properties and uses of unsaturated hydrocarbons assignment

20.1 Hydrocarbons

Learning objectives.

By the end of this section, 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 characteristic of saturated and unsaturated hydrocarbons
• Identify structural and geometric isomers of hydrocarbons

The largest database 1 of organic compounds lists about 10 million substances, which include compounds originating from living organisms and those synthesized by chemists. The number of potential organic compounds has been estimated 2 at 10 60 —an astronomically high number. The existence of so many organic molecules is a consequence of the ability of carbon atoms to form up 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 called hydrocarbons. Even though they are composed of only two types of atoms, there is a wide variety 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 present in their molecules. Many hydrocarbons are found in plants, animals, and their fossils; other hydrocarbons have been prepared in the laboratory. We use hydrocarbons every day, mainly as 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 , or saturated hydrocarbons , contain only single covalent bonds between carbon atoms. Each of the carbon atoms in an alkane has sp 3 hybrid orbitals and is bonded to four other atoms, each of which is either carbon or hydrogen. The Lewis structures and models of methane, ethane, and pentane are illustrated in Figure 20.2 . Carbon chains are usually drawn as straight lines in Lewis structures, but one 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 lie in a straight line. Because of the sp 3 hybridization, the bond angles in carbon chains are close to 109.5°, giving such chains in an alkane a zigzag shape.

The structures of alkanes and other organic molecules may also be represented in a less detailed manner by condensed structural formulas (or simply, condensed formulas ). Instead of the usual format for chemical formulas in which each element symbol appears just once, a condensed formula is written to suggest the bonding in the molecule. These formulas have the appearance of a Lewis structure from which most or all of the bond symbols have been removed. Condensed structural formulas for ethane and pentane are shown at the bottom of Figure 20.2 , and several additional examples are provided in the exercises at the end of this chapter.

A common method used by organic chemists to simplify the drawings of larger molecules is to use a skeletal structure (also called a line-angle structure). In this type of structure, carbon atoms are not symbolized with a C, but represented by each end of a line or bend in a line. Hydrogen atoms are not drawn if they are attached to a carbon. Other atoms besides carbon and hydrogen are represented by their elemental symbols. Figure 20.3 shows three different ways to draw the same structure.

Example 20.1

Drawing skeletal structures, check your learning, example 20.2, interpreting skeletal structures.

Location of the hydrogen atoms:

All alkanes are composed of carbon and hydrogen atoms, and have similar bonds, structures, and formulas; noncyclic alkanes all have a formula of C n H 2n+2 . The number of carbon atoms present in an alkane 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 point and boiling point ( Table 20.1 ) usually change smoothly and predictably as the number of carbon and hydrogen atoms in the molecules change.

Hydrocarbons with the same formula, including alkanes, can have different structures. For example, two alkanes have the formula C 4 H 10 : They are called n -butane and 2-methylpropane (or isobutane), and have the following Lewis structures:

The compounds n -butane and 2-methylpropane are structural isomers (the term constitutional isomers is also commonly used). Constitutional isomers have the same molecular formula but different spatial arrangements of the atoms in their molecules. 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 20.4 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 Basics of Organic Nomenclature: 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 be adjusted from there to account for more complicated structures. The nomenclature for alkanes is based on two rules:

• To name an alkane, first identify the longest chain of carbon atoms in its structure. A two-carbon chain is called ethane; a three-carbon chain, propane; and a four-carbon chain, butane. Longer chains are named as follows: pentane (five-carbon chain), hexane (6), heptane (7), octane (8), nonane (9), and decane (10). These prefixes can be seen in the names of the alkanes described in Table 20.1 .
• Add prefixes to the name of the longest chain to indicate the positions and names of substituents . Substituents are branches or functional groups that replace 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. We number the carbon atoms in the chain by counting from the end of the chain nearest the substituents. Multiple substituents are named individually and placed in alphabetical order at the front of the name.

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).

Example 20.3

Naming halogen-substituted alkanes.

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-bromo-1-chlorobutane.

3,3-dibromo-2-iodopentane

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.

Example 20.4

Naming substituted alkanes.

4-propyloctane

Some hydrocarbons can form more than one type of alkyl group when the hydrogen atoms that would be removed have different “environments” in the molecule. 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 20.2 . 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 20.2 ) 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 20.5 .

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 20.6 ). You may recall that boiling point is a function of intermolecular interactions, which was discussed in the chapter on solutions and colloids.

