Sykes CH3 Lewis structures_ pKas

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					CHEM43-6311                  Sykes CH3 Lewis structures, pkas, 7Sep2011                                        page 1




   1. Show the Lewis structures of all important resonance forms for the following and suggest the
      relative energies of occupied valence orbitals within each. Determine the hybridization of P, S,
      C, N, O, and B and explain what determines the hybridization.

           a.   CH2P(CH3)3
           b.   BCl3
           c.   SO2
           d.   SO3
           e.   CH3NC
           f.   CO
           g.   NH2CONH2
           h.   CNO-

   2. Order the following columns or rows of compounds according to pKa’s and explain the
      order.

                     A           B                C                      D                  E
                                                                         O                  O         O
      F          CH3CH2SH        ROH2
                                                       CH2                         R
                                                                    RO       CH2       RO       CH2       OR



                                     H            O         O
                                 O                                                      NH3
                                                                    CH3CN
       H         HC CH                        R       CH2       R
                             R       OH
                                                                         O
                                                                                              +
                                                                                        NH4
                                          +       H2CO3             R        OH
                CH3NO2                   NH
       J

                                                        OH

       I                         HCl


   3. Which compound is more acidic? Explain all relevant effects: field, inductive, Any other
      effect?



                             +H3N
                                                        CO 2H
      NH 3+       CO 2H

   4. Derive an analytical expression that relates pKa to pKb and does not depend on the
      concentration of any acid or base.
CHEM43-6311              Sykes CH3 Lewis structures, pkas, 7Sep2011             page 2


   5. Estimate the pKa’s of the most acidic proton on following compounds and explain your
      reasoning.




   6. Show all resonance structures for the intermediate cation that is formed when benzene
      is protonated.




   7. Three isomeric cations are formed when furan is protonated. A) Show all isomers and
      all of their resonance structures. B) Which isomer is most stable and explain.




   8. Explain why A is a stronger acid.
CHEM43-6311             Sykes CH3 Lewis structures, pkas, 7Sep2011              page 3


   9. A) Show all tautomers (isomers where only the position of protons change) of the
      following ketone. As for the ketone, no atom should have a formal charge. (Hint: this
      ketone has two inequivalent isomers). B) Of the three isomers which is most stable and
      explain.

				
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