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    Ester Reduction Questions

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    1. In the preparation of the esters given in this experiment, the reaction
    product was extracted with 5% sodium bicarbonate solution (NaHCO3) in
    the isolation step. Why? What gas was evolved during this washing step?
    Write a balanced equation for the reaction that produced it.
    2. Why is a large excess of acetic acid used in the preparation of isopentyl
    acetate?
    3. Concentrated sulfuric acid is used as a catalyst for the esterification of
    acetic acid in the preparation of isopentyl acetate. Why is sulfuric acid
    needed if another acid, acetic acid, is already present?
    4. Fatty acids are long-chain carboxylic acids, usually of 12 or more carbon
    atoms, isolated from saponification of fats and oils (esters of glycerol).
    Draw the structure of the two fatty acids named below and also determine
    their common name.
    Hexadecanoic acid
    Octadecanoic acid
    5. Gas chromatographic analysis of a mixture of organic compounds gave
    the following peak areas (sq cm): hexane = 2.7; heptane = 1.6; hexanol =
    1.8; toluene = 0.5.
    a. Calculate the mole percent composition of the
    mixture. Assume that the response of the detector (area per
    mole) is the same for each component.
    b. Calculate the weight percent composition of the
    mixture, using the same assumptions as in part a.
    6. When tert-pentyl bromide is treated with 80% ethanol, the amounts of
    alkene products indicated in your lab textbook on pg. 218 (#6.57) are
    detected on analysis. Explain why Compound I is formed in far greater
    amount than the terminal alkene.
    7. Why is sulfuric acid, rather than hydrochloric acid, used to catalyze the
    dehydration of alcohols?
    8. A sample of 150 mg of an organic compound is dissolved in 7.5 mL of
    water. The solution is placed in a 20-cm polarimeter tube and the rotation
    measured in a polarimeter. The rotation observed was +2.676 degrees.
    Distilled water, in the same tube, gave a reading of +0.016 degrees.
    Calculate the specific rotation for the compound.
    9. Compound A is optically active and has the molecular formula C5H10O. On
    catalytic hydrogenation (addition of hydrogen) of A, Compound B is
    obtained. Compound B has the molecular formula C5H12O and is optically
    inactive. Give the structure for Compounds A and B.
    10. Which of the following compounds have a meso form?
    2,3-Dibromopentane
    2,4-Dibromopentane
    2,3-Dibromobutane
    11. Compounds such as naphthalene and 1,4-dichlorobenzene find use as
    mothballs since they sublime at a slow rate at atmospheric pressure.
    Explain this behavior in terms of the structure of the molecules.
    12. a. How many peaks would you expect to find in the NMR spectrum of
    caffeine?
    b. What characteristic absorption bands would you expect to find in
    the infrared spectrum of caffeine?
    13. The vapor pressures of 1,2-diphenylethane, p-dichlorobenzene, and 1,3,5-
    trichlorobenzene are 0.06, 11.2, and 1.4 torr, respectively, at their melting
    point (52-54 degrees C). Which compound is likely to be sublimed most
    rapidly at a reduced pressure of 15 torr and a temperature of 40 degrees
    C?
    14. To color spots on TLC plates for easier visualization after elution with
    solvent, the plates can be "developed" in a sealed chamber containing
    solid iodine. Explain how the solid-vapor equilibrium operates in this
    instance.
    15. Caffeine is soluble in ethyl acetate. Do you think that the purity of your
    product could be checked by TLC using ethyl acetate as an elution
    solvent? Explain.
    16. List several advantages and disadvantages of steam distillation as a
    method of purification.
    17. Explain why the distillate collected from the steam distillation of cinnamon
    is cloudy.
    18. Calculate the weight of water required to steam distill 500 mg of
    bromobenzene at 95 degrees C. The vapor pressure of water at this
    temperature is 640 torr; bromobenzene, 120 torr.
    19. Steam distillation may be used to separate a mixture of p-nitrophenoln and
    o-nitrophenol. The ortho isomer distills at 93 degrees C; the para isomer
    does not. Explain.
    20. The chiral carboxylic acid A (C5H6O2) reacts with 1 mol of hydrogen gas
    on catalytic hydrogenation. The product is an achiral carboxylic acid B
    (C5H8O2). What are the structures of Compounds A and B?
    21. What chemical test would you use to distinguish between the 1-octene
    starting material and the octane product?
    22. Give the structure and names of five alkenes having the molecular formula
    C6H12 that produce hexane on catalytic hydrogenation.
    23. In an unsymmetrical alkene, the boron atom adds predominantly to the
    least substituted carbon atom. For example, 2-methyl-2-butene gives the
    products indicated in your lab textbook on pg. 259 (#6-90). Explain the
    ratio obtained.
    24. The decomposition of 3-sulfolene to form 1,3-butadiene generates 1 mole
    of sulfur dioxide gas per mole of 1,3-butadiene. Substantial quantities of
    SO2 would be generated if this decomposition were carried out on a large
    scale. Suggest a method for trapping the gas to prevent its escape into the
    environment.
    25. Two structural isomers are formed when 2-methyl-1,3-butadiene reacts
    with ethyl acrylate (ethyl 2-propenoate). Draw structures for these
    isomers.

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    25 Organic Lab Questions are answered with detailed explanations.

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