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Chapter 4 Introduction to Hydrocabons

Chapter 4 Introduction to Hydrocabons Carbon Backbone, Nomenclature, Physical & Chemical Properties. HYDROCARBONS. Compounds composed of only carbon and hydrogen atoms ( C , H ). Each carbon has 4 bonds .

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Chapter 4 Introduction to Hydrocabons

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  1. Chapter 4 Introduction to Hydrocabons Carbon Backbone, Nomenclature, Physical & Chemical Properties

  2. HYDROCARBONS • Compounds composed of only carbon and hydrogen atoms (C, H). Eachcarbon has 4 bonds. • They represent a “backbone” when other “heteroatoms” (O, N, S, .....) are substituted for H. (The heteroatoms give function to the molecule.) • Acyclic (without rings); Cyclic (with rings); Saturated: only carbon-carbon single bonds; Unsaturated: contains one or more carbon-carbon double and/or triple bond

  3. HYDROCARBONS • Alkanes contain only single ( ) bonds and have the generic molecular formula: [CnH2n+2] • Alkenes also contain double ( + )bonds and have the generic molecular formula: [CnH2n] • Alkynes contain triple ( + 2)bonds and have the generic molecular formula: [CnH2n-2] • Aromatics are planar, ring structures with alternating single and double bonds: eg. C6H6

  4. Types of Hydrocarbons Each C atom is tetrahedral with sp3 hybridized orbitals. They only have single bonds. Each C atom is trigonal planar with sp2 hybridized orbitals. There is no rotation about the C=C bond in alkenes.

  5. Question 4.1 • What is the hybridization of the starred carbon in humulene (shown)? • A)sp • B)sp2 • C)sp3 • D)1s2 2s2 2p2

  6. Question 4.2 • What is the hybridization of the starred carbon of geraniol? • A)sp • B)sp2 • C)sp3 • D)1s2 2s2 2p2

  7. Types of Hydrocarbons Each C atom is linear with sp hybridized orbitals. Each C--C bond is the same length; shorter than a C-C bond: longer than a C=C bond. The concept of resonance is used to explain this phenomena.

  8. Propane It is easy to rotate about the C-C bond in alkanes.

  9. Naming Alkanes C1 - C10 : the number of C atoms present in the chain. Each member C3 - C10differs by one CH2 unit. This is called a homologous series. Methane to butane are gases at normal pressures. Pentane to decane are liquids at normal pressures.

  10. Nomenclature of Alkyl Substituents

  11. Examples of Alkyl Substituents

  12. Constitutional or structural isomers have the same molecular formula, but their atoms are linked differently. Naming has to account for them.

  13. Question 4.3 • How many hydrogens are in a molecule of isobutane? • A)6 • B)8 • C)10 • D)12

  14. A compound can have more than one name, but a name must unambiguously specify only one compound C7H16 can be any one of the following:

  15. Question 4.4 • How many isomeric hexanes exist? • A)2 • B)3 • C)5 • D)6

  16. Question 4.5 • The carbon skeleton shown at the bottom right accounts for 9 carbon atoms. How many other isomers of C10H22 that have 7 carbons in their longest continuous chain can be generated by adding a single carbon to various positions on this skeleton? • A) 2 • B) 3 • C) 4 • D) 5

  17. Alkanes (Different types of sp3 carbon atoms) • Primary, 1o, a carbon atom with 3 hydrogen atoms: [R-CH3] • Secondary, 2o, a carbon atom with 2 hydrogen atoms: [R-CH2-R] • Tertiary, 3o, a carbon atom with 1 hydrogen atom: • [R-CH-R] R • Quaternary, 4o, a carbon atom with 0 hydrogen atoms: CR4

  18. Different Kinds of sp3 Carbons and Hydrogens

  19. Question 4.6 • In 3-ethyl-2-methylpentane, carbon #3 (marked by a star) is classified as: • A)primary (1°) • B)secondary (2°) • C)tertiary (3°) • D)quaternary (4°)

  20. Question 4.7 • How many primary carbons are in the molecule shown at the bottom right? • A)2 • B)3 • C)4 • D)5

  21. Nomenclature of Alkanes 1. Determine the number of carbons in the parent hydrocarbon 2. Number the chain so that the substituent gets the lowest possible number

