Alkenes

10 Key excerpts on "Alkenes"

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  eBook - PDF

  Introduction to General, Organic, and Biochemistry

  • Frederick Bettelheim, William Brown, Mary Campbell, Shawn Farrell(Authors)
  • 2019(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  347 CONTENTS 12.1 Introduction to Alkenes and Alkynes 12.2 Structures of Alkenes and Alkynes 12.3 Naming Alkenes and Alkynes 12.4 Physical Properties of Alkenes and Alkynes 12.5 Characteristic Reactions of Alkenes 12.6 Important Polymerization Reactions of Ethylene and Substituted Ethylenes 12.7 Structure of Benzene 12.8 Naming Aromatic Compounds 12.9 Reactions of Benzene and Its Derivatives 12.10 Phenols Alkenes, Alkynes, and Aromatic Compounds 12 12.1 Introduction to Alkenes and Alkynes In this chapter, we begin our study of unsaturated hydrocarbons. Recall from Section 11.1 that unsaturated compounds contain one or more carbon–carbon double bonds, triple bonds, or benzene-like rings. In this chapter, we first study Alkenes and alkynes . Alkenes are unsaturated hydrocarbons that contain one or more carbon–carbon double bonds. The simplest alkene is ethylene. Ethylene (an alkene) Acetylene (an alkyne) H H H H H ! C # C ! H C C Alkynes are unsaturated hydrocarbons that contain one or more carbon–carbon triple bonds. The simplest alkyne is acetylene. Because alkynes are not widespread in nature and have little importance in biochemistry, we will not study their chemistry in depth. Compounds containing carbon–carbon double bonds are especially widespread in nature. Furthermore, several low-molecular-weight Alkenes Unsaturated hydrocarbons that contain a carbon–carbon double bond Alkynes Unsaturated hydrocarbons that contains a carbon–carbon triple bond Charles D. Winters Carotene is a naturally occurring polyene in carrots and tomatoes (Problem 85). Copyright 2020 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience.

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  eBook - ePub

  Handbook of Industrial Hydrocarbon Processes

  • 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

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  eBook - PDF

  General Chemistry: Atoms First

  • Young, William Vining, Roberta Day, Beatrice Botch(Authors)
  • 2017(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Alkenes and alkynes are generally more reactive than alkanes due to their unsaturation, but benzene, an unsaturated cyclic hydrocarbon, is actually quite unreactive. Alkenes Alkenes are hydrocarbons that contain at least one carbon–carbon double bond. Alkenes with one carbon–carbon double bond and no rings have the general formula C n H 2 n . The carbon atoms involved in the double bond are linked by one sigma bond and one pi bond, and each is sp 2 -hybridized with trigonal planar geometry. Recall that mol-ecules with pi bonds can exist as more than one isomer because of restricted rotation around the pi bond. Note that the two trigonal planes are coplanar due to the overlap of p orbitals (Figure 22.1.4). Alkene names contain a parent alkane name with the -ane ending changed to -ene . In large alkanes a numbering system is used to indicate the position of the double bond. Branched Alkenes are named using the same rules used for branched alkanes. For example, consider the Alkenes in Figure 22.1.5. 1 2 3 4 5 6 The compound name is 4-ethyl-2-methylhexane. b. The parent name is the cycloalkane name, cyclobutane. The carbon atoms in the ring are numbered to give the substituents, the two methyl groups, the lowest possible numbers. The prefix di - is used to indicate the fact that there are two identical substituents. 1 2 3 4 The compound name is 1,2-dimethylcyclobutane.

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  eBook - ePub

  Understanding Advanced Organic and Analytical Chemistry

  The Learner's ApproachRevised Edition

  • Kim Seng Chan, Jeanne Tan;;;(Authors)
  • 2016(Publication Date)
  • WS EDUCATION

    (Publisher)

  CHAPTER 5

  Alkenes

  5.1 Introduction

  Alkenes are unsaturated hydrocarbons containing the C=C double bond. They have the general formula Cn H

  2n

  . Sharing this same general formula are the cycloalkanes, which are constitutional/structural isomers to the corresponding Alkenes. Apart from functional group isomerism, constitutional/structural isomerism in Alkenes can also arise due to the different degree of branching in the main carbon chain of their molecules (chain isomerism) and the location of the C=C bond (positional isomerism).

  Alkenes also exhibit cis-trans isomerism, otherwise known as geometrical isomerism (see Chapter 2 ). This form of stereoisomerism is attributed to the restricted rotation about the C=C bond.