In a substitution reaction , another typical reaction of alkanes, one or more of the alkane’s hydrogen atoms is replaced with a different atom 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 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.

Link to Learning

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 . Carbon atoms linked by a double bond are bound together by two bonds, one σ bond and one π bond. 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 20.7 ); 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 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 process called cracking, in which the long hydrocarbon chains in a petroleum mixture are broken into smaller molecules.

Chemistry in Everyday Life

Recycling plastics.

Polymers (from Greek words poly meaning “many” and mer meaning “parts”) are large molecules made up of repeating units, referred to as monomers. 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 20.8 . 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 20.9 ). These operations have been in effect since the 1970s 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:

Isomers of Alkenes

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. Geometric isomers of alkenes differ in the orientation of the groups on either side of a C = C C = C bond.

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. When structures of butene are drawn with 120° bond angles around the sp 2 -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 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 20.10 ). The different geometries produce different physical properties, such as boiling point, that may make separation of the isomers possible:

Alkenes are much more reactive than alkanes because the C = C C = C moiety is a reactive functional group. A π bond, being a weaker bond, is disrupted much more easily than a σ bond. Thus, alkenes undergo a characteristic reaction in which the π bond is broken and replaced by two 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 addition reaction. For example, halogens add to the double bond in an alkene instead of replacing hydrogen, as occurs in an alkane:

Example 20.5

Alkene reactivity and naming.

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.

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

Hydrocarbon molecules with one or more triple bonds are called alkynes ; they make up another series of unsaturated hydrocarbons. Two carbon atoms joined by a triple bond are bound together by 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 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. For example, CH 3 CH 2 C ≡ CH CH 3 CH 2 C ≡ CH is called 1-butyne.

Example 20.6

Structure of alkynes.

carbon 1: 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 C ≡ C C ≡ C functional group has two π bonds, alkynes typically react even 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 also burn readily. An acetylene torch takes advantage of the high heat of combustion for acetylene.

Aromatic Hydrocarbons

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. Three valence electrons in the sp 2 hybrid orbitals of each carbon atom and the valence electron of each hydrogen atom form the framework of σ bonds in the benzene molecule. The fourth valence electron of each carbon atom is shared with an adjacent carbon atom in their unhybridized p orbitals to yield the π bonds. Benzene does not, however, exhibit the characteristics typical of an alkene. Each of the six bonds between its carbon atoms is equivalent and exhibits properties that are intermediate between those of a C–C single bond and a C = C C = C double bond. 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 20.11 .

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.

Example 20.7

Structure of aromatic hydrocarbons.

• 1 This is the Beilstein database, now available through the Reaxys site (www.elsevier.com/online-tools/reaxys).
• 2 Peplow, Mark. “Organic Synthesis: The Robo-Chemist,” Nature 512 (2014): 20–2.
• 3 Physical properties for C 4 H 10 and heavier molecules are those of the normal isomer , n -butane, n -pentane, etc.
• 4 STP indicates a temperature of 0 °C and a pressure of 1 atm.

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• Unsaturated Hydrocarbon

What is Unsaturated Hydrocarbon?

We are completely aware that an organic compound is made up of carbons and hydrogen atoms. But unsaturated carbons state that adjacent carbon atoms have formed either a double or triple bond with each other. To make them saturated, we need to add more hydrogen atoms to them.

These unsaturated ones can be in the form of straight-chain or branched chains or aromatic compounds . The ones which have at least one double bond between carbon atoms are known as alkenes . But if there is at least one triple bond between carbons in an organic compound, they are alkynes. Below you will understand different types, examples, and the uses of Unsaturated Hydrocarbons in detail.

What are Hydrocarbons? Give Examples.

An organic compound is a hydrocarbon when it contains carbon and hydrogen atoms in it. These can be either saturated or unsaturated. Saturated ones are those having a single bond between two carbon atoms or with a hydrogen atom. Unsaturated ones are those which have either a double or triple bond with two adjacent carbon atoms.

Some basic saturated hydrocarbon examples are methane and ethane. Unsaturated Hydrocarbon examples are Ethene and Ethyne .

What are Different Types of Unsaturated Carbon Compounds?

According to the basic unsaturated hydrocarbon definition, there are three different types. These are:

The classification is based upon the type of carbon-carbon bond in the compound. Also, it is defined by its basic structure.

If there is at least one double bond between two adjacent carbon atoms in a hydrocarbon, those are alkenes or olefins. Ethene is an example of such a type given by \[C_{2}H_{4}\]. These will have only one double bond with no functional groups. The basic formula is given by \[C_{2}H_{2n}\].

