a double bond are jump together by two bonds, 1 σ bail and one π bond. Double and triple bonds give rise to a unlike 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, C₂H₄, is the simplest alkene. Each carbon cantlet in ethene, commonly called ethylene, has a trigonal planar construction. The 2nd member of the serial 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, too as a new form of isomerism.

Figure 6. Expanded structures, ball-and-stick structures, and infinite-filling models for the alkenes ethene, propene, and 1-butene are shown.

Ethylene (the mutual industrial name for ethene) is a basic raw material in the production of polyethylene and other important compounds. Over 135 million tons of ethylene were produced worldwide in 2010 for use in the polymer, petrochemical, and plastic industries. Ethylene is produced industrially in a procedure called bully, in which the long hydrocarbon bondage in a petroleum mixture are cleaved into smaller molecules.

Recycling Plastics

Polymers (from Greek words poly meaning "many" and mer meaning "parts") are big molecules made upward of repeating units, referred to as monomers. Polymers can be natural (starch is a polymer of saccharide residues and proteins are polymers of amino acids) or constructed [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. Calculation functional groups to the construction of a polymer can result in significantly different properties (run into the word about Kevlar later in this chapter).

An example of a polymerization reaction is shown in Effigy 7. The monomer ethylene (C₂H_iv) is a gas at room temperature, but when polymerized, using a transition metallic catalyst, it is transformed into a solid material made up of long chains of –CH_two– units called polyethylene. Polyethylene is a commodity plastic used primarily for packaging (bags and films).

Figure 7. The reaction for the polymerization of ethylene to polyethylene is shown.

Polyethylene is a member of i subset of synthetic polymers classified as plastics. Plastics are synthetic organic solids that tin be molded; they are typically organic polymers with loftier 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 than of the petrochemical supplies and also minimizes the environmental damage acquired by throwing away these nonbiodegradable materials.

Plastic recycling is the process of recovering waste material, scrap, or used plastics, and reprocessing the textile into useful products. For example, polyethylene terephthalate (soft potable bottles) can be melted downward and used for plastic furniture, in carpets, or for other applications. Other plastics, similar polyethylene (bags) and polypropylene (cups, plastic food containers), tin be recycled or reprocessed to be used once again. Many areas of the country have recycling programs that focus on 1 or more of the commodity plastics that accept been assigned a recycling code (come across Figure eight). These operations have been in outcome since the 1970s and accept made the production of some plastics amidst the most efficient industrial operations today.

Figure 8. Each type of recyclable plastic is imprinted with a code for easy identification.

The proper 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 bail:

Isomers of Alkenes

Molecules of 1-butene and 2-butene are structural isomers; the arrangement of the atoms in these 2 molecules differs. As an case of organisation differences, the first carbon atom in 1-butene is bonded to 2 hydrogen atoms; the commencement carbon cantlet in two-butene is bonded to three hydrogen atoms.

The compound 2-butene and another alkenes also form a 2nd type of isomer called a geometric isomer. In a set of geometric isomers, the same types of atoms are fastened to each other in the same social club, but the geometries of the 2 molecules differ. Geometric isomers of alkenes differ in the orientation of the groups on either side of a [latex]\text{C}\;=\;\text{C}[/latex] bond.

Carbon atoms are gratuitous to rotate effectually a single bond but not around a double bail; a double bond is rigid. This makes it possible to take ii isomers of 2-butene, ane with both methyl groups on the same side of the double bond and one with the methyl groups on opposite sides. When structures of butene are drawn with 120° bond angles effectually the sp ^two-hybridized carbon atoms participating in the double bond, the isomers are apparent. The 2-butene isomer in which the two methyl groups are on the aforementioned side is chosen a cis-isomer; the one in which the ii methyl groups are on contrary sides is called a trans-isomer (Figure 9). The unlike geometries produce different physical properties, such as boiling point, that may make separation of the isomers possible:

Figure 9. These molecular models show the structural and geometric isomers of butene.

