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Introduction to Organic Chemistry: Visual Aids for Lectures

Understand the basics of organic chemistry with Dr. Nabila Aljaber through this comprehensive document containing visual aids. Learn about hydrocarbons, organic compounds, and bond structures. Recognize the importance of carbon and its unique bonding abilities. Explore alkynes, alkanes, and isomerism in organic molecules.

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Introduction to Organic Chemistry: Visual Aids for Lectures

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  1. First Course in Organic Chemistry 2010 - 2011 Introduction to Organic Chemistry By Dr. Nabila Aljaber

  2. WARNING! • This document contains visual aids for lectures • It does not contain lecture notes • It does not contain actual lectures • Failure to attend lectures can harm your performance in module assessment

  3. What is Organic Chemistry? It is defined as the study of hydrocarbons (compounds of hydrogen and carbon) and their derivatives 7 million Organic Compounds 1.5 million Inorganic Compounds Animal and plant matter, Foods, Pharmaceuticals, Cosmetics, Fertilizers, Plastics, Petrochemicals, Clothing

  4. Periodic Table

  5. Carbon Why is it the element of life on earth? Has Four Bonding Electrons Unique Strong Covalent Bonds Strong Single, Double and Triple Bonds Average Bond Energies (KJ mol-1) C-C 607 Si-Si 230 C-H 416 Si-H 323 C-N 754 Si-N 470 C-O 336 Si-O 368 O-Si-O = Sand and Rocks

  6. Simplest Organic molecule Covalent Bonding – Atoms Share Electrons

  7. lowest energy state Excited state 4 sp3 Hybridization

  8. p Orbitals Px Px Pz Pz Py Py

  9. 3 sp 1s 2s 2px 2py 2pz sp3 sp3 sp3 sp3 y Hybridize Promote x 109.5o z Methane: Carbon

  10. H C H H H Methane building blocks C H H H C H H

  11. Methane is Tetrahedral Sp3 hybridized carbon 4 equivalent C-H bonds (s-bonds) All purely single bonds are called s-bonds

  12. Flat molecule – “Planar” Hybridization 3 sp2 p-bond Three s-bonds p-bond s-bonds – One C-C, two C-H bonds per carbon atom

  13. s-bond Spherical Symmetry end to end overlap of orbitals leads to s-bond When a single bond is present between atoms, that bond is alwayss-bond DB contains one s-bond and one p-bond The p-bond lies perpendicular to the s-bond – overlapping lobes above and below the plane of s-bond Groups or atoms can be rotated about a single bond, but DB is rigid – No rotation about a DB is possible without breaking the p-bond – This leads to cis-trans Isomerism 19/12/2019 14

  14. Linear Molecule Alkynes Sp3 hybridisation in Saturated Bonds (e.g. alkanes) Sp2 hybridisation in DB (e.g. alkenes) Sp hybridisation in TB (e.g. alkynes) Hybridization Two s-bonds (C-H) and (C-C) And Two p-bonds between C-C per C atom 2sp 2p-bonds

  15. ALKANES

  16. Alkanes CnH2n+2 consist of only carbon and hydrogen bonded by single covalent bonds single

  17. Skeletal structure of only carbon atoms C1 – C4 n-alkanes are all gases Methane main component of natural gas Propane and butane often stored as compressed gases

  18. Rotation about single covalent bonds occurs freely. The energy barrier is small. The position of hydrogen atoms relative to one is thus constantly changing

  19. Nomenclature* General Formula CnH2n+2

  20. Alkyl groups (R): (-H) • # Methane CH4 CH3Methyl • # Ethane C2H6 C2H5Ethyl • # Propane C3H8(2 R) • CH3-CH2-CH3 • - CH2-CH2-CH3OR CH3-CH-CH3 • n-PropylIsopropyl

  21. # Butane (C4H10) • Butane • n -butane Isobutane • CH3 • CH3-CH2-CH2-CH3 CH3-CH-CH3 • n-butyl 2 butyl • CH2-CH2-CH2-CH3 CH3-CH-CH2-CH3 • Isobutyl 3 butyl • CH3CH3 • CH2-CH-CH3 CH3-C-CH3

  22. Degree of carbon 4º 4ry quat. 1º 1ry Pry. 2º 2ry Sec. 3º 3ry ter.

  23. isopropyl 3ry-butyl 2ry -butyl methyl n-propyl isobutyl

  24. International Union of Pure and Applied Chemistry IUPAC 1-Longest continuous chain • CH3–CH2–CH–CH2–CH3 • CH2 • CH2 • CH3 3-Ethyl hexane CH3–CH2–CH–CH2–CH3 CH2 CH2 CH3 3-Propyl pentane Not

  25. 2-Lowest number of attachment of substation CH3–CH2–CH–CH2–CH3 CH2 CH2 CH3 CH3– CH2–CH–CH2–CH3 CH2 CH2 CH3 Not 3-ethylhexane 4-ethyl hexane

  26. 3-Same alkyl substitute (di -, tri-, tetra, penta.. etc.) CH3 CH3 – CH – CH2 –C – CH3 CH3 CH3 2, 2, 4-Trimethylpentane Not 2,4,4-Trimethyl pentane

