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Topic 10 Organic chemistry

Topic 10 Organic chemistry. Inorganic chemistry? Chemistry of life (now biochemistry)  Carbon chemistry Introduction Alkanes Alkenes Alkohols Halogenalkanes Reaction pathways. 10.1 Carbon molecules. Carbon has 4 valence electron’s (1s 2 2s 2 2p 2 )

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Topic 10 Organic chemistry

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  1. Topic 10Organic chemistry • Inorganic chemistry? Chemistry of life (now biochemistry)  Carbon chemistry • Introduction • Alkanes • Alkenes • Alkohols • Halogenalkanes • Reactionpathways

  2. 10.1 Carbon molecules • Carbon has 4 valence electron’s (1s22s22p2) • Tetrahedral structures if single bonds • Planar triangular if double bond • Linear if triple bonded

  3. Organic substances • Carbon is often (almost always) covalently bonded • Other common atoms is hydrogen, oxygen, nitrogen ….. • Molecules can be long chains or ring form • Hydrocarbons: Compounds only containing carbon and hydrogen

  4. HYDROCARBONS • Molecules containing only C and H • Alkanes, alkenes, alkynes, arenes, cycloalkanes

  5. Homologous series • Same general formula • Neighbouringmembersdiffer by –CH2- • Similarchemicalproperties • Gradation in physicalproperties, such as boilingpoint

  6. The first straight-chain alkanes, general formula CnH2n+2 Explain the trend! Predict the boilingpointofheptane!

  7. Different ways of representing structural formulas Skeletal formula Empiricalformula?

  8. IsomersSame molecular formula but different structural formulas Butane have 2 isomers: • CH3-CH2-CH2-CH3 Butane • CH3-CH-(CH3)-CH3 Methyl-propane

  9. Methyl-group 1 2 3 4 5 6 7 Find the longestcarbonchain and youhave the ”last name” of the compound: 7→ heptane Find and namesubstituents: 1 metyl-group Number the carbons in the chain so thatsubstituents gets as low no. as possible: the methyl-group is attached at carbon no. 2 Put it together: 2-methyl-heptane

  10. Ethyl-group Methyl-group 1 2 3 4 5 Find the longestcarbonchain and youhave the ”last name” of the compound: 5→ pentane Find and namesubstituents: 1 metyl-group and 1 ethyl-group Number the carbons in the chain so thatsubstituents gets as low no. as possible: the methyl-group is attached at C no. 3, and the ethyl-group at C no. 2 Put it together: 3-etyl-2-methyl-pentane

  11. Whichnames?

  12. The names 2-methyl-propane 2-methyl-butane 2,2-dimethyl-propane 2, 3-dimethyl-butane 2,2-dimethyl-butane 2-methyl-pentane

  13. 10.2 Alkanes • Homologous series of a saturated hydrocarbon with only single bonds between carbon atoms • General formula CnH2n+2 • Low m.p. and b.p. due to only van der Waal´s forces • Often gases and liquids at room temperature • Low reactivity

  14. Alkaneshavehighbondentalpiesand lowreactivity

  15. Alkaneshavelowbondpolarityand lowreactivity The higher the difference in electronegativity, the higher the reactivity in reactionswithe.g. nucleophiles (as weshallsee later…)

  16. Abouthydrocarbons • Alkanes and other hydrocarbons are good fuels • Complete combustion: Hydrocarbons + oxygen Carbon dioxide + water +heat • If oxygen is limited then incomplete combustion: carbon monoxide, CO and elementary carbon, C, may be formed

  17. Combustionofoctane • Complete (withplentyof O2): C8H18 + 25 O216 CO2 + 18 H2O • Incomplete (not enough O2): C8H18 + 9 O2 C + CO +2 CO2 + 9 H2O

  18. Reactivity • Alkanes can react with radicals- eg. chlorine in UV-light Cl-Cl2 Cl• unpaired electron • Compounds with unpaired electrons are called free radicals and are very reactive • Cl-Cl 2 Cl• homolytic fission • A-B A+ + B-heterolytic fission UV UV

  19. The reaction of methane and chlorine by radical reactions • 2 Cl• + CH4 CH3Cl + HCl • 2 Cl• + CH3Cl  CH2Cl2 +HCl • 2 Cl• + CH2Cl2  CHCl3+ HCl • 2 Cl• + CHCl3  CCl4 + HCl • Amixture of chlorinated methanes is achieved • Radical reactions involve an initiation step, one or more propagation steps, and a termination step

  20. Radicalreactions

  21. 10.3 Alkenes • Homologous series of unsaturated hydrocarbons with one or more double bonds between carbon atoms • General formula CnH2n • Low m.p. and b.p. due to only van der Waal´s forces • Often gases and liquids at room temperature

  22. Ethene CH2=CH2 Propene CH3-CH=CH2 ButeneCH3-CH2-CH=CH2 1-Butene or But-1-ene CH3-CH2=CH-CH3 2-Butene or But-2-ene Pentene CH3-CH2-CH2-CH=CH2 1-Pentene or Pent-1-ene CH3-CH2-CH2=CH-CH3 2-Pentene or Pent-2-ene

  23. Reactions of alkenes • Reactivedouble bonds • Lowactivationenergy • Addition and polymerizationreactions

  24. Addition reactions with bromine and hydrogen chloride • H2C=CH2 + Br2 H2BrC-CH2Br Spontaneous at NTP colourless red/brown colourless Used as proof of C-C-double bonds • H2C=CH2 + HCl  H3C-CH2ClSpontaneous at NTP

  25. Addition reactions with hydrogen and water • H2C=CH2+ H2H3C-CH3 E.g. Ni-catalyst. Industrially important when transformation of vegetable oil to margarine • H2C=CH2 + H2O H3C-CH2OH Catalyst: H2SO4, H3PO4or Al2O3 ~300oC, 7 MPa. At 1 atm the reversed reaction is favoured. Synthesis of alcohols

