Most of the times, these double bonds are arranged in an alternative manner. Alkenes are colorless and nonpolar. Alkenes are considered as reactive molecules due to the presence of a double bond.
This double bond is composed of a sigma bond and a pi bond. This pi bond can be broken down; this is called the opening up of the double bond. Then electrophiles can be attached to these carbon atoms that was in a double bond. These are called addition reaction s of alkenes.
In addition, polymerization is a major reaction that alkenes are able to undergo. The opening up of the double bond allows alkenes to undergo polymerization. Here, one alkene molecule is called a monomer. This leads to the production of very important polymers. Alkenes show geometrical isomerism. This is also called cis-trans isomerism. When naming an alkene, one should also consider the cis-trans geometry of these molecules. Alkenes: Alkenes are unsaturated hydrocarbons having the chemical formula C n H 2n.
Alkanes: Alkanes are composed of only single bonds. Alkenes: Alkenes are composed of double bonds as well as single bonds. Alkenes: The chemical formula for alkenes is C n H 2n. Alkanes: Alkanes cannot undergo polymerization. Alkenes: Alkenes can undergo polymerization.
Alkanes and alkenes are important hydrocarbons. Although there are similarities between alkanes and alkenes such as nonpolar behavior and insolubility in water, they have many distinct features. Accessed 21 Aug. Alkanes are non-polar compounds and insoluble in water.
They have low boiling and melting points. Natural gas, camping gas, lighter gas and much of gasoline are all alkanes. All the alkanes burn but they need a lot of air or oxygen to burn completely. Alkenes and alkynes are more reactive than alkanes. Keep your current shopping and add the saved Cart?
Remove your current shopping cart and replace with the saved cart? Add the items to your existing shopping cart? Replace your shopping cart with these items? 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.
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. 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. 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. These operations have been in effect since the s and have made the production of some plastics among the most efficient industrial operations today.
The name of an alkene is derived from the name of the alkane with the same number of carbon atoms. The presence of the double bond is signified by replacing the suffix -ane with the suffix -ene. The location of the double bond is identified by naming the smaller of the numbers of the carbon atoms participating in the double bond:. Molecules of 1-butene and 2-butene are structural isomers; the arrangement of the atoms in these two molecules differs. As an example of arrangement differences, the first carbon atom in 1-butene is bonded to two hydrogen atoms; the first carbon atom in 2-butene is bonded to three hydrogen atoms.
The compound 2-butene and some other alkenes also form a second type of isomer called a geometric isomer. In a set of geometric isomers, the same types of atoms are attached to each other in the same order, but the geometries of the two molecules differ.
Carbon atoms are free to rotate around a single bond but not around a double bond; a double bond is rigid. This makes it possible to have two isomers of 2-butene, one with both methyl groups on the same side of the double bond and one with the methyl groups on opposite sides.
The different geometries produce different physical properties, such as boiling point, that may make separation of the isomers possible:. This reaction is called an addition reaction. The hybridization of the carbon atoms in the double bond in an alkene changes from sp 2 to sp 3 during an addition reaction. For example, halogens add to the double bond in an alkene instead of replacing hydrogen, as occurs in an alkane:.
The reactant is a five-carbon chain that contains a carbon-carbon double bond, so the base name will be pentene. We begin counting at the end of the chain closest to the double bond—in this case, from the left—the double bond spans carbons 2 and 3, so the name becomes 2-pentene. Since there are two carbon-containing groups attached to the two carbon atoms in the double bond—and they are on the same side of the double bond—this molecule is the cis- isomer, making the name of the starting alkene cis pentene.
The product of the halogenation reaction will have two chlorine atoms attached to the carbon atoms that were a part of the carbon-carbon double bond:.
This molecule is now a substituted alkane and will be named as such. The base of the name will be pentane. We will count from the end that numbers the carbon atoms where the chlorine atoms are attached as 2 and 3, making the name of the product 2,3-dichloropentane.
Hydrocarbon molecules with one or more triple bonds are called alkynes ; they make up another series of unsaturated hydrocarbons. The simplest member of the alkyne series is ethyne, C 2 H 2 , commonly called acetylene. The Lewis structure for ethyne, a linear molecule, is:. The IUPAC nomenclature for alkynes is similar to that for alkenes except that the suffix -yne is used to indicate a triple bond in the chain.
Describe the geometry and hybridization of the carbon atoms in the following molecule:. Carbon atoms 1 and 4 have four single bonds and are thus tetrahedral with sp 3 hybridization. Carbon atoms 2 and 3 are involved in the triple bond, so they have linear geometries and would be classified as sp hybrids. Identify the hybridization and bond angles at the carbon atoms in the molecule shown:. Chemically, the alkynes are similar to the alkenes. The reaction of acetylene with bromine is a typical example:.
Acetylene and the other alkynes also burn readily. An acetylene torch takes advantage of the high heat of combustion for acetylene. Benzene, C 6 H 6 , is the simplest member of a large family of hydrocarbons, called aromatic hydrocarbons.
These compounds contain ring structures and exhibit bonding that must be described using the resonance hybrid concept of valence bond theory or the delocalization concept of molecular orbital theory. To review these concepts, refer to the earlier chapters on chemical bonding. The resonance structures for benzene, C 6 H 6 , are:. Valence bond theory describes the benzene molecule and other planar aromatic hydrocarbon molecules as hexagonal rings of sp 2 -hybridized carbon atoms with the unhybridized p orbital of each carbon atom perpendicular to the plane of the ring.
Benzene does not, however, exhibit the characteristics typical of an alkene. There are many derivatives of benzene.
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