Alkyne

9 Key excerpts on "Alkyne"

• 

  eBook - PDF

  Experimental Organic Chemistry

  A Miniscale & Microscale Approach

  • John Gilbert, Stephen Martin(Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  403 C H A P T E R Alkynes You may have been introduced to the simplest Alkyne, acetylene, because it is frequently used as a fuel in welding. Indeed, when acetylene is burned with oxygen, the flame reaches temperatures of about 3300 °C (6000 °F), hotter than all but two or three other mixtures of combustible gases. You already know that flames and organic labs can be a dangerous combination, so we will explore tamer properties of Alkynes, avoiding studies of their combustibility. Like the alkenes discussed in Chapter 10, Alkynes are unsaturated hydrocarbons, and their chemistry is also dominated by the presence of carbon-carbon multiple or p -bonds. Whereas alkenes have a double bond, Alkynes are characterized by a triple bond, which is composed of two orthogonal carbon-carbon p -bonds. Hence, if you understand the reactions that lead to the formation of alkenes, you will be able to apply this knowledge to preparing Alkynes. Similarly, you will be able to extend your knowledge of the reactions of alkenes to predicting products of reactions of Alkynes. Because Alkynes have two double bonds, however, they basically just do everything twice. Well, it’s almost that simple. 11.1 I N T R O D U C T I O N Unsaturated organic compounds that contain a carbon-carbon triple bond as the functional group are called Alkynes . Acetylene (ethyne), H–C ≡ C–H, is the simplest Alkyne and is widely used in industry as a fuel and as a chemical feedstock for the preparation of other organic compounds such as acetic acid (CH 3 CO 2 H), vinyl chlo-ride (CH 2 = CHCl), a monomer used in the manufacture of polyvinyl chloride, and chloroprene (CH 2 = CCl–CH = CH 2 ), which polymerizes to give neoprene, the material from which your protective gloves may be made. The value of acetylene to Germany during World War II is described in the Historical Highlight Acetylene: A Valuable Small Molecule , which is available online.

  Sign up to read

  Learn more about book
• 

  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.

  Sign up to read

  Learn more about book
• 

  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.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Chemistry, 5th Edition

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

    (Publisher)

  C C H 3 C H CH 3 H 842 Chemistry We have looked at molecules with one double bond. Molecules with more than one carbon–carbon double bond undergo the same addition reactions. However, there is a class of unsaturated molecules that do not undergo any of these addition reactions. These molecules are called aromatic compounds and are covered in section 16.7. 16.6 Reactions of Alkynes LEARNING OBJECTIVE 16.6 Correlate the reactivity of Alkynes with alkenes and describe how Alkynes may be converted to alkenes. Much of the chemistry of Alkynes mirrors the chemistry of alkenes; they undergo the same reduction reactions, as well as hydrogen halide addition and halogen addition reactions. Alkynes also undergo hydration, but unlike alkenes the synthetic outcome is a ketone and this is covered in the chapter on aldehydes and ketones. Reduction of Alkynes is particularly important in the synthesis of complicated molecules used in making pharmaceuticals. Alkynes are easily reduced to alkanes by addition of hydrogen gas using a metal catalyst. This differs from the reduction of alkenes in that the reduction occurs in stages and the choice of catalyst can control the synthetic outcome. Complete reduction of the Alkyne occurs when palladium coated onto carbon is used as the catalyst. Another catalyst involving deactivated palladium, called Lindlar catalyst, produces the cis alkene from the triple bond. The trans alkene can be generated using sodium or lithium dissolved in liquid ammonia. CH 3 CH 2 C CH 3 NH 3 2H 2 Li H 2 Pd/C CH 3 CH 2 CH 2 CH 2 CH 3 Lindlar catalyst CH 3 CH 2 C C CH 3 H H cis-pent-2-ene pentane trans-pent-2-ene CH 3 CH 2 C C CH 3 H H C 16.7 Aromatic compounds LEARNING OBJECTIVE 16.7 Describe how aromatic hydrocarbons differ from alkenes and Alkynes through the presence of remarkably stable cyclic  bonds. The simplest example of an aromatic compound is benzene, C 6 H 6 .

