1.5 h; 120 points please print clearly Dr. Kathleen Nolta Signature. Problem Points Score GSI I 20 II 27 III 25 IV 22 V 26 Total 120

Transcription

1 hemistry 0 First ame econd Examination Last ame. 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 7 III IV V Total 0 omplete Lewis structures are required unless you are given other specific instructions. Precision in drawing counts. heck all three-dimensional ations 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 pages in addition to this cover page. A pka table is on the last page.

2 I. (0 points) A. Page onvert name to structure or structure to name as needed. Be sure to include all information on connectivity and stereochemistry in both your drawings and your naming. (i) ame this compound: (ii) Draw this compound: (,R)--ethylcyclohepta-,-dien--ol B. Provide the missing information for the following substitution reaction. (i) Provide the curved arrow mechanism (ii) Draw the single ionic product that forms.. Provide the missing information for the following addition reactions. 7 equivalent equivalent regioselected product

3 II. (7 points) Page Threonine is an essential amino acid (you must eat it because you cannot synthesize it). The natural form of this compound (under physiological conditions) is shown at right, with optical activity (α) given. View down the - bond indicated ( being the front atom), and answer the following questions. view T threonine - 8 (a) Draw a ewman projection of the - bond in threonine in the conformation shown; view with the in front. (b) ne conformation of threonine allows the group to serve as both a hydrogen bond donor and a hydrogen bond acceptor across the rotating bond. Draw a ewman projection of the - bond under these circumstances and show the hydrogen bonding; view with the in front. (c) Indicate the relationship (if any) between the drawing (and conformation) of threonine (T) shown above and each of the drawings (L, M,, and ) shown below. heck all the descriptions that apply when comparing these drawings, and answer the questions about optical activity based on this relationship, either by using numerical values or by writing BP ("cannot be predicted"). (i) (ii) (iii) (iv) L L, these drawings M M, these drawings, these drawings, these drawings L's optical activity: M's optical activity: 's optical activity: 's optical activity:

4 III. ( points) Page A. Tetracycline is a broad-spectrum antibiotic that is used to treat a wide variety of infections, including acne, rosacea, and cholera. ircle and label every chiral (tetrahedral) stereocenter in tetracycline. tetracycline Label the double bonds indicated with arrows and boxes with their appropriate label. B. Alkynes may undergo electrophilic addition like alkenes in many cases. pectra taken on this 8 starting alkyne should show: MR signals MR signals with ratio ( equivalent) (cat.) pectra taken on these 9 8 products reveal: The two different products that form share the same molecular formula; draw each clearly and distinctly. 9 MR signals 8 MR signals ( equivalent) (cat.) pectra taken on this 0 product should show: MR signals MR signals

5 IV. ( points) A. Dienes undergo electrophilic addition reactions with sometimes surprising results due to the added reactivity of a second set of pi electrons. (cat.) Page *The complete transformation requires mechanistic steps. *Two carbocation intermediates form; the more stable carbocation forms first. *The complete transformation is energetically favorable overall Provide the most straightforward curved arrow mechanism for this addition reaction, using (and regenerating) the appropriate acid indicated for these conditions; be sure to use the information given. B. Using positional labels (-9) answer the following questions regarding these energy diagrams and their possible connection to the transformation shown above. Energy, G 7 8 reaction coordinate (a) What is the rate determining step for the transformation of to 9 (forward) shown in I? 9 Energy, G 7 8 reaction coordinate 9 Energy, G reaction coordinate I II III (b) What is the E a of the rate determining step for the 9 to (reverse) transformation shown in II? (c) What is the ΔG for the second step of the to 9 (forward) transformation shown in III? (d) Which of the energy diagrams shown best s the transformation you explored in part A above? (circle one) I II III

6 V. ( points) Page Treatment of ompound with an excess of yields a number of stereoisomeric products, one of these is drawn for you; please discuss the other products. (b) (i) excess ompare with ; these drawings : (check all that apply) Product A the +? (a) Including Product A, what is the total number of stereoisomeric products expected to form in this reaction? (ii) If was used as a starting material in the above reaction, the product set: (circle one) would remain the same would be different is impossible to predict (c) (i) ompare with ; these drawings : (check all that apply) the (ii) If was used as a starting material in the above reaction, the product set: (circle one) would remain the same would be different is impossible to predict (d) Draw the two chair conformations for Product A and indicate the K eq for your pair of chairs. As always, be sure to clearly and accurately show the axial and equatorial positions for all substituted ring atoms. You do not have to show axial and equatorial hydrogen atoms for unsubstituted ring atoms. circle one K eq > = < (e) ircle all the descriptions that apply to ompound (f) ircle all the descriptions that apply to Product A is chiral has an enantiomer is optically active is chiral has an enantiomer is optically active is achiral has at least one diastereomer is meso is achiral has at least one diastereomer is meso

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