Alkenes are much more reactive than alkanes because the [latex]\text{C}\;=\;\text{C}[/latex] moiety is a reactive functional group. A π bond, being a weaker bail, is disrupted much more hands than a σ bond. Thus, alkenes undergo a feature reaction in which the π bond is broken and replaced by ii σ bonds. 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 improver reaction. For example, halogens add together to the double bail in an alkene instead of replacing hydrogen, every bit occurs in an alkane:

Example v

Alkene Reactivity and Naming
Provide the IUPAC names for the reactant and production of the halogenation reaction shown here:

Solution
The reactant is a v-carbon concatenation that contains a carbon-carbon double bond, so the base of operations name will be pentene. We begin counting at the terminate 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 ii-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-2-pentene. The product of the halogenation reaction will have ii chlorine atoms attached to the carbon atoms that were a part of the carbon-carbon double bond:

This molecule is now a substituted methane series and will be named as such. The base of the name will exist pentane. We will count from the end that numbers the carbon atoms where the chlorine atoms are attached as two and 3, making the proper noun of the product ii,3-dichloropentane.

Check Your Learning
Provide names for the reactant and product of the reaction shown:

Answer:

reactant: cis-3-hexene product: 3,4-dichlorohexane

Alkynes

Hydrocarbon molecules with one or more triple bonds are called alkynes; they make up another series of unsaturated hydrocarbons. Ii carbon atoms joined past a triple bail are bound together past one σ bond and two π bonds. The sp-hybridized carbons involved in the triple bond have bond angles of 180°, giving these types of bonds a linear, rod-like shape.

The simplest member of the alkyne series is ethyne, C_twoH₂, usually called acetylene. The Lewis structure for ethyne, a linear molecule, is:

The IUPAC classification for alkynes is like to that for alkenes except that the suffix -yne is used to indicate a triple bond in the concatenation. For example, [latex]\text{CH}_3\text{CH}_2\text{C}\;{\equiv}\;\text{CH}[/latex] is chosen 1-butyne.

Instance 6

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 ⁱⁱⁱ hybridization. Carbon atoms ii and 3 are involved in the triple bail, so they have linear geometries and would exist classified equally sp hybrids.

Check Your Learning
Identify the hybridization and bond angles at the carbon atoms in the molecule shown:

Answer:

carbon one: sp, 180°; carbon 2: sp, 180°; carbon 3: sp ², 120°; carbon 4: sp ², 120°; carbon 5: sp ³, 109.5°

Chemically, the alkynes are similar to the alkenes. Since the [latex]\text{C}\;{\equiv}\;\text{C}[/latex] functional group has two π bonds, alkynes typically react fifty-fifty more readily, and react with twice as much reagent in addition reactions. The reaction of acetylene with bromine is a typical example:

Acetylene and the other alkynes besides burn readily. An acetylene torch takes reward of the high estrus of combustion for acetylene.

Aromatic Hydrocarbons

Benzene, C₆H₆, is the simplest member of a big family of hydrocarbons, chosen 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 capacity on chemical bonding). The resonance structures for benzene, C_sixH_six, 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 band. Three valence electrons in the sp ² hybrid orbitals of each carbon cantlet and the valence electron of each hydrogen cantlet form the framework of σ bonds in the benzene molecule. The fourth valence electron of each carbon atom is shared with an side by side carbon atom in their unhybridized p orbitals to yield the π bonds. Benzene does non, however, showroom the characteristics typical of an alkene. Each of the half-dozen bonds between its carbon atoms is equivalent and exhibits properties that are intermediate between those of a C–C unmarried bond and a [latex]\text{C}\;=\;\text{C}[/latex] double bail. To represent this unique bonding, structural formulas for benzene and its derivatives are typically drawn with single bonds betwixt the carbon atoms and a circle within the ring as shown in Figure 10.

Figure 10. This condensed formula shows the unique bonding structure of benzene.

There are many derivatives of benzene. The hydrogen atoms can be replaced by many different substituents. Effluvious compounds more readily undergo substitution reactions than addition reactions; replacement of one of the hydrogen atoms with another substituent will exit 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 chemic industry. Styrene is used to produce the polymer polystyrene.