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Foundations of Chemistry

  An Introductory Course for Science Students

  • Philippa B. Cranwell, Elizabeth M. Page(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  13 Alkanes, alkenes, and Alkynes At the end of this chapter, students should be able to: • Understand and explain the structural difference between alkanes, alkenes, and Alkynes • Suggest a test for the presence of an alkene in a molecule and explain the test in terms of the chemical reaction • Understand the difference between sigma ( σ ) and pi ( π ) bonds in relation to alkanes, alkenes, and Alkynes • Be able to explain and describe the general reactivity of alkanes, alkenes, and Alkynes. 13.1 Alkanes: an outline Alkanes are arguably the simplest molecule that you will encounter during your chemistry studies and are a type of hydrocarbon. Strictly speaking, a hydrocar-bon only contains the elements carbon and hydrogen. The carbon atoms can be joined together, making the backbone of the molecule a long chain (also called a straight-chain alkane ), a long chain with branches, or a ring. An alkane only con-tains single bonds between the carbon and hydrogen atoms, with each carbon atom making four single bonds. A molecule that contains only single C ─ C and C ─ H bonds can also be called saturated . All alkanes that are in a straight chain must have molecular formula C n H 2n+2 , whereas alkanes that are cyclic have molecular formula C n H 2n . In both cases, n is a whole number. The naming of alkanes has already been covered in Chapter 12, so it will not be covered again here. However, in order to succeed in this chapter, you need to be able to name and draw the first 10 alkanes. All alkanes that are in a straight chain have molecular formula C n H 2n+2 . For a refresher on naming and draw-ing alkanes, see Section 12.2 Foundations of Chemistry: An Introductory Course for Science Students , First Edition. Philippa B. Cranwell and Elizabeth M. Page. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd. Companion website: www.wiley.com/go/Cranwell/Foundations

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Organic Chemistry

  • David R. Klein(Author)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  + NH 3 (l ) 1) xs NaNH 2 2) H 2 O 1) NaNH 2 2) RX 1 12 11 9 8 10 7 5 4 3 1 2 1) xs NaNH 2 2) H 2 O xs HX 6 R X X R X X R R R R R R X R CH 3 O R O H R X X R X X X X C O O R OH O R R SECTION 9.1 • A triple bond is comprised of three separate bonds: one σ bond and two π bonds. • Alkynes exhibit linear geometry and can function as bases or as nucleophiles. SECTION 9.2 • Alkynes are named much like alkanes, with the following additional rules: • The suffix “ane” is replaced with “yne.” • The parent is the longest chain that includes the CC bond. • The triple bond should receive the lowest number possible. • The position of the triple bond is indicated with a single locant placed either before the parent or the suffix. • Monosubstituted acetylenes are terminal Alkynes, while disubstituted acetylenes are internal Alkynes. SECTION 9.3 • The conjugate base of acetylene, called an acetylide ion, is rela- tively stabilized because the lone pair occupies an sp-hybridized orbital. • The conjugate base of a terminal Alkyne is called an alkynide ion, which can only be formed with a sufficiently strong base, such as NaNH 2 . SECTION 9.4 • Alkynes can be prepared from either geminal or vicinal dihalides via two successive E2 reactions. SECTION 9.5 • Catalytic hydrogenation of an Alkyne yields an alkane. • Catalytic hydrogenation in the presence of a poisoned cata- lyst (Lindlar’s catalyst or Ni 2 B) yields a cis alkene. • A dissolving metal reduction will convert an internal Alkyne into a trans alkene. The reaction involves an intermediate radi- cal anion and employs fishhook arrows, which indicate the movement of only one electron. SECTION 9.6 • Alkynes react with HX via a Markovnikov addition. • One possible mechanism for the hydrohalogenation of Alkynes involves a vinylic carbocation, while another possi- ble mechanism is termolecular.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Klein's Organic Chemistry

