Faculty of Science Mid-Term Examination I. Chem 222/234 Introductory Organic Chemistry I

Transcription

1 Student Name: Student ID #: Faculty of Science Mid-Term Examination I Chem 222/234 Introductory rganic Chemistry I Examiner: Professor James L. Gleason Tuesday, ctober 6, 2009 Associate Examiner: Professor Dmytro Peripichka 6:30-9:00 PM Instructions: 1. Fill in your student ID number and the first two initials of your name on the SCANTRN CARD. Write your name and student ID number on both TIS SEET and the SCANTRN CARD. 2. This exam has several versions. This is Version 1. Be sure that the correct version is listed on your exam card. 3. The exam booklet contains three sections. Section 1 contains questions from the lectures and has 20 multiple choice questions. Section 2 has lab questions. nly CEM 222 students need to answer this section. Section 3 has written questions. ANSWER TESE DIRECTLY N TE EXAM PAPER 4. Molecular model sets and calculators are allowed. 5. No notes or textbooks. 6. Both the exam booklet and the exam card must be turned in for a mark to be issued.

2 Section 1. Multiple Choice Questions (4.5 pts each) 1. What is the formal oxidation state of the carbon indicated in bold: C Cl a) +1 b) +2 c) +3 d) +4 e) none of the above 2. In order to have an absorbance in NMR, a nuclei must have what: a) electrons to shield it b) a nuclear spin c) neutrons d) a dipole moment e) none of the above 3. What is the product of the following reaction? Assume one equivalent of bromoethane is used. Br Mg a) b) c) d) e)

3 4. What would be the best reagent to accomplish the following reaction? a) NaB 4, followed by + b) Na, followed by + c) MgBr, followed by + d) LiAl 4, followed by + e) Br 2 5. The following IR is most consistent with which structure? a) b) c) d) e)

4 6. What is the product of the following reaction? Assume one equivalent of bromoethane is used. Br Mg a) b) c) d) e) 7. The MS below is most likely which isomer of C 6 14? a) n-hexane b) 2-methylpentane c) 3-methylpentane d) 2,2-dimethylbutane e) 2,3-dimethylbutane

5 8. Which reaction would not produce dicyclohexylmethanol (shown) (c-c 6 11 ) 2 C= = a) NaB 4 + (c-c 6 11 ) 2 C= b) LiAl 4 + (c-c 6 11 ) 2 C= c) c-c 6 11 Br + Mg, then c-c 6 11 C d) c-c 6 11 Br + Mg, then (c-c 6 11 ) 2 C= e) c-c 6 11 Br + Mg, then C c-c 6 11 C = C = 3 C 9. What is the expected order of reactivity, from most to least reactive, of the following carbonyl compounds towards reducing agents. a) aldehyde > ketone > ester > acid b) acid > ester > ketone > aldehyde c) aldehyde > ketone > acid > ester d) acid > aldehyde > ester > ketone e) none of the above 10. Which of the pairs of groups indicated are diastereotopic? a) b) c) d) e) Br 3 C 3 C C 3 Br 11. Which of the pairs of groups indicated are enantiotopic? a) b) c) d) e) Br 3 C 3 C C 3 Br

6 12. The NMR below is most consistent with which structure with the formula C 4 9 Br a) 1-bromobutane b) 2-bromobutane c) 1-bromo-2-methylpentane d) 2-bromo-2-methylpentane e) consistent with more than one of the above 13. What is the product of the following reaction sequence? MgBr a) 3 C b) 3 C c) d) e) 3 C

7 14. The 13 C NMR below is most consistent with which structure 2 peaks 2 peaks a) b) c) d) e) 15. Given the MS below, what is a likely molecular formula. a) C 5 5 Cl b) C 6 12 c) C 7 6 d) C 5 8 S e) C 5 12 N M=

8 16. What is the most likely molecular formula? a) C 2 2 Br 2 b) C 5 11 BrClN c) C 3 6 Br 2 d) C 4 9 I e) none of the above M= ow many 13 C signals would you expect to see in the following molecule? N a) 14 b) 12 c) 10 d) 9 e) 8 Cl

9 18. What is the most likely structure for a molecule with the formula C given the following 1 and 13 CNMR 2 peaks a) C b) 3 c) d) C e) 3 C 3 3 C 3 C

10 Lab Exam Questions (1 point each) 19. In the Grignard experiment, a student observed a m.p. for triphenylcarbinol of C, which was several degrees above the literature value. What might be the reason for this anomalous result? a) the sample was not well dried b) the sample had impurities c) the student raised the temperature of the melting point apparatus too quickly d) none of the above 20. What was the purpose of adding hexanes to the reaction mixture at the end of the Grignard experiment? a) to precipitate the biphenyl impurity b) to precipitate the triphenylcarbinol c) to ensure all the water was out of the reaction mixture d) to help the rotary evaporation 21. Fractional distillation of a mixture of cyclohexanone/water will not give complete separation of the mixture into its components because (QUESTIN DRPPED: EVERYNE GETS A PINT) a) the boiling point differences between the two liquids is not high enough to distill properly b) it is an azeotropic mixture c) they are miscible liquids following Raoult s Law d) none of the above 22. The phase-transfer catalyst used in the carbene lab was benzyltriethylammonium chloride. In what form is it present in the mixture? a) the chloride form in the organic phase and the hydroxide form in the aqueous phase b) the hydroxide form in the organic phase and the chloride from in the aqueous phase. c) both forms in both phases d) Neither is soluble 23. What is the first thing you should you do if you have spilled base on your skin? a) neutralize the base with an acid of the appropriate molarity. b) wash with copious amounts water. c) tightly wrap affected area with gauze to localize the burn. Notify an instructor immediately. d) drying agents, such as calcium chloride, will adsorb the base, preventing a skin burn.

11 Written Questions (10 points each) 1. Draw the mechanism and predict the product of the following reaction: MgBr mild acid workup MgBr or BrMg (or BrMg) + MgBr

12 2. Solve the structure of the following, given the following information: IR: 3400 (strong, broad), 2948, 1717 MS: M = 164 (100%), M+1 =165 (7.6%), M+2 = 166 (32%) Note 1: Under certain conditions, the peak at 3.7 ppm shows up as a triplet and at the same time, the peak at 4.7 ppm shows up as a doublet. Furthermore, upon shaking with D 2, the peak at 3.7 ppm disappears. Note 2: A blow up of the peak at 1.6 ppm is shown at the bottom. The arrows indicate part of the signal which is difficult to see but is definitely part of the signal PPM

13 2. Write Answer Below Cmax = 7 bvious ketone or aldehyde by 13C NMR Ketone confirmed from IR stretch and lack of aldehyde C at 9-10ppm in 1 NMR Chlorine indicated by M+2 peak in MS 13C has 6 carbons, but one may be doubled. 1 NMR has 13 s proton is at 3.7 (disappears with D2) proton is sometimes coupled to 2 proton signal at 4.7 ppm: C 2 Since the C2 is farther downfield than normal proton adjacent to oxygen, it may be adjacent to the ketone as well (C 2 C=). 6 at 0.9 ppm consistent with two methyl groups. Signal at 1.6 ppm is a nonet, it therefore must be adjacent to 8 hydrogens. The only way this is possible is to have ( ) 2 CC 2 - C2 group at 1.8 ppm is not deshielded enough to be next to a ketone, so: If signal at 4.7 ppm is adjacent to oxygen, 4.3 must be adjacent to the chlorine and perhaps ketone as well. Add all together and you get the following as a reasonable structure. Cl