Chapter 11The Unsaturated Hydrocarbons:Alkenes, Alkynes, and Aromatics
1. StructureAlkenes are hydrocarbons with a double bond.               CnH2n
1. StructureAlkynes are hydrocarbons with a triple bond.                        CnH2n-2
1. StructureAlkenes and alkynes are unsaturated (don’t have themaximum number of hydrogens bonded to each carbon).        ...
1. Comparison
1. Geometry
1. Geometry [3.4 Lewis structures]   Four groups of electrons       Ethane       tetrahedral           extend toward t...
1. Geometry [3.4 Lewis structures]                                     8
1. Geometry [3.4 Lewis structures]   Three groups of electrons       Ethene       All in the same plane       Trigonal...
1. Geometry [3.4 Lewis structures]                                     10
1. Geometry [3.4 Lewis structures]   Two groups of electrons       Ethyne       Linear       Bond angle = 180o
1. Geometry [3.4 Lewis structures]                                     12
1. Physical properties    Name        Melting point   Boiling point   ethene        -160.1oC         -103.7oC  propene    ...
1. Physical properties   In each case, the alkyne has a higher boiling point than the    alkene.       Its structure is ...
2. NomenclatureThe root name is based on the longest chain thatincludes both carbons of the multiple bond.The –ane ending ...
2. NomenclatureThe chain is numbered from the end nearest the multiplebond.                                          2-pen...
2. NomenclatureDetermine the name and number of each substituentand add in front of the name of the parent compound.      ...
2. NomenclatureAlkenes with more than one double bond are called   alkadienes (2 double bonds)   alkatrienes (3 double bon...
2. NomenclatureCycloalkenes must be numbered so the double bond isbetween carbons one and two.                         3-c...
2. NomenclatureName the following compounds.                CH3CH=C(CH2CH3)2                H2C=C-CH2-CH=CH2    pencast
2. NomenclatureName the following compounds.              pencast
2. NomenclatureWrite a structural formula for each of the followingcompounds.                       1-hexene              ...
2. NomenclatureDraw a structural formula for each of the followingcompounds:                    1-bromo-3-hexyne          ...
3. Geometric isomers   Rotation around a double bond is restricted, in much the    same was as rotation is restricted for...
3. Cis-trans isomers   If both constituents are on the same side of the double    bond, the isomer is cis-.              ...
3. Cis-trans isomers   Alkenes without substituents also may exhibit cis-trans    isomerism.                             ...
3. Cis-trans isomers   In order for cis and trans isomers to exist, neither double-    bonded carbon may have two identic...
3. Cis-trans isomers                       28
3. Cis-trans isomers   Which of the following compounds can exist as geometric    isomers?       1-bromo-1-chloro-2,2-di...
5. Reactions of alkenes and alkynes   The most common reactions of alkenes and alkynes are    addition reactions.       ...
5. General addition reaction   A double bond consists of       a sigma bond: two electrons        concentrated on a line...
5. General addition reaction                               32
5. General addition reaction   In an addition reaction, the pi bond is lost and its electrons    become part of the singl...
5. General addition reaction   For hydrogenation, halogenation, hydration, and    hydrohalogenation, identify the A and B...
5. Hydrogenation   In hydrogenation of an alkene, one molecule of hydrogen    (H2) adds to one mole of double bonds.   R...
5. Hydrogenation   In hydrogenation of an alkyne, two molecules of hydrogen    (H2) add to one mole of triple bonds.   R...
5. Hydrogenation   Compare the products resulting from the hydrogenation of    trans-2-pentene and cis-2-pentene.        ...
5. Hydrogenation   Compare the products resulting from the hydrogenation of    1-butene and cis-2-butene.                ...
5. Vegetable oil and margarine   Why does hydrogenation make oils more solid?                                            ...
5. Halogenation   In halogenation of an alkene, one mole of a halogen (Cl2,    Br2, I2) adds to one mole of double bonds....
5. Halogenation   In halogenation of an alkyne, two moles of a halogen (Cl2,    Br2, I2) add to one mole of double bonds.
