Chapter 21

Which of the following polymers would be stronger or more rigid? Explain your choices. a. The copolymer of ethylene glycol and terephthalic acid or the copolymer of 1,2 -diaminoethane and terephthalic acid (1,2-diaminoethane \(=\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\) ) b. The polymer of \(\mathrm{HO}-\left(\mathrm{CH}_{2}\right)_{6}-\mathrm{CO}_{2} \mathrm{H}\) or that of c. Polyacetylene or polyethylene (The monomer in polyacetylene is ethyne.)

Poly(lauryl methacrylate) is used as an additive in motor oils to counter the loss of viscosity at high temperature. The structure is The long hydrocarbon chain of poly(lauryl methacrylate) makes the polymer soluble in oil (a mixture of hydrocarbons with mostly 12 or more carbon atoms). At low temperatures the polymer is coiled into balls. At higher temperatures the balls uncoil and the polymer exists as long chains. Explain how this helps control the viscosity of oil.

When pure crystalline amino acids are heated, decomposition generally occurs before the solid melts. Account for this observation. (Hint: Crystalline amino acids exist as \(\mathbf{H}_{3} \mathrm{NCRHCOO}^{-}\) called zwitterions.)

Aspartame, the artificial sweetener marketed under the name NutraSweet, is a methyl ester of a dipeptide: a. What two amino acids are used to prepare aspartame? b. There is concern that methanol may be produced by the decomposition of aspartame. From what portion of the molecule can methanol be produced? Write an equation for this reaction.

Draw the structures of the tripeptides gly-ala-ser and ser-alagly. How many other tripeptides are possible using these three amino acids?

Write the sequence of all possible tetrapeptides composed of the following amino acids. a. two phenylalanines and two glycines b. two phenylalanines, glycine, and alanine

How many different pentapeptides can be formed using five different amino acids?

What types of interactions can occur between the side chains of the following amino acids that would help maintain the tertiary structure of a protein? a. cysteine and cysteine b. glutamine and serine c. glutamic acid and lysine d. proline and leucine

Oxygen is carried from the lungs to tissues by the protein hemoglobin in red blood cells. Sickle cell anemia is a disease resulting from abnormal hemoglobin molecules in which a valine is substituted for a single glutamic acid in normal hemoglobin. How might this substitution affect the structure of hemoglobin?

Draw cyclic structures for D-ribose and D-mannose.

Indicate the chiral carbon atoms found in the monosaccharides D-ribose and D-mannose.

Glucose can occur in three forms: two cyclic forms and one open-chain structure. In aqueous solution, only a tiny fraction of the glucose is in the open-chain form. Yet tests for the presence of glucose depend on reaction with the aldehyde group, which is found only in the open-chain form. Explain why these tests work.

What are the structural differences between \(\alpha\) - and \(\beta\) -glucose? These two cyclic forms of glucose are the building blocks to form two different polymers. Explain.

Cows can digest cellulose, but humans can't. Why not?

Why is glycine not optically active?

Which of the noncyclic isomers of bromochloropropene are optically active?

Part of a certain DNA sequence is G-G-T-C-T-A-T-A-C. What is the complementary sequence?

The codons (words) in DNA (that specify which amino acid should be at a particular point in a protein) are three bases long. How many such three- letter words can be made from the four bases adenine, cytosine, guanine, and thymine?

Which base will hydrogen-bond with uracil within an RNA molecule? Draw the structure of this base pair.

The base sequences in mRNA that code for certain amino acids are Glu: GAA, GAG Val: \(\quad\) GUU, GUC, GUA, GUG Met: AUG Trp: UGG Phe: UUU, UUC Asp: GAU, GAC These sequences are complementary to the sequences in DNA. a. Give the corresponding sequences in DNA for the amino acids listed above. b. Give a DNA sequence that would code for the peptide trp-glu-phe-met. c. How many different DNA sequences can code for the tetrapeptide in part b? d. What is the peptide that is produced from the DNA sequence T-A-C-C-T-G-A- A-G? e. What other DNA sequences would yield the same tripeptide as in part d?

