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BONDING IN ORGANIC MOLECULES

7. BONDING IN ORGANIC MOLECULES. CHAPTER. 7.1 Petroleum Refining and the Hydrocarbons 7.2 The Alkanes 7.3 The Alkenes and Alkynes 7.4 Aromatic Hydrocarbons 7.5 Fullerenes 7.6 Functional Groups and Organic Reactions 7.7 Pesticides and Pharmaceuticals.

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BONDING IN ORGANIC MOLECULES

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  1. 7 BONDING IN ORGANIC MOLECULES CHAPTER 7.1 Petroleum Refining and the Hydrocarbons 7.2 The Alkanes 7.3 The Alkenes and Alkynes 7.4 Aromatic Hydrocarbons 7.5 Fullerenes 7.6 Functional Groups and Organic Reactions 7.7 Pesticides and Pharmaceuticals General Chemistry I

  2. 307 7.1 PETROLEUM REFINING AND THE HYDROCARBONS Organic Chemistry: the study of the compounds of carbon Hydrocarbons: compounds of carbon and hydrogen

  3. 309 7.2 THE ALKANES • Normal alkanes,n-alkanes • ~ straight-chain (linear) alkanes, CnH2n+2

  4. 309 s(sp3-s) s(sp3-sp3) s(sp3-s) Fig. 7.1. Bonding in alkanes involves sp3 hybridized orbitals. ‘eclipsed’ conformer ‘staggered’ conformer Fig. 7.2.Rotation about C–C bond  variable conformations Conformers (conformations) are isomers that can be interconverted via bond rotations. They are stereoisomers. 4

  5. 310 London dispersion force Two conformations of C16H34

  6. 311 Fig. 7.5. Fractional distillation of petroleum.

  7. 311 Cyclic Alkanes: Carbon atoms arranged in rings - cycloalkanes have one ring: CnH2n - angle strain energy reducing the stability of small rings (< C5) CCC bond angle smaller than the sp3 tetrahedral angle of 109.5o Cyclopropane, C3H6 Cyclobutane, C4H8Cyclohexane, C6H12 unstrained angle strained

  8. 312 Cyclohexane, C6H12 Fig. 7.7. Conformations of cyclohexane. (a) Chair. (b) Boat.

  9. 312 Branched-Chain Alkanes and Isomerism • Branched chain hydrocarbons contain only C-C and C-H • single bonds, but not in a straight chain. They are constitutional • (structural) isomers of normal alkanes. Isomers are different • structures with the same molecular formula. Fig. 7.8. Two isomeric hydrocarbons with the molecular formula C4H10. (a) Butane. (b) 2-Methylpropane (branched chain isomer).  Constitutional isomers have different atomic connectivities: they can be interconverted only by bond-breaking and bond- making processes.

  10. Slide 18 Slide 9 Slide 17 Slide 18 Slides 4 & 8 Have same atomic connectivity, but differ in spatial arrangement of atoms Slide 33 Differ in atomic connectivity  Interconversion of all isomers, except conformers, requires requires bond breaking and remaking

  11. 313 • Nomenclature for isomeric alkanes •  (IUPAC: International Union of Pure and Applied Chemistry) 1. Find the longest (backbone) alkane chain 2. Alkyl groups (branches) Methyl –CH3 Ethyl –CH2CH3 Propyl –CH2CH2CH3Isopropyl –CH(CH3)2 3. Numbering of carbon atoms (lowest number for the attached position) 4. Prefixes for many alkyl groups di-, tri-, tetra- , penta- 5. Alphabetical order for different alkyl groups

  12. 313 EXAMPLE 7.1 Name the following branched-chain alkane: 6 1 2 3 4 5 4-ethyl-2,4-dimethylhexane

  13. 314 • Octane number • Straight-chain alkanes burn very unevenly  “knocking” • Heptane (octane number, 0) Isooctane (octane number, 100) • Octane number, 90  90% (by vol) isooctane + 10% heptane • Anti-knocking additive: tetraethyllead, Pb(C2H5)4(now banned!)

  14. 314 7.3 THE ALKENES AND ALKYNES • Unsaturated hydrocarbons • Alkene ~ double bonds E.g. Ethene (Ethylene), C2H4 • Alkyne ~ triple bonds E.g. Ethyne (Acetylene), C2H2 Fig. 7.10. Reaction with KMnO4. (a) No reaction with hexane. (b) Redox reaction with 1-hexene. Products: MnO2 and CH3(CH2)3CH(OH)CH2OH

  15. 315 Ethylene, H2C=CH2

  16. 315 Acetylene, HC≡CH

  17. 314 • Optical isomerism and chirality • Optical isomers: • Non-superimposable mirror images • Same physical properties but with different optical activity • Chemical properties can differ when they interact with other • optically active molecules →Pharmaceutically important! • Optical activity: • Rotating the plane polarized light clockwise or anti-clockwise • Chirality (handedness) ~ C*: chiral center Fig. 7.9. Non-superimposable optical isomers of a molecule CHBrClF.