5. Halogenation   Draw the structure and write a balanced equation for the    halogenation of each of the following compo...
5. Halogenation   A solution of bromine in water    has a reddish-orange color.   A simple test for the presence    of a...
5. Hydration   In hydration, one mole of water (H2O) is added to one mole    of double bonds.   A trace of acid is requi...
5. Hydration   Unlike hydrogenation and halogenation, hydration is not a    symmetric addition to a double bond.   If th...
5. Hydration   The predominant product is determined by Markovnikov’s    rule: The rich get richer.   OR: The carbon tha...
5. Hydration   Write a balanced equation for the hydration of each of the    following compounds:       2-butene       ...
5. Hydrohalogenation   Like hydration, hydrohalogenation is an asymmetric addition    to a double bond.       Hydrohalog...
5. Hydrohalogenation                   2-butene + HBr  ?               3-methyl-2-hexene + HCl  ?                 cyclop...
6. Aromatic compounds   Consider the following molecular formulas for unsaturated    hydrocarbons:       Hexane (all sin...
6. Aromatic compounds   The molecular formula for benzene is C6H6.       The structure must be highly unsaturated.     ...
6. Benzene structure   The benzene ring consists of:       six carbon atoms       joined in a planar hexagonal arrangem...
6. Benzene structure   Sigma and pi bonding in benzene:   The sharing of six electrons over the entire ring gives the   ...
6. Nomenclature   Most single-substituent compounds are named as    derivatives of benzene.       Bromobenzene       Et...
6. Nomenclature   A few “common” names have been adopted as IUPAC    nomenclature.       toluene       phenol       an...
6. Nomenclature   There are three ways for the methyl groups on xylene to be    arranged.       1,2 [ortho-xylene]     ...
6. Nomenclature   The substituent created by removing one hydrogen from the    benzene ring is called phenyl-.       2-p...
6. Nomenclature   The substituent consisting of a –CH2 attached to a benzene    ring is called benzyl-.       Benzyl chl...
6. Polynuclear aromatic hydrocarbons   These consist of rings joined along one side.         Good news! You don’t have to...
6. Reactions of benzene   Because of the stability of benzene’s ring structure, only    substitution reactions are charac...
7. Heterocyclic aromatic compounds   Heterocyclic aromatic compounds have at least one non-    carbon atom incorporated i...
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11 unsaturated-hydrocarbons(1)

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Chapter 11 of General, Organic, and Biochemistry, Denniston, 7th edition

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  • 1-bromo-1-chloro-2,2-dimethylpropene: Looking at the double bond, we can see that the right carbon has identical groups (methyls) attached to it, so there CANNOT be geometric (cis-trans) isomers.1,1-dichloroethene: The name itself gives this one away. There are 2 chlorines on the left carbon so there can’t be geometric isomers.1,2-dibromoethene: This molecule has cis-trans geometric isomers. It doesn’t matter that both carbons have the same two groups attached, as long as NEITHER carbon has 2 identical groups attached to it.3-ethyl-2-methyl-2-hexene: Because the double bond begins at carbon 2 and there is also a methyl attached to carbon 2, the left carbon has identical (methyl) groups and there cannot be cis-trans isomers.
  • Hydrogenation: A-B is H-H. Both A and B represent a hydrogen atom.Halogenation: A-B is X-X (F-F or Cl-Cl or Br-Br or I-I). Both A and B represent X (F or Cl or Br or I).Hydration: A-B is H-OH. So A represents H and B represents OH (or vice versa: A represents OH and B represents H).Hydrohalogenation: A-B is H-X (H-F or H-Cl or H-Br or H-I). So A represents H and B represents X (F or Cl or Br or I).
  • Linear molecules pack together very efficiently, which maximizes the intermolecular forces. Saturated oils have long, linear chains of carbons.Nonlinear molecules don’t pack together as efficiently and experience weaker intermolecular forces. The weaker the forces, the lower the melting point.Natural oils (vegetable oils) are unsaturated so the molecules are nonlinear. These oils are liquid at room temperature.Hydrogenation adds hydrogens to the double bonds, making the molecules more nearly linear. This increases the intermolecular forces and raises the melting point. So, the more an oil is hydrogenated, the higher its melting point and the more solid it is at room temperature.
