Shapes And Bond Angles Of Simple Organic Compounds


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Shapes And Bond Angles Of Simple Organic Compounds

  1. 1. Shapes of and Bond Angles in Simple Organic Compounds A. Miller
  2. 2. Simple Organic Compounds <ul><li>Ethane </li></ul><ul><li>Etnene </li></ul><ul><li>Benzene </li></ul>
  3. 3. Simple Organic Compounds <ul><li>Organic Compounds- consisting of carbon and hydrogen mostly </li></ul>
  4. 4. Recall <ul><li>Overlapping of atomic orbitals </li></ul><ul><li>Formation of sigma bonds </li></ul><ul><li>The simple picture of overlap of half-filled atomic orbitals cannot be used to explain the geometry of all molecules especially organic molecules </li></ul>
  5. 5. Hybridisation <ul><li>The mixing of orbitals </li></ul><ul><li>Stronger orbitals are created </li></ul>
  6. 6. Methane -CH 4 <ul><li>Structure </li></ul>
  7. 7. How Does Methane Forms Four Single Bonds <ul><li>Ground state configuration </li></ul><ul><li>1s 2 2s 2 2p 2 </li></ul>
  8. 8. Methane <ul><li>Needs to have four single bonds </li></ul><ul><li>Need four single electrons </li></ul><ul><li>Promotion of an electron from the 2s orbital to the 2p orbital </li></ul><ul><li>Mixing the 2s and 2p orbitals </li></ul>
  9. 9. Methane <ul><li>Formation of sp 3 electronic configuration </li></ul><ul><li>Energy is required to do this </li></ul>
  10. 10. Promotion of electron and orbital mixing <ul><li>hybridization </li></ul>
  11. 11. Mixing of Orbitals <ul><li>Four single electrons </li></ul>
  12. 12. sp 3 Hybrid Orbitals <ul><li>The promotion electrons followed by the mixing of the orbitals create stronger orbitals </li></ul><ul><li>The s orbital mixes with the three p orbitals producing four equivalent sp 3 orbitals </li></ul>
  13. 13. <ul><li>Each hybrid orbital contains 25% s character and 75 % p character. </li></ul><ul><li>The 4 sp 3 hybrid orbitals each contains an electron </li></ul><ul><li>Will arrange themselves in a three dimensional space to get as far apart as possible (to minimize repulsion) </li></ul>
  14. 14. Electrons Arrangement in Carbon <ul><li>Arrangement gives rise to a tetrahedral structure bond angle of 109.5 </li></ul>
  15. 15. Overlapping of C and H orbitals <ul><li>The sp 3 hybrid orbitals of carbon overlap with the s orbital of hydrogen containing an electron. </li></ul><ul><li>Give rise to the C-H sigma bond </li></ul>
  16. 16. Formation of methane <ul><li>Overlapping of orbitals </li></ul>
  17. 17. Structure of Methane <ul><li>C-H bonds </li></ul>
  18. 18. Ethane <ul><li>overlapping </li></ul>
  19. 19. Etnane <ul><li>overlapping </li></ul>
  20. 20. Sp 2 hybridization <ul><li>Found in compounds such as alkenes </li></ul><ul><li>Formation of bonds to three other atoms (two hydrogens and one carbon) </li></ul><ul><li>Each carbon employs a set of sp 2 hybrids </li></ul>
  21. 21. sp 2 Hybridization <ul><li>Electron promotion still occur in carbon </li></ul><ul><li>Mixing of the 2s and 2p orbitals. </li></ul><ul><li>Only two of the p orbitals are mixed with the s orbital. </li></ul>
  22. 22. sp 2 Hybridization <ul><li>The other p orbital remains pure (unhybridized) </li></ul><ul><li>Three sp 2 hybrid orbitals are created </li></ul><ul><li>Two will overlap with hydrogen 1s orbital </li></ul>
  23. 23. Formation of Ethene <ul><li>The third will overlap with a similar sp 2 orbital on the other carbon atom. </li></ul><ul><li>Accounting for all the C-H bonds and the C-C sigma bond of the double bond </li></ul><ul><li>Each carbon has a pure p orbital containing an electron </li></ul>
  24. 24. Formation of Ethene <ul><li>The orbitals are perpendicular to the plane of the sp 2 orbitals- </li></ul><ul><li>Projects above and below the plane </li></ul><ul><li>Orbitals close proximity causes overlap sideways forming a pi bond </li></ul>
  25. 25. Ethene <ul><li>Pi bonds are weaker than sigma bonds </li></ul>
  26. 26. sp 2 Hybridization- mixing of orbitals
  27. 28. Hybridized Structure of Ethene <ul><li>Ethene </li></ul>
  28. 29. Ethene
  29. 30. Benzene <ul><li>Six carbon atoms in a ring </li></ul><ul><li>Shows resonance hybrid </li></ul><ul><li>Hexagonal in shape- at each apex there is a carbon bonded to a hydrogen </li></ul>
