Alkanes for SBI Class


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Alkanes for SBI Class

  1. 1. Organic Chemistry Alkanes & cycloalkanes
  2. 2. Alkanes Alk general formula CnH2n+2 alkanes are saturated (each C is bound to 4 other atoms)
  3. 3. Alkanes • Hydrocarbon chains where all the bonds between carbons are SINGLE b d b t b bonds • Name uses the ending –ane • Examples: Methane, Propane, Butane, Octane, Methane, Propane, Butane, Octane, 2-methylpentane methylpentane
  4. 4. Summary: IUPAC Rules for Alkane Nomenclature 1. Find and name the longest continuous carbon chain. This is called the parent c a . (Examples: methane, s s ca ed e pa e t chain ( a p es e a e, chain. propane, etc.) 2. Number the chain consecutively, starting at the end nearest an attached group (substituent). g p (substituent). ) 3. Identify and name groups attached to this chain. (Examples: methyl-, bromo-, etc.) methyl- bromo- 4. Designate the location of each substituent group with the number of the carbon parent chain on which the group is attached. Place a dash between numbers and letters. (Example: 3-chloropentane) 3- 5. Assemble the name, listing groups in alphabetical order. The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing. Pl l h b ti i Place a comma b t between multiple lti l numbers. (Example: 2,3-dichloropropane) 2,3-
  5. 5. Step 1 Find the parent chain 1. chain. • Where is the longest continuous chain of carbons?
  6. 6. Prefixes for # of Carbons 1 Meth 6 Hex 2 Eth 7 Hept p 3 Prop 8 Oct 4 But 9 Non 5 Pent 10 Dec
  7. 7. IUPAC Names for Alkanes Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 7
  8. 8. Endings • Alkanes (all C-C single bonded parent chain) C- end in –ane – Methane CH4 Methane – Ethane C2H6 Ethane – Propane C3H8 Propane • Attached carbon groups (substituents) end i –yl Att h d b (substituents) d in l b tit t – Methyl CH3 - Methyl – Ethyl CH3CH2- Ethyl l – Propyl CH3CH2CH2 – Propyl 3-ethylpentane
  9. 9. Step 2. Number the parent chain. • Number the parent chain so that the attached groups are on the lowest numbers Methyl is on carbon #2 of the parent chain Methyl is on carbon #4 of the parent chain 1 2 3 4 5 GREEN is the right 5 4 3 2 1 way for this one! 1 8 27 3 6 7 2 8 1 1 2 3 4 5 6 4 5 5 4 6 3 7 6 5 4 3 72 1 Groups on 4, 6, and 7 Groups on 2 and 5 Groups on 2, 3, and 5 Groups on 3 and 6
  10. 10. Step 3. Name the attached groups 3 groups. • Carbon (alkyl) groups ( y (alkyl) g p – Methyl CH3 - Methyl – Ethyl CH3CH2- Ethyl y – Propyl CH3CH2CH2 – Propyl • Halogens – Fluoro (F-) (F- – Chloro (Cl-) Cl- – Bromo (Br-) (Br- – Iodo (I-) (I-
  11. 11. Step 4. Designate where the group is i attached to the parent chain. h d h h i • Use the numbers of the parent chain from step 2 to designate the location of the attached groups to the parent chain. 2-methyl 1 2 3 4 5
  12. 12. Step 5. Alphabetize the groups, combine lik groups, and assemble. bi like d bl • The prefixes di, tri, tetra di, etc., used to designate several groups of the same kind ki d • Prefixes are not considered when alphabetizing 1,1,1-trichloro-1- 1,1-dichloro-1,1- (Example: dimethyl = m for fluoromethane difluoromethane alphabetizing) • Parent chain goes LAST
  13. 13. Draw Some Simple Alkanes • 2-methylpentane • 3-ethylhexane th lh • 2,2-dimethylbutane 2,2- • 2,3-dimethylbutane 2,3-
  14. 14. Order of Priority • IN A TIE halogens get the lower number TIE, before alkyl groups 4-chloro-2-methylpentane or chloro- 2-chloro-4-methylpentane? chloro-
  15. 15. Order of Priority • IN A TIE between SIMILAR GROUPS the GROUPS, group lower ALPHABETICALLY gets the lower number 4 bromo 2 chloropentane 4-bromo-2-chloropentane or 2-bromo-4-chloropentane ?
