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practice2withkey

# practice2withkey - Y our Y our S tudent Y our Name 10 TA...

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\ Your Name: . Your Student 10# . Your TA . CHE~H~lfR1V ~ 08l f~~~ll [E~~m version 1 Problem Score 1 (19 D) 2 (10 D) 3 (25 D) 4 (20 D) 5 (12 D) 6 (14 D) Total (100 0)

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Problem 1 (19 points) a) (5 points) Consider the following solvents: methanol, toluene, hexanes, acetone, and water. Arrange them in order of increasing polarity, beginning with the least polar (1), and finishing with the most polar (5). (1) . (2) . (3) . (4) . (5) . b) (5 points) Consider the following compounds A-E: ~ ~ ~ ~ ~ # OH 0 A B ~ OH OH 0 C E Arrange them in order of increasing polarity, beginning with the least polar (1) and ending with the most polar (5). (1) . (2) . (3) . (4) . (5) .
c) (3 points) After running a silica-gel TLC plate with a solvent of medium polarity, the plate showed one spot (see figure below). Consider the distances x, y, and z as indicated in the figure, and circle the correct formula for the Rt value of the spot: Rt = x/z Rt = ylz Rt = zly Rt = y/x Rt = x/y Rt = zlx solvent tront y .- --~- -_. spot level x z origin d) (6 points) Compounds 8, C and E from part b were analyzed by TLC using silica gel and a mixture of toluene and acetone as a solvent. The TLC plate after the run is shown below. Which compound do you think ran the most, which one the least? Identify them on the plate by writing their names (8, C or E) next to the spots. solvent tront a o origin

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Problem 2 (10 points) True or false. Circle the option that you consider correct. a) In IR spectroscopy, IR radiation interacts with electronic energy levels of a molecule. T / F b) In TLC on silica gel, in general, the higher the polarity of the solvent, the larger the Rt value. T / F c) The normal boiling point of a mixture of an essential oil (such as citrus oil) and water is always higher than 100°C. T / F d) The optical rotation of a chiral sample is directly proportional to its concentration and the length of the cell. T / F e) The melting point of A is 120-121 oC. The melting point of an unknown substance X is also 120-121 0C. The melting point of a mixture of A and X is 120-121 0C. Therefore we can conclude that A and X are not the same compound. T / F 1) Replacing H3P04 with HCI in the dehydration of 2-methylcyclohexanol (or 1 - methylcyclohexanol) would have no consequences in the reaction outcome. T / F g) Alkyl bromides give a positive Beilstein test. T / F h) The GC retention time of a compound is not affected by the temperature of the column. T / F i) In adsorption column chromatography on silica gel, it is customary to run the column starting with a solvent of high polarity and ending with one of low polarity. T / F j) In the extraction of caffeine from tea leaves, calcium carbonate is used to form calcium salts of caffeine. T / F
Problem 3 (25 points; 5 points each) Complete the following reactions. If more than one organic product forms, underline the

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practice2withkey - Y our Y our S tudent Y our Name 10 TA...

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