Alkenes
Alkenes are a class of hydrocarbons that contain carbon-carbon double bonds. They are unsaturated hydrocarbons and are characterized by the general formula CnH2n. Alkenes are important in organic chemistry and are used in the production of plastics, solvents, and other industrial chemicals. They also participate in various chemical reactions, such as addition reactions and polymerization.
6 Key excerpts on "Alkenes"
eBook - ePub- James G. Speight(Author)
- 2010(Publication Date)
- Gulf Professional Publishing(Publisher)
...Alkanes can have straight or branched chains, but without any ring structure. 2. Alkenes (olefins) are unsaturated hydrocarbons insofar as not all of the carbon valencies are satisfied by another atom and have a double bond (C=C) between carbon atoms. Alkenes have the general formula C n H 2 n, assuming no ring structures in the molecule. Alkenes may have more than one double bond between carbon atoms, in which case the formula is reduced by two hydrogen atoms for each additional double bond. For example, an alkene with two double bonds in the molecule has the general formula C n H 2 n – 2. Because of their reactivity and the time involved in crude oil maturation, Alkenes do not usually occur in petroleum. 3. Alkynes (acetylenes) are hydrocarbons which contain a triple bond (C≡C) and have the general formula C n H 2 n – 2. Acetylene hydrocarbons are highly reactive and, as a consequence, are very rare in crude oil. 4. Cycloalkanes (naphthenes) are saturated hydrocarbons containing one or more rings, each of which may have one or more paraffinic side chains (more correctly known as alicyclic hydrocarbons). The general formula for a saturated hydrocarbon containing one ring is C n H 2 n. 5. Aromatic hydrocarbons (arenes) are hydrocarbons containing one or more aromatic nuclei, such as benzene, naphthalene, and phenanthrene ring systems, which may be linked up with (substituted) naphthene rings and/or paraffinic side chains. 5.1. Bonding in hydrocarbons Since carbon adopts the tetrahedral geometry when there are four σ bonds, only two bonds can occupy a plane simultaneously. The other two bonds are directed to the rear or to the front of the plane...
eBook - ePub- Graham Patrick(Author)
- 2004(Publication Date)
- Taylor & Francis(Publisher)
...SECTION B — ALKANES AND CYCLOALKANES B1 Definition Key Notes Alkanes Alkanes are organic molecules consisting solely of carbon and hydrogen atoms linked by single σ bonds. All the carbon atoms are tetrahedral and sp 3 hybridized. Alkanes are stable molecules and unreactive to most chemical reagents. They have the general formula C n H 2 n +2 Cycloalkanes Cycloalkanes are cyclic alkane structures. They have the general formula C n H 2 n. Most cycloalkanes are unreactive to chemical reagents. However, three- and four-membered rings are reactive due to ring strain and behave like Alkenes. Related topics (A3) sp 3 Hybridization (D4) Conformational isomers Alkanes Alkanes are organic molecules with the general formula C n H 2 n +2, which consist of carbon and hydrogen atoms linked together by C–C and C–H single bonds. They are often referred to as saturated hydrocarbons — saturated because all the bonds are single bonds, hydrocarbons because the only atoms present are carbon and hydrogen. All the carbon atoms in an alkane are sp 3 hybridized and tetrahedral in shape. The C–C and C–H bonds are strong σ bonds, and so alkanes are unreactive to most chemical reagents. Alkanes are sometimes referred to as straight chain or acyclic alkanes to distinguish them from cycloalkanes or alicyclic compounds. Cycloalkanes Cycloalkanes are cyclic alkanes (alicyclic compounds) having the general formula C n H 2 n where the carbon atoms have been linked together to form a ring. All sizes of ring are possible. However, the most commonly encountered cycloalkane in organic chemistry is the six-membered ring (cyclohexane). Most cycloalkanes are unreactive to chemical reagents. However, small three- and four-membered rings are reactive and behave like Alkenes...
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
...If the carbon atom is bonded to one other carbon atom, it is primary. If it is bonded to two other carbon atoms, it will be secondary and if it is bonded to three other carbon atoms it will be tertiary. Also, if the carbon atom is bonded to four other carbon atoms, it is called quaternary. A quaternary carbon atom will contain no bonds to hydrogen. The central carbon atom in neopentane, shown in Fig. 13.7, is a quaternary carbon atom. Another class of hydrocarbons is the Alkenes. Alkenes are a series of hydrocarbons that contain a double bond and have the general formula C n H 2 n. They are named by using the alkane root names in Table 13.1 and replacing the -ane ending with -ene. Alkenes are a type of unsaturated hydrocarbon. Unsaturated hydrocarbons have at least two less hydrogens than a normal alkane. They include compounds with double and triple bonds, as well as cyclic structures. The presence of a double bond is known as one site of unsaturation because the two carbon atoms involved in the double bond have one less hydrogen atom each. The simplest alkene ethene (C 2 H 4), with two carbon atoms and four hydrogen atoms, was discussed in Section 3.1. The alkene with three carbon atoms and six hydrogen atoms, propene (C 3 H 6), can be viewed as an ethene molecule with one hydrogen atom replaced with a methyl group. The Alkenes with more carbon atoms than propene are named according to the IUPAC conventions by using an Arabic numeral in front of the alkane root name to identify the carbon with the double bond, immediately followed by the name of the alkene backbone. The Alkenes with four carbon atoms and eight hydrogen atoms are the butenes (C 4 H 8). Like butane, butene can also have structural isomers as shown in Fig. 13.8. The structural isomers 1-butene and isobutene, commonly called 2-methypropene, are similar to those in the alkanes: butane and isobutane (2-methylpropane)...
