Ch 10 slides

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Ch 10 slides

  1. 1. 2 Hydrocarbons Chapter 10 2-1
  2. 2. 2 Structure Hydrocarbon: a compound composed only of carbon and hydrogen Saturated hydrocarbon: a hydrocarbon containing only single bonds Alkane: a saturated hydrocarbon whose carbons are arranged in a open chain Aliphatic hydrocarbon: another name for an alkane 2-2
  3. 3. 2 Structure Shape • tetrahedral about carbon • all bond angles are approximately 109.5° 2-3
  4. 4. 2 Nomenclature Alkanes have the general formula C nH 2n+2 Molecular Condensed Name Formula Structural Formula methane CH 4 CH 4 ethane C2 H6 CH 3 CH 3 propane C3 H8 CH 3 CH 2 CH 3 butane C 4 H 10 CH 3 (CH 2 ) 2 CH 3 pentane C 5 H 12 CH 3 (CH 2 ) 3 CH 3 hexane C 6 H 14 CH 3 (CH 2 ) 4 CH 3 heptane C 7 H 16 CH 3 (CH 2 ) 5 CH 3 2-4
  5. 5. 2 Nomenclature Alkanes (contd.) octane C8 H18 CH 3 (CH 2 ) 6 CH 3 nonane C9 H20 CH 3 (CH 2 ) 7 CH 3 decane C10 H22 CH 3 (CH 2 ) 8 CH 3 dodecane C12 H26 CH 3 (CH 2 ) 10 CH 3 tetradecane C14 H30 CH 3 (CH 2 ) 12 CH 3 hexadecane C16 H34 CH 3 (CH 2 ) 14 CH 3 octadecane C18 H38 CH 3 (CH 2 ) 16 CH 3 eicosane C20 H42 CH 3 (CH 2 ) 18 CH 3 2-5
  6. 6. 2 Constitutional Isomerism Constitutional isomers: compounds with the same molecular formula but a different connectivity (order of attachment of their atoms) • example: C 4 H 10 CH 3 CH 3 CH 2 CH 2 CH 3 CH3 CHCH3 Butane 2-Methylpropane 2-6
  7. 7. 2 Prob 1 Which sets represent pairs of constitutional isomers? O O(a) CH3 CH2 OH and CH 3 OCH 3 (b) CH3 CCH3 and CH3 CH2 CH O O OH O(c) CH 3 COCH 3 and CH 3 CH2 COH (d) CH3 CHCH2 CH3 and CH3 CCH2 CH 3(e) and CH 3 CH 2 CH2 CH2 CH3 (f) and CH2 = CHCH2 CH2 CH3 2-7
  8. 8. 2 Constitutional Isomerism Molecular Constitutional Formula Isomers CH4 1 C5 H1 2 3 C1 0 H2 2 75 C1 5 H3 2 4,347 C2 5 H5 2 36,797,588 C3 0 H6 2 4,111,846,763 2-8
  9. 9. 2 Nomenclature - IUPAC Suffix - ane specifies an alkane Prefix tells the number of carbon atoms Prefix Carbons Prefix Carbons meth- 1 undec- 11 eth- 2 dodec- 12 prop- 3 tridec- 13 but- 4 tetradec- 14 pent- 5 pentadec- 15 hex- 6 hexadec- 16 hept- 7 heptadec- 17 oct- 8 octadec- 18 non- 9 nonadec- 19 dec- 10 eicos- 20 2-9
  10. 10. 2 Nomenclature - IUPAC Parent name: the longest carbon chain Substituent: a group attached to the parent chain • alkyl group: a substituent derived by removal of a hydrogen from an alkane; group Name symbol R- Alkane Name Alkyl given the CH 4 Methane CH3 - Methyl group CH 3 CH 3 Ethane CH3 CH 2 - Ethyl group 2-10
  11. 11. 2 Nomenclature 1.The name of a saturated hydrocarbon with an unbranched chain consists of a prefix and suffix 2. For branched alkanes, the parent chain is the longest chain of carbon atoms 3. Each substituent is given a name and a number CH 3 2 CH3 CHCH 3 1 3 2-Methylpropane 4. If there is one substituent, number the chain from the end that gives it the lower number CH3 4 3 2 CH3 CH2 CH 2 CHCH3 5 1 2-Methylpentane 2-11
  12. 12. 2 Nomenclature 6. If there are two or more different substituents, • list them in alphabetical order • number from the end of the chain that gives the substituent encountered first the lower number CH3 2 4 6 3 5 7 CH3 CH2 CHCH2 CHCH2 CH3 1 CH2 CH3 3-Ethyl-5-methylheptane 2-12
