Chem 102 (Organic Chemistry II), Hour Exam 3 - PDF

							                                Chem 102 (Organic Chemistry II), Hour Exam 3
                                                                                                                                              November 20, 2007

A. Explain thoroughly the following facts, using mechanistic reasoning.

    1.          A good way of preparing an ethyl ester from the corresponding carboxylic acid, RCO2H, is to
                convert it to an acid chloride, RCOCl, and then to the ester by the reaction of RCOCl with
                ethanol in pyridine solvent. (1) How do you prepare RCOCl from RCO2H? (2) The pyridine
                used as a solvent in the second step plays 2 additional roles. Explain. (3) The method is better
                than the direct esterification of RCO2H with ethanol in the presence of an acid catalyst (Fischer
                esterification). Why? (4) The direct esterification (Fischer esterification) is usually carried out
                with slow distillation of ethanol solvents. Explain what happens in this process? (30 points)
                                                                                                  O
    2.
                                                                                                      OH
                                                                 in H2O
                                OH                                                                O
                                         + CrVI species

                                                                in anhydrous                          H
                                                                solvent
                                                                                                            (10 points)
                                                                     Me OH
    3.
                   O                                  2. H3O+
                               1. MeLi
                                  ether                                O
                                                     2. H3O+
                               1. LiCuMe2
                                                                               Me   (5 points)
                                                                                              OH
    4.                               OH CH COOCOCH
                                          3        3                       O                                            O
                                                                                                      or
                                                    (1 equiv)                  N                                             O
                H 2N                                                                                       H 2N
                                                                               H                                                 (5 points)
                                     Ph         Me
    5.
                                     HS         N         (5 mol%)                           OH                        OH
                       O                                                                                    +
                                                                                        Ph    Et                  Ph    Et
                Ph         H                                                                           99 : 1
                                     Et2Zn, ether, 0 oC, 12 h                                          98% ee
                                            99% yield           (5 points)
    6.          Explain how you would describe the oxidation states of organic compounds using CH4 as an
                example. (http://orgsyn.byus.net/research-09.htm) (5 points)

B. Identify the chemical species (b, e and h) and the necessary chemical reagents (a, c, f, g and
   i) in the following synthetic scheme. (30 pts)
        OH
                           a                                    c
                                            b


                                                d

                                                                                   OH
                           g
                                                                 f
        h                                   e



            i

   HO       CO2H




C. Explain briefly for each of the following terms, using an example. (20 pts)

  1) McLafferty rearrangement
  2) Molozonide
  3) Bürgi-Dunitz angle (http://en.wikipedia.org/wiki/B%C3%BCrgi-Dunitz_angle)
  4) oxaphosphetane
  5) Wolf-Kishner reaction