  16. 16. Isomers • St i ht chain alkanes: A alkane Straight h i alkanes: An lk lk that has all its carbons connected in a row. row. • Branched chain alkanes: An alkane alkanes: that has a branching connection of carbons. carbons. • Isomers: Compounds with same Isomers: molecular formula but different structures. structures.
  17. 17. • There is only one possible way that the carbons in methane (CH4), ethane (C2H6), and propane (C3H8) can be arranged. arranged.
  18. 18. However, However carbons in butane (C4H10) can be arranged in two ways; four carbons in a row ways; (linear alkane) or a branching (branched alkane) alkane) alkane). These two structures are two isomers for butane. butane.
  19. 19. Isomers methane ethane propane 1 isomer 1 isomer 1 isomer
  20. 20. Isomers normal butane isobutane (n-butane) (n butane)
  21. 21. Different isomers are completely different compounds. compounds. They have different structures, different physical properties such as melting p y p p g point and boiling point, and may have different physiological properties. properties.
  22. 22. Learning Check • Draw all possible structural isomers of C5H12
  23. 23. Types of Carbon Atoms • Primary carbon y ( o) (1 H – a carbon bonded to C C H one other carbon H • Secondary carbon (2o) H – a carbon bonded to C C C two other carbons H H • Tertiary carbon(3o) – a carbon bonded to C C C three other carbons C
  24. 24. Alkanes Example: Name the following compounds: CH3 CH3 CHCH3 CH CH3 CH3 CH CH CH2 CH CH3 CH3 C CH2 CH2Br CH3 C CH3 CH2CH3 CH2CH3 CH3
  25. 25. Structural Formulas Alkanes are written with structural formulas that are • Expanded to show each bond bond. • Condensed to show each carbon atom and its attached hydrogen atoms atoms. • Line to show bonds as lines and omit hydrogens H H H H2 H C C C H H3C C CH3 H H H 30
  26. 26. Expanded and Condensed Structures St t TABLE 11.3 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 31
  27. 27. Line Bond Line-Bond Formulas • Because each C atom has a tetrahedral arrangement, the order of atoms is not a straight line, but a zigzag pattern. • A line-bond formula abbreviates the carbon atoms and shows only the zigzag pattern of bonds from carbon atom t carbon atom. b d f b t to b t 32
  28. 28. Alkanes Example: Write the condensed structure for the following compounds: t t f th f ll i d 3,3- 3,3-dimethylpentane 2-methyl-4-sec-butyloctane methyl- sec-bu y oc a e e y 1,2-dichloro- 1,2-dichloro-3-methylheptane
  29. 29. Cycloalkanes Are cyclic alkanes alkanes. Have 2H fewer than the open chain. Are named by using the prefix cyclo before cyclo- the name of the alkane chain with the same number of carbon atoms. 34
  30. 30. Cycloalkanes The structural formulas of cycloalkanes are usually y y represented by geometric figures, Cyclopropane CH2 CH2 CH2 Cyclobutane CH2 CH2 CH2 CH2 35
  31. 31. Cycloalkanes = cyclopropane
  32. 32. Cycloalkanes cyclobutane cyclopentane cyclohexane
  33. 33. Cycloalkanes
  34. 34. Naming Cycloalkanes with Substituents S b tit t The name of a substituent is placed in front of the cycloalkane name. CH3 methylcyclobutane Number ring with two substituents 1-bromo-2-chlorocyclopentane 1 bromo 2 chlorocyclopentane Br B Cl 39
  35. 35. Nomenclature of Cycloalkanes
  36. 36. Name each of the following :
  37. 37. Name each of the following :
  38. 38. Name each of the following :
  39. 39. Name each of the following :
  40. 40. Some Properties of Alkanes The properties of alkanes include being • N Nonpolar. l • Insoluble in water. • L Less d dense th water than t • Flammable in air. • Relatively unreactive. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 46
  41. 41. Alkanes with 1-4 Carbon Atoms 14 Alkanes with 1-4 carbon atoms are 14 • Methane, ethane, propane, and butane. • Gases at room temperature. • Used as heating fuels fuels. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 47
