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IB Organic Reactions I

IB Organic Reactions I. http://moodle.rockyview.ab.ca/mod/book/print.php?id=58486. 10.2.1. Low reactivity of alkanes. I-Combustion of Alkanes. Alkanes are very unreactive due to single C C bonds. All combustion reactions are highly exothermic.(low polarity &van der waals )

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IB Organic Reactions I

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  1. IB Organic Reactions I http://moodle.rockyview.ab.ca/mod/book/print.php?id=58486

  2. 10.2.1.Lowreactivityofalkanes

  3. I-Combustion of Alkanes • Alkanes are very unreactive due to single C C bonds. All combustion reactions are highly exothermic.(low polarity &van derwaals) • Complete Combustion: 2C8 H18 + 25O2 => 16CO2 + 18 H2 O II. Incomplete Combustion C8 H18 + 9O2 => 2CO2 + 9 H2 O + C + 5CO C and CO are emitted as particulates. Read page 193 Solve Hodderpage 300, question 10.

  4. OrganicPacket : • Question 9

  5. Homolytic X Heterolytic Fission Homolytic Fission: When the cleavage of covalent bond between two atoms takes place in a manner, which enables each atom to retain one electron of the shared pair. This fission is symmetrical and leads to the formation of atoms or groups of atoms having unpaired electrons, called free radicals. Cl-Cl => Cl● + Cl● chlorine free radical ( Cl atom )

  6. Heterolytic Fission • Heterolytic fission is unsymmetrical , one of the fragments takes both the electrons of the shared pair, leaving none on the other. This results into two charged particles as: C6 H5CH2 Cl => C6 H5CH2+ + Cl-

  7. ALKANES UNDERGO SUBSTITUTION ALKENES UNDERGO ADDITION

  8. Free Radical Substitution • Alkanes undergo free radical substitution. This reaction takes place in a series of steps. With excess of the halogen, it continues until all the hydrogens were substituted) CH4 (g) + Cl2 (g) => CH3 Cl(g) + HCl(g) • Initiation Step: (2) Propagation Step: (3) Termination Step: With excess of the halogen, it continues until all the hydrogens were substituted) Solve Hodder page 300, question #8 and 11

  9. IB Questions 1. The active species in the chlorination of an alkane is A. Cl2 molecules B. Cl atoms C. Cl– ions D. Cl+ ions 2. This question concerns several different compounds with two carbon atoms. Ethane, C2H6 , reacts with chlorine to produce chloroethane as the first product. (i) Write a balanced equation for this reaction. (ii) This reaction will not occur simply by mixing the chemicals. What else is required? (iii) What mechanism is involved in this reaction?

  10. ALKANES UNDERGO FREE RADICAL SUBSTITUTION.

  11. ALKENES AND ALKYNES UNDERGO ADDITION !!

  12. Themain source ofalkenes is fromthecrackingofthehigherfractions. C10H22 (g) => C8H18 (g) + C2H4(g) About 10% ofthecrudeoil is convertedintoalkenes. They are used as a chemicalfeedstock: plastics, solvents,detergents.

  13. You may have heard of biofuels being used to fuel automobiles. Biofuel, or gasohol as it is called in many countries, is a mixture of gasoline and ethanol. • Margarines • PVC

  14. There are threekeyareas for the use ofalkenes: • Hydrogenationofunsaturatedlipids to makemargarine, theproductionofethanolandtheproductionofpolymers.

  15. Addition of Alkenes • Alkenes undergo addition due to the presence of the double bond.

  16. SummaryofAdditionReactionsofEthene

  17. 1. Hydrogenation,add H2 Catalyst: Ni , 180◦C

  18. HydrogenationofUnsaturatedFats • Unsaturated fatty acids may be converted to saturated fatty acids by the relatively simple hydrogenation reaction. Addition of hydrogen to an alkene (unsaturated) results in an alkane (saturated). H2C=CH2 + H2 ---> CH3CH3

  19. Hydrogenation of a oleic fatty acid • Vegetable oils are commonly referred to as "polyunsaturated". This simply means that there are several double bonds present. Vegetable oils may be converted from liquids to solids by the hydrogenation reaction. Margarines and shortenings are "hardened" in this way to make them solid or semi-solids.