  22. 3. Number the substituents to yield the lowest possible number in the number of the compound (substituents are listed in alphabetical order) 4. Assign the lowest possible numbers to all of the substituents

  23. 5. When both directions lead to the same lowest number for one of the substituents, the direction is chosen that gives the lowest possible number to one of the remaining substituents 6. If the same number is obtained in both directions, the first group receives the lowest number

  24. 7. In the case of two hydrocarbon chains with the same number of carbons, choose the one with the most substituents 8. Certain common nomenclatures are used in the IUPAC system

  25. Question 4.7 • The correct structure of 3-ethyl-2-methylpentane is: • A) B) • C) D)

  26. Cycloalkane Nomenclature CnH2n

  27. Cycloalkanes • Cycloalkanes are alkanes that contain a ring of three or more carbons. • Count the number of carbons in the ring, and add the prefix cyclo to the IUPAC name of the unbranched alkane that has that number of carbons. Cyclopentane Cyclohexane

  28. CH2CH3 Cycloalkanes • Name any alkyl groups on the ring in the usual way. A number is not needed for a single substituent. Ethylcyclopentane

  29. H3C CH3 CH2CH3 Cycloalkanes • Name any alkyl groups on the ring in the usual way. A number is not needed for a single substituent. • List substituents in alphabetical order and count in the direction that gives the lowest numerical locant at the first point of difference. 3-Ethyl-1,1-dimethylcyclohexane

  30. For more than two substituents,

  31. Question 4.8 • Which one contains the greatest number of tertiary carbons? • A)2,2-dimethylpropane • B)3-ethylpentane • C)sec-butylcyclohexane • D)2,2,5-trimethylhexane

  32. Physical Properties of Alkanesand Cycloalkanes

  33. Crude oil Naphtha (bp 95-150 °C) Kerosene (bp: 150-230 °C) C5-C12 C12-C15 Light gasoline (bp: 25-95 °C) C15-C25 Gas oil (bp: 230-340 °C) Refinery gas C1-C4 Residue

  34. Question 4.9 Arrange octane, 2,2,3,3-tetramethylbutane and 2-methylheptane in order of increasing boiling point. • A) 2,2,3,3-tetramethylbutane < octane < 2-methylheptane • B) octane < 2-methylheptane < 2,2,3,3- tetramethylbutane • C) 2,2,3,3-tetramethylbutane < 2-methylheptane < octane • D) 2-methylheptane < 2,2,3,3- tetramethylbutane < octane

  35. Crude Oil and Uses of Alkanes • The gasoline fraction of crude oil only makes up about 19%, which is not enough to meet demand.

  36. van der Waals Forces Weak Intermolecular Attractive Forces The boiling point of a compound increases with the increase in van der Waals force…and a Gecko uses them to walk!

  37. Gecko: toe, setae, spatulae6000x Magnification Full et. al., Nature (2000) 5,000 setae / mm2 600x frictional force; 10-7 Newtons per seta Geim, Nature Materials (2003) Glue-free Adhesive 100 x 10 6 hairs/cm2 http://micro.magnet.fsu.edu/primer/java/electronmicroscopy/magnify1/index.html

  38. Intermolecular Forces • Ion-Dipole Forces(40-600 kJ/mol) • Interaction between an ion and a dipole (e.g. NaOH and water = 44 kJ/mol) • Strongest of all intermolecular forces.

  39. Ion-Dipole & Dipole-Dipole Interactions: like dissolves like • Polar compounds dissolve in polar solvents • & non-polar in non-polar

  40. Intermolecular Forces Dipole-Dipole Forces (permanent dipoles) 5-25 kJ/mol

  41. Intermolecular Forces Dipole-Dipole Forces

  42. Boiling Points & Hydrogen Bonding

  43. Hydrogen Bonding • Hydrogen bonds, a unique dipole-dipole (10-40 kJ/mol).

  44. Intermolecular Forces • London or Dispersion Forces • An instantaneous dipole can induce another dipole in an adjacent molecule (or atom). • The forces between instantaneous dipoles are called London or Dispersion forces ( 0.05-40 kJ/mol).

  45. Boiling Points of Alkanes • governed by strength of intermolecular attractive forces • alkanes are nonpolar, so dipole-dipole and dipole-induced dipole forces are absent • only forces of intermolecular attraction are induced dipole-induced dipole forces

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