Problem Points Score GSI I 30 II 21 III 28 IV 30 V 31 Total 140

Transcription

1 hemistry 0 First ame Third Examination Last ame.5 h; 0 points please print clearly Dr. Kathleen olta ignature UM ID # PRIT TE FIRT LETTER F YUR LAT AME ERE: Problem Points core GI I 0 II III 8 IV 0 V Total 0 omplete Lewis structures are required unless you are given other specific instructions. Precision in drawing counts. heck all three-dimensional representations to ensure you are implying an unequivocal direction of bonding. Do not forget to include important features such as nonbonding electron pairs and formal charges when appropriate. Individual point values are given in the corner of each answer space. The exam has 6 pages in addition to this cover page. A pka table is on the last page.

2 I. (0 points) ame Page (a) Molecule was treated with one equivalent of a nucleophile under different conditions of p, resulting in a neutral or anionic nucleophile. tructurally isomeric products were obtained under these different conditions, suggesting that different subtitution mechanisms occurred, with a preference at different electrophilic sites. For each reaction, predict the product(s) most likely to form. If more than one stereoisomer forms, draw one and write "+ enantiomer" or "+ diastereomer" in the box. (i) ubstitution product(s) equiv. l a equiv. (ii) ubstitution product(s) l (iii) Under more aggressive conditions, with an excess of a much stronger base, double elimination is observed. Draw the product(s) expected. l l excess, strong base 6 8 (b) Each of the following reactions produces a pair of distinct products, generally formed in approximately equal concentrations. Draw these products and state how they are related to each other by circling the best description. (i) l 9 l These products are: (circle one) enantiomers diastereomers structural isomers (ii) l 0 8 l These products are: (circle one) enantiomers diastereomers structural isomers (b) The reaction shown in (ii) above also leads to the formation of the product shown below. Two high-energy intermediates have been observed to form in this highly stereoselective transformation; draw each. You may ignore stereochemistry in your drawings. l l st intermediate nd intermediate l forms as: (check one) a pair of enantiomers a pair of diastereomers more than stereoisomers a single product; unique connectivity 8

3 II. ( points) ame Page Provide all missing information as these syntheses merge. Draw the product(s) that are required for the next step in the synthesis. ote that only major organic products are given for any one reaction (byproducts, undesired products are ignored). When providing reagents, be sure to number steps when more than one chemical transformation is being done. tereochemistry is not a concern, so only connectivity is required for drawings. (a) -MR: signals -MR: signals + Li draw all products that are formed in the appropriate boxes ) ) Zn a/ ) ) a l 8 ) Li ) major organic product ) /Pd + other byproducts (b) omplete the following synthesis using the directions from above Pd/a Pb ) ) /a equivalents +

4 III. (8 points) ame Page (a) onsider each of the following reactions carefully. For each you are asked to provide product(s); if regioselection is expected, draw major products only. If any product forms as a stereoisomeric mixture, draw one showing stereochemistry clearly and write "+ enantiomer" or "+ diastereomer" in the box. Answer any other questions posed about the reaction. You may assume that rearrangement is not part of any of these reactions. (i) s (iii) (ii) If the starting material was changed to: (iv) If the starting material was changed to: the number of products would be (circle one): the same smaller larger the number of products would be (circle one): the same smaller larger (b) onsider each of the following reactions carefully. For each you are asked to provide product(s); if regioselection is expected, draw major products only. If any product forms as a stereoisomeric mixture, draw one showing stereochemistry clearly and write "+ enantiomer" or "+ diastereomer" in the box. (i) (iii) ) B 6 / ) /a Pd/ (ii) (c) Molecule shown below undergoes bimolecular elimination when treated with a strong base. This reaction yields only one product. Draw a ewman projection for the conformation of the - bond that undergoes this elimination reaction ( should be in front), and draw the expected product. ewman projection showing the conformation of - that undergoes E product of E reaction 5

5 IV. (0 points) ame Page Provide the missing information for each of the transformations of molecule shown below. If more than one stereoisomer is predicted to form draw one and write "+enantiomer" or "+diastereomer" in the box. (a) draw all organic product(s) ) (b) draw reagent(s) l + ai ) ai + ) a (c) Under acidic conditions, and without any indication of rearrangement, alcohol undergoes dehydration to form a mixture of structurally isomeric products - draw each. If more than one stereoisomer is predicted to form for any connectivity, draw one and write "+enantiomer" or "+diastereomer" in the box. 8 (d) Rearrangement (a single shift) provides the only explanation for one of the major products that forms from the dehydration conditions shown above. Provide the simplest and most efficient curved arrow mechanism for the formation of the product shown. Use + and appropriately and as needed for proton transfers. (e) ther compounds form from the reaction above. ne of which has the properties indicated. This compound can also be explained using a single rearrangement step. Please draw this other product, based on the data provided. 8 -MR: 5 signals

6 V. ( points) Provide the missing information for each of the following transformations. ame Page 5 (a) When Molecule is treated with a strong, bulky base, only two structurally isomeric products form. Draw each in the appropriate box, and circle the best description regarding this product mixture. (i) -MR: 9 signals Products share the molecular formula (ii) -MR: 8 signals K (b) owever, when Molecule is treated with the same base, one product forms alone. K (ii) Draw the chair conformation that is expected to undergo this reaction Draw both axial and equatorial substituents for each ring atom that has a substituent. (iii) circle one: nly one product is optically active Both products are optically active either product is optically active (iii) Draw the product (i) What is the relationship between molecules and? 5 (iv) This product is (circle one): optically active optically inactive (c) Follow the fate of Molecule after each of these treatments; both reactions yield a mixture of two products that share the same molecular formula. Draw each product carefully, showing stereochemistry when required. And circle the best description for each product set. (i) 5 0 l (iii) 5 l ) B 6 (ii) circle one: nly one product is optically active Both products are optically active either product is optically active ) a / (iv) circle one: nly one product is optically active Both products are optically active either product is optically active v) Provide the complete IUPA name (including any stereochemistry) for Molecule

7 AID (trongest Acid) l I l F pk a JUGATE BAE (Weakest Base) - l -7. I l -.6 F AID l l l pk a JUGATE BAE l l l (Weakest Acid) 9 (trongest Base)