  • Transcript of "11 unsaturated-hydrocarbons(1)"

    1. 1. Chapter 11The Unsaturated Hydrocarbons:Alkenes, Alkynes, and Aromatics
    2. 2. 1. StructureAlkenes are hydrocarbons with a double bond. CnH2n
    3. 3. 1. StructureAlkynes are hydrocarbons with a triple bond. CnH2n-2
    4. 4. 1. StructureAlkenes and alkynes are unsaturated (don’t have themaximum number of hydrogens bonded to each carbon). Tegrity lecture video
    5. 5. 1. Comparison
    6. 6. 1. Geometry
    7. 7. 1. Geometry [3.4 Lewis structures] Four groups of electrons  Ethane  tetrahedral  extend toward the corners of a regular tetrahedron  bond angle = 109.5o
    8. 8. 1. Geometry [3.4 Lewis structures] 8
    9. 9. 1. Geometry [3.4 Lewis structures] Three groups of electrons  Ethene  All in the same plane  Trigonal planar  Bond angle = 120o
    10. 10. 1. Geometry [3.4 Lewis structures] 10
    11. 11. 1. Geometry [3.4 Lewis structures] Two groups of electrons  Ethyne  Linear  Bond angle = 180o
    12. 12. 1. Geometry [3.4 Lewis structures] 12
    13. 13. 1. Physical properties Name Melting point Boiling point ethene -160.1oC -103.7oC propene -185.0oC -47.6oC 1-butene -185.0oC -6.1oCmethylpropene -140.0oC -6.6oC ethyne -81.8oC -84.0oC propyne -101.5oC -23.2oC 1-butyne -125.9oC 8.1oC 2-butyne -32.3oC 27.0oC
    14. 14. 1. Physical properties In each case, the alkyne has a higher boiling point than the alkene.  Its structure is more linear.  The molecules pack together more efficiently.  Intermolecular forces are stronger. Tegrity lecture video
    15. 15. 2. NomenclatureThe root name is based on the longest chain thatincludes both carbons of the multiple bond.The –ane ending is changed to –ene for double bondsand –yne for triple bonds. ethyne ethene propyne propene
    16. 16. 2. NomenclatureThe chain is numbered from the end nearest the multiplebond. 2-pentyne 1-butene [not 3-pentyne] [not 3-butene]The position of the multiple bond is indicated with thelower-numbered carbon in the bond.
    17. 17. 2. NomenclatureDetermine the name and number of each substituentand add in front of the name of the parent compound. 5-chloro-4-methyl-2-hexene 2,6-dimethyl-3-octene 5-bromo-4-ethyl-2-heptene
    18. 18. 2. NomenclatureAlkenes with more than one double bond are called alkadienes (2 double bonds) alkatrienes (3 double bonds) etc…Each double bond is designated by its lower-numberedcarbon. 2,4-hexadiene
    19. 19. 2. NomenclatureCycloalkenes must be numbered so the double bond isbetween carbons one and two. 3-chloro-cyclopentene 4-ethyl-5-methylcyclooctene
    20. 20. 2. NomenclatureName the following compounds. CH3CH=C(CH2CH3)2 H2C=C-CH2-CH=CH2 pencast
    21. 21. 2. NomenclatureName the following compounds. pencast
    22. 22. 2. NomenclatureWrite a structural formula for each of the followingcompounds. 1-hexene 1,3-dicholoro-2-butene 4-methyl-2-hexyne pencast 1,4-cyclohexadiene
    23. 23. 2. NomenclatureDraw a structural formula for each of the followingcompounds: 1-bromo-3-hexyne 2-butyne pencast dichloroethyne 9-iodo-1-nonyne
    24. 24. 3. Geometric isomers Rotation around a double bond is restricted, in much the same was as rotation is restricted for the cycloalkanes. In the alkenes, geometric isomers occur when there are two different groups on each of the double-bonded carbon atoms. 1,2-dichloroethene
    25. 25. 3. Cis-trans isomers If both constituents are on the same side of the double bond, the isomer is cis-. cis-1,2-dichloroethene If the constituents are on opposite sides of the double bond, the isomer is trans-. trans-1,2-dichloroethene