  18. 316 • Position isomers of alkenes and alkynes C4H8: CH2=CH-CH2-CH3 CH3-CH=CH-CH3 1-butene 2-butene C4H6: HCC–CH2–CH3 H3C–CC–CH3 1-butyne 2-butyne • Geometric isomers of alkenes E.g. 2-butene

  19. 317 Fig. 7.13. The overlap between the two p orbitals decreases when the 2-butene molecule is twisted about the C=C bond. Fig. 7.14. Configurational change of the trans isomer of 2-butene to its cis isomer upon absorbing UV light. * transition.

  20. 319 • Polyenes 1,3-butadiene, CH2=CH–CH=CH2 conjugated p electron system Fig. 7.15. The four  MOs formed from four 2pz AOs in 1,3-butadiene. Only the two lowest orbitals are occupied in the ground state.

  21. 319 7.4 AROMATIC HYDROCARBONS • Benzene, C6H6 Fig. 7.16. The six π molecular orbitals for benzene.

  22. 321 • BTX (benzene-toluene-xylene) (methylbenzene) (1,2; 1,3; 1,4-dimethylbenzenes) - hydrodealkylation: from toluene to benzene, 550-650 oC, 40-80 atm

  23. 322 • Reforming reactions: • producing BTX aromatics from straight chain alkanes

  24. 322 7.5 FULLERENES - Buckminster fullerene: the third allotrope of carbon - a whole family of closed-cage carbon molecules

  25. 323 The Nobel Prize in Chemistry 1996 “for their discovery of fullerenes” Robert F. Curl, Jr. Harold W. Kroto Richard E. Smalley

  26. 323 Carbon Nanotubes (CNTs) Carbon nanotubes : one of the purest carbon forms • Single-walled nanotubes (SWNTs) - a single graphite sheets wrapped into a cylindrical tube • Multi-walled nanotubes (MWNTs) - an array of concentrically nested nanotubes Baughman, R. H. et al. Science 2002, 297, 787

  27. 323 Graphene-Based Materials • graphenes – monolayers of carbon atoms arranged in a honeycomb network • simply prepared by pulling an atomic layer off of a graphite crystal with a piece of sticky tape • a giant aromatic macromolecule that conducts both electricity and heat well in two dimensions • high specific surface area, high mechanical strength comparable to CNTs • production cost lower than that of CNTs D. Li et al. Science 2008, 320, 1170

  28. 324 7.6 FUNCTIONAL GROUPS AND ORGANIC REACTIONS

  29. 325 • Halides R–X (X = F, Cl, Br, I) Halo- • Free radical chain reaction + other products CH4 + Cl2 CH3Cl + HCl chloromethane Cl2→ 2 Cl ∙ (initiation) Cl ∙ + CH4→ HCl + ∙ CH3 (propagation) ∙ CH3 + Cl2→ CH3Cl + Cl ∙ (propagation) • Addition and elimination reactions CH2=CH2 + Cl2→ ClCH2CH2Cl 1,2-dichloroethane ClCH2CH2Cl CH2=CHCl + HCl vinyl chloride (chloroethene) monomer of PVC

  30. 326 – OH group -ol, hydroxy- • Alcohols R–OH • Methanol (methyl alcohol), CH3OH • CH4(g) + H2O(g) → CO(g) + 3 H2(g) (reforming reaction) • CO(g) + 2 H2(g) → CH3OH • synthesis gas • Ethanol (ethyl alcohol), C2H5OH • CH2=CH2 + H2O → CH3CH2OH • CH3CH2CH2OH: 1-propanol (propylalcohol) • CH3CH(OH)CH3: 2-propanol (isopropyl alcohol) • CH3CH(OH)CH2CH3: 2-butanol or 2-hydroxybutane

  31. 327 • Types of Alcohols • Primary alcohol: RCH2–OH • ethanol • Secondary alcohol: R2CH–OH • 2-butanol • Tertiary alcohol: R3C–OH • 2-methyl-2-propanol • tertiary-butyl alcohol or tert-butanol • (CH3)3COH

  32. 327 • Phenols C6H5OH or Carbolic acid • Weak acid, but stronger than EtOH • Partial oxidation of benzene, distillation of coal • Toxic: lethal dosage, 1g • Major Synthetic Process (the cumene process)

  33. 328 • Ethers R–O–R’ –O– group CH3CH2–O–CH2CH3, diethyl ether - methyl t-butyl ether (MTBE) - cyclic ethers: epoxides E.g. epoxyethane (ethylene oxide)  Alcohols and ethers of same molecular formula are functional group isomers E.g. ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3), both C2H6O

  34. 329 • Aldehydes -CHO group–al ▶ HCHO, methanal(formaldehyde) • “Formalin” : aqueous solution of HCHO preservation of biological specimens • ‘Sick house syndrome’ ▶ CH3CHO, ethanal(acetaldehyde) Fig. 7.23. Bonding in formaldehyde involves sp2 hybrid orbitals of both C and O.

