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Organic Chemistry

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Published in: Chemical | Chemistry
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Simplified notes for basic concepts of organic chemistry

Muhammed I / Umm Salal Muhammad

8 years of teaching experience

Qualification: Msc. chemistry

Teaches: Chemistry

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  1. Organic Chemistry Unit 10 and 20 - Functional group chemistry (10.2)
  2. 10.2 Alkanes
  3. Alkanes General formula -C H Hydrocarbons because they contain Carbon and hydrogen only Saturated compounds because they consist of single C-C bonds, these bonds are relatively strong so require a lot of energy to break them up. They are nonpolar so are not susceptible to to attack by many reagents. They are not very reactive but do undergo combustion so are used as fuels, They also undergo substitution reactions
  4. Reactions of alkanes Combustion of alkanes Alkanes are used a fuels in internal combustion engines and household heating. They produce a great deal of energy. Alkanes burn in the presence of oxygen to produce carbon dioxide and water and lots of energy - exothermic reactions. Complete combustion I ncomplete combustion Limited oxygen C3H8(g) + 502(g) 3C02(g) + 4H20(g) 2C3H8(g) + 702(g) 3CO(g) + H20(g) C3Hs(g) + 202(g) 3C(g) + 4H20(g)
  5. N/A
  6. Combustion in hydrocarbons Other hydrocarbons such as s alkenes, alkynes and arenes undergo either complete or incomplete combustion depending on the availability of oxygen with the release of lots of energy. As the C: H ratio increases, with unsaturation there is an increase in smokiness of the flame which is due to the unburned carbon Burning these fossil fuels on a large scale are recognized as a global problem Carbon dioxide and water are known as greenhouse gases because they absorb infra-red so contribute to global warming and climate change. Carbon monoxide is a toxin and binds irreversibly with haemoglobin in the blood preventing it from binding with oxygen Unburned carbon - can be released as particulate matter in the air - leads to health problems
  7. Substitution reactions-halogenation Alkanes undergo substitution reactions - where a halogen atom takes the place of a hydrogen in an alkane . Methane reacts with chlorine to produce chloromethane and hydrogen chloride The reaction does not take place in the dark but in the presence of UV light, which is required to break the C-H bond. UV light CH4(g) + C12(g) CH3Cl(g) + HCl(g)
  8. Free radical substitution This occurs in a series of steps known as Free Radical Substitution, the conditions required are UV light and plenty of methane and halogen Homolytic fission - equal breaking leads to free radicals
  9. Initiation Cl UVlight 2 Cl• radicals UV light 2 chlorine radicals
  10. Propagation step - Chain reaction Propagation both uses and produces free radicals Cl• + CH4-* CH3• + HCI CHy• + CH3Cl + Cl• CH3Cl+ Cl• CH2Cl• + HCI CH2Cl• + C12 CH2C12+C1•
  11. Termination step Termination reactions remove free radicals from the mixture by causing the electrons to pair up cl. + cl. C12 CH3. + Cl.. CH3Cl + -4 C2H6
  12. Similar reactions occur with bromine water in UV light hexane C6H14 bromine water in dark bromine water is decolourized as a photochemical reaction occurs no reaction occurs; no change in colour of bromine water
  13. Alkenes
  14. Alkenes - also known as alkenyLs General structure - C H Alkenes are unsaturated hydrocarbons containing a carbon -carbon double bond Planar molecule- 1200 The double bond consists of sigma and pi bonds and is Sp2 hybridized
  15. Reactions of alkenes - addition Alkenes are unsaturated hydrocarbons and undergo addition reactions because the pi bond is easily broken. Addition of hydrogen - conditions - nickel catalyst and 1500C (this is known as hydrogenation - manufacture of margarine —9 H—C c— Ni catalyst CH3CHCH2 + H 2 CH3CH2CH3 propane
  16. Addition of halogens - di-haLogens Conditions - room temperature, reaction with bromine water, the orange, yellow colour is decolourised- this reaction is used to distinguish between alkanes and alkenes H C—C— C— H + Br2 H c—c C H CH3CHCH2 + CH3CHBrCH2Br propene 1 ,2-dibromoprop
