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Practice Exam 2 - Name Exam#2 Monday 1 For each of the...

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Unformatted text preview: Name Exam #2 Monday, November 29, 2010 1. For each of the following pairs of reagents, circle the one that Will react faster in the indicated reaction. /\ /\ v with CH3I NH2 PH2 , - B SOZCHg /\/ r /\O/ with NaCN - with H2304 > I /\/ I with NaN3 — H ~/\ With H2» Pd/C ' 0 Br CH3I with /H\ » OH ~>‘Br CH3CH21 with (ma | B , U r With NH3 Name 2. For the following reactions, provide the missing starting materials, reagents or products. Indicate stereochemistry, if any. If you expect no reaction, say so. —_"'—‘_" SH OH st04 NaH OH ———-————-> CH3CH21 0 Br H f O NaO ———————-—> NaNH2 _____.___> H . 4 then I Name 3. Design syntheses of the following compounds from the indicated starting materials. Provide all reagents. NC SCH3 from a hydmhalocarbon from compounds of fewer than 7 carbons (C, H, and halogen only) Name 4. Draw a step-by-step mechanism for the following reaction: 0” HBr ’ Br 5. Draw the following compounds. Identify them as chiral or achiral. For the chiral compounds, draw one of the two possible enantiomers and assign the stereochemistry of I each stereogenic center. a. cis— 1 -ethyl-3 -methylcyclobutane b. 2,3-dimethylpentane -c. cycloheX-Z-enol d. All stereoisomers of 2-chloro-3-hexene Name 6. George Olah (USC) received the Nobel Prize in Chemistry in 1994 for his work on carbocations. He discovered that by dissolving alcohols in Magic Acid (HSO3F), he could generate stable carbocations that he could observe using NMR spectroscopy. a. Draw the carbocation obtained from the following reaction. Be sure to include the counterion. OH HSO3F ———-—-—-> b. Draw the expected carbocation from the following reaction. OH _ HSO3F \ ————————> V c. Draw the expected carbocation from the following reaction. OH HSO3F —> d. Draw the expected carbocation from the following reaction. ‘ HSO3F ——> /\/\OH e. For each carbocation above, write next to it the number of peaks in the 13C NMR spectrum you expect to see. f. It turns out that the reaction in part c has only 4 peaks in its 13C NMR spectrum, and the reaction in part (1 has only 2 peaks in its 13 C spectrum. What has happened? Draw a mechanism for the formation of the actually observed carbocation in part d. Name 7. Phytic acid (drawn below) is the main storage form of phosphorus in most plants. ' a. Draw both chair conformations of phytic acid. Which one is more stable? b. Is phytic acid chiral or achiral? c. A phytic acid derivative called 1P5 is missing one phosphate group (i.e. replace one PO3H2 with an H). How many isomers of IP5 can be made by replacing one PO3H2 group with an H group? Draw them all. Label each one as chiral or achiral. Identify any pairs of enantiomers, if there are any. d. Based on your answers to all of these questions, draw the IPS isomer that you expect to be most stable. Why? ' Name 8. You have a sample (A) of a pure compound with molecular formula C4HgO. It has optical rotation of +1 5°. You also have a sample (B) of a 60:40 mixture of this compound and its enantiomer. What is the optical rotation of sample B? I b. You take sample B above and hydrogenate it. The optical rotation of this new mixture (C) is +20. If you hydrogenate sample A above to get pure stereoisomer D, what rotation would you get? c. What is the structure of A? What is the structure of D? H2 -——> Pd/C A: C4H80 ' D d. You treat compound A with a mild acid (e. g. dilute H2804). After some time, you isolate the leftover A and measure its optical rotation. It is now optically inactive. Draw a mechanism that explains this. e. What is the optical rotation of an equal mixture of every possible isomer of A? Name ...
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