CH251Midterm2AU2010BLANK

CH251Midterm2AU2010BLANK - Callam Chemistry 251 Autumn...

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Unformatted text preview: Callam Chemistry 251 Autumn 2010 Midterm 2 200 points HI 131 – Tuesday, November 16, 2010 – 7:00 pm – 9:00 pm Name (PRINT)_____________________________________________________________ I have neither given or received aid on this exam (SIGN)___________________________________________________ Place an X in the column next to your recitation section. Failure to mark your correct recitation section will result in –5 points from your exam total. Day Time Room Teaching Assistant Tuesday Tuesday Thursday Thursday Tuesday Tuesday Thursday Thursday Tuesday Tuesday Thursday Thursday 1:30 pm – 2:18 pm 1:30 pm – 2:18 pm 1:30 pm – 2:18 pm 1:30 pm – 2:18 pm 2:30 pm – 3:18 pm 2:30 pm – 3:18 pm 2:30 pm – 3:18 pm 2:30 pm – 3:18 pm 3:30 pm – 4:18 pm 3:30 pm – 4:18 pm 3:30 pm – 4:18 pm 3:30 pm – 4:18 pm MP1005 MP1008 MP1005 MP1008 MP1005 MP1008 MP1005 MP1008 SM1042 SM2186 SM2186 MP1045 Kamala Kunchithapatham Ryan Yoder Kamala Kunchithapatham Ryan Yoder Kamala Kunchithapatham Ryan Yoder Kamala Kunchithapatham Ryan Yoder Kamala Kunchithapatham Ryan Yoder Kamala Kunchithapatham Ryan Yoder Please read all of the directions for each section of the exam carefully. There are 12 pages including this cover page (Page 1), scoring page (Page 2), and scrap paper (Page 12) for Midterm #2, please check to make sure you have all of the pages. For 3 points extra credit draw a smiley face in the bottom left hand corner of page 2. Make sure your answers are clear. Any structures or answers that are unclear or ambiguous are considered wrong. 1/12 Points/Page = Callam Chemistry 251 Autumn 2010 Section 1 2 3 4 5 6 7 Extra Credit Total 2/12 SCORING PAGE Points Possible 15 15 30 50 25 20 45 10 200 Your Score Points/Page = Callam Chemistry 251 Autumn 2010 Part 1. Stereochemistry and Optical Rotation. (15 points) Answer the following questions based on the molecule and information given below. O OH [α] = +183° NH2 (a) How many stereogenic centers are present in the molecule shown above? What is the maximum number of stereoisomers possible? (4 points) (b) Label R and S stereochemistry on the molecule shown above. (3 points) (c) If a sample contains 5% of the isomer above and 95% of its enantiomer, what is the [α] of this solution? (4 points) (d) Calculate the ee of a solution having [α] = +100°. What is the percentage of each enatiomer present? (Be specific) (4 points) Part 2. Nomenclature. (15 points) (a) For each of the following molecules shown provide the IUPAC name. Br (b) For each of the IUPAC names provided draw the skeletal structure of the molecule. (Z) ­2 ­methyl ­3 ­octene (3R) ­3 ­bromo ­1 ­cyclohexene 3/12 Points/Page = Callam Chemistry 251 Autumn 2010 Part 3. Stereo ­chemical Relationships. For each of the following pairs of molecules identify them as one of the following: constitutional isomers (I), same molecule (S), enantiomers (E), diastereomers (D), or none of the above (N). (3 points each for 30 points) H3CH2C Br Br Cl Cl D CH2CH3 H H (a) H3C (f) D CH2CH3 Br CH3 CH2CH3 Br OH HO (b) OH (g) H3C SH CH2CH3 SH H HS CH3 SH H CH2CH3 HO Br (c) Cl Cl (h) H3C H H Br CH2CH3 CH3 H Br Br H CH2CH3 (d) CHO H HO H HO H HO CH2OH OH H O HO OH OH (i) CH3 (e) Cl H3C CH3 Cl H3C CH3 (j) OH CH3 OH 4/12 Points/Page = Callam Chemistry 251 Autumn 2010 Part 4. Predict the Products. Predict the organic product(s) of the following reactions. When appropriate, be sure to indicate stereochemistry. If more than one product is formed be sure to indicate the major product. Draw all answers in skeletal form. You will be graded on the product your draw from the reaction no other information is needed for this question. (5 points each for a total of 50 points) O O D NaOCH3, H3C S O O 1. Cl2, hv, CCl4 2. HSH Br CH3CH2SeNa O 1. Br2, hv, CCl4 2. NaOC(CH3)3 H2O I 5/12 