    26. 26. 3. Cis-trans isomers Alkenes without substituents also may exhibit cis-trans isomerism. cis-4-octene trans-4-octene
    27. 27. 3. Cis-trans isomers In order for cis and trans isomers to exist, neither double- bonded carbon may have two identical substituents. 2-methyl-2-butene no cis/trans isomerism 1-butene no cis/trans isomerism
    28. 28. 3. Cis-trans isomers 28
    29. 29. 3. Cis-trans isomers Which of the following compounds can exist as geometric isomers?  1-bromo-1-chloro-2,2-dimethylpropene  1,1-dichloroethene  1,2-dibromoethene  3-ethyl-2-methyl-2-hexene
    30. 30. 5. Reactions of alkenes and alkynes The most common reactions of alkenes and alkynes are addition reactions.  Hydrogenation: addition of H2  Halogenation: addition of X2  Hydration: addition of H2O  Hydrohalogenation: addition of HX
    31. 31. 5. General addition reaction A double bond consists of  a sigma bond: two electrons concentrated on a line between the two connected atoms;  a pi bond: two electrons concentrated in planes above and below the sigma bond.
    32. 32. 5. General addition reaction 32
    33. 33. 5. General addition reaction In an addition reaction, the pi bond is lost and its electrons become part of the single bonds to A and B.
    34. 34. 5. General addition reaction For hydrogenation, halogenation, hydration, and hydrohalogenation, identify the A and B portions of what is being added to the double bond.  hydrogenation, H2  halogenation, X2 (where X = F, Cl, Br, or I)  hydration, H2O  hydrohalogenation, HX (where X = F, Cl, Br, or I)
    35. 35. 5. Hydrogenation In hydrogenation of an alkene, one molecule of hydrogen (H2) adds to one mole of double bonds. Reaction conditions:  platinum, palladium, or nickel catalyst  [sometimes] heat and/or pressure
    36. 36. 5. Hydrogenation In hydrogenation of an alkyne, two molecules of hydrogen (H2) add to one mole of triple bonds. Reaction conditions: same as for alkenes.
    37. 37. 5. Hydrogenation Compare the products resulting from the hydrogenation of trans-2-pentene and cis-2-pentene. pencast
    38. 38. 5. Hydrogenation Compare the products resulting from the hydrogenation of 1-butene and cis-2-butene. pencast
    39. 39. 5. Vegetable oil and margarine Why does hydrogenation make oils more solid? MP = 13-14oC MP = 69.6oC MP = 62.9oC
    40. 40. 5. Halogenation In halogenation of an alkene, one mole of a halogen (Cl2, Br2, I2) adds to one mole of double bonds. Since halogens are more reactive than hydrogen, no catalyst is needed.
    41. 41. 5. Halogenation In halogenation of an alkyne, two moles of a halogen (Cl2, Br2, I2) add to one mole of double bonds.
    42. 42. 5. Halogenation Draw the structure and write a balanced equation for the halogenation of each of the following compounds.  3-methyl-1,4-hexadiene  4-bromo-1,3-pentadiene  3-chloro-2,4-hexadiene pencast
    43. 43. 5. Halogenation A solution of bromine in water has a reddish-orange color. A simple test for the presence of an alkene or alkane is to add bromine water.  If a double or triple bond is present, the bromine will be used up in a halogenation Test of cyclohexane reaction and the color will and cyclohexene disappear.
    44. 44. 5. Hydration In hydration, one mole of water (H2O) is added to one mole of double bonds. A trace of acid is required as a catalyst.
    45. 45. 5. Hydration Unlike hydrogenation and halogenation, hydration is not a symmetric addition to a double bond. If the double bond is not symmetrically located in the molecule, there are two possible hydration products.