  17. Reactions with bromine water Hexane Hex- -ene
  18. Addition of hydrogen halides Hydrogen halides such as HCI and HBr react with alkenes to produce halogenoalkanes. The reaction takes place rapidly at room temperature. All the Hydrogen halides react in this way - order of reactivity is HI >HBr>HCl due to decreasing bond strength H—C— CH2CH2 + cH3CH2Cl ethene chloroethane
  19. Addition of water This reaction is known as hydration where the alkene is converted to an alcohol (ethanol widely used as a C—C— OH solvent Conditions - Heat with steam and a concentrated acid as a catalyst H SO H H H C + H2S04 H H CH2CH2 H H C— C— H + H20 H— H OS03H H20 H H H H CH3CH2(HS04) —i CH3CH20H + ethyl hydrogensulfate ethanol
  20. Polymerization of alkenes Alkenes undergo addition reactions to produce long chain polymers The alkenes used is known as monomers
  21. Polythene Monomer - Ethene Polymer - polyethylene eth ene the repeating unit
  22. Examples of polymers polypropene H H H c CH3 H c H H c CH3 n propene the repeating unit
  23. Polymers PVC - polyvinyl chloride /polychloroethene and polytetrafluorine Cl ? ? ? ? ? ? PVC
  24. Summary of alkenes addition polymers H 20 (conc. H alcohol alkane (Ni catalyst sooc) dihalogenoalkane brown colourless +HCI halogenoalkane
  25. Alcohols - functional group (hydroxyl) General formula - C H OH n 2n*1 Alcohols have an OH functional group Polar molecules, solubility in water relative to alkanes of comparable mass
  26. Reactions of alcohols Combustion 2CH30H(l) + 302(g) 2C02(g) + 4H20(g) Oxidation of alcohols AH? = -726.1 k) React with acidified potassium dichromate reacts with alcohols to produce either carbonyls
  27. 0xidation ? hcat ?— ? ? ? ?? + , he.t + heat ethanol alcohol ? ? ethanai aldehyde + heat ethana1 «??? aldchydc ethanoic acid carboy.yhc ?? ethanoic acid rboxylic acid cr(llI)
  28. Distillation - warm
  29. Reflux - primary alcohol to a carboxylic acid
  30. Secondary alcohols are oxidized to the ketone by a similar process of oxidation. H H H OH H CH3CHOHCH3 propan-2-ol propan-2-ol CH3CHOHCH3 +10], heat reflux + heat WICr(V1) cr(lll) (CH3)2CO propanone (CH3)2CO H20
  31. Tertiary alcohols
  32. Summary of oxidation of alcohols Summary of oxidation of alcohols primary alcohol secondary alcohol tertiary alcohol Oxidation product aldehyde carboxylic acid ketone not oxidized Colour change with acidified K2Cr207(aq) green orange —+ green no colour change
  33. Esterification - condensation reactions acid ester water For example. the reaction bctwccn cthanoic acid and ethanol is follows. H20 H H 70 CH,COOH C2Hi0H 4 H-O-H
  34. Esterification reactions HCOOH + C2H50H HCOOC2H5 + H20 methanoic ethanol acid ethyl methanoate C3H7COOH + CH30H C3H7COOCH3 + H20 butanoic acid methanol methyl butanoate
  35. Halogenoalkanes General formula - C H X (where X is a halogen) n 2n*1 Halogenoalkane contains an atom of fluorine, chlorine, bromine and iodine bonded to carbon skeleton of a molecule Halogenoalkanes are saturated molecules, contain a polar molecule makes them reactive
  36. NucleophiLic Substitution reactions of halogenoalkanes The carbon-halogen bond is polar, the halogen is more electroegative so becomes more negative while the carbon becomes positive - electron deficient. 8-
  37. The hydroxide ion, OH- is a good nucleophiLe The hydroxide ion, OH-, is a good nucleophile. For example, halogenoalkanes react with alkalis such as NaOH to form alcohols. chloromethane C3H7Br + 1 -bromopropane NaOH NaOH + Nacl methanol C3H70H + NaBr propan -1-01
  38. Benzene Benzene has delocalized electrons which give it extra stability. This means addition reactions would mean it loses its stability. Instead they undergo substitution reactions.
  39. Electrophilic substitution reactions For example, benzene reacts with the nitronium ion, N02+ (derived from nitric acid, HN03), as follows: conc. H 2SO, C6H6 + 3 C 6H5N02 + 50T N02 O The reaction ofbenzene with halogens is as follows: AIC13 in dry ether C6H6+C12 O) O

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