Points/Page = Callam Chemistry 251 Autumn 2010 Part 4. (cont.) H3C H I H NaCN O S Br CH3 (CH3)3COK (CH3)3COH Br Cl I NaN3 (1 equiv) CH3CH2OCH2CH3 Br OCH3 CH3NH2, NaHCO3 Br O OH NaOH 6/12 Points/Page = Callam Chemistry 251 Autumn 2010 Part 5. Provide the Reagents. (25 points) Provide the reagents necessaryto perform the indicated transformations. More than one reaction may be required. (5 points each) OH O OH O OH O + O NH2 OH H N O Cl O 7/12 O Points/Page = Callam Chemistry 251 Autumn 2010 Part 6. Mechanism and Reaction Coordinate Diagrams. (20 points) (a) Provide the mechanism for the following reaction. Be sure to include all arrows, formal charges and intermediates formed. (6 points) Cl Li C C CH3 THF (b) The above reaction is exothermic. With this idea in mind, draw the transition state for the above reaction indicating stereochemistry , partial charges, and relative bond lengths for forming and breaking bonds. (6 points) (c) Draw the energy diagram for the above reaction. Label the axes, starting material, product, Ea, and ΔH°. (6 points) (d) Write the rate equation for the above reaction. (2 points) 8/12 Points/Page = Callam Chemistry 251 Autumn 2010 Part 7. Explain. (a) When menthyl chloride is treated with sodium ethoxide in ethanol, one alkene product is observed. Draw the expected product of the reaction and provide the mechanism for its formation. Your answer should include clearly drawn chair conformations for full credit (10 points) Cl NaOCH2CH3, CH3CH2OH Menthyl chloride Mechanism (b) When neomenthyl chloride is subjected to the same conditions, two alkene products are formed in a 78:22 ratio. Draw the structures of the two expected products and label which product is major. (5 points) Cl NaOCH2CH3, CH3CH2OH Neomenthyl chloride (c) Would you expect menthyl chloride or neomenthyl chloride to have a faster rate of reaction? Explain using pictures and a minimum of words. (5 points) (d) Provide the expected product(s) when menthyl chloride is reacted with ethanol and heat. Label the major product if more than one is produced. (5 points) 9/12 Points/Page = Callam Chemistry 251 Autumn 2010 (e) Propose a mechanism for the following reaction that explains the following chemical transformation including stereochemistry. (10 points) OH OH OH H2O, H2SO4 + (f) The first demonstration of the stereochemistry of the SN2 reaction was done in 1935 by Hughes and co ­workers. They allowed enantiomerically pure (R) ­2 ­iodooctane to react with radioactive iodide ion (*I ­). (10 points) *II S (i) The rate of substitution (rate coefficient k ) was determined by measuring the rate of incorporation of radioactivity into the alkyl halide. The rate of loss of optical activity from the alkyl halide (rate coefficient k°) was also determined under the same conditions. The two rates were then compared to determine the mechanism. What ratio k° / k is predicted for each of the following stereochemical scenarios? Explain.  ­inversion S  ­equal amounts of both retention and inversion  ­retention (ii) The experimental rate coefficients were found to be as follows: S –4 –1 –1 k = (13.6 ± 1.1) x 10 M s –4 –1 –1 k° = (26.2 ± 1.1) x 10 M s Which scenario in part (i) is consistent with these data? Explain. 10/12 Points/Page = Callam Chemistry 251 Autumn 2010 Extra Credit. (a) Base catalysed hydrolysis of the 1,2 chlorohydrin (1) is found to give a chiral glycol (2) with retention of configuration. Propose a mechanism that would account for this transformation, be sure to include all formal charges and arrows showing the movement of electrons. (5 points) HO Cl H 1 (b) How many stereoisomers are possible for the following molecule? (5 points) CH3 CH3 OH CH3 H 2 NaOH, H2O HO OH OH 11/12 Points/Page = Callam Chemistry 251 Autumn 2010 SCRAP PAPER Periodic Table I H Li II III IV V VI VII Be B C Si N P O S Se F Cl Br I Na Mg AI K 12/12 Ca Points/Page = ...
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