    46. 46. 5. Hydration The predominant product is determined by Markovnikov’s rule: The rich get richer. OR: The carbon that already has more hydrogens will get the hydrogen from the water. Hydration of propene: + H 2O 
    47. 47. 5. Hydration Write a balanced equation for the hydration of each of the following compounds:  2-butene  2-ethyl-3-hexene pencast  2,3-dimethylcyclohexene Alkynes undergo a much more complicated hydration that you don’t need to remember at this time!
    48. 48. 5. Hydrohalogenation Like hydration, hydrohalogenation is an asymmetric addition to a double bond.  Hydrohalogenation also follows Markovnikov’s rule.
    49. 49. 5. Hydrohalogenation 2-butene + HBr  ? 3-methyl-2-hexene + HCl  ? cyclopentene + HI  ?pencast
    50. 50. 6. Aromatic compounds Consider the following molecular formulas for unsaturated hydrocarbons:  Hexane (all single bonds): C6H14  Cyclohexane (one ring): C6H12  Hexene (one double bond): C6H12  Hexadiene (two double bonds): C6H10  Cyclohexene (one ring, one double bond): C6H10  Hexatriene (three double bonds): C6H8  Cyclohexadiene (one ring, two double bonds): C6H8
    51. 51. 6. Aromatic compounds The molecular formula for benzene is C6H6.  The structure must be highly unsaturated.  One ring, three double bonds? Reactions of benzene:  Benzene does not decolorize bromine solutions.  Benzene does not undergo typical addition reactions.  Benzene reacts mainly by substitution. The first three items are opposite from what is expected from unsaturated compounds. The last item is identical to what is expected for alkanes.
    52. 52. 6. Benzene structure The benzene ring consists of:  six carbon atoms  joined in a planar hexagonal arrangement  with each carbon bonded to one hydrogen atom. Two equivalent structures proposed by Kekulé are recognized today as resonance structures. The real benzene molecule is a hybrid with each resonance structure contributing equally to the true structure.
    53. 53. 6. Benzene structure Sigma and pi bonding in benzene: The sharing of six electrons over the entire ring gives the benzene structure extra stability. Removing any one of the six electrons would destroy that stability.
    54. 54. 6. Nomenclature Most single-substituent compounds are named as derivatives of benzene.  Bromobenzene  Ethylbenzene
    55. 55. 6. Nomenclature A few “common” names have been adopted as IUPAC nomenclature.  toluene  phenol  aniline  xylene (any benzene ring with two methyl groups)
    56. 56. 6. Nomenclature There are three ways for the methyl groups on xylene to be arranged.  1,2 [ortho-xylene]  1,3 [meta-xylene]  1,4 [para-xylene]
    57. 57. 6. Nomenclature The substituent created by removing one hydrogen from the benzene ring is called phenyl-.  2-phenylhexane  3-phenylcyclopentene
    58. 58. 6. Nomenclature The substituent consisting of a –CH2 attached to a benzene ring is called benzyl-.  Benzyl chloride
    59. 59. 6. Polynuclear aromatic hydrocarbons These consist of rings joined along one side. Good news! You don’t have to memorize these names!
    60. 60. 6. Reactions of benzene Because of the stability of benzene’s ring structure, only substitution reactions are characteristic.  Halogenation: substitution of one or more halogen atoms for hydrogen atoms.  Cl2 requires FeCl3 catalyst.  Br2 requires FeBr3 catalyst.  Nitration: substitution of one or more nitro- (-NO2) groups for hydrogen atoms.  Requires nitric acid and concentration sulfuric acid.  Sulfonation: substitution of one sulfonic acid (-SO3H) group for a hydrogen atom.  SO3 reactant and concentration sulfuric acid.
    61. 61. 7. Heterocyclic aromatic compounds Heterocyclic aromatic compounds have at least one non- carbon atom incorporated in an aromatic ring or polynuclear aromatic compound.  Many of these compounds are biologically important.  Components of DNA and RNA  Components of hemoglobin and chlorophyll  Pharmaceuticals pyridine
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