  42. 42. Alkanes with 5-17 Carbon Atoms Alkanes with 5-8 carbon atoms are • Liquids at room temperature. • Pentane, hexane, heptane, and octane. • Very volatile. • Used to make gasoline. Alkanes with 9-17 carbon atoms • Are liquids at room temperature • Have higher boiling p g g points. • Are found in kerosene, diesel, and jet fuels. 48
  43. 43. Alkanes with 18 or more Carbon Atoms Alkanes with 18 or more carbon atoms • Have high molar masses. • Are waxy solids at room temperature temperature. • Used in waxy coatings of fruits and vegetables. vegetables Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 49
  44. 44. Crude Oil The hydrocarbons in crude oil are • Separated by boiling points. • Heated to higher temperatures to produce prod ce gases that can be removed and cooled. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 50
  45. 45. Alkane Reactions 1. Combustion The Th combustion of carbon compounds, especially h d b ti f b d i ll hydrocarbons, h b b has been th the most important source of heat energy for human civilizations throughout recorded history. CH3-CH2-CH3 + 5 O2 ——> 3 CO2 + 4 H2O + heat Two points concerning this reaction are important: 1. Since all the covalent bonds in the reactant molecules are broken, the quantity of heat evolved in this reaction is related to the strength of these bonds (and of course, the strength of the bonds formed in (and, course the products). 2. The stoichiometry of the reactants is important. If insufficient oxygen is supplied some of the p pp products will consist of carbon monoxide, a , highly toxic gas.
  46. 46. Combustion of Alkanes Alkanes • Undergo combustion by reacting with oxygen to p produce carbon dioxide, , water, and energy. • Are typically not very reactive d t strong C- ti due to t C C single bonds. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings alkane + O2 CO2 + H2O + energy gy 52
  47. 47. Balancing A Combustion Equation Write the equation C5H12 + O2 CO2 + H2O Balance C C5H12 + O2 5CO2 + H2O Balance H C5H12 + O2 5CO2 + 6H2O Balance O with O2 C5H12 + 8O2 5CO2 + 6H2O balanced 53
  48. 48. 2. Halogenation Halogenation is the replacement of one or more hydrogen atoms in an organic compound by a halogen ( g p y g (fluorine, chlorine, bromine or , , iodine). CH4 + Cl2 + energy ——> CH3Cl + HCl When alkanes react with halogens: • One or more hydrogens will be replaced with halogens y g p g • Halogens prefer to go to the more substituted (location with more surrounding carbons) location • Tertiary is more reactive than secondary which is more reactive than primary • Light or heat is required to form the radicals • Radicals have unpaired electrons and violate the octet rule (reactive)
  49. 49. Free Radical Halogenation Mechanism M h i Light Li ht 1. X X X + X 2. 2 R H + X R + X H 3. R + X X R X + X used to indicate an unpaired electron (free radical) X = shorthand for a halogen atom R = shorthand for an organic compound or group 55
  50. 50. Free Radical Halogenation g Mechanism 1. inisiation 1 inisiation,
  51. 51. 2. propagation radical reaction with Cl2:
  52. 52. 3. termination;
  53. 53. Predicting the Major Product of Free Radical H l R di l Halogenation ti • Halogens p g prefer more substituted location on molecule • Tertiary is more reactive than secondary which is more reactive than primary • Reactivity depends on ease of forming radical • Below radicals listed from easiest to form to hardest C H H H C C C C H C H C C C C H tertiary secondary primary methyl 59
  54. 54. Predict the Major Product H H H H C C C H + Cl2 H H H CH3 H2C CH + B2 Br H2C CH2 + Br2 60
  55. 55. Predict the Major Product H H H H Cl H H C C C H + Cl2 H C C C H + HCl H H H H H H CH3 CH3 Br H2C CH H2 C C + Br2 + HBr H2C CH2 H2 C CH2 + Br2 Br + HBr 61