The change of a single base in the DNA sequence for normal hemoglobin can encode for the abnormal hemoglobin giving rise to sickle cell anemia. Which base in the codon for glu in DNA is replaced to give the codon(s) for val? (See Exercises 93 and \(109 .\) )

Draw the following incorrectly named compounds and name them correctly. a. 2 -ethyl- 3 -methyl- 5 -isopropylhexane b. 2 -ethyl-4-tert-butylpentane c. 3 -methyl- 4 -isopropylpentane d. 2 -ethyl- 3 -butyne

In the presence of light, chlorine can substitute for one (or more) of the hydrogens in an alkane. For the following reactions, draw the possible monochlorination products. a. 2,2 -dimethylpropane \(+\mathrm{Cl}_{2} \stackrel{\mathrm{hv}}{\longrightarrow}\) b. 1,3 -dimethylcyclobutane \(+\mathrm{Cl}_{2} \stackrel{\mathrm{hv}}{\longrightarrow}\) c. 2,3 -dimethylbutane \(+\mathrm{Cl}_{2} \stackrel{\mathrm{hv}}{\longrightarrow}\)

The two isomers having the formula \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\) boil at \(-23^{\circ} \mathrm{C}\) and \(78.5^{\circ} \mathrm{C} .\) Draw the structure of the isomer that boils at \(-23^{\circ} \mathrm{C}\) and of the isomer that boils at \(78.5^{\circ} \mathrm{C}.\)

Explain why methyl alcohol is soluble in water in all proportions, while stearyl alcohol \(\left[\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{OH}\right]\) is a waxy solid that is not soluble in water.

Is octanoic acid more soluble in \(1 \mathrm{M} \mathrm{HCl}, 1 M \mathrm{NaOH},\) or pure water? Explain. Drugs such as morphine \(\left(\mathrm{C}_{17} \mathrm{H}_{19} \mathrm{NO}_{3}\right)\) are often treated with strong acids. The most commonly used form of morphine is morphine hydrochloride \(\left(\mathrm{C}_{1} \mathrm{H}_{20} \mathrm{ClNO}_{3}\right) .\) Why is morphine treated in this way? (Hint: Morphine is an amine.)

Consider the compounds butanoic acid, pentanal, \(n\) -hexane, and \(1-\) pentanol. The boiling points of these compounds (in no specific order) are \(69^{\circ} \mathrm{C}, 103^{\circ} \mathrm{C}, 137^{\circ} \mathrm{C},\) and \(164^{\circ} \mathrm{C} .\) Match the boiling points to the correct compound.

A compound containing only carbon and hydrogen is \(85.63 \%\) C by mass. Reaction of this compound with \(\mathrm{H}_{2} \mathrm{O}\) produces a secondary alcohol as the major product and a primary alcohol as the minor product. (See Exercise 62.) If the molar mass of the hydrocarbon is between 50 and 60 g/mol, name the compound.

Three different organic compounds have the formula \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}\). Only two of these isomers react with KMnO_ (a strong oxidizing agent). What are the names of the products when these isomers react with excess \(\mathrm{KMnO}_{4} ?\)

When acrylic polymers are burned, toxic fumes are produced. For example, in many airplane fires, more passenger deaths have been caused by breathing toxic fumes than by the fire itself. Using polyacrylonitrile as an example, what would you expect to be one of the most toxic, gaseous combustion products created in the reaction?

Ethylene oxide,is an important industrial chemical. Although most ethers are unreactive, ethylene oxide is quite reactive. It resembles \(\mathrm{C}_{2} \mathrm{H}_{4}\) in its reactions in that addition reactions occur across the C-O bond in ethylene oxide. a. Why is ethylene oxide so reactive? (Hint: Consider the bond angles in ethylene oxide as compared with those predicted by the VSEPR model.) b. Ethylene oxide undergoes addition polymerization, forming a polymer used in many applications requiring a nonionic surfactant. Draw the structure of this polymer.