  13. 13. 2 Nomenclature 7. The prefixes di-, tri-, tetra-, etc. are not included in alphabetization CH3 CH2 CH3 CH3 CCH2 CH CH2 CH3 4 6 1 2 3 5 CH3 4-Ethyl-2,2-dimethylhexane 8. Substituents are named by the same set of rules. 2-13
  14. 14. 2 Nomenclature Alkyl groups Condensed CondensedName Structural Formula Name Structural Formulabutyl - CH 2 CH2 CH2 CH 3 methyl - CH 32-methylpropyl - CH 2 CHCH3 ethyl - CH 2 CH3 (isobutyl) CH3 propyl - CH 2 CH2 CH31-methylpropyl - CH CH 2 CH3 1-methylethyl - CH CH 3 (sec- butyl) (isopropyl) CH3 CH3 CH31,1-dimethylethyl - CCH3 (tert-butyl) CH3 2-14
  15. 15. 2 Classification of C & H Primary (1° ) C: a carbon bonded to one other carbon • 1° H: a hydrogen bonded to a 1° carbon Secondary (2° ) C: a carbon bonded to two other carbons • 2° H: a hydrogen bonded to a 2° carbon Tertiary (3° ) C: a carbon bonded to three other carbons • 3° H: a hydrogen bonded to a 3° carbon Quaternary (4° ) C: a carbon bonded to four C other carbons 2-15
  16. 16. 2 Physical Properties Intermolecular forces of attraction • ion-ion (Na + and Cl - in NaCl) • ion-dipole (Na + and Cl - solvated in aqueous solution) • dipole-dipole and hydrogen bonding • dispersion forces (very weak electrostatic attraction between temporary dipoles) 2-16
  17. 17. 2 Physical Properties Low-molecular-weight alkanes (methane....butane) are gases at room temperature Higher molecular-weight alkanes (pentane, decane, gasoline, kerosene) are liquids at room temperature High-molecular-weight alkanes (paraffin wax) are semisolids or solids at room temperature 2-17
  18. 18. 2 Physical Properties Constitutional isomers have different physical properties mp bp Density Name (°C) (°C) (g/mL) hexane -95 68.7 0.659 2-methylpentane -154 60.3 0.653 3-methylpentane -118 63.3 0.664 2,3-dimethylbutane -129 58.0 0.661 2,2-dimethylbutane -98 49.7 0.649 2-18
  19. 19. 2 Oxidation of Alkanes Oxidation is the basis for their use as energy sources for heat and power • heat of combustion: heat released when one mole of a substance in its standard state is oxidized to carbon dioxide and water ∆H° kJ (kcal)/mol CH4 + 2 O 2 CO 2 + 2 H2 O -890 (-212) Methane CH3 CH2 CH3 + 5 O 2 3 CO 2 + 4 H 2 O -2220 (-530) Propane 2-19
  20. 20. 2 Sources of Alkanes Natural gas • 90-95% methane Petroleum • gases (bp below 20° C) • naphthas, including gasoline (bp 20 - 200° C) • kerosene (bp 175 - 275° C) • fuel oil (bp 250 - 400° C) • lubricating oils (bp above 350° C) • asphalt (residue after distillation) Coal 2-20
  21. 21. 2 Gasoline Octane rating: the percent 2,2,4-trimethylpentane (isooctane) in a mixture of isooctane and heptane that has equivalent antiknock properties CH3 CH3 CH3 ( CH2 ) 5 CH 3 CH3 CCH2 CH CH3 CH3 Heptane 2,2,4-Trimethylpentane (octane rating 0) (octane rating 100) 2-21
  22. 22. 2 Synthesis Gas A mixture of carbon monoxide and hydrogen in varying proportions which depend on the means by which it is produced C + H2 O heat CO + H2 Coal 1 catalyst CH4 + O2 CO + 2 H2 2 Methane 2-22
  23. 23. 2 Synthesis Gas Synthesis gas is a feedstock for the industrial production of methanol and acetic acid catalyst CO + 2 H2 CH 3 OH Methanol O catalyst CH3 OH + CO CH 3 COH Methanol Acetic acid • it is likely that industrial routes to other organic chemicals from coal via methanol will also be developed 2-23

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