CHEM 321 ORGANIC CHEMISTRY I Exam 2 101008 by sxh61317

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									                                 CHEM 321 ORGANIC CHEMISTRY I
                                         Exam 2 10/10/08

Name:


I.      Short Answer – (52 Total points) Answer all parts for the following questions.

     1) (1 point each/6 total points) Give the hybridization (H) of the * starred atom and
     the shape (S) of the molecule for the following compounds:


        a) Al*Br3               H                           S


        b) (CH3)2C*O            H                           S


        c) Br2C*Cl2             H                           S


     2) (3 points) Name the following compound using IUPAC nomenclature.




                        CH3
                       CH3




     3) (3 points each) Show the chair interconversion for the following compound. Clearly indicate
     which conformer is more stable.




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2
4) (8 points) Circle the most acidic proton for all compounds listed below. Then circle the most
acidic compound in each pair in the solution phase.

   (a)    (CH3)3CCH2CH2OH                           CH3 CH2CH2OH



   (b)    CH3CH2CHClCH2OH                           CH3CH2CHCH2ClCHOH



   (c)    HF                                        HI



   (d)    CH3CH2SH                                  CH3CH2OH




5) (1 point each/8 points) Chiral/Achiral.       Cirle either Chiral or Achiral for the following
molecules.

     (A) Chiral or Achiral    1,1-dibromo-2,3-dichlorobutane


     (B) Chiral or Achiral    pentahelicene


     (C) Chiral or Achiral    trans-1,2-dimethylcyclopropane


     (D) Chiral or Achiral    cis-1,3-dimethylcyclopropane


     (E) Chiral or Achiral    trans-1,4-dichlorocyclohexane


     (F) Chiral or Achiral    2,4-dimethyl-2,3-pentadiene


     (G) Chiral or Achiral    2,3-dibromo-2,3-dichlorobutane


     (H) Chiral or Achiral    2,3.4-hexatriene




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6) (1 point each/16 points) True/False. Circle either TRUE OR FALSE for the each of the
following statements.

   (A) TRUE OR FALSE         All chiral compounds contain stereogenic centers.

   (B) TRUE OR FALSE The conformational chair flip does not racemize cis-1,3-
       dichlorocyclohexane.

   (C) TRUE OR FALSE The heat of formation in their standard states is less per CH2 unit
       for cyclobutane than cyclopentane.

   (D) TRUE OR FALSE The angle strain increases while the torsional strain decreases
       when the size of the ring is increased from planar cyclopropane to planar cyclobutane.

   (E) TRUE OR FALSE For the cyclic compounds, the strain energy per CH2 group is the
       lowest for cyclohexane.

   (F) TRUE OR FALSE         The heat of combustion is larger for less stable compounds.

   (G) TRUE OR FALSE The heat of combustion for every molecule of octane reacting with
       12.5 molecules of O2 results in 8 molecules of CO2 and 9 molecules of H2O.

   (H) TRUE OR FALSE The half chair is the lowest transition state during the chair flip of
       one chair to the other.

   (I) TRUE OR FALSE        The ranking of decreasing bond lengths are: C-N > C-C > C=C
       > C=O > C-H > N-H> O-H.

   (J) TRUE OR FALSE A group in the axial position is more stable than in the equatorial
       position due to the resulting gauche interactions between the group and the ring when
       it is in the equatorial position.

   (K) TRUE OR FALSE The chirality at a stereocenter (chiral carbon) in a cyclohexane
       changes from R to S during a chair conformation change from one ring to the other.

   (L) TRUE OR FALSE         The optical rotation of a meso compound is not equal to 0.

   (M) TRUE OR FALSE         All compounds, which are not superimposable and not mirror
       images are achiral.

   (N) TRUE OR FALSE The barrier to inversion is higher when nitrogen is included in a
       three-membered ring than in simple amines because of angle strain.

   (O) TRUE OR FALSE         Diethyl ether is both a protic and polar solvent.

   (P) TRUE OR FALSE In the formation of a Grignard reagent, the alkyl halide starts as an
       electrophile and becomes a nucleophile.


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7) (9 points)
    (a)    Identify with an asterisk (*) all of the stereogenic carbons in chloesterol below.
           (0.5 point each).
    (b)    Then, identify whether the stereogenic center is R or S. (0.5 points each)
    (c)    How many total stereoisomers would you possibly have for the molecular below? (1
           point)


                         H3C
                       H3 C
                                          CH3
             H3C       H            H3C
                   H       H
      HO




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Part II. (21 total points) Reactions and mechanisms.
For the following reactions predict all of the products. Note the stereochemistry (R/S) or *
depending on your product (7 points each). Also pick one reaction, show the mechanism for
the formation of the product. Put an X in the box for your choice of mechanisms to be graded.
Circle your product(s).

                           CH3
               H3C                     H-OH2
          a)
                H3C                        H2O




                                 1) D-Br
     b)
                     CH3         2) Mg, ether
                                 3) OD2




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Part III. Essay. (26 points)
8) (13 points) Draw all of the possible chair forms and stereoisomers of cis- and trans-1-(2-
chloroethyl)-2-(2-bromoethyl)cyclohexane. [2-haloethyl = -CH2CH2X] State the relationships
between isomers, state the relationships between their flipped isomers, label R/S if applicable,
and specify their stability.




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9) (13 points) Draw all of the possible chair forms and stereoisomers of cis- and trans-1,3-
dipropylcyclohexane. State the relationships between isomers, state the relationships between
their flipped isomers, label R/S if applicable, and specify their stability.




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