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Organic Chemistry

Organic Chemistry. The unique chemistry of carbon. Learning objectives. Describe two reasons for abundance of carbon compounds Distinguish between inorganic and organic carbon and other compounds Distinguish between isomers and non-isomers

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Organic Chemistry

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  1. Organic Chemistry The unique chemistry of carbon

  2. Learning objectives • Describe two reasons for abundance of carbon compounds • Distinguish between inorganic and organic carbon and other compounds • Distinguish between isomers and non-isomers • Describe differences between optical and geometric isomerism • Distinguish between aromatic and non-aromatic • Identify common functional groups

  3. One element – one branch of chemistry • Organic compounds based on carbon: 13 million and rising (fast) • 100,000 new compounds synthesized annually • All 91 other elements combined: only 300,000 compounds

  4. Factoids about carbon • Fairly abundant in earth’s crust – but not enough to explain domination

  5. Highly significant to life • Key element in the human organism – and all others

  6. “God’s goof”: The absence of stable mass 5 • C and O are abundant because the atom with mass 5 is unstable • Otherwise atom building after the Big Bang would have resulted in much heavier elements • The thoughts of a cosmological atheist Fred Hoyle: “Some supercalculating intellect must have designed the properties of the carbon atom, otherwise the chance of my finding such an atom through the blind forces of nature would be utterly minuscule….The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question”

  7. Organic and inorganic carbon • Inorganic carbon: ionic compounds where carbon is incorporated as carbonate – CO32- • Organic carbon: compounds of carbon with itself, hydrogen and other elements – by far the most important

  8. Organic carbon forms a thin canopy • Unique (?) conditions on earth that support life Earth’s surface - organic Earth’s crust - inorganic

  9. Vitalism and organic chemistry • Inorganic compounds were salts of the earth • Stable and easily synthesized • Organic compounds were of living organisms • Fragile and not easily synthesized • Belief in Vitalism posited that only living organisms possessed a vital force necessary to create organic compounds • In 1828 urea was synthesized and vitalism was on the way out

  10. Seven ages of man - many ages of a carbon atom • Combustion: C + O2 CO2 • Neutralization by seawater: CO2 + Ca(OH)2  CaCO3 + H2O • Reaction with acid rain: CaCO3 + H2SO4  CO2 • Photosynthesis: CO2  Organic compounds (OC) • Vegetation decomposes: OC  fossil fuels (FF) • Vegetation consumed by animal: OC  new compounds (proteins, DNA etc.) • Respiration: sugars  CO2 + energy • Industrialization: FF  C, CO2 + energy • Manufacturing: FF  Plastics, polymers, drugs etc. • Waste disposal Fossil fuels, CO2

  11. Two reasons why carbon is unique • Carbon can form four bonds – four valence electrons • Carbon forms very strong bonds with itself – chains, rings etc.

  12. Classifying organic compounds

  13. Hydrocarbons are the simplest organic compounds • Contain only C and H • Simplest is CH4 (natural gas) • Intermediate C8H18 (petroleum) • Synthetic polymers contain thousands of atoms

  14. Alkanes • All bonds are single • Saturated • No new bonds can be added • General formula CnH2n+1

  15. Summary of types

  16. Representing molecules • Molecular formula • Shows atoms in the molecule • Structural formula • Shows how they are all connected • Condensed structural formula • Simplified representation of connections

  17. Naming organic compounds • Meth - ane Number of carbon atoms Type of compound

  18. Numbers game: count the carbon atoms in the chain

  19. Saturation bonding:Multiple bonds and unsaturation • Saturated: no more bonds can be added • Unsaturated: more bonds can be formed • More reactive compounds

  20. Alkenes contain double bonds

  21. Going bananas: Ethylene and fruit ripening

  22. Examples of alkynes

  23. Isomerism • Same number and type of atoms • Different arrangements • Hydrocarbons can have straight and branched chains

  24. Isomers simplified • Alkane isomers • General formula CnH2n+1 • Three isomers of pentane • C5H12 • Five isomers of hexane • C6H14

  25. Number of isomers mushrooms as chain length increases • CH4 – 1 possibility • C2H6 – 1 • C3H8 – 1 • C4H10 – 2 • C5H12 – 3 • C8H18 – 18 • C10H22 – 75 • C20H42 – 366,319

  26. Optical isomerism is a special variation • Molecules exhibit handedness – mirror images which are not super-imposable • Must have tetrahedral carbon with four different groups attached • This carbon is chiral

  27. Isomers and reaction yield • Each chiral carbon produces two isomers • If there are n chiral carbon atoms there are 2n isomers

  28. Optical isomers are important in nature • Amino acids are building blocks of proteins • Amino acids are chiral • Proteins contain hundreds – thousands of amino acids • Getting the correct isomer is a big deal

  29. Geometric isomers: Isomerism and a healthy diet • What’s with all this trans fats anyway? • Ask a Chicago Alderman • Different geometry - same attachments • Cis isomers: • Don’t pack together • Cis isomers have low viscosity - good • Trans isomers: • Pack together tightly • Trans isomers are solids - bad

  30. Aromatic: the stuff of dreams • Benzene ring contains 6 C atoms • Bonding is resonant – more stable than expected • All aromatic compounds contain at least one benzene ring • Benzene, C6H6, is one of the most important industrial chemicals

  31. Toxicity of benzene • Benzene is regarded as a highly carcinogenic substance • Use and disposal of benzene are regulated • Compounds containing benzene rings are not necessarily toxic

  32. Functional groups • Chemistry of organic compounds is determined by functional groups • Functional group is an atom or group of atoms that are different from C • Heteroatoms confer very different properties on the substance

  33. Heteroatoms affect physical and chemical properties • C2H6 (ethane) is a gas at RT • C2H6 is insoluble in water • C2H6O (ethanol) is a liquid at RT • C2H6O is soluble in water • Differences in cohesive forces: O-H bonds are polar, C-H bonds are not

  34. Functionalized hydrocarbons

  35. Chlorocarbons and the environment • Important uses – important problems • Solvents CH2Cl2 • Insecticides DDT • Refrigerants CFCs

  36. Alcohols: hic • Functional group –OH • Polar molecules dissolve in H2O • Ethanol: good for your health/bad for your health?

  37. Smoke gets in my eyes: olefactory pleasures of aldehydes • C=O is carbonyl group • Aldehyde contains RCHO • Formaldehyde is a preservative and a product of burning wood • Acrolein is a product of barbequing • Common smells and flavours

  38. Ketones • Ketone is R1R2CO • Acetone is a common solvent • Smell found in cinnamon • Raspberries

  39. Carboxylic acids • Commonly found in citrus fruits and any sour foods • Formic acid present in ant and bee stings

  40. Esters: sweet aromas and flavours • Ester group is R1COOR2 • Sweet aroma in pineapples, jasmine • Synthetic versions are very common

  41. Ethers • Ethers contain R1-O-R2 • No -OH bonds • Not soluble in water • Anesthetics

  42. Amines: the stench of death • Amines contain NR1R2R3 • Rotting fish • Decaying flesh • Illicit drugs

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