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In Alkynes, there is at least one triple bond between two adjacent carbon atoms. An example of such a kind is acetylene given by \[C_{2}H_{2}\]. The basic unsaturated hydrocarbon formula for alkynes is given by \[C_{2}H_{2n - 2}\].

Aromatic hydrocarbons do not share common properties with other unsaturated carbon compounds . However, listed among these because these are relatively stable. 

If you want to check if a particular hydrocarbon is unsaturated, you can add bromine water to it. In case water turns decolourised, it is unsaturated. If it forms a precipitate, then it is phenol . Also, benzene is the one that will not decolorize bromine water. 

What are the Different Uses of Unsaturated Carbon Compounds?

Uses of compounds listed among unsaturated category are:

It is the usual case of ripening fruits with the help of alkenes.

In chemistry, we include unsaturated carbons to synthesize various compounds. They are usually used as monomers in such areas.

Mustard gas is prepared with the help of alkenes which is often required for chemical warfare. It is poisonous.

Acetylene is the fuel used inside a torch that we generally use in a home project.

Unsaturated compounds are generally used in the manufacturing of plastics .

Alkenes are used in industries for synthesizing fuel, detergent, plastic, and alcohol.

The use of Polystyrene is generally for disposable cups, egg cartons, and other convenient products.

Physical Properties of Unsaturated Carbon

As talked about above, unsaturated compounds have either one double or triple bond. These are generally given by the formula \[C_{2}H_{2n}\] and \[C_{2}H_{2n - 2}\].

To make unsaturated as saturated compounds, we need to add hydrogen atoms to them. This will form more carbon and hydrogen bonds.

The carbon-carbon bond formed in a double bond of carbons will form 120 degree angles.

The carbon-carbon bond formed in the triple bond of carbons will form 180 degree angles.

Unsaturated compounds get through different reactions, including combustion reactions, addition reactions , oxidation reactions performed by alkenes, polymerization of alkenes.

Combustion reactions include the formation of carbon dioxide and water.

The addition reaction is either symmetrical or unsymmetrical.

Oxidation Reactions include either addition of oxygen in a molecule or the removal of hydrogen from a molecule.

If reactions are conducted under pressure at a particular temperature with the help of a catalyst, these are polymerization reactions. The molecules produced are polymers.

The most common example of aromatic compounds universally considered is benzene. It forms 120 degrees between constituent carbon atoms.

Saturated Vs Unsaturated Hydrocarbons:

Both the compounds are organic compounds i.e, made up of hydrogen and carbon atoms. The major difference between both is the type of bonds they form. Saturated hydrocarbons have one covalent carbon bond, for example, methane, propane, and butane are some of the saturated hydrocarbons as they have a single carbon covalent bond and unsaturated hydrocarbons on the other hand have either a double covalent carbon bond or a triple covalent carbon bond. 

Unsaturated hydrocarbons are further divided into alkenes and alkynes based on the number of covalent bonds that the carbon atoms form. The hydrogenation reaction is the test used to figure out whether a compound is a saturated hydrocarbon or an unsaturated hydrocarbon. Hydrogenation is a type of reduction reaction where a hydrogen atom is added to a particular compound to know whether it is saturated or unsaturated. When the hydrogen atom is added to a compound it gets saturated and it tells us the previous stage of the compound. 

The above article has discussed different properties, types, and uses of unsaturated hydrocarbons. Surely, this will help you understand and clarify your concepts on the topic.

FAQs on Unsaturated Hydrocarbon

1. Are Alkynes Unsaturated Compounds in Organic Compounds?

According to the basic unsaturated hydrocarbon definition, there must be at least one double or a triple bond between two adjacent carbons in an organic compound. Alkynes have at least one triple bond between two adjacent carbon atoms. Thus these are unsaturated compounds. These have the triple bond; thus, the naming convention is given by “-one” as the suffix. The basic formula for alkynes is given by \[C_{2}H_{2n - 2}\]. These are made up of functional groups with a traditional name as acetylene. As compared to other hydrocarbons, alkynes are hydrophobic. These have formed a maximum carbon-carbon bond. Thus in terms of bond strength, it is given by 839 kJ/mol. This is very hard to break.