  30. 31. Benzene <ul><li>Each carbon is bonded to three other atoms; a hydrogen and two other carbon atoms </li></ul><ul><li>Each carbon uses sp 2 hybrid orbitals </li></ul><ul><li>Each carbon contains a pure p orbital perpendicular to the plane of the ring </li></ul>
  31. 32. Benzene <ul><li>Each unhybridized p orbital overlaos with two other p orbitals, one on each of the two neighbouring carbon atoms </li></ul><ul><li>A large circular pi-type bond is formed above and below the plane </li></ul><ul><li>Electrons are delocalized in the benzene ring </li></ul>
  32. 33. Benzene <ul><li>Overlapping of p orbitals </li></ul>
  33. 34. Benzene
  34. 35. Benzene <ul><li>Canonical forms </li></ul>
  35. 36. Benzene <ul><li>Hybridized structure </li></ul>
  36. 37. Structure of solids <ul><li>Solids can either be </li></ul><ul><li>- Amorphous (non-crystalline) or </li></ul><ul><li>- Crystalline </li></ul>
  37. 38. Amorphous Solids <ul><li>Particles have no orderly structure </li></ul><ul><li>Lack well-defined faces and shapes </li></ul><ul><li>Many are mixtures of molecules that do not stack together </li></ul><ul><li>Most composed of large complicated molecules </li></ul><ul><li>Example; rubber, glass </li></ul>
  38. 39. Crystalline Solids <ul><li>Highly regular/orderly arrangement of atoms, molecules or ions in a crystal. </li></ul><ul><li>Usually have flat surfaces, or faces that make definite angle with one another </li></ul><ul><li>Example; quartz, diamond </li></ul>
  39. 40. Lattice Structure <ul><li>Consists of repeating units called unit cell </li></ul><ul><li>Solid can be represented by a three dimensional array of points called crystal lattice </li></ul><ul><li>Each point in the lattice is called a Lattice points </li></ul>
  40. 41. Lattice Structure <ul><li>Structural units in the lattice are held by; </li></ul><ul><li>- electrostatic forces in ionic crystals </li></ul><ul><li>- van der Waals forces in simple </li></ul><ul><li>molecular crystals </li></ul><ul><li>- hydrogen bonds as in ice </li></ul>
  41. 42. Lattice Structure <ul><li>Structural units in lattice are held by; </li></ul><ul><li>- Covalent bonds as in giant molecular structures as in silicon dioxide (quartz), giant atomic structures as in diamond and graphite </li></ul><ul><li>- metallic bond as in metallic crystals such as copper </li></ul>
  42. 43. Ionic Solid-sodium chloride <ul><li>Face-centred cubic structure </li></ul><ul><li>Lattice points are occupied by ions </li></ul><ul><li>Each Na+ surrounded by 6 Cl- ions as next nearest neighbour and vice-versa </li></ul><ul><li>Strong forces of attraction between oppositely charged ions </li></ul>
  43. 44. Ionic Structure- Sodium Chloride <ul><li>Blue- chloride ions </li></ul><ul><li>Red-sodium ions </li></ul>
  44. 45. Simple Molecular structure <ul><li>Atoms held by strong covalent bonds </li></ul><ul><li>Molecules held by weak van der Waals </li></ul><ul><li>forces </li></ul><ul><li>Gases or liquids at room temperature </li></ul>
  45. 46. Simple Molecular-Iodine <ul><li>Atoms covalently bonded in pairs as I 2 molecules </li></ul><ul><li>Discrete molecules held by weak van der Waals forces </li></ul><ul><li>Shiny in appearance due to regular arrangement of molecules </li></ul>
  46. 47. Iodine <ul><li>Very slightly soluble in water </li></ul><ul><li>Dissolve freely in organic solvent </li></ul><ul><li>Does not conduct electricity- no separation of charge </li></ul>
  47. 48. Face-centred Cubic Structure
  48. 49. Simple Molecular-Iodine <ul><li>Molecules in corners and face of unit cell </li></ul>
  49. 50. Giant Molecular-Silicon dioxide <ul><li>Formed by strong, directional covalent bonds, and has a well-defined local structure </li></ul><ul><li>Each silicon atom can bond to four oxygen atoms, giving rise to a giant covalent network structure </li></ul>
  50. 51. Silicon dioxide <ul><li>Each Si is bonded to four oxygens and each O to two silicon atoms. </li></ul><ul><li>The bonding between the atoms goes on and on in three dimensions. </li></ul><ul><li>Four oxygen atoms are arrayed at the corners of a tetrahedron around a central silicon atom: </li></ul>
  51. 52. Giant Molecular-Silicon dioxide <ul><li>Three dimensional structure </li></ul>
  52. 53. Silicon dioxide <ul><li>bonding </li></ul>