eBook - ePub- James G. Speight(Author)
- 2019(Publication Date)
- Gulf Professional Publishing(Publisher)
...Each successive member of a homologous series of hydrocarbon derivatives has one more carbon and two more hydrogen atoms in its molecule than the preceding member. The second alkane is ethane, C 2 H 6, and the third is propane, C 3 H 8. Alkane derivatives have the general formula C n H 2n+2 (where n is an integer greater than or equal to 1). Other homologous series of hydrocarbon derivatives include the alkene derivatives and the alkyne derivatives (Chapter 1). Hydrocarbon mixtures are composed of hydrocarbon derivatives, naphtha, benzine, and petroleum ether. Naphtha is a flammable liquid hydrocarbon mixture that typically boils over the range 0–200°C (32–390°F). Benzine (which should not be confused with benzene— an aromatic hydrocarbon) also known as petroleum ether is a hydrocarbon mixture of alkane derivatives, such as pentane, hexane, and heptane. Petroleum ether is obtained from crude oil refineries as the portion of the distillate which is intermediate between the low boiling naphtha and the higher boiling kerosene. It has a specific gravity of between 0.6 and 0.8 depending on its composition. Petroleum ether should not be confused with the class of organic compounds called ethers. The physical properties of the unsaturated hydrocarbons (alkane derivatives and cycloalkanes derivatives) are similar to (but not the same as) the properties of the corresponding saturated hydrocarbons (alkene derivatives and alkyne derivatives). The molecules are nonpolar and thus relatively insoluble in water and any intermolecular bonds are weak van der Waal’s bonds. Melting points and boiling points for the small molecules are fairly low. The higher the molecular weight of the hydrocarbon derivative, the higher the melting point and the boiling point. Finally, the chemical and physical properties of hydrocarbon derivatives are also dictated by stereochemistry (Olah and Molnár, 2003)...
eBook - ePub- Tony Farine, Mark A. Foss(Authors)
- 2013(Publication Date)
- Routledge(Publisher)
...You may also have used propane (C 3 H 8) and butane (C 4 H 10) as fuels in portable heaters and cookers. Take a moment to draw the structures of butane and propane. Now check your diagrams against Figure 3.10. Figure 3.10 The structural formulae of methane, butane and propane. Hydrocarbons that contain double or triple bonds are said to be unsaturated. This is a reference to the fact that the molecule contains less than the maximum number of substituents. The multiple bond could be chemically broken and further hydrogen atoms added, a process called hydrogenation. You will find reference is made to it on the back of margarine tubs. In this case, hydrogenation ensures that margarine remains solid at room temperature. Alkenes contain a double bond; the simplest member of this family is ethene (C 2 H 4), the structure of which is shown in Figure 3.11. Note that Alkenes are named using the suffix –ene. Alkynes contain a triple bond; the simplest member of this group is ethyne (C 2 H 2), the structure of which is also given in Figure 3.11. Once again, note that the family to which this molecule belongs is given by the use of a suffix – in this case, it is –yne. You may be more familiar with ethyne by its alternative name, acetylene – the gas used in welding torches. Figure 3.11 The structural formulae of ethene and ethyne. So are hydrocarbons important in health care? The alkanes, Alkenes and alkynes are among the simplest organic molecules. In health care, we are interested in the function of the body, which contains some very complex organic molecules. You will no doubt encounter them later in your studies, but it would be too much to introduce them now. Many, such as saturated fats, contain chains of carbon atoms such as the alkanes and some, such as polyunsaturated fats, contain double bonds such as the Alkenes. If you learn about the simpler organic molecules now, you will find it easier later on to understand the structure of more complex molecules found in the body...
eBook - ePub- Christian Vargel(Author)
- 2020(Publication Date)
- Elsevier Science(Publisher)
...C 6 H 5 C 2 H 5 ; Ethylene, C 2 H 4 ; Ethylene, oxide, (CH 2) 2 O; Fatty acids; Fresh water; Heptane, C 7 H 16 ; Hexane, C 6 H 14 ; Hydrocarbons; Isobutane, C 4 H 10 ; Isoprene; Kerosene; Lime mud; Liquid natural gas (LNG); Methane, CH 4 ; Methyl esters; Microbiologically influenced corrosion (MIC); Naphthenes; Naphthalene, C 10 H 8 ; Octane, C 8 H 18 ; Paraffins; Pentane, C 5 H 12 ; Pinene; Propane; Propylene, C 3 H 6 ; Rubber; Seawater; Styrene, C 6 H 5 C 2 H 3 ; Sulphates; Terebenthine; Terphenyl,. C 6 H 5 C 6 H 4 C 6 H 5 ; Toluene, C 6 H 5 CH 3 ; Vegetable oils; Water; Xylene, C 6 H 4 (CH 3) 2 1.1 Alkanes 1.2 Alkenes 1.3 Alkynes 1.4 Arenes or aromatic hydrocarbons 1.5 Terphenyls 1.6 Cyclic, non-benzenic hydrocarbons 1.7 Engine fuels 1.7.1 Conventional fuels 1.7.2 Biofuels 1.8 Petroleum industry 1.9 Drilling muds References Hydrocarbons are the main constituents of crude oil and natural gas. They are used as fuels and lubricants and are the raw materials for the production of plastics, solvents and industrial chemicals. Hydrocarbons are organic chemical compounds composed only of carbon and hydrogen. Depending on how the carbon atoms are bonded together, hydrocarbons can be aliphatic or cyclic. The aliphatic compounds include alkanes (C n H 2n+2), Alkenes (C n H 2n) and alkynes (C n H 2n − 2), depending on the number of unsaturated C–C bonds in the molecule. Cyclic compounds include aromatic hydrocarbons and cycloparaffins (non-benzenic hydrocarbons). Hydrocarbons are chemically relatively inert and, therefore, have no action on aluminium. They are insoluble in water. 1.1...