2. Are Unsaturated Hydrocarbons Good for You?

As compared to saturated compounds, unsaturated carbons are healthier—these help in removing the level of bad cholesterol present in our body. This helps in improving blood circulation on a good scale. You are not prompted to form heart disease with such compounds and also reduces inflammation in your body. Unsaturated ones are affluent in polyunsaturated fats. Thus they also bring Vitamin E into your diet, which is highly required for good body growth. Your body is not on the verge of forming rheumatoid arthritis. These compounds bring good development in your body cells and introduce an antioxidant diet to your body. These compounds are known to provide body nourishment.

3. What are unsaturated hydrocarbons?

All the organic material around us is made up of hydrocarbons which are different combinations of hydrogen and carbon atoms. Unsaturated hydrocarbons are one such compound in which the carbon atoms have formed double or triple bonds and to make them stable and saturated, we should add more hydrogen atoms. The alkenes in hydrocarbons have one double bond and the alkynes have triple bonds. Cyclic hydrocarbons which have at least one double bond or a triple bond are also considered unsaturated hydrocarbons. For example, propane, ethene, ethyne are some unsaturated hydrocarbons. When a compound is less saturated, it is more active and bonds easily with other elements or compounds and if the compound is saturated, it is less active and can not react with other compounds and elements easily.

4. What are the applications of hydrocarbons in real life?

Hydrocarbons are made up of hydrogen and carbon elements in different combinations. They are the base that forms the entire organic world around us. Based on the combinations and bonds formed, hydrocarbons are divided into saturated and unsaturated hydrocarbons and are further divided into alkenes, alkynes, etc, Following are some of the applications of Hydrocarbons in real life:

Hydrocarbons are an energy source when they are combusted and are cheaply available in the market as a fuel resource

The amount of carbon dioxide they release when they are burnt can be controlled by us

PETE, HDPE, etc are used to make plastic items like cups, bottles, etc 

Methane is an alkane that is used to generate electricity and it is generally produced from the waste generated in landfills and urban areas. When the bacteria decompose the waste material, methane is produced and it is further processed to generate electricity. 

Hexane is another such alkane that is used as glue in the leather and footwear industry to form layers of the material

Coal, petroleum, and natural gas are formed with different mixtures of hydrocarbons and are the major source of energy not only for India but also for many developing countries. But this source is not sustainable as it releases harmful gases and is also a limited source.

5. What is the difference between saturated and unsaturated hydrocarbons?

Hydrocarbons are organic compounds that have different combinations of hydrogen and carbon atoms. They are divided into saturated and unsaturated hydrocarbons. The main difference between saturated and unsaturated hydrocarbons is the bond formed by carbon atoms. In saturated hydrocarbons, carbon atoms form only one covalent bond between the carbon atoms present, and in unsaturated hydrocarbons, carbon atoms form either two covalent bonds or a triple covalent bond. 

If the carbon makes a double covalent bond, they are called alkenes and if they form a triple covalent bond, they are called alkyne. For example, ethene is an alkene that has a double covalent bond and ethylene is an example of alkyne which has a triple covalent bond. Whereas ethane has only one covalent bond and is a saturated hydrocarbon. To read more about hydrocarbons, their types, subtypes, examples, structure, and application in real-life, please visit Vedantu .

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Organic chemistry worksheets | 14–16 years

• 1 Introduction
• 2 Crude oil
• 3 Hydrocarbons
• 4 Cracking hydrocarbons
• 7 Carboxylic acids
• 8 Addition polymerisation
• 9 Condensation polymerisation
• 10 Natural polymers
• 11 Burning hydrocarbons
• 12 Reactions of alkanes and alcohols

Hydrocarbons

By Rob King

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Differentiated, editable worksheets providing a wide range of assessment questions exploring hydrocarbons, including structural formulae, writing word equations and balancing symbol equations

In context worksheets

These write-on worksheets will ask learners to use their knowledge of hydrocarbons in an applied context. Calculation questions are included to give opportunities to practise mathematical skills within this topic. Foundation and higher level worksheets are available and fully editable versions give you the flexibility to select the questions most relevant to a particular lesson. The teacher versions (also editable) give answers to all questions.

Foundation level

• Download the student worksheet as MS Word or pdf .
• Download the teacher version including answers to all questions as MS Word or pdf .

Higher level

Knowledge check worksheets.

Provide a series of questions on hydrocarbons to assess learners’ knowledge and understanding of this topic at both foundation and higher levels. The worksheets could be used for individual student work in class or at home. Separate answer sheets allow these resources to be used by teachers or by students during self-assessment of progress.

• Download the student worksheet as  MS Word  or  pdf .
• Download the teacher version including answers to all questions as  MS Word  or  pdf .
• Download the teacher version including answers to all questions as  MS Word  or  pdf .

