Midterm_2_W11_Key

Midterm_2_W11_Key - Chem 6AL W11 Russak 14 February...

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Unformatted text preview: Chem 6AL W11 Russak 14 February 2011 Midterm 2 Key The following questions are all multiple choice. Please fill out the score sheet with your name. You must put your perm number on the score sheet and fill in the bubbles associated with it to receive credit for the exam. There are equations/spectral keys on the back sheet that you may need to calculate/solve your answers. You may use a calculator. There is only 1 correct choice for each question; filling in multiple answers will result in no credit given. 1. Benzoic acid is allowed to react with sodium hydroxide. What is the equilibrium constant Keq? (Use pKa’s on chart on back page of exam) a. 1.0 x 1010 b. 1.0 x 1015 c. 1.0 x 10 ­10 d. 1.0 x 10 ­15 e. None of the above reflect the correct Keq 2. A brine wash is used to remove water from organic liquids. It works by: a. Increasing the concentration of NaCl in the water later b. Decreasing the concentration of NaCl in the water layer c. Trapping water in small pockets that they cannot be removed from easily d. Forming hydrates e. None of the above 3. What is true of vapor pressure? a. The higher the vapor pressure, the lower the boiling point b. Vapor pressure is not a colligative property c. The higher the vapor pressure, the higher the boiling point d. The lower the vapor pressure, the lower the boiling point e. A and B 4. Consider a 33 mol % mixture of dichloromethane (P°=47 kPa) in ether (P°=53 kPa). What is the combined vapor pressure? a. 6 kPa b. 49 kPa c. 51 kPa d. 100 kPa e. None of the above 5. From the question above, calculate the fraction of dichloromethane molecules that reside in the vapor above the solution? a. 20 % b. 25% c. 31% d. 66 % e. None of the above 6. Consider that you have a partition coefficient of 3.0 for a substance in an ether/water solution. You perform 2 extractions using ether. What is the total amount of material in the organic layer assuming equal volumes of liquids were used? a. 4.0% b. 6.3% c. 94% d. 96% e. None of the above 7. Place the following solvents in order of highest to lowest polarity from left to right a. Ethyl acetate, hexanes, acetone, water b. Water, ethyl acetate, acetone, hexanes c. Hexanes, ethyl acetate, water, acetone d. Hexanes, ethyl acetate, acetone, water e. None of the above 8. The photoisomerization reaction in experiment 5 was done in homogeneous solution to start with. Why? a. Molecules in solution allow space between themselves so reactions can take place b. In a solid form, most of the trans compound would be protected from light by the crystal lattice c. The solution provided a medium that was sparingly soluble so that precipitation of the product was possible d. A and B e. A, B, and C 9. In Thin Layer Chromatography, which technique(s) of visualization is(are) ultimately non ­destructive to the compound? a. Visible detection b. Iodine stain c. UV detection d. KMNO4 e. A, B and C 10. You perform a TLC analysis but all of the spots are very large and overlap over each other. What could be the problem? a. The sample spotted is too polar to travel on the plate b. The sample spotted is too concentrated c. The sample spotted is too dilute d. The mobile phase is too polar e. None of the above 11. Look at the TLC below and answer the question that follows. Lane A is the starting material, lane B is the co ­spot and lane C a sample of the reaction at some point in time. The TLC of reaction A C tells you that: a. Starting material is still present in the reaction b. The reaction is complete c. Product C is less polar that starting material A d. A and C e. None of the above 12. In the electromagnetic spectrum,__________ wavelength and __________ wavenumbers are associated with high energy. a. Low, high b. High, low c. High, high d. Low, low 13. What functionality has the highest C=O bond order? a. Ester b. Amide c. Aldehyde d. Ketone e. None of the above 14. 