Which hydrocarbon has a double bond

The n -butane molecule contains an unbranched chain , meaning that no carbon atom is bonded to more than two other carbon atoms. We use the term normal , or the prefix n , to refer to a chain of carbon atoms without branching. The compound 2—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 as easy as it looks. Lewis structures that look different may actually represent the same isomers.

For example, the three structures in Figure 3 all represent the same molecule, n -butane, and hence are not different isomers. They are identical because each contains an unbranched chain of four carbon atoms. 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 be adjusted from there to account for more complicated structures. The nomenclature for alkanes is based on two rules:. When more than one substituent is present, either on the same carbon atom or on different carbon atoms, the substituents are listed alphabetically.

Because the carbon atom numbering begins at the end closest to a substituent, the longest chain of carbon atoms is numbered in such a way as 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 two fluoride substituents.

Naming Halogen-substituted Alkanes Name the molecule whose structure is shown here:. The four-carbon chain is numbered from the end with the chlorine atom. This puts the substituents on positions 1 and 2 numbering from the other end would put the substituents on positions 3 and 4. Four carbon atoms means that the base name of this compound will be butane. The bromine at position 2 will be described by adding 2-bromo-; this will 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 name of the molecule being 2-bromochlorobutane. Check Your Learning Name the following molecule:. We call a substituent that contains one less hydrogen than the corresponding alkane an alkyl group.

The name of an alkyl group is obtained by dropping the suffix -ane of the alkane name and adding -yl :. The open bonds in the methyl and ethyl groups indicate that these alkyl groups are bonded to another atom.

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 also need to incorporate the name of the branch.

In this case, we want to number from right to left as shown by the blue numbers so the branch is connected to carbon 3 imagine the numbers from left to right—this would put the branch on carbon 4, violating our rules. The branch attached to position 3 of our chain contains two carbon atoms numbered in red —so we take our name for two carbons eth- and attach -yl at the end to signify we are describing a branch.

Putting all the pieces together, this molecule is 3-ethylhexane. This diversity of possible alkyl groups can be identified in the following way: The four hydrogen atoms in a methane molecule are equivalent; they all have the same environment.

They are equivalent because each is bonded to a carbon atom the same carbon atom that is bonded to three 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. Likewise, the six hydrogen atoms in ethane are equivalent Figure 1 and removing any one 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 atom. However, in both propane and 2—methylpropane, there are hydrogen atoms in two different environments, distinguished by the adjacent atoms or groups of atoms:. Each of the six equivalent hydrogen atoms of the first type in propane and each of the nine equivalent hydrogen atoms of that type in 2-methylpropane all shown in black are bonded to a carbon atom that is bonded to only one other carbon atom.

The two purple hydrogen atoms in propane are of a second type. They differ from the six hydrogen atoms of the first type in that they are bonded to a carbon atom bonded to two other carbon atoms.

The green hydrogen atom in 2-methylpropane differs from the other nine hydrogen atoms in that molecule and from the purple hydrogen atoms in propane. The green hydrogen atom 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.

Note that alkyl groups do not exist as stable independent entities. They are always a part of some larger molecule. The location of an alkyl group on a hydrocarbon chain is indicated in the same way as any other substituent:. Alkanes are relatively stable molecules, but heat or light will activate reactions that involve the breaking of C—H or C—C single bonds. Combustion is one such reaction:.

Alkanes burn in the presence of oxygen, a highly exothermic oxidation-reduction reaction that produces carbon dioxide and water. As a consequence, alkanes are excellent fuels. For example, methane, CH 4 , is the principal component of natural gas. Butane, C 4 H 10 , 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 nine carbon atoms, plus various additives to improve its performance as a fuel.

Kerosene, diesel oil, and fuel oil are primarily mixtures of alkanes with higher molecular masses. 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. Aromatic compounds derive their names from the fact that many of these compounds in the early days of discovery were grouped because they were oils with fragrant odors.

Alkanes are organic compounds that consist entirely of single-bonded carbon and hydrogen atoms and lack any other functional groups. Alkanes can be subdivided into the following three groups: the linear straight-chain alkanes , branched alkanes , and cycloalkanes.

Alkanes are also saturated hydrocarbons. Alkanes are the simplest and least reactive hydrocarbon species containing only carbons and hydrogens.