In context sheet - Hydrocarbons - Foundation - Student

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Introduction

Cracking hydrocarbons

Carboxylic acids

Addition polymerisation

Condensation polymerisation

Natural polymers

Burning hydrocarbons

Reactions of alkanes and alcohols

• 14-16 years
• Maths skills
• Organic chemistry

Specification

• Standard temperature and pressure (s.t.p). Molar volume ar s.t.p., molar mass, relative molar mass (Mr).
• Alkanes, alkenes and alkynes as homologous series. For alkynes only ethyne to be considered.
• Systematic names, stuctural formulas and structural isomers of alkanes to C-5.
• Chemical reactions can result in a change in temperature. Exothermic and endothermic reactions (and changes of state).
• Combustion of alkanes and other hydrocarbons.
• Recognise and use significant figures as appropriate.
• Use of alkanes as as fuels.
• Awareness of the contributions of chemistry to society, e.g. provision of pure water, fuels, metals, medicines, detergents, enzymes, dyes, paints, semiconductors, liquid crystals and alternative materials, such as plastics, and synthetic fibres; increasi…
• Equations (full and ionic).
• The melting and boiling points of molecular substances are influenced by the strength of these intermolecular forces.
• Alkanes are used as fuels.
• Alkanes are saturated hydrocarbons.
• 6. be able to write balanced full and ionic equations, including state symbols, for chemical reactions
• 8. know the general formula for alkanes
• 9. know that alkanes and cycloalkanes are saturated hydrocarbons
• 1. know that a hydrocarbon is a compound of hydrogen and carbon only
• 20 i. understand, in terms of intermolecular forces, physical properties shown by materials, including: the trends in boiling temperatures of alkanes with increasing chain length
• Chemical reactions can be represented by word equations or equations using symbols and formulae.
• Write formulae and balanced chemical equations for the reactions in this specification.
• Chemical equations can be interpreted in terms of moles.
• Some properties of hydrocarbons depend on the size of their molecules, including boiling point, viscosity and flammability. These properties influence how hydrocarbons are used as fuels.
• Students should be able to recall how boiling point, viscosity and flammability change with increasing molecular size.
• The combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised. The complete combustion of a hydrocarbon produces carbon dioxide and water.
• Students should be able to write balanced equations for the complete combustion of hydrocarbons with a given formula.
• Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only.
• Most of the hydrocarbons in crude oil are hydrocarbons called alkanes. The general formula for the homologous series of alkanes is C₂H₂ₙ₊₂
• The first four members of the alkanes are methane, ethane, propane and butane.
• Alkane molecules can be represented in the following forms: (C₂H₆ or drawn out version). Students should be able to recognise substances as alkanes given their formulae in these forms.
• Describe the fractions as largely a mixture of compounds of formula CₙH₂ₙ₊₂ which are members of the alkane homologous series.
• Most of the hydrocarbons in crude oil are hydrocarbons called alkanes. The general formula for the homologous series of alkanes is CₙH₂ₙ₊₂
• 0.3 Write balanced chemical equations, including the use of the state symbols (s), (l), (g) and (aq)
• 8.1 Recall that hydrocarbons are compounds that contain carbon and hydrogen only
• 8.4 Recall the names and uses of the following fractions: gases, used in domestic heating and cooking; petrol, used as fuel for cars, kerosene, used as fuel for aircraft; diesel oil, used as fuel for some cars and trains; fuel oil, used as fuel for large…
• 8.5 Explain how hydrocarbons in different fractions differ from each other in: the number of carbon and hydrogen atoms their molecules contain; boiling points; ease of ignition; viscosity; and are mostly members of the alkane homologous series
• 8.6 Explain an homologous series as a series of compounds which: have the same general formula; differ by CH₂ in molecular formulae from neighbouring compounds; show a gradual variation in physical properties, as exemplified by their boiling points; have…
• 8.7 Describe the complete combustion of hydrocarbon fuels as a reaction in which: carbon dioxide and water are produced; energy is given out