  • David R. Klein(Author)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  + NH 3 (l ) 1) xs NaNH 2 2) H 2 O 1) NaNH 2 2) RX 1 12 11 9 8 10 7 5 4 3 1 2 1) xs NaNH 2 2) H 2 O xs HX 6 R X X R X X R R R R R R X R CH 3 O R O H R X X R X X X X C O O R OH O R R SECTION 10.1 • A triple bond is comprised of three separate bonds: one σ bond and two π bonds. • Alkynes exhibit linear geometry and can function either as bases or as nucleophiles. SECTION 10.2 • Alkynes are named much like alkanes, with the following additional rules: • The suffix “ane” is replaced with “yne.” • The parent is the longest chain that includes the C    C bond. • The triple bond should receive the lowest number possible. • The position of the triple bond is indicated with a single locant placed either before the parent or the suffix. • Monosubstituted acetylenes are terminal Alkynes, while disubstituted acetylenes are internal Alkynes. SECTION 10.3 • The conjugate base of acetylene, called an acetylide ion, is relatively stabilized because the lone pair occupies an sp-hybridized orbital. • The conjugate base of a terminal Alkyne is called an alkynide ion, which can only be formed with a sufficiently strong base, such as NaNH 2 . SECTION 10.4 • Alkynes can be prepared from either geminal or vicinal dihalides via two successive E2 reactions. SECTION 10.5 • Catalytic hydrogenation of an Alkyne yields an alkane. • Catalytic hydrogenation in the presence of a poisoned cata- lyst (Lindlar’s catalyst or Ni 2 B) yields a cis alkene. • A dissolving metal reduction will convert an Alkyne into a trans alkene. The reaction involves an intermediate radi- cal anion and employs fishhook arrows, which indicate the movement of only one electron. SECTION 10.6 • Alkynes react with HX via a Markovnikov addition. • One possible mechanism for the hydrohalogenation of Alkynes involves a vinylic carbocation, while another pos- sible mechanism is termolecular.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Organic Chemistry

  • David R. Klein(Author)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  9.1 Introduction to Alkynes 401 π Bond σ Bond π Bond C H H C FIGURE 9.1 The atomic orbitals used to form a triple bond. The σ bond is formed from the overlap of two hybridized orbitals, while each of the two π bonds is formed from overlapping p orbitals. 9.1 Introduction to Alkynes Structure and Geometry of Alkynes The previous chapter explored the reactivity of alkenes. In this chapter, we expand that dis- cussion to include the reactivity of Alkynes, compounds containing a C≡C bond. Recall from Section 1.9 that a triple bond is comprised of three separate bonds: a σ bond and two π bonds. The σ bond results from the overlap of sp-hybridized orbitals, while each of the π bonds results from overlapping p orbitals (Figure 9.1). These π bonds occupy large regions of space (larger than the p orbitals depicted in Figure 9.1), giving rise to a cylindrical region of high electron density encircling the triple bond. This can be visualized with an electrostatic potential map of acetylene (H − C≡C − H), shown in Figure 9.2. The region shown in red (high electron density) explains why Alkynes are reactive. Indeed, Alkynes are similar to alkenes in their ability to function either as bases or as nucleo- philes. We will see examples of both behaviors in this chapter. FIGURE 9.2 An electrostatic potential map of acetylene, indicating a cylindrical region of high electron density (red). The bond angles of acetylene are observed to be 180° (linear geometry), consistent with sp hybridization (Section 1.9). This linear geometry makes it difficult to incorporate a triple bond into a small ring, because ring strain would force the bond angles to deviate from the ideal 180°. Indeed, the smallest cycloAlkyne that can be prepared is a 9-membered ring, and it decomposes at room tem- perature as a result of ring strain: Cyclononyne Some important trends emerge if we compare properties of ethane, ethylene, and acetylene.

  Sign up to read

  Learn more about book
• 

  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.

  Sign up to read

  Learn more about book