Chemistry 21 Exam 3

Exam 3 Chem 21 Nov 19, 2009 6* Name page 1 (35) 2 (45) total (200) 3 (40) chk 4 (35) 5 (25) 6 (25) Please don’t write in this space. . 1 (19 points) Draw the following compounds. Show stereochemistry clearly. 3" - (a) (i?)-4- bromo 1-cyclopropyl-1-phenylbutane 7 (b) mcso-2,4,5,7-tetramethyloctane “ Hr i (c) Draw the product of an SN2 reaction of the compound in part a with sodium borohydride, NaBHU, in Et? 0. 5044 * CJU 'V: . QS 6, v / ^ I 2 (16 points) Consider the two compounds below. The structures below are not meant to imply any stereochemistry, only to show connectivity. O. HN t c =c Et * — (a) How many stereoisomers of each compound can exist? % (b) How many stereoisomers are achiral? O 21 (c) How many tetrahedral stereo- * centers does each cmpd have? 1. Cl r= I - CH C CO2H c 3. (24 points) Which of the following compounds are chiral? Please circle each chiral compound and write an A below each achiral compound. ct C ) 2,4-dichloro- 1- butene F L#TJ /y X. =C = CH c — CH ^/ oU, w « . 4 (21 points) (a) Label each stereocenter of the compound in the box below as R or S. 6 C 1 enantiomer: (b) Draw the enantiomer of the compound in the space provided above. (c) Look carefully at the compounds below, then label each one as: the same as, the enantiomer of, a diastereomer of, a resonance structure of, or a constitutional isomer of the compound in the box. Br V \Cl Br v / ^CO2H one contains deuterium and the 5. ( 18 points) The following E2 reaction forms two alkenes other does not. Draw them below, showing their stereochemistry clearly . 10 EtO +- “ EtOH L_ / ef (b) Would you expect an SN2 reaction to o OT also? * 3 bsd <+ bIf so, draw the product(s) below. If not, write = 0 pet 3 (c) If the compound above were solvolyzed in ethanol (with no ethoxide), would you expect a reaction to occur? If so, state what type of reaction would occur; if not, write none". Note that you are not asked to draw products this time g j , / ^ 6. (22 points) The reactions below may proceed by SN2, E2, or SN1/E1 pathways, or not at all. Draw the organic products, showing stereochemistry where necessary, and indicate which reaction mechanism(s) is/are operative. Or, if no reaction occurs, write NR. (a ) // 'CF3 o acetone CH 3CO2 H 7G I * T - (c ) 7 Br NaOCH Ph CH3OH I 7. (18 points) Write the mechanism of the Sjvjl solvolysis of the optically active alkenyl chloride below, illustrating each step clearly with curved arrows, and draw the product(s), showing stereochemistry where relevant. £ ( b) Based on your mechanism, would you expect the product mixture to be optically active or inactive? . i -J-J c, 8. (17 points) When the optically active bromo-acetate below is solvolyzed in ethanol, only racemic tram product is formed. Furthermore, the tram bromo-acetate reacts much faster than the cis stereoisomer. Suggest a mechanism that is consistent these observations. racemic ; trans only ' 9. (25 points) Suggest a synthetic route for carrying out each of the following transformations in good yield. Pay attention to stereochemistry. As long as you start with the compound shown, you can use any other organic or inorganic compounds you need . (a ) YtiP ( b) O OCH3 Ph LAA “0 /s a ay Sf / bU . • 10. (8 points) Upon treatment with NaHCCb, the (Z)-chloro-carboxylic acid below undergoes an acid - base reaction, followed by a rapid mframolecular “S 2" cyclization. Draw the product, ^ showing its structure and stereochemistry clearly. NaHC03 SpCy \ •J Cf ( S / Jl 11. (17 points) The reaction below is one you haven't seen before, but you are familiar with all the steps of the mechanism. Write the mechanism, showing each step clearly with curved arrows. H+