The distinguishing feature of an alkane, making it distinct from other compounds that also exclusively contain carbon and hydrogen, is its lack of unsaturation.

That is to say, it contains no double or triple bonds, which are highly reactive in organic chemistry. Though not totally devoid of reactivity, their lack of reactivity under most laboratory conditions makes them a relatively uninteresting, though very important component of organic chemistry. As you will learn about later, the energy confined within the carbon-carbon bond and the carbon-hydrogen bond is quite high and their rapid oxidation produces a large amount of heat, typically in the form of fire.

Cycloalkanes are hydrocarbons containing one or more carbon rings to which hydrogen atoms are attached. The general formula for a cyclic hydrocarbon containing one ring is C n H 2n as shown in cyclohexane C 6 H 12 below.

Akenes contain at least one carbon-carbon double bond and alkynes contain at least one carbon-carbon triple bond. Alkenes have the general formula C n H 2n. Alkynes have the general formula C n H 2n The ratio of carbon to hydrogen increased because hydrogen atoms are replaced with pi bonds as shown in transbutene C 4 H 8 and 2-butyne C 4 H 6 below. Since both double and triple bonds include pi bonds, Alkenes and alkynes share similar chemical reactivity.

Aromatic hydrocarbons, also known as arenes, are hydrocarbons that have at least one aromatic ring. Aromatic compounds contain the benzene unit. Benzene itself is composed of six C atoms in a ring, with alternating single and double C—C bonds:. There are many ways one can go about determining the structure of an unknown organic molecule.

Although, nuclear magnetic resonance NMR and infrared radiation IR are the primary ways of determining molecular structures, calculating the degrees of unsaturation DU is useful information. Knowing the degrees of unsaturation tells us the combined number of pi bonds and rings within a compound which makes it easier to figure out the molecular structure. As stated before, a saturated molecule contains only single bonds and no rings.

Another way of interpreting this is that a saturated molecule has the maximum number of hydrogen atoms possible to be an acyclic alkane. Cycloalkanes again only contain carbon-hydrogen bonds and carbon-carbon single bonds, but this time the carbon atoms are joined up in a ring. The smallest cycloalkane is cyclopropane. By joining the carbon atoms in a ring, you have had to lose two hydrogen atoms. You are unlikely to ever need it, but the general formula for a cycloalkane is C n H 2n. Don't imagine that these are all flat molecules.

All the cycloalkanes from cyclopentane upwards exist as "puckered rings". This is known as the "chair" form of cyclohexane - from its shape which vaguely resembles a chair. For a monosubstituted cycloalkane the ring supplies the root name and the substituent group is named as usual. A location number is unnecessary. If two different substituents are present on the ring, they are listed in alphabetical order, and the first cited substituent is assigned to carbon 1.

The numbering of ring carbons then continues in a direction clockwise or counter-clockwise that affords the second substituent the lower possible location number. If several substituents are present on the ring, they are listed in alphabetical order. Location numbers are assigned to the substituents so that one of them is at carbon 1 and the other locations have the lowest possible numbers, counting in either a clockwise or counter-clockwise direction.

The name is assembled, listing groups in alphabetical order and giving each group if there are two or more a location number. Another series of compounds is called the alkenes. These have a general formula: C n H 2n. Alkenes have fewer hydrogen atoms than the alkanes. The extra valencies left over occur as double bonds between a pair of Carbon atoms. The double bonds are more reactive than single bonds making the alkenes chemically more reactive.

The ene suffix ending indicates an alkene or cycloalkene. The longest chain chosen for the root name must include both carbon atoms of the double bond. The root chain must be numbered from the end nearest a double bond carbon atom. If the double bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.

The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator. If more than one double bond is present the compound is named as a diene, triene or equivalent prefix indicating the number of double bonds, and each double bond is assigned a locator number. In cycloalkenes the double bond carbons are assigned ring locations 1 and 2. Which of the two is 1 may be determined by the nearest substituent rule. A third series are the alkynes.

These have the following formula: C n H 2n Alkynes have two carbon atoms joined by a triple bond. This is highly reactive making these compounds unstable. The yne suffix ending indicates an alkyne or cycloalkyne. The longest chain chosen for the root name must include both carbon atoms of the triple bond. The root chain must be numbered from the end nearest a triple bond carbon atom.