"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