• 9.10C Recall the formulae of molecules of the alkanes, methane, ethane, propane and butane, and draw the structures of these molecules, showing all covalent bonds
• 9.11C Explain why the alkanes are saturated hydrocarbons
• 9.16C Describe how the complete combustion of alkanes and alkenes involves the oxidation of the hydrocarbons to produce carbon dioxide and water
• 8.2 Describe crude oil as: a complex mixture of hydrocarbons; containing molecules in which carbon atoms are in chains or rings (names, formulae and structures of specific ring molecules not required); an important source of useful substances…
• C3.4.1 recall that crude oil is a main source of hydrocarbons and is a feedstock for the petrochemical industry
• C3.4.4 describe the fractions of crude oil as largely a mixture of compounds of formula CₙH₂ₙ₊₂ which are members of the alkane homologous series
• C3.4.17 name and draw the structural formulae, using fully displayed formulae, of the first four members of the straight chain alkanes and alkenes, alcohols and carboxylic acids
• C3.4.18 predict the formulae and structures of products of reactions (combustion, addition across a double bond and oxidation of alcohols to carboxylic acids) of the first four and other given members of these homologous series
• C6.1j describe the fractions as largely a mixture of compounds of formula CₙH₂ₙ₊₂ which are members of the alkane homologous series
• C6.1k recall that crude oil is a main source of hydrocarbons and is a feedstock for the petrochemical industry
• C6.2b name and draw the structural formulae, using fully displayed formulae, of the first four members of the straight chain alkanes, alkenes, alcohols and carboxylic acids
• C6.2c predict the formulae and structures of products of reactions of the first four and other given members of the homologous series of alkanes, alkenes and alcohols
• C6.2l describe the fractions as largely a mixture of compounds of formula CₙH₂ₙ₊₂ which are members of the alkane homologous series
• Alkanes: are a homologous series of saturated hydrocarbons
• can be represented by the general formula CₙH₂ₙ₊₂
• Straight-chain and branched alkanes can be systematically named from structural formulae containing no more than 8 carbons in the longest chain.
• Molecular formulae can be written and structural formulae can be drawn, from the systematic names of straight-chain and branched alkanes, containing no more than 8 carbons in the longest chain.
• A homologous series is a family of compounds with the same general formula and similar chemical properties.
• Patterns are often seen in the physical properties of the members of a homologous series.
• The subsequent members of a homologous series show a general increase in their melting and boiling points. This pattern is attributed to increasing strength of the intermolecular forces as the molecular size increases. The type of intermolecular force do…
• Hydrocarbons are compounds containing only hydrogen and carbon atoms.
• Compounds containing only single carbon–carbon bonds are described as saturated.
• Compounds containing at least one carbon–carbon double bond are described as unsaturated.
• The structure of any molecule can be drawn as a full or a shortened structural formula.
• (f) the combustion reactions of hydrocarbons and other fuels
• (k) the general formula CₙH₂ₙ₊₂ for alkanes and CₙH₂ₙ for alkenes
• (l) the names and molecular and structural formulae for simple alkanes and alkenes
• (n) the names of more complex alkanes and alkenes
• 2.5.2 define a homologous series as a family of organic molecules that have the same general formula, show similar chemical properties, show a gradation in their physical properties and differ by a CH₂ group;
• 2.5.3 recall that a hydrocarbon is a compound/molecule consisting of hydrogen and carbon only;
• 2.5.4 recall the general formula of the alkanes and the molecular formula, structural formula and state at room temperature and pressure of methane, ethane, propane and butane;
• 2.5.9 describe the complete combustion of alkanes to produce carbon dioxide and water, including observations and tests to identify the products.
• 1.7.6 calculate the reacting masses of reactants or products, given a balanced symbol equation and using moles and simple ratio, including examples here there is a limiting reactant;
• 1.7.5 calculate the reacting masses of reactants or products, given a balanced symbol equation and using moles and simple ratio, including examples here there is a limiting reactant;