  53. 54. Metallic Structures <ul><li>Consist entirely of metal atoms. </li></ul><ul><li>Usually have hexagonal close-packed, cubic close-packed (face-centred cubic) or body-centred cubic structures </li></ul><ul><li>Each atom typically has 8 or 12 adjacent atoms. </li></ul>
  54. 55. Metallic Structure <ul><li>Bonding due to valence delocalized electrons throughout the entire lattice </li></ul><ul><li>i.e. positive ions immersed in a sea of delocalized valence electrons. </li></ul>
  55. 56. Metallic Structure Body-centerd Cubic <ul><li>There is one host atom (lattice point) at each corner of the cube and one host atom in the center of the cube: Z = 2. </li></ul><ul><li>Each corner atom touches the central atom along the body diagonal of the cube </li></ul>
  56. 57. Metallic Structure <ul><li>Body-centred cubic </li></ul>
  57. 58. Body-centred <ul><li>Unit cell </li></ul>
  58. 59. Cubic Close-packed/ Face-centred <ul><li>Arranging layers of close-packed spheres such that the spheres of every third layer overlying one another gives cubic close packing </li></ul>
  59. 60. Cubic Close-packed/Face-centred Cubic <ul><li>Unit cell has one host atom at each corner and one host atom in each face.  </li></ul><ul><li>Each corner atom contributes one eighth of its volume to the cell interior </li></ul><ul><li>Each face atom contributes one half of its volume to the cell interior (and there are six faces), then Z = 1/8 . 8 + 1/2 . 6 = 4. </li></ul>
  60. 61. Cubic Close-packed/ Face-centred eg. Copper <ul><li>Face-centred cubic </li></ul>
  61. 62. Hexagonal Close-packed <ul><li>The unit cell consists of three layers of atoms. </li></ul><ul><li>  The top and bottom layers contain six atoms at the corners of a hexagon and  one  atom  at  the  center  of  each hexagon.     </li></ul><ul><li>The  middle  layer  contains  three  atoms nestled between the atoms of the top and bottom layers </li></ul>
  62. 63. Hexagonal Close-packed <ul><li>layers </li></ul>
  63. 64. Giant Atomic Structures <ul><li>Covalent-network solids </li></ul><ul><li>Consist of atoms held together in large network or chains by covalent bonds </li></ul><ul><li>Solids are much harder and have higher melting points than molecular solids. </li></ul>
  64. 65. Giant Atomic Structure <ul><li>Two examples are; diamond and graphite. </li></ul><ul><li>Diamond and graphite are two allotropes of carbon </li></ul>
  65. 66. Diamond <ul><li>Lattice points occupied by carbon atoms </li></ul><ul><li>Each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement. </li></ul><ul><li>Interconnected three-dimensional array of strong C-C single bonds </li></ul>
  66. 67. Diamond <ul><li>Diamond is very hard as a result. </li></ul><ul><li>Multitude of covalent bonds causes diamond to have a very high melting point 3550 degree Celsius </li></ul><ul><li>Does not conduct electricity- no free electrons. </li></ul>
  67. 68. Diamond <ul><li>Insoluble in water and organic solvents. </li></ul><ul><li>No possible attractions which could occur between solvent molecules and carbon atoms which could outweigh the attractions between the covalently bound carbon atoms </li></ul>
  68. 69. Giant Atomic Structure- Diamond <ul><li>C-C single bonds </li></ul>
  69. 70. Diamond <ul><li>Tetrahedral arrangement </li></ul>
  70. 71. Giant Atomic Structure- Graphite <ul><li>Each carbon is covalently bonded to three other in a trigonal planar arrangement. </li></ul><ul><li>Each carbon has a single electron that is delocalized and free to move about in the lattice. </li></ul><ul><li>Hence graphite conducts electricity along the layers </li></ul>
  71. 72. Giant Atomic Structure- Graphite <ul><li>Lattice structure consists of layers of interconnected hexagonal rings </li></ul><ul><li>Layers are held by weak van der Waals forces </li></ul><ul><li>Layers readily slide past each other when rubbed. Giving a greasy feel. </li></ul><ul><li>Hence used as a lubricant and in lead pencils </li></ul>
  72. 73. Giant Atomic Structure- Graphite <ul><li>Insoluble in water and organic solvents - for the same reason that diamond is insoluble. </li></ul><ul><li>Attractions between solvent molecules and carbon atoms will never be strong enough to overcome the strong covalent bonds in graphite. </li></ul>
  73. 74. Giant Atomic Structure- Graphite <ul><li>Layers of carbon atoms </li></ul>
  74. 75. Graphite <ul><li>Van der Waals forces between layers </li></ul>
  75. 76. Structure of Ice