  26. Polymerisation reactions • Alkenes forming plastics, making plastics • Radical reactions involving Cl2 and UV-light • Initiation: Cl-Cl2 Cl• • Propagation; adding monomers to a long chain, e.g. H2C=CH2+ Cl• •H2C-CH2Cl monomer •H2C-CH2Cl + H2C=CH2•H2C-CH2-H2C-CH2Cl •H2C-CH2-H2C-CH2Cl + H2C=CH2•H2C-CH2-H2C-CH2-H2C-CH2Cl UV

  27. Termination Two radicals meet and a bond is formed. R-CH2•+ R’-CH2•  R-CH2-CH2-R’ • The polymer is ready!

  28. Addition polymerisation reactions (I)

  29. Addition polymerisation reactions (II) Teflon

  30. Benzene ring • Identify when present in structural formula, phenyl ring

  31. Functional groups • C-C double and triple bonds, phenyl ring • Other elements bonded in different ways with the carbon chain; alcohol, aldehyde, keton, carboxylic acid, amine, ester, halide • Give the molecule other chemical and physical properties

  32. 10.4 Alcohols • The functional group –OH • Name: stem + the suffix –anol(or as prefix: hydroxy) • H-bonds => higher b.p., smaller ones (C1-C3) are water-soluble

  33. Methanol CH3OH Wood spirit, formed by pyrolysis of wood. Highly toxic! Ethanol CH3-CH2-OH Alcohol, formed during fermentation of sugar. Technically very important; In drinks, as a solvent, desinfectant and fuel

  34. Propanol CH3-CH2-CH2-OH 1-propanol or propan-1-ol a primary alcohol CH3-CHOH-CH3 2-propanol or propan-2-ol a secondary alcohol Isopropanol, used as windscreen de-icer

  35. Butanol CH3-CH2-CH2-CH2-OH 1-butanol or butan-1-ol Non-water soluble CH3-CCH3OH-CH3 2-metyl-2-propanol or 2-metylpropan-2-ol,a tertiary alcohol Water soluble

  36. Combustion Alcohol + Oxygen  Carbon dioxide + water CH3-CH2-OH + 3 O2 2 CO2 + 3 H2O

  37. Redox reactions in organic chemistry • The carbon with a functional group (eg. –OH) will be oxidised first • Oxidation: Add oxygen and/or remove hydrogen from the carbon • Reduction: Add hydrogen and/or remove oxygen from the carbon

  38. The morebondsto oxygen, the higher oxidation stateof a carbon • oxidation  reduction  Alcohol Aldehyde Carboxylic acid CH4CH3OH HCHO H-COOH CO2 Methane Methanol MethanalMethanoic Carbon acid dioxide

  39. Oxidation of alcohols • Primary alcohol  Aldehyde Carboxylic acid • Secondary alcohol Ketone • Tertiary alcohol  no oxidation (unless C-C-bonds are broken)

  40. K2Cr2O7, Potassiumdichromate, a common oxidizing agent CH3CH2OH + Cr2O72- + H+ CH3CHO  CH3COOH + Cr3+ + H2O Reactive. Stable. Distill of Reflux when formed Otheroxidizing agents KMnO4, CuO, CuSO4

  41. Aldehyde • The functional group –CHO or • Name: stem + suffix: -anal • Dipoles => slightly higher bp’s, smaller ones are water-soluble etc. • Quite reactive compounds • Methanal H-CHO • EthanalCH3-CHO • Formed by light oxidation of primary alcohols

  42. Ketone • The functional group –CO- or • Name: stem + suffix: -anone • Dipoles => slightly higher bp’s, smaller ones are water-soluble etc. • Propanone (acetone) CH3-CO-CH3 • Pentane-2-one CH3-CO-CH2-CH2-CH3 • Formed by oxidation of secondary alcohols

  43. Carboxylic acids • The functional group –COOH or • Name: stem + suffix: -anoic acid • H-bonds => higher bp’s, smaller ones are water-soluble etc. • Acidic reactions • Methanoic acid H-COOH • Ethanoic acid CH3-COOH • Formed by strong oxidation of primary alcohols

  44. Salt of Carboxylic acids • Salt form: -COO-or • Name: stem + suffix: -oate ion • Methanoate H-COO- • Ethanoate CH3-COO- • Formed by reactionofcarboxylicacid and base: NaOH + CH3COOH Na+ + CH3COO-

  45. Halogenoalkane • Functional group: -X (-F, -Cl, -Br, -I) • Name: e.g. prefix: Chloro- + alkane • Chloromethane CH3-Cl • Bromoethane CH3-CH2-Br

  46. Ester • Identify when present in structural formula • Functional group: -COOC- • Alcohol + carboxylic acid  ester + water • Condensation reaction or esterification

  47. Amines • Identify when present in structural formula • Relatives to ammonia; weak base • Functional group –NH2 • H-bonds => higher bp’s, smaller ones are water-soluble etc. • Name: stem + suffix: -ylamine(or prefix amino-) • Ethylamine CH3-CH2-NH2

  48. 10.5 HalogenoalkanesReactions C—X d+ d- => Iodine compounds most reactive

  49. Nucleophiles and electrophiles- oftenneeded in organicreactions • Nucleophile- nucleuslover • Has freeelectronpair and whole or part negative charge • The larger the negative charge - the better the nucleophile • Eg: C=C, H2O, -OH, -CN, NH3 • Electrophile-electronlover • Has wholeor part positive charge • The larger the positive charge - the better the Electrophile • Eg: C=O, H+, C-Cl,

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