Notes to the Instructor

Note to the Instructor If this special assignment is to be made, it is worthwhile to inform the class about it as early as possible in order to give them time to browse properly. In the author s course the problem has been used in place of any other homework assignments during the last month and has counted significantly in the final grade. 

Inject a sample of old soda. (Note to the instructor If you cannot find an old soda, a fresh one can be degraded rather rapidly at a pH below 2 or above 7). 

Note to the instructor Grind up the benzophenone flakes into a powder. 

Note to the instructor The individual compounds and the reference mixture containing aU three compounds are prepared as 2% solutions in acetone. The unknown mixture may contain one, two, or all three of the compounds dissolved in acetone. 

Note to the instructor Possible pairs of compounds are given in the following list. The two compounds to be resolved are given first, followed by the three developing solvents to try (1) benzoin and benzil acetone, methylene chloride, hexane (2) vanillin and vanillyl alcohol acetone, 50% toluene-50% ethyl acetate, hexane (3) diphenylmethanol and benzophenone acetone, 70% hexane-30% acetone, hexane. Each compound in a pair should be prepared individually and as a mixture of the two compounds. Prepare all of them as 1% solutions in acetone. 

Note to the Instructor The sodium borohydride should be checked to see whether it is active Place a small amount of jxjwdered material in some methanol and heat it gently. If the hydride is active, the solution should bubble vigorously. If using an old bottle, it is also good to check the material for stickiness due to absorption of water. If it is too sticky, it can be difficult for students to weigh it out. 

Note to the instructor This solution should be prepared for the entire class by dissolving 0.3 g of fluorene and 0.3 g of fluorenone in 9.0 mL of a mixture of 5% methylene chloride-95% hexane. Store this solution in a closed container to prevent evaporation of solvent. This will provide enough solution for 20 students, assuming little spillage or other types of waste. 

Wrap the glass section of the air condenser between the two plastic caps with plastic tubing as described in Notes to the Instructor. Alternatively, use the method with a cotton pad (see Notes to the Instructor). Hold the pad in place with tape or twist ties. 

Note to the instructor It is recommended that the C-18 silica in the SPE columns not be reused. See footnote 3 for information on the expected yield of caffeine from tea and coffee. 

Note to the Instructor If pure samples of each product are available, check the assumption used here that the gas chromatograph responds equally to each substance. Response factors (relative sensitivities) are easily determined by injecting an equimolar mixture of products and comparing the peak areas. 

Note to the Instructor To obtain reasonable results for the gas chromatographic analysis of the fert-butyl halides, it may be necessary to supply the students with response factor correction (Technique 22, Section 22.13B). 

Note to the Instructor In some cases, the resolution is so successful that it is very difficult to detect the doublet arising from the (R)-(+)-a-phenylethylamine -i- (S)-(+)-0-ace1ylmandelic acid diastereomer. If this occurs, it is useful to have the students add a single drop of racemic a-phe-nylethylamine to the NMR tube and redetermine the spectrum. In this way, both diastereomers can be clearly seen. 

The percentages of each of the isomeric alcohols (iosborneol and borneol) in the borohydride mixture can also be determined by gas chromatography. Your instructor or assistant will be required to set up the gas chromatograph for this analysis (see Notes to the Instructor). Isobomeol has a lower retention time than borneol and will emerge from the column before borneol. Your instructor will provide you with retention times for the type of chromatograph and column used for the analysis. 

The vacuum pump is helpful to remove aU traces of hexane and methylene chloride. In the NMR spectrum, these p>eaks app>ear at 0.9 ppm (triplet) and 1.3 p>pm (multiplet). Any remaining CH2CI2 appears at about 5.3 p>pm (singlet). See notes to the instructor. 

The vacuum pump helps remove any dimer present in the sample. Be sine to use a good quality vacuum pump to remove the dimer from the product. See notes to the instructor. 

NOTE TO THE INSTRUCTOR Prepare the brominating mixture in advance. 

Note to the Instructor The brominating mixture is prepared by adding 2.6 mL of bromine to 17.4 mL of 48% hydrobromic acid. This will provide enough solution for 20 students, assuming no waste of any type. This solution should be stored in the hood. 

Note to the Instructor Benzocaine may be tested for its effect on a frog s leg muscle. See Instructor s Manual for instructions. 

Note to the instructor. The experiment will be more interesting if the diet soft drink TAB is included among the choices. TAB is one of the few readily available diet soft drinks that contains substantial amounts of saccharine. 

Note to the Instructor For those not equipped to perform carbon-13 NMR spectroscopy, carbon-13 NMR spectra can be found reproduce in the Instructor s Manual. 

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