Example seven

Structure of Aromatic Hydrocarbons
I possible isomer created by a substitution reaction that replaces a hydrogen atom fastened to the effluvious ring of toluene with a chlorine cantlet is shown hither. Draw ii other possible isomers in which the chlorine atom replaces a different hydrogen atom fastened to the effluvious ring:

Solution
Since the half-dozen-carbon ring with alternating double bonds is necessary for the molecule to be classified as aromatic, advisable isomers can be produced merely by changing the positions of the chloro-substituent relative to the methyl-substituent:

Check Your Learning
Draw three isomers of a vi-membered effluvious ring compound substituted with 2 bromines.

Answer:

Primal Concepts and Summary

Strong, stable bonds between carbon atoms produce complex molecules containing chains, branches, and rings. The chemical science of these compounds is called organic chemistry. Hydrocarbons are organic compounds composed of merely carbon and hydrogen. The alkanes are saturated hydrocarbons—that is, hydrocarbons that contain only single bonds. Alkenes comprise one or more than carbon-carbon double bonds. Alkynes contain one or more than carbon-carbon triple bonds. Effluvious hydrocarbons contain ring structures with delocalized π electron systems.

Chemistry Cease of Chapter Exercises

1. Write the chemical formula and Lewis structure of the following, each of which contains five carbon atoms:

   (a) an paraffin

   (b) an alkene

   (c) an alkyne

2. What is the deviation between the hybridization of carbon atoms' valence orbitals in saturated and unsaturated hydrocarbons?
3. On a microscopic level, how does the reaction of bromine with a saturated hydrocarbon differ from its reaction with an unsaturated hydrocarbon? How are they like?
4. On a microscopic level, how does the reaction of bromine with an alkene differ from its reaction with an alkyne? How are they like?
5. Explain why unbranched alkenes can form geometric isomers while unbranched alkanes cannot. Does this caption involve the macroscopic domain or the microscopic domain?
6. Explicate why these two molecules are non isomers:
   
7. Explain why these 2 molecules are non isomers:
   
8. How does the carbon-cantlet hybridization modify when polyethylene is prepared from ethylene?
9. Write the Lewis construction and molecular formula for each of the following hydrocarbons:

   (a) hexane

   (b) 3-methylpentane

   (c) cis-3-hexene

   (d) iv-methyl-1-pentene

   (e) iii-hexyne

   (f) four-methyl-2-pentyne

10. Write the chemical formula, condensed formula, and Lewis construction for each of the following hydrocarbons:

    (a) heptane

    (b) 3-methylhexane

    (c) trans-three-heptene

    (d) 4-methyl-1-hexene

    (e) 2-heptyne

    (f) 3,4-dimethyl-1-pentyne

11. Give the consummate IUPAC name for each of the following compounds:

    (a) [latex]\text{CH}_3\text{CH}_2\text{CBr}_2\text{CH}_3[/latex]

    (b) [latex](\text{CH}_3)_3\text{CCl}[/latex]

    (c)
    

    (d) [latex]\text{CH}_3\text{CH}_2\text{C}\;{\equiv}\;\text{CH\;CH}_3\text{CH}_2\text{C}\;{\equiv}\;\text{CH}[/latex]

    (e)
    

    (f)
    

    (grand) [latex](\text{CH}_3)_2\text{CHCH}_2\text{CH} = \text{CH}_2[/latex]

12. Give the consummate IUPAC name for each of the following compounds:

    (a) [latex](\text{CH}_3)_2\text{CHF}[/latex]

    (b) [latex]\text{CH}_3\text{CHClCHClCH}_3[/latex]

    (c)
    

    (d) [latex]\text{CH}_3\text{CH}_2\text{CH} = \text{CHCH}_3[/latex]

    (e)
    

    (f) [latex](\text{CH}_3)_3\text{CCH}_2\text{C}{\equiv}\text{CH}[/latex]