  35. 329 –one >CO group • Ketones • (CH3)2CO, propanone(acetone) • Good solvent, miscible with water • Oxidation of secondary alcohol: • CH3CH2CH2COCH3, 2-pentanone • CH3CH2COCH2CH3, 3-pentanone

  36. 330 • Carboxylic Acids R–COOH –oic acid • ▶ Carboxyl group: • HCOOH, methanoic acid(formic acid) • CH3COOH, ethanoic acid(acetic acid)

  37. 331 • Esters –oate • Product of the reaction between a carboxylic acid • and an alcohol • Fragrant odors, flavors of fruits Ethyl ethanoate(ethyl acetate)

  38. 331 • ★Fats • Hydrogenation of oils (esters of cis-unsaturated fatty acids) Triglyceride ester + 6H2 → saturated fats • Saturated fats with higher m.p.: • →solid, good for baking and extended shelf-life • Remaining double bonds converted from • cis to trans isomers →bad for health!

  39. 334 • Amines >N- group–amine (or amino-) • Primary amine: RNH2 Secondary amine: R2NH Tertiary amine: R3N ◆ Amides: R–(CO)–(NH)–R’ -CONH- group -amide (or amido-) • Condensation product of an amine with a carboxylic acid an amide

  40. 332 Functional Groups in Proteins • Amino acids, NH2–R–COOH • ~ bifunctional molecules • Glycine, NH2CH2COOH • α-amino acid, +H3NCH2CO2– (pH = 7) ‘zwitterion’ • Peptide • ~ Condensation product of two or more amino acids • Peptide bonds –(CO)–(NH)– (amide bonds)

  41. 333 • Protein ~ Polypeptide • primary, secondary, tertiary, quaternary structures tertiary structure of the enzyme chymotrypsin binding of phenylalanine in the active site of chymotrypsin expanded view of the active site of chymotrypsin

  42. 335 7.7 PESTICIDES AND PHARMACEUTICALS • Insecticides (살충제) • First-generation • Copper, Lead, Arsenic, Nicotine → aphid • Second-generation • DDT (dichlorodiphenyltrichloroethane):→lice • Methyl parathion • Third-generation • target oriented, environmentally degradable • E.g. sex attractant, Juvenile hormone ~ Methoprene

  43. 336 • Herbicides(제초제) • 2,4-D (2,4-dichlorophenoxyacetic acid) • 2,4,5-T (“Agent Orange,” or 2,4,5-trichlorophenoxyacetic acid) → Defoliant used during Vietnam war • → Contains trace amount (10 ppb) of TCDD • TCDD (“dioxin,” or 2,3,7,8-tetrachlorodibenzo-p-dioxin) • Extremely toxic ! Waste-burning incinerator • → major source of dioxin in the environment

  44. 338 • Analgesics(진통제) • Aspirin(acetylsalicylic acid) • Analgesic (pain reliever), Antipyretic (reduces fever), • Prevents heart disease (thins the blood) • Carboxylic acid  Irritates stomach • Acetaminophen (4-acetaminophenol) • “Tylenol” ~ weakly acidic phenol

  45. 338 • Much more powerful pain relievers • Morphine ~ natural product from “opium poppy” • Codeine ~ also cough suppressant • Heroin ~ 3,6-diacetylmorphine • 2~3 times powerful than morphine and more addictive Morphine Codeine Heroin

  46. 339 • Antibacterial Agents (Antibiotics) • Sulfanilamide • Bacteria mistake sulfanilamide for p-aminobenzoic acid • → Interferes with bacteria’s synthesis of folic acid, • Penicillin ~ natural product formed by certain molds • ~ Total synthesis by John C. Sheehan (1957) • ~ Fermentation (more economic)

  47. 340 • Steroids: derived from cholesterol • “Steroid nucleus” 3 six-atom rings and 1 five-atom ring • Cholesterol ~ synthesized in the liver from acetate units via the ‘mevalonate pathway’. It is the biological precursor to most other steroids • Cortisone ~ secreted from adrenal glands • ~ controls metabolism of sugars, fats, and proteins • Progesterone, Estrogen • ~ Female sex hormones, oral contraceptives • Testosterone ~ male sex hormone

  48. 340

  49. 10 Problem Sets For Chapter 7, 4, 12, 20, 28, 30, 32, 40, 44, 46, 50

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