  20. http://www.elmhurst.edu/~chm/vchembook/558hydrogenation.html • It has long been recognized that saturated fats tend to increase the blood level of the "bad" LDL cholesterol. Monounsaturated (one double bond) and polyunsaturated fats (two or more double bonds) found primarily in vegetable oils tend to lower "bad" LDL cholesterol. An elevated LDL-C increases the risk of developing coronary heart disease.

  21. 2.Halogenation, addition of alkene to Br, Cl and I page 200 • Test for unsaturation: Bromine water is a yellow/orange solution. The color will disappear because the product is • colorless: alkenes with Br2 (aq)

  22. 3. With Hydrogen Halides,HCl and HBr The hydrogen will tend to migrate to the side with the greater number of hydrogen atoms. This preference is known as Markovnikoff´s Rule. DO THE REACTION WITH But 2 ene and HBr !!!!

  23. 4. Hydration, with Water • Water does not react directly with alkenes under normal conditions, concentrated sulfuric acid is required:(page 201) • Reaction:

  24. 5. AdditionPolymerization • Monomer: ethene • Polymer: Polyethene

  25. Oxidation of Alcohols • http://www.chem.umn.edu/services/lecturedemo/info/Breathalyzer.html

  26. Different types of Alcohols Primary (1º) Secondary (2º ) Tertiary (3º) H CH3CH3 │ │ │ CH3─C─OH CH3─C─OHCH3─C─OH │ │ │ H HCH3 1 C 2 C3 C attached attachedattached to C-OH to C-OH to C-OH

  27. Oxidation of 1° Alcohols In the oxidation [O] of a primary alcohol 1, one H is removed from the –OH group and another H from the C bonded to the –OH. primary alcohol aldehyde OHO │ ║ CH3─C─HCH3─C─H + H2O │ H ethanol ethanal (ethyl alcohol) (acetaldehyde) [O] K2Cr2O7 H2SO4

  28. Oxidation of 2° Alcohols The oxidation of 2 alcohols is similar to 1°, except that a ketone is formed. secondary alcohol ketone OH O │ ║ CH3─C─CH3CH3─C─CH3+ H2O │ H 2-propanol 2-propanone [O] K2Cr2O7 H2SO4

  29. Oxidation of 3° Alcohols Tertiary 3 alcohols do not oxidize. Tertiary alcohol no reaction OH │ CH3─C─CH3 no product │ CH3 no H on the C-OH to oxidize 2-methyl-2-propanol [O] K2Cr2O7 H2SO4

  30. If we compare the physical properties of ethanol, ethanal and ethanoic acid we can devise a way of obtaining a good yield of ethanal before further oxidation to ethanoic acid. • Ethaol and ethanoic acid: hydrogen bonds • Ethanal: dipole dipole , lower BP • Distillation apparatus

  31. Distillation& Reflux Apparatus ethanolH+ /Cr2 O7-2

  32. Reaction Pathways(SG 67) • The scheme below can be used to devise reaction pathways. They should involve no more than two steps. • Converting 2 butene to butanone:

  33. Oxidation of Alcohols(Alkanols) • http://www.chem.umn.edu/services/lecturedemo/info/Breathalyzer.html • 1. Which alcohol undergoes oxidation most easily? • A. CH3CH2CH2CH2CH2OH • B. CH3CH(OH)CH2CH2CH3 • C. CH3CH2CH(OH)CH2CH3 • D. (CH3)2C(OH)CH2CH3 • A small amount of alkanol, RCH2OH, is added to a warm solution of potassium dichromate(VI) and sulphuric acid and left for some time. When the reaction is complete, which functional group will be present in the product? • A. RCH2––O––CH2R • O • B. RC––H • O • C. RC––O––H • O O • D. RC––O––CH2R

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