Assignment:
Q1. 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.
Q2. Why is a large excess of acetic acid used in the preparation of isopentyl acetate?
Q3. 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?
Q4. 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
Q5. 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.
Q6. When tert-pentyl bromide is treated with 80% ethanol, the amounts of alkene products are detected on analysis. Explain why Compound I is formed in far greater amount than the terminal alkene.
Q7. Why is sulfuric acid, rather than hydrochloric acid, used to catalyze the dehydration of alcohols?
Q8. 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.
Q9. 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.
Q10. Which of the following compounds have a meso form?
2,3-Dibromopentane
2,4-Dibromopentane
2,3-Dibromobutane
Q11. 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.
Q12. 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?
Q13. 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?
Q14. 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.
Q15. 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.
Q16. List several advantages and disadvantages of steam distillation as a method of purification.
Q17. Explain why the distillate collected from the steam distillation of cinnamon is cloudy.
Q18. 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.
Q19. 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.
Q20. 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?
Q21. What chemical test would you use to distinguish between the 1-octene starting material and the octane product?
Q22. Give the structure and names of five alkenes having the molecular formula C6H12 that produce hexane on catalytic hydrogenation.
Q23. In an unsymmetrical alkene, the boron atom adds predominantly to the least substituted carbon atom. For example, 2-methyl-2-butene gives the products. Explain the ratio obtained.
Q24. 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.
Q25. Two structural isomers are formed when 2-methyl-1,3-butadiene reacts with ethyl acrylate (ethyl 2-propenoate). Draw structures for these isomers.
Provide complete and step by step solution for the question and show calculations and use formulas.