  As the doubly bonded carbon atoms are sp2 hybridized, the geometry about each of them is trigonal planar. To show the trigonal planar geometry, the structure of an alkene is normally drawn in such a way as to depict an angle of 120° about the double bond, as follows:

  This form of drawing is especially important in illustrating both the cis and trans isomers.

  5.2 Nomenclature

  For Alkenes, their chemical names end with the suffix −ene. Table 5.1 lists the names of the first few members of the alkene family. For an alkene with four carbon atoms onwards, there exists different ways in which the carbon atoms can be connected to each other, hence giving rise to the notion of constitutional/structural isomerism (see Chapter 2 ). For instance, both but-1-ene and but-2-ene have a chain of four carbon atoms. The difference between them is the location of the C=C bond.

  Table 5.1

  The word “butene” does not just wrongfully account for the two constitutional/structural isomers mentioned above, ambiguity is also found in the word “but-2-ene,”which actually constitutes a pair of cis-trans (geometrical) isomers:

  Hence, “butene” actually stands for a total of three distinct compounds – but-1-ene, cis-but-2-ene and trans

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  eBook - PDF

  Organic Chemistry

  A Mechanistic Approach

  • Penny Chaloner(Author)
  • 2014(Publication Date)
  • CRC Press

    (Publisher)

  37 3.1 Alkenes 3.1.1 BONDING IN Alkenes The next group of hydrocarbons that we will study is the Alkenes (old name olefins), compounds containing one or more carbon–carbon double bonds. The first member of the class is ethene ( 3.1) in which there is a double bond between the two carbon atoms. The old name for this com- pound was ethylene, and this is still widely used in the polymer industry. There are two carbon– carbon bonds along the same direction—so clearly, we cannot use sp 3 hybrid orbitals, which we used to make alkanes, for this molecule. 3.1 C C H H H H In order to describe a carbon–carbon double bond, we need to return to the electronic configura- tion of carbon: C 1s 2 2s 2 2p x 1 2p y 1 2p z 0 As before, we formally promote one electron to obtain C 1s 2 2s 1 2p x 1 2p y 1 2p z 1 This time, we set aside the 2p z orbital, which we will use to make a π-bond, and take the 2s, 2p x , and 2p y orbitals to make three 2p 2 hybrid orbitals. These sp 2 hybrids point toward the corners of an equilateral triangle (by VSEPR or some serious mathematics), with angles of 120 o between them. The calculated orbitals are shown in Figure 3.1. We can now use these orbitals with the 1s orbitals from hydrogen to make the σ-bonds of ethene (3.2). The σ-bonds to hydrogen are each made from a hydrogen 1s and the sp 2 orbital. The carbon–car- bon σ-bond is formed from two sp 2 orbitals, coming together effectively nose to nose. Since we used s, p x , and p y to make these hybrid orbitals, the σ-framework must be planar in the xy plane (Figure 3.2). 3.2, σ-framework of ethene C C H H H H Alkenes, Alkynes, and Aromatic Compounds 3 38 3.1 Alkenes On each carbon atom, we are left with a 2p z orbital containing one electron. The orbitals are brought together side to side (they are perpendicular to the plane of the rest of the molecule) and combined to give a π- and a π*-orbital (Figure 3.3). We have two electrons to accommodate, and these are both in the π-orbital.

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  Chemistry for Today

  General, Organic, and Biochemistry

  • Spencer Seager, Michael Slabaugh, Maren Hansen, , Spencer Seager, Spencer Seager, Michael Slabaugh, Maren Hansen(Authors)
  • 2021(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Because they work with inhaled anes- thetics such as nitrous oxide, halothane, isoflurane, desflurane, sevoflurane, in conjunction with oxygen and intravenous anes- thetics like midazolam, and propofol, proficiency in chemistry and knowledge of human physiology is critical to success in this field. Concept Summary 12.1 The Nomenclature of Alkenes Learning Objective: Can you classify unsaturated hydrocarbons as Alkenes, alkynes, or aromatics? Can you write the IUPAC names of Alkenes from their molecular structures? ● Compounds containing double or triple bonds between carbon atoms are said to be unsaturated. ● The Alkenes contain double bonds. ● Alkynes contain triple bonds. ● Aromatics contain a six-member ring with three double bonds. ● In the IUPAC nomenclature system, alkene names end in -ene, and alkynes end in -yne. 12.2 The Geometry of Alkenes Learning Objective: Can you predict the existence of cis-trans isomers from formulas of compounds? Can you write the names and structural formulas for cis-trans isomers? ● In Alkenes, the double-bonded carbons and the four groups at- tached to these carbons lie in the same plane. ● Because rotation about the double bond is restricted, Alkenes may exist as cis-trans isomers. ● This type of stereoisomerism is possible when each double- bonded carbon is attached to two different groups. ● IUPAC names of stereoisomers contain the prefixes cis- or trans-. 12.3 Properties of Alkenes Learning Objective: Can you write equations for addition reactions of Alkenes, and use Markovnikov’s rule to predict the major products of certain reactions? ● The physical properties of the Alkenes are very similar to those of the alkanes. ● They are nonpolar, insoluble in water, less dense than water, and soluble in nonpolar solvents. ● Alkenes are quite reactive, and their characteristic reaction is addition to the double bond.