13. Butane is used as a fuel in dispensable lighters. Write the Lewis structure for each isomer of butane.
14. Write Lewis structures and proper noun the five structural isomers of hexane.
15. Write Lewis structures for the cis–trans isomers of [latex]\text{CH}_3\text{CH} = \text{CHCl}[/latex].
16. Write structures for the three isomers of the aromatic hydrocarbon xylene, [latex]\text{C}_6\text{H}_4(\text{CH}_3)_2[/latex].
17. Isooctane is the common proper noun of the isomer of [latex]\text{C}_8\text{H}_18[/latex] used equally the standard of 100 for the gasoline octane rating:
    

    (a) What is the IUPAC name for the compound?

    (b) Name the other isomers that contain a five-carbon chain with iii methyl substituents.

18. Write Lewis structures and IUPAC names for the alkyne isomers of [latex]\text{C}_4\text{H}_6[/latex].
19. Write Lewis structures and IUPAC names for all isomers of [latex]\text{C}_4\text{H}_9\text{Cl}[/latex].
20. Name and write the structures of all isomers of the propyl and butyl alkyl groups.
21. Write the structures for all the isomers of the [latex]-\text{C}_5\text{H}_{xi}[/latex] alkyl group.
22. Write Lewis structures and describe the molecular geometry at each carbon cantlet in the post-obit compounds:

    (a) cis-3-hexene

    (b) cis-1-chloro-2-bromoethene

    (c) two-pentyne

    (d) trans–half dozen-ethyl-vii-methyl-ii-octene

23. Benzene is one of the compounds used as an octane enhancer in unleaded gasoline. It is manufactured by the catalytic conversion of acetylene to benzene:[latex]3\text{C}_2\text{H}_2\;{\longrightarrow}\;\text{C}_6\text{H}_6[/latex]

    Depict Lewis structures for these compounds, with resonance structures as advisable, and determine the hybridization of the carbon atoms in each.

24. Teflon is prepared by the polymerization of tetrafluoroethylene. Write the equation that describes the polymerization using Lewis symbols.
25. Write 2 complete, balanced equations for each of the post-obit reactions, one using condensed formulas and one using Lewis structures.

    (a) i mol of i-butyne reacts with ii mol of iodine.

    (b) Pentane is burned in air.

26. Write two complete, counterbalanced equations for each of the following reactions, one using condensed formulas and i using Lewis structures.

    (a) 2-butene reacts with chlorine.

    (b) benzene burns in air.

27. What mass of 2-bromopropane could be prepared from 25.5 g of propene? Assume a 100% yield of product.
28. Acetylene is a very weak acrid; however, it will react with moist silverish(I) oxide and form h2o and a chemical compound composed of argent and carbon. Addition of a solution of HCl to a 0.2352-m sample of the compound of silver and carbon produced acetylene and 0.2822 g of AgCl.

    (a) What is the empirical formula of the chemical compound of silver and carbon?

    (b) The production of acetylene on addition of HCl to the compound of silverish and carbon suggests that the carbon is present as the acetylide ion, [latex]\text{C}_2^{\;\;2-}[/latex]. Write the formula of the compound showing the acetylide ion.

29. Ethylene can be produced by the pyrolysis of ethane:[latex]\text{C}_2\text{H}_6\;{\longrightarrow}\;\text{C}_2\text{H}_4\;+\;\text{H}_2[/latex]

    How many kilograms of ethylene is produced by the pyrolysis of one.000 × ten³ kg of ethane, bold a 100.0% yield?