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Hydrocarbons

What are hydrocarbons.

Hydrocarbons are organic compounds that are entirely made up of only two kinds of atoms – carbon and hydrogen. Typically, hydrocarbons are colourless gases that have very weak odours. Hydrocarbons can feature simple or relatively complex structures and can be generally classified into four subcategories, namely alkanes, alkenes, alkynes, and aromatic hydrocarbons. The study of hydrocarbons can provide insight into the chemical properties of other functional groups and their preparation. Furthermore, hydrocarbons such as propane and butane are used for commercial fuel purposes in the form of Liquefied Petroleum Gas (LPG). Benzene, one of the simplest aromatic hydrocarbons, serves as the raw material for the synthesis of many synthetic drugs.

Download Complete Chapter Notes of Hydrocarbons Download Now

Structure of Hydrocarbon

Download hydrocarbons JEE Previous Year Solved Questions PDF

Table of Contents

• Classification
• Preparation

The molecular formula for these compounds is  C x H y . The existence of hydrocarbons is seen in plants and trees. For example, Carotenes is an organic pigment that is found in green leaves and carrots. These hydrocarbons make up 98% of natural crude rubber. Further, they possess large internal energy, which renders them their importance.

⇒ Check: Basic Concepts of Organic Chemistry

Classification and Types of Hydrocarbons

Earlier, chemists classified hydrocarbons as either aliphatic or aromatic. The classification was done based on their source and properties. And accordingly, it was found that aliphatic hydrocarbons were derived from the chemical degradation of fats or oils, whereas aromatic hydrocarbons contained substances that were a result of the chemical degradation of certain plant extracts. However, today we classify hydrocarbons on the basis of structure and not merely on their origin.

Classification of Hydrocarbons

Types of Hydrocarbons

• Saturated Hydrocarbons : In these compounds, carbon-carbon atoms and carbon-hydrogen atoms are held together by single bonds. These single-bonded compounds are the simplest hydrocarbons. These types of hydrocarbons don’t have double or triple bonds. In terms of hybridization , they have Sp 3 hybridised carbon atoms with no Sp 2 or Sp hybridised carbon atoms. They are together called alkanes which have a general formula of C n H 2n+2 . For example, CH 4 C 3 H 6 .
• Unsaturated Hydrocarbons : These compounds consist of a single, double or triple bond between carbon-carbon atoms. The double-bonded compounds are called alkenes, and the triple-bonded compounds are called alkynes. The general formula for alkenes is C n H 2n, and for alkynes, the general formula is C n H 2n-2 .
• Cycloalkanes : These hydrocarbons possess one or multiple carbon rings. The hydrogen atom is attached to the carbon ring.
• Aromatic Hydrocarbons : They are also called arenes. Arenes are compounds which consist of at least one aromatic ring.
• Aliphatic Hydrocarbons : They are straight chain structures having no rings in them.
• Alicyclic Hydrocarbons :  They are hydrocarbons having a ring structure in them. The carbons atoms can be Sp, Sp 2 , or Sp 3 hybridised.

Properties of Hydrocarbons

Due to their different molecular structures, the empirical formula of hydrocarbons is also different from each other. For instance, in alkanes, alkynes or alkenes, the amount of bonded hydrogen decreases in alkenes and alkynes. This is mainly due to the “self-bonding” or catenation of carbon that prevents the complete saturation of the hydrocarbon by the formation of double or triple bonds. The ability of hydrocarbons to bond to themselves is known as catenation. With such capabilities, they can form more complex molecules like cyclohexane and, in rare instances, aromatic hydrocarbons like benzene.

The cracking of Hydrocarbons is a process in which heavy organic molecules are broken down into lighter molecules. This is accomplished by supplying an adequate amount of heat and pressure. Sometimes, catalysts are used to speed up the reaction. This process plays a very important role in the commercial production of diesel fuel and gasoline.

⇒ Check: Combustion of Hydrocarbons

Physical Properties

Alkanes with 10 C-atoms or less are generally gases at room temperatures of more than 10 C-atoms, and the molecules are gases or liquids. Alkanes generally have low boiling and melting points owing to their weak Vanderwal interaction.

The boiling point depends on the following factors:

• Molecular mass

Alkanes have high molecular mass and high boiling points. For example, C 2 H 6 has more boiling point than CH 4.

Alkanes that have the same molecular mass but have a different number of branches, the one with less branching has a more boiling point. This is because Vanderwal’s force becomes weak as the area increases.

For example, CH 3 -CH 2 -CH 2 -CH 3 has more boiling point. Alkanes are very feebly soluble in water, but they are soluble in non-polar solvents such as Benzene, CCl 4 , etc.

Preparation of Hydrocarbons –  Alkanes

From alkenes and alkynes.

The alkanes can be produced from alkenes or alkynes through hydrogenation. H 2 gas is passed over a metal surface, such as Ni or Pt, along with the alkenes to produce alkane.

CH 2 =CH 2 → (+Hz/Ni) CH 3 -CH 3

The above reaction is called the “Sabatier-Sender son’s” reaction. Other catalysts which can be used are Pt, Pd-BaSo 4 , Adams catalyst (Pt 2 O) or Wilkinson catalyst (R 3 PRhCl), etc.

From Alkyl Halides

Alkyl halides can be converted to alkanes through various methods. They are as follows.

1. Using Zn/Protic solvents

2. Using courts reactions

Note:  Alkanes with only an even number of carbons atoms can be produced.