  27. 4-Different alkyl substation ( alphabetical) CH3 CH2 CH3 –CH2 – CH2 – CH – CH – C – CH2 – CH3 CH2CH3CH2 CH2CH3 CH3 3,3-Diethyl-4-methyl-5-n-propyloctane

  28. CH3 CH2 CH3 –CH2 – CH2 – CH – CH – C – CH2 – CH3 CH2CH3CH2 CH2CH3 CH3

  29. Name the following compound 3D – models show that because of the tetrahedral carbon atoms the chains are zig-zagged and not at all straight

  30. Physical Properties of Alkanes Non-polar molecules, which are less dense than water. Alkanes are immiscible with water making two layers. Van-der Waals or dipole-dipole attractive forces, and not H-bonding (as in polar molecules) are the main intermolecular forces Alkanes show regular increases in bpt and mpt as molecular weight increases down the homolgous series

  31. Physical Properties of Alkanes These weak intermolecular forces operate over small distances, arising because the electron distribution within molecules at any given instance is not uniform. Resulting in tiny electrical attractions between molecules. These temporary dipoles hold alkanes as liquids or solids, and must be overcome in order to vaporize a liquid or melt a solid (wax)

  32. Isomers – they have the same molecular formula, but a different structures Structural Isomers – same molecular formula, but atoms are bonded in different orders . C4H10 – has two isomers, n-butane and isobutane (2-methylpropane) Has the same molecular formula as n-pentane, C5H12 (2-methylbutane) Have different Physical Properties, Mpt, Bpt, densities, (2,2-dimethylpropane)

  33. Fractional distillation of crude oil Natural Gas (C1-C4) Gasoline (C4-C12) Bpt (40-200 ºC) Kerosene (C12-C16) Bpt (200-250 ºC) Petroleum Heating oil (C15-C18) Bpt (250-300 ºC) Straight-chain alkanes are a pure fuel, because of engine knock. n-Heptane has an octane rating = 0 2,2,4-trimethylpentane has an octane rating = 100 Catalytic cracking

  34. CYCLOALKANES and Conformational Analysis

  35. Cycloalkanes CnH2n Cyclopropane Cyclobutane Cyclopentane

  36. Angle Strain in Cyclopropane and Cyclobutane – weaker “Bent” C-C bonds C-C Bond angles 60 and 88o respectively Eclipsed hydrogens – Torsional Angle Reduced in Cyclobutane by folding or bending Pentane has C-C bond angles of 108o C-C bonds slightly bent out of planarity in order to reduce torsional strain The most stable cycloalkane with 109.5o C-C bond angles Cycloalkanes have higher bpt/mpt than straight chain alkanes with the same number of carbon atoms

  37. Sir D.H.R. Barton, Nobel Prize 1969

  38. How to draw Cyclohexane ? put in axial H’s put in equitorial H’s

  39. Reactions of Alkanes Combustion Dehydrogenation Halogenation – radical substitution reactions

  40. Heterolytic Fission Homolytic Fission

  41. Heterolytic Fission When bonds break ions are created – driven by the energy of solvation Homolytic Fission Each atom gets one electron each – results in the formation of radicals Radical – neutral species with one unpaired electron Using Curly Arrows

  42. Sir Robert Robinson, Nobel Prize 1947 Introduced curly arrows in 1922, numerous brilliant syntheses of complex natural products

  43. Halogenation Substitution Reaction – a reaction in which part of a small reacting molecule replaces an atom or a group of atoms on the organic molecule

  44. Mechanisms are widely used by organic chemists to explain reaction pathways to observed reaction products Initiation Two highly reactive Chlorine radicals formed Hydrogen abstraction to form a methyl radical

  45. Propagation Chlorine atom is abstracted to form a chlorine radical Propagation are the product forming steps Chain Reaction – thousands of radical forming cycles

  46. Termination Radicals Couple Product forming Chains are broken As the reaction progresses chloromethane accumulates and its hydrogen atoms can be abstracted.

  47. Fluorine is the most reactive halogen – mixtures of fluorine and methane can be explosive. Fluorine radical is very reactive. The reaction is controlled with the addition of an inert gas to dilute the reaction. Chlorine is next most reactive, followed by bromine. Cl2 and Br2 require heat or light. Iodine does not react with methane easily. Iodine radical is disperse and large - unreactive

  48. Alkyl Halides or Haloalkanes

  49. Naming them Tend to be Heavier than water More Toxic than Alkanes Tetrachloromethane or carbon tetrachloride 2-Chloro-3-methylbutane 3-Bromo-1-chlorobutane 1-Bromobutane 2-Chloropropane or Isopropyl chloride 1-Ethyl-2-fluorocyclohexane Trichlorofluoromethane (Freon-11) Dichlorodifluoromethane (Freon-12) 1,1,1, 2-Tetrafluoroethane Chlorofluorocarbons (CFCs) Refrigerant Gases, Ozone Depletion, More H’s more degradable

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