Chemistry 232 PRACTICE Midterm 2 September / October 2010 Your name:

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1 1 You will need to be able to show picture ID to take the test. D NT PEN TIS TEST UNTIL EVERYNE AS NE I encourage following instructions: ten (10) points will be deducted if items 1 to 4 below are not answered legibly. 1. Your name: 2. Lab section (if no lab say no lab ) 3. Your ID number (last four digits are K): 4. Your signature (required for grading): Instructions: 1. In fairness to all, do not open this test until everyone has one. 2. Relax!! Put your TA s name, your name, ID number and signature on this page. 3. This test is designed to last from 5:00 to 6:50 pm. 4. Nothing other than writing implements and a molecular model of ten atoms maximum are allowed. 5. Problems 1-6 are multiple choice. Some problems may have more than one answer. Answers are to be recorded on the test -- no Scantron needed. 6. If you finish early, quietly give the test to Grotjahn or a TA. Problems 1-6 (4 points each) /24 Problem 7 Problem 8 /6 Problem 9 Problem 10 Problem 11 /8 Problem 12 Problem 13 /6 Problem 14 Problem 15 Problem 16 /8 Problem 17 Problem 18 Problem 19 /8 Problem 20 TTAL /150

2 2 Note: problems 1-6 are multiple choice. Some can have one or two right answers. These questions are indicated by "maximum of two." If you get both answers right, you get the full 5 points. If you pick one right answer only, you get 3 points. If you pick one right answer and other wrong answer(s), or if you pick both right answers and wrong answer(s), you get zero points. So don't over-guess! 1. What are the configurations of carbons 3 and 7 of the molecule below? The ketone carbon is 2. F 3 (A) 3R, 7S (B) 3R, 7R () 3S, 7S (D) 3S, 7R (E) none of the above 2. What is the configuration of 2 and 3 in the molecule below? 1 is the aldehyde carbon. S N 2 2 (A) 2R, 3S (B) 2R, 3R () 2S, 3S (D) 2S, 3R (E) none of the above 3. The compound at the right was used as a seasoning in antiquity. ow many chiral centers are in the compound? (A) 7 (B) 6 () 5 (D) 4 (E) What functional group(s) are in the molecule at the right? (Maximum of 2) (A) Amide (B) Ether () Ketone (D) Aldehyde (E) Ester 3

3 3 5. A forensic chemist (chemist who deals with crime-related investigations) analyzed a sample of a poisonous alkaloid (generic term for a naturally occurring nitrogen-containing molecule) and determined that its specific rotation [ ] at 25 o using sodium D light was +12 o. What can the chemist properly conclude? (a) there is one enantiomer in the sample (b) the enantiomer present has the R configuration (c) the sample is optically pure (d) the butler did it (e) none of the above 6. Select the correct ranking of the compounds shown according to their acidity. "A > B" means A is more acidic than B. l l l l (A) 1 > 2 > 3> 4 (B) 1 > 3 > 4 > 2 () 1 > 3 > 2 > 4 (D) 2 > 4 > 3 > 1 (E) none of the above 7. List the range of typical infrared absorptions for the following (in cm -1 ) (a) carbonyl stretch (b) alkane, - stretching (c) hydroxyl group stretch (d) a compound with molecular formula 3 6 showed key IR absorptions at 3300 (broad), 3050, 2960, and 1620 cm -1, among others. Given these data, propose the most likely structure of the compound and briefly explain your answer.

4 4 8. Give correct IUPA names for the following compounds. (a) (b) 9. Give correct IUPA names for the following compounds. (a) 2 (b) (c) 3

5 5 10. For each of the following acid-base reactions, draw the products, on the lines provided identify acid, base, conjugate acid and conjugate base, and predict whether equilibria will lie on the side or products or reactants. alculate or estimate K eq as 10 to some power. (a) F 3 2 ( ) 2 N + + (b) 2 + Nal + (c) Mg + + Please note: I told you in class that I expect you to have memorized the pk a of the following: (1) a very strong acid, such as hydrochloric or sulfuric acid; (2) hydronium ion; (3) acetic acid; (4) protonated amine; (5) water; (6) methane. With these numbers memorized, you can at least estimate pk a values for related things like protonated methanol or trifluoroacetic acid using some of the chemical principles we ve learned about, for example using what you know about effects of structure on acidity or basicity.

6 6 11. Which are meso compounds? For molecules which can readily change their conformations, assume that any meso conformation(s) are accessible through bond rotations. 3 N 2 2 N 2 2 l N l 2

7 7 12. Draw the mirror images of the following molecules. orrectly identify the absolute configuration of each chiral center in both the molecules shown and their mirror images. Are any of these molecules superposable on their mirror image? 2 N 13. ne chair form of the carbohydrate galactose is shown below. Draw the other chair form. If the free energy change in going from the chair form shown to the other one is kcal per mole, calculate K eq for the equilibrium at 25 o. 2 galactose

8 8 14. Draw all the stereoisomers of 1,2-diaminocyclohexane. (The amino substituent is -N 2, e.g. aminomethane would be N 2.) Indicate which pairs of stereoisomers are enantiomers and which are diastereomers. orrectly identify the absolute configurations of any chiral centers. 15. onsider trans-1-chloro-3-methylcyclohexane. (A) ow many stereocenters are in this compound? (B) The compound undergoes reaction with zinc metal in the presence of acid to yield a new compound. Draw the new compound, showing all stereochemistry, and name it. () ow many stereocenters are in the new compound? (D) Which compound do you think would have the higher boiling point, the reactant or the product? iefly explain.

9 9 16. Identify the relationships between the following structures. (a) (b) l l (c) N N (d)

10 Using correct arrow-pushing and Lewis structures, show the ønsted-lowry acid-base reaction between water and 2-butyl cation (shown below). Make sure that the product is a stable organic molecule satisfying the octet rule. If the pk a of the cation is - 8, on which side will the equilibrium lie? alculate the equilibrium constant. 2-butyl cation 18. Using correct arrow-pushing and Lewis structures, show the Lewis acid-base reaction between water and 2-butyl cation. Draw all isomeric products which could be formed, identify the relationship(s) between them, and also the ratio between them. Explain briefly.

11 onsider a single enantiomer of trans-1-methyl-3-tert-butylcyclohexane. (For this problem, it does not matter which one.) There are two chair forms. Draw both of them. Which one is more stable? Why?

12 (a) Propose a structure for compound with the following IR spectrum and molecular formula 5 12, and briefly explain your choice. (b) The IR absorption frequencies of the - bond in alkanes, alkenes and alkynes are measurably different. iefly explain why. (c) For the following reaction sequence (it is not necessary to understand the chemistry) what significant change(s) would be expected by IR (ignoring - absorptions)? N 1. DIBAL-, ether 2. 2, l

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