3. Using Reducing Agents

R-X → [H]R – H

The reducing agents which can be used are  LiAlH 4 , NaBH 4 , NaNH 2 , etc.

• LiAlH 4   can’t reduce 3° halides.
• NaBH 4  can’t reduce 1° halide.

2. From Aldehydes/Ketones

• Clemmensen’s Reduction
• Wolf-Kishner Reduction

3. From Carboxylic Acids through Decarboxylation

• Kolbe’s Electrolysis
• Using Soda-lime

⇒ Also Read:  Pyrolysis of Hydrocarbons

Preparation of Hydrocarbons –  Alkenes

General formula: C n H 2n

Preparation Methods

Most of the reactions involving the preparation of alkenes involve an elimination process . There are 3 mechanisms suggested for the elimination reactions, and all these are β- eliminations.

E 2  Mechanism

• Second order kinetics
• Single step process
• Order & reactivity 1° > 2° > 3°

Because of steric hindrance,

• More favoured in non-polar, aprotic solvents.
• Less substituted alkenes formed as the major product.

E 1  Mechanism

• Two-step process
• 1 st order kinetics
• Order of reactivity: 3° > 2° > 1°

Because of the stability of carbonation,

• More favoured by polar, protic solvents.
• Rearrangement is possible.
• Gives more substituted alkenes as major products.

(i) Acid catalysed

• Markovnikov product

(ii) Hydroboration-oxidation

• Anti – Markonikov
• No rearrangement

(iii) Oxymercuration-demercuration

• Markovnikov

Oxidation Reactions

• Using Baeyer’s reagent
• Using hot KMnO 4
• Using O 5 O 4
• Addition of peroxy acid

Preparation of Hydrocarbons –   Alkynes

Alkynes can be prepared from alkyl halides and alcohols.

Addition reaction:

All addition reactions  in alkenes are possible.

Benzene –  Preparation

• From ethyne
• From phenol
• From aniline

Chemical Properties:

Benzene generally undergoes electrophilic substitution reactions.

• Friedel Crafts alkylation, halogenation and acylation

Uses of Hydrocarbons

• Hydrocarbons are widely used as fuels. For example, LPG (Liquefied Petroleum Gas), and CNG (Liquefied Natural Gas).
• They are used in the manufacturing of polymers such as polyethene, polystyrene etc.
• These organic compounds find their application in the manufacturing of drugs and dyes as a starting material.
• They serve as lubricating oil and grease.

Hydrocarbons – Important Topics

Hydrocarbons – Important Questions

Hydrocarbons – Top 12 Most Important and Expected Questions

Hydrocarbons – JEE Advanced Questions

Hydrocarbons Revision for JEE Main

Hydrocarbons Chemistry One-Shot for JEE

Frequently Asked Questions on Hydrocarbons

What are the 4 types of hydrocarbons, what are hydrocarbons made up of, what are the characteristics of hydrocarbons, why are alkanes the least reactive hydrocarbons, what is the product of ozonolysis of ethene.

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That article is very good and simple for understanding the concept of hydro-carbons. it also described the types of hydrocarbons.

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• 2.1: Alkenes- Structures and Names Alkenes are hydrocarbons with a carbon-to-carbon double bond.
• 2.2: Cis-Trans Isomers (Geometric Isomers) Cis-trans (geometric) isomerism exists when there is restricted rotation in a molecule and there are two nonidentical groups on each doubly bonded carbon atom.
• 2.3: Physical Properties of Alkenes The physical properties of alkenes are much like those of the alkanes: their boiling points increase with increasing molar mass, and they are insoluble in water.
• 2.4: Chemical Properties of Alkenes Alkenes undergo addition reactions, adding such substances as hydrogen, bromine, and water across the carbon-to-carbon double bond.
• 2.5: Alkynes Alkynes are similar to alkenes in both physical and chemical properties. For example, alkynes undergo many of the typical addition reactions of alkenes. The International Union of Pure and Applied Chemistry (IUPAC) names for alkynes parallel those of alkenes, except that the family ending is -yne rather than -ene. The IUPAC name for acetylene is ethyne. The names of other alkynes are illustrated in the following exercises.
• 2.6: Polymers Molecules having carbon-to-carbon double bonds can undergo addition polymerization.
• 2.7: Aromatic Compounds- Benzene Aromatic hydrocarbons appear to be unsaturated, but they have a special type of bonding and do not undergo addition reactions.