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Chapter 11: Problem 13
Draw all possible isomers for the molecule \(\mathrm{C}_{4} \mathrm{H}_{8}\).
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Fats and oils are names for the same class of compounds, called triglycerides, which contain three ester groups in which \(\mathrm{R}, \mathrm{R}^{\prime},\) and \(\mathrm{R}^{\prime \prime}\) represent long hydrocarbon chains. (a) Suggest a reaction that leads to the formation of a triglyceride molecule, starting with glycerol and carboxylic acids (see p. 398 for structure of glycerol). (b) In the old days, soaps were made by hydrolyzing animal fat with lye (a sodium hydroxide solution). Write an equation for this reaction. (c) The difference between fats and oils is that at room temperature, the former are solid and the latter are liquids. Fats are usually produced by animals, whereas oils are commonly found in plants. The melting points of these substances are determined by the number of \(\mathrm{C}=\mathrm{C}\) bonds (or the extent of unsaturation) present- -the larger the number of \(\mathrm{C}=\mathrm{C}\) bonds, the lower the melting point and the more likely the substance is a liquid. Explain. (d) One way to convert liquid oil to solid fat is to hydrogenate the oil, a process by which some or all of the \(\mathrm{C}=\mathrm{C}\) bonds are converted to \(\mathrm{C}-\mathrm{C}\) bonds. This procedure prolongs shelf life of the oil by removing the more reactive \(\mathrm{C}=\mathrm{C}\) group and facilitates packaging. How would you carry out such a process (that is, what reagents and catalyst would you employ)? (e) The degree of unsaturation of oil can be determined by reacting the oil with iodine, which reacts with the \(\mathrm{C}=\mathrm{C}\) as follows: The procedure is to add a known amount of iodine to the oil and allow the reaction to go to completion. The amount of excess (unreacted) iodine is determined by titrating the remaining iodine with a standard sodium thiosulfate \(\left(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\right)\) solution: $$\mathrm{I}_{2}+2 \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3} \longrightarrow \mathrm{Na}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}+2 \mathrm{NaI}$$ The number of grams of iodine that reacts with \(100 \mathrm{~g}\) of oil is called the iodine number. In one case, \(43.8 \mathrm{~g}\) of \(\mathrm{I}_{2}\) were treated with \(35.3 \mathrm{~g}\) of corn oil. The excess iodine required \(20.6 \mathrm{~mL}\) of \(0.142 \mathrm{M} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) for neutralization. Calculate the iodine number of the corn oil.
Use ethane as an example to explain the meaning of conformations. What are Newman projections? How do the conformations of a molecule differ from structural isomers?
Why is it that alkanes and alkynes, unlike alkenes, have no geometric isomers?
A compound having the molecular formula \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}\) does not react with sodium metal. In the presence of light, the compound reacts with \(\mathrm{Cl}_{2}\) to form three compounds having the formula \(\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{OCl}\). Draw a structure for the original compound that is consistent with this information.
Comment on the extra stability of benzene compared to ethylene. Why does ethylene undergo addition reactions while benzene usually undergoes substitution reactions?
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