1H nuclei located near electronegative atoms tend to be __________ relative to 1H nuclei which are not. a. shielded b. deshielded c. resonanced d. split e. none of the above A B C 15. How many signals would you expect to see in the 1H NMR spectrum of the following compound? a. 2 b. 3 c. 4 d. 5 e. 6 16. How many signals would you expect to see in the 1H NMR spectrum of the following compound? a. 6 b. 3 c. 5 d. 4 e. 2 17. How many signals would you expect to see in the 1H NMR spectrum of the following compound? a. 1 b. 2 c. 3 d. 4 e. 5 18. What splitting pattern is observed in the proton NMR spectrum for the indicated hydrogens? a. Singlet b. doublet c. triplet d. quartet e. septet 19. How many signals would you expect to see in the 1H NMR spectrum of the following compound? a. 3 O b. 4 c. 5 d. 6 e. 7 20. How many signals would you expect to see in the 1H NMR spectrum of the following compound? O a. 2 b. 3 c. 4 d. 5 e. 6 Infrared Spectroscopy Match the following structures to their Infrared Spectra: O O N H A B C D E O O OH O 21. C O O N H O O OH O A B C D E 22. E 23. A O O N H O O OH O A B C D E 24. B 25. D Match the following structures to their 1H NMR Spectra: s=singlet, d=doublet, t=triplet, q=quartet, qt= quintet, sx=sextet, st=septet, ot=octet, m=multiplet (multiplet signals are overlapped and difficult to determine splitting). The integrations are givin in parentheses next to the splitting pattern. Match the following structures to their 1H NMR spectra: 26. q(1H), s(6H), d(3H) D 27. singlet. No integration given.C 28. st(1H),s(3H),d(6H) A 29. t(3H) E d(2H),s(1H),s(1H),qt(1H),qt(2H), 30. t(2H),s(3H),t(2H),qt(2H),s(2H) B Equations: N=c/ʋ E=hc/λ h=6.626 E ­34 J.s c = 3.00 E8 m/s d=m/V P=P°X P=PA+PB Υ=P/Ptotal K = [A]org / [A]aq [A]aq final / [A]aq initial = [(V2/(V2+V1K)]n Infrared Absorptions Vibration Alkanes CȺH stretch CȺH bend Alkenes C=CȺH stretch C=C stretch C=CȺH bend Alkynes C≡CȺH stretch C≡C stretch Aromatic Compounds CȺH stretch C=C stretch CȺH bend Alcohols OȺH stretch CȺO stretch Position (cm ) 2990 ­2850 1480 ­1430 and 1395 ­1340 3100 ­3000 1680 ­1620 sat, 1650 ­1600 conj 995 ­685 3310 ­3200 2250 ­2100 3100 ­3000 1620 ­1440 900 ­680 3650 ­3550 non ­hydrogen bonded 3550 ­3200 hydrogen bonded 1300 ­1000 Amines 3550 ­3250 NȺH stretch Nitriles 2280 ­2200 C≡N stretch Aldehydes 2900 ­2800 and 2800 ­2700 CȺH stretch 1740 ­1720 sat, 1715 ­1680 conj C=O stretch Ketones C=O stretch 1750 ­1705 sat, 1715 ­1650 conj Esters C=O stretch 1765 ­1735 sat, 1730 ­1715 conj 1300 ­1000 CȺO stretch Carboxylic Acids 3200 ­2500 OȺH stretch 1725 ­1700 sat, 1715 ­1680 conj C=O stretch 1300 ­1000 CȺO stretch Amides 3500 ­3150 NȺH stretch 1700 ­1630 C=O stretch Anhydrides C=O stretch 1850 ­1800 and 1790 ­1740 1300 ­1000 CȺO stretch Acid Chlorides C=O stretch 1815 ­1770 Nitro Compounds NO2 stretch 1570 ­1490 and 1390 ­1300 s = strong, m = medium, w = weak, br = broad, sat = saturated, conj = conjugated  ­1 Intensity m to s m to w m w to m s s m to w m to w m to w s m br, s s br, m s w, Fermi Doublet s s s br, m to w s s m s s s s s ...
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This note was uploaded on 04/09/2011 for the course CHEM 6a taught by Professor Pettus during the Winter '07 term at UCSB.

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