Glossary

addition reaction

reaction in which a double carbon-carbon bail forms a single carbon-carbon bond past the addition of a reactant. Typical reaction for an alkene.

alkane series

molecule consisting of only carbon and hydrogen atoms connected by single (σ) bonds

alkene

molecule consisting of carbon and hydrogen containing at least ane carbon-carbon double bond

alkyl grouping

substituent, consisting of an paraffin missing one hydrogen atom, attached to a larger structure

alkyne

molecule consisting of carbon and hydrogen containing at to the lowest degree one carbon-carbon triple bond

aromatic hydrocarbon

cyclic molecule consisting of carbon and hydrogen with delocalized alternating carbon-carbon single and double bonds, resulting in enhanced stability

functional group

part of an organic molecule that imparts a specific chemical reactivity to the molecule

organic compound

natural or constructed compound that contains carbon

saturated hydrocarbon

molecule containing carbon and hydrogen that has only single bonds between carbon atoms

skeletal structure

autograph method of drawing organic molecules in which carbon atoms are represented by the ends of lines and bends in between lines, and hydrogen atoms attached to the carbon atoms are not shown (but are understood to be present by the context of the structure)

substituent

branch or functional grouping that replaces hydrogen atoms in a larger hydrocarbon concatenation

substitution reaction

reaction in which one atom replaces some other in a molecule

Solutions

Answers to Chemistry End of Chapter Exercises

1. In that location are several sets of answers; one is:

(a) [latex]\text{C}_5\text{H}_{12}[/latex]
;

(b) [latex]\text{C}_5\text{H}_{10}[/latex]
;

(c) [latex]\text{C}_5\text{H}_8[/latex]

3. Both reactions result in bromine being incorporated into the structure of the production. The difference is the fashion in which that incorporation takes place. In the saturated hydrocarbon, an existing C–H bond is cleaved, and a bail between the C and the Br can then be formed. In the unsaturated hydrocarbon, the simply bond broken in the hydrocarbon is the π bond whose electrons can be used to course a bond to ane of the bromine atoms in Br_ii (the electrons from the Br–Br bond course the other C–Br bond on the other carbon that was office of the π bond in the starting unsaturated hydrocarbon).

5. Unbranched alkanes take free rotation almost the C–C bonds, yielding all orientations of the substituents well-nigh these bonds equivalent, interchangeable by rotation. In the unbranched alkenes, the inability to rotate about the [latex]\text{C}\;=\;\text{C}[/latex] bond results in fixed (unchanging) substituent orientations, thus permitting different isomers. Since these concepts pertain to phenomena at the molecular level, this explanation involves the microscopic domain.

7. They are the same chemical compound because each is a saturated hydrocarbon containing an unbranched chain of half dozen carbon atoms.

nine. (a) [latex]\text{C}_6\text{H}_{14}[/latex]
;

(b) [latex]\text{C}_6\text{H}_{14}[/latex]
;

(c) [latex]\text{C}_6\text{H}_{12}[/latex]
;

(d) [latex]\text{C}_6\text{H}_{12}[/latex]
;

(e) [latex]\text{C}_6\text{H}_{10}[/latex]
;

(f) [latex]\text{C}_6\text{H}_{10}[/latex]

11. (a) 2,2-dibromobutane; (b) 2-chloro-2-methylpropane; (c) 2-methylbutane; (d) 1-butyne; (e) 4-fluoro-four-methyl-one-octyne; (f) trans-one-chloropropene; (g) 5-methyl-1-pentene

thirteen.

15.

17. (a) ii,2,4-trimethylpentane; (b) 2,ii,3-trimethylpentane, 2,3,iv-trimethylpentane, and 2,iii,3-trimethylpentane:

19.

21. In the post-obit, the carbon backbone and the advisable number of hydrogen atoms are shown in condensed form:

23.

In acetylene, the bonding uses sp hybrids on carbon atoms and s orbitals on hydrogen atoms. In benzene, the carbon atoms are sp ^two hybridized.

25. (a) [latex]\text{CH}\;{\equiv}\;\text{CCH}_2\text{CH}_3\;+\;2\text{I}_2\;{\longrightarrow}\;\text{CHI}_2\text{CI}_2\text{CH}_2\text{CH}_3[/latex]

(b) [latex]\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_3\;+\;8\text{O}_2\;{\longrightarrow}\;5\text{CO}_2\;+\;half-dozen\text{H}_2\text{O}[/latex]

27. 65.ii grand

29. nine.328 × 10ⁱⁱ kg

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Source: https://opentextbc.ca/chemistry/chapter/20-1-hydrocarbons/

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