Questions from lab - Esters, Sulfuric Acid...

Questions:

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 terl-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 CSH100. On
catalytic hydrogenation (addition of hydrogen) of A, Compound 8 is
obtained. Compound B has the molecular formula CSH120 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?