Monosodium glutamate (MSG) is commonly used as a flavoring in foods. Draw the structure of MSG.

The reaction to form a phosphate-ester linkage between two nucleotides can be approximated as follows: Would you predict the formation of a dinucleotide from two nucleotides to be a spontaneous process?

Considering your answers to Exercises 130 and \(131,\) how can you justify the existence of proteins and nucleic acids in light of the second law of thermodynamics?

All amino acids have at least two functional groups with acidic or basic properties. In alanine, the carboxylic acid group has \(K_{a}=4.5 \times 10^{-3}\) and the amino group has \(K_{b}=7.4 \times 10^{-5}.\) Three ions of alanine are possible when alanine is dissolved in water. Which of these ions would predominate in a solution with \(\left[\mathrm{H}^{+}\right]=1.0 \mathrm{M} ?\) In a solution with \(\left[\mathrm{OH}^{-}\right]=1.0 \mathrm{M} ?\)

The average molar mass of one base pair of nucleotides in DNA is approximately 600 g/mol. The spacing between successive base pairs is about \(0.34 \mathrm{nm},\) and a complete turn in the helical structure of DNA occurs about every \(3.4 \mathrm{nm}\). If a DNA molecule has a molar mass of \(4.5 \times 10^{9} \mathrm{g} / \mathrm{mol}\), approximately how many complete turns exist in the DNA \(\alpha\)-helix structure?

When heat is added to proteins, the hydrogen bonding in the secondary structure is disrupted. What are the algebraic signs of \(\Delta H\) and \(\Delta S\) for the denaturation process?

In glycine, the carboxylic acid group has \(K_{\mathrm{a}}=4.3 \times 10^{-3}\) and the amino group has \(K_{b}=6.0 \times 10^{-5} .\) Use these equilibrium constant values to calculate the cquilibrium constants for the following. a. \(^{+} \mathrm{H}_{3} \mathrm{NCH}_{2} \mathrm{CO}_{2}^{-}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2}^{-}+\mathrm{H}_{3} \mathrm{O}^{+}\) b. \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2}^{-}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2} \mathrm{H}+\mathrm{OH}^{-}\) c. \(\mathbf{H}_{3} \mathrm{NCH}_{2} \mathrm{CO}_{2} \mathrm{H} \rightleftharpoons 2 \mathrm{H}^{+}+\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2}^{-}\)

Consider a sample of a hydrocarbon at 0.959 atm and \(298 \mathrm{K}\). Upon combusting the entire sample in oxygen, you collect a mixture of gaseous carbon dioxide and water vapor at 1.51 atm and 375 K. This mixture has a density of 1.391 g/L and occupies a volume four times as large as that of the pure hydrocarbon. Determine the molecular formula of the hydrocarbon and name it.

Mycomycin, a naturally occurring antibiotic produced by the fungus Nocardia acidophilus, has the molecular formula \(\mathrm{C}_{13} \mathrm{H}_{10} \mathrm{O}_{2}\) and the systematic name 3,5,7,8 -tridecatetraene-10,12-diynoic acid. Draw the structure of mycomycin.

Consider the following reactions. For parts \(\mathrm{b}-\mathrm{d},\) see Exer cise 62 a. When \(\mathrm{C}_{5} \mathrm{H}_{12}\) is reacted with \(\mathrm{Cl}_{2}(g)\) in the presence of ultraviolet light, four different monochlorination products form. What is the structure of \(\mathrm{C}_{5} \mathrm{H}_{12}\) in this reaction? b. When \(C_{4} H_{8}\) is reacted with \(H_{2} O\), a tertiary alcohol is produced as the major product. What is the structure of \(\mathrm{C}_{4} \mathrm{H}_{8}\) in this reaction? c. When \(\mathrm{C}_{7} \mathrm{H}_{12}\) is reacted with HCl, 1 -chloro- 1 -methylcyclo hexane is produced as the major product. What are the two possible structures for \(\mathrm{C}_{7} \mathrm{H}_{12}\) in this reaction? d. When a hydrocarbon is reacted with \(\mathrm{H}_{2} \mathrm{O}\) and the major product of this reaction is then oxidized, acetone (2-propanone) is produced. What is the structure of the hydrocarbon in this reaction? e. When \(\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}\) is oxidized, a carboxylic acid is produced. What are the possible structures for \(\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}\) in this reaction?