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  eBook - PDF

  Brown's Introduction to Organic Chemistry

  • William H. Brown, Thomas Poon(Authors)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  What you need to remember at this point is that a benzene ring is not chemically reactive under any of the conditions we describe in Chapters 4–8. In other words, their pi bonds will remain unchanged (at least until we get to Chapter 9). Alkene An unsaturated hydrocarbon that contains a carbon–carbon double bond. Alkyne An unsaturated hydrocarbon that contains a carbon–carbon triple bond. Arenes A compound containing one or more benzene rings. 104 C H A P T E R 4 Alkenes and Alkynes C C C C C C H H H H H Benzene (an arene) H although benzene and other arenes contain C–C double bonds, we must remember that their double bonds are not reactive in the ways we will describe in Chapters 4–8 (i.e., we will leave them unreacted in reactions that we cover in these chapters) Compounds containing carbon–carbon double bonds are especially widespread in nature. Ethylene, for example, is produced by all higher order plants. Furthermore, several low‐ molecular‐weight Alkenes, including ethylene and propene, have enormous commercial importance in our modern, industrialized society. The organic chemical industry produces more pounds of ethylene worldwide than any other chemical. Annual production in the United States alone exceeds 20 billion kg (45 billion pounds). What is unusual about ethylene is that it occurs only in trace amounts in nature. The enor- mous amounts of it required to meet the needs of the chemical industry are derived the world over by thermal cracking of hydrocarbons. In the United States and other areas of the world with vast reserves of natural gas, the major process for the production of ethylene is thermal cracking of the small quantities of ethane extracted from natural gas. In thermal cracking, a saturated hydrocarbon is converted to an unsaturated hydrocarbon plus H 2 . Heating ethane in a furnace to 800–900 °C for a fraction of a second cracks it to ethylene and hydrogen.

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  eBook - PDF

  Introduction to Organic Chemistry

  • William H. Brown, Thomas Poon(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  103 IN THIS CHAPTER , we begin our study of unsaturated hydrocarbons, compounds of car- bon and hydrogen that contain at least one pi bond. Look at the two compounds shown below. Ethene is an alkene, a hydrocarbon containing one or more carbon–carbon double bonds, and ethyne is an alkyne, a hydrocarbon containing one or more carbon—carbon triple bonds. Ethyne (an alkyne) Ethene (an alkene) H C C H C C H H H H Arenes are the third class of unsaturated hydrocarbons and are represented by the compound benzene. How is benzene structurally similar to either ethene or ethyne? How is it different? One unobvious but very important difference is that the chemistry of benzene and its deriva- tives is quite different from that of Alkenes and alkynes. We don’t study the chemistry of arenes until Chapter 9, but we will encounter many compounds containing benzene rings. What you need to remember at this point is that a benzene ring is not chemically reactive under any of the conditions we describe in Chapters 4–8. In other words, their pi bonds will remain unchanged (at least until we get to Chapter 9). Alkene An unsaturated hydrocarbon that contains a carbon–carbon double bond. Alkyne An unsaturated hydrocarbon that contains a carbon–carbon triple bond. Arenes A compound containing one or more benzene rings. Alkenes and Alkynes K E Y Q U E S T I O N S 4.1 What Are the Structures and Shapes of Alkenes and Alkynes? 4.2 How Do We Name Alkenes and Alkynes? 4.3 What Are the Physical Properties of Alkenes and Alkynes? 4.4 Why Are 1–Alkynes (Terminal Alkynes) Weak Acids? H O W TO 4.1 How to Name an Alkene C H E M I C A L C O N N E C T I O N S 4A Ethylene, a Plant Growth Regulator 4B Cis–Trans Isomerism in Vision 4C Why Plants Emit Isoprene Carotene and carotene‐like molecules are alkene‐containing compounds in nature that assist in the harvest of sunlight. The red color of tomatoes comes from lycopene, a molecule closely related to carotene.

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  eBook - PDF

  Chemistry, 5th Edition

  • Allan Blackman, Steven E. Bottle, Siegbert Schmid, Mauro Mocerino, Uta Wille(Authors)
  • 2022(Publication Date)
  • Wiley

    (Publisher)

  Polymers arise from the sequential 830 Chemistry addition of many low-molar-mass molecules to create very large molecules of high molar mass, as illustrated here by the formation of polyethylene from ethene (ethylene). nCH 2  CH 2 initiator ← → ( CH 2 CH 2  ) n To achieve such an addition, Alkenes first react with a specific reagent called an initiator and then with each other to form a steadily growing chain. In alkene-derived polymers of industrial and commercial importance, n is a large number, typically several thousand. We discuss the formation of polymers from Alkenes in more detail in the chapter on polymers. Another reaction of Alkenes is reduction to alkanes, which is essentially the addition of H 2 across the double bond. We will discuss this after we look at the addition reactions. Electrophilic addition reactions The basis of reactivity is the attraction between positive and negative species. The double bond in Alkenes is an electron-rich (i.e. negative) target for positive species. These positive species are called electrophiles (which literally means ‘attracted to electrons’). Alkenes undergo addition reactions with electrophiles to produce saturated compounds. In this section we examine the three most important types of electrophilic addition reactions: the addition of hydrogen halides (HCl, HBr and HI), water (H 2 O) and halogens (Br 2 , Cl 2 ). We first study some of the experimental observations about each addition reaction and then its mechanism. By examining these particular reactions, we develop a general understanding of how Alkenes undergo addition reactions. Addition of hydrogen halides The hydrogen halides HCl, HBr and HI (commonly abbreviated HX) add to Alkenes to give haloalkanes (alkyl halides). These additions may be carried out either with the pure reagents or in a polar solvent such as acetic acid.

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  eBook - ePub

  Organic Chemistry

  An Acid-Base Approach, Third Edition

  • Michael B. Smith(Author)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  4 Alkanes, Isomers, and an Introduction to Nomenclature

  DOI: 10.1201/9781003174929-4

  The video clips for this chapter are available at: https://routledgetextbooks.com/textbooks/9780367768706/chapter-4.php

  Carbon is only one atom in the periodic table, so why is it so special? Carbon forms covalent single, double, and triple bonds to a variety of atoms. Carbon can bond with itself, which leads to an almost limitless number of organic molecules. No other atom does this to the same degree. This chapter will discuss the structural features and nomenclature of a class of organic molecules with only carbon and hydrogen (hydrocarbons ).

  To begin this chapter, you should know the following points:

  • The fundamental nature of atoms (Section 3.1).
  • Covalent bonding between carbon and carbon or carbon and hydrogen (Sections 3.3, 3.6, and 3.8).
  • sp3 Hybridization (Section 3.5).
  • Carbon forms four covalent bonds in neutral molecules (Section 3.5).
  • The VSEPR model for carbon (Section 3.6).
  • How to draw simple structures and the connectivity of atoms (Section 3.6).

  4.1 Alkanes

  If a molecule contains only carbon and hydrogen it is known as a hydrocarbon . Hydrocarbons may contain any number of carbon-carbon bonds in linear chains, chains with branches, or rings of carbon atoms. A hydrocarbon with only sp3 carbons and bonds between sp3 carbon and hydrogen is known as an alkane . Each sp3 hybridized carbon in a hydrocarbon has a valence of four. In an alkane, there are a total of four covalent bonds to each C must be attached to another carbon. In an alkane, there is a tetrahedral array of hydrogen atoms around each carbon. This leads to a general formula for acyclic alkanes (no rings): Cn H2n+2 where n is an integer in the series: 1,2,3,4,... When n = 1, for example, the alkane is called methane, CH4 , and when n = 2, the molecule is called ethane CH3 —CH3 , C2 H6 . The quantity of each different atom in the formula is indicated by a subscript, so C6 H14 means that there are six carbon atoms and fourteen hydrogen atoms. While n may be very large, this book will mostly discuss molecules that have linear carbon chains of 2–20 carbon atoms. The alkane general formula defines the maximum number of hydrogen atoms that are possible in any organic molecule. There may be fewer hydrogen atoms, but never

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