ABS plastic is a tough, hard plastic used in applications requiring shock resistance. The polymer consists of three monomer units: acrylonitrile \(\left(\mathrm{C}_{3} \mathrm{H}_{3} \mathrm{N}\right),\) butadiene \(\left(\mathrm{C}_{4} \mathrm{H}_{6}\right),\) and styrene \(\left(\mathbf{C}_{8} \mathbf{H}_{8}\right)\) a. Draw two repeating units of ABS plastic assuming that the three monomer units react in a 1: 1: 1 mole ratio and react in the same order as the monomers listed above. b. A sample of ABS plastic contains \(8.80 \%\) N by mass. It took 0.605 g Br_ to react completely with a 1.20-g sample of ABS plastic. What is the percent by mass of acrylonitrile, butadiene, and styrene in this polymer sample? c. ABS plastic does not react in a 1: 1: 1 mole ratio among the three monomer units. Using the results from part b, determine the relative numbers of the monomer units in this sample of ABS plastic.

Stretch a rubber band while holding it gently to your lips. Then slowly let it relax while still in contact with your lips. a. What happens to the temperature of the rubber band on stretching? b. Is the stretching an exothermic or endothermic process? c. Explain the above result in terms of intermolecular forces. d. What is the sign of \(\Delta S\) and \(\Delta G\) for stretching the rubber band? e. Give the molecular explanation for the sign of \(\Delta S\) for stretching.

Alcohols are very useful starting materials for the production of many different compounds. The following conversions, starting with 1 -butanol, can be carried out in two or more steps. Show the steps (reactants/catalysts) you would follow to carry out the conversions, drawing the formula for the organic product in each step. For each step, a major product must be produced. (See Exercise 62.) (Hint: In the presence of \(\mathrm{H}^{+},\) an alcohol is converted into an alkene and water. This is the exact reverse of the reaction of adding water to an alkene to form an alcohol.) a. \(1-\) butanol \(\longrightarrow\) butane b. \(1-\) butanol \(\longrightarrow 2\) -butanone

Integrative Problems. These problems require the integration of multiple concepts to find the solutions. An organometallic compound is one containing at least one metal-carbon bond. An example of an organometallic species is \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right) \mathrm{MBr},\) which contains a metal-cthyl bond. How does the hybridization of the starred carbon atom change, if at all, in going from reactants to products? c. What is the systematic name of the product? (Hint: In this shorthand notation, all the \(\mathrm{C}-\mathrm{H}\) bonds have been eliminated and the lines represent \(\mathrm{C}-\mathrm{C}\) bonds, unless shown differently. As is typical of most organic compounds, cach carbon atom has four bonds to it and the oxygen atoms have only two bonds.) a. If \(\mathrm{M}^{2+}\) has the electron configuration \([\mathrm{Ar}] 3 d^{10},\) what is the percent by mass of \(\mathrm{M}\) in \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right) \mathrm{MBr} ?\) b. A reaction involving \(\left(\mathrm{CH}, \mathrm{CH}_{2}\right) \mathrm{MBr}\) is the conversion of a ketone to an alcohol as illustrated here:

Integrative Problems. These problems require the integration of multiple concepts to find the solutions. Helicenes are extended fused polyaromatic hydrocarbons that have a helical or screw-shaped structure. a. \(A 0.1450\) -g sample of solid helicene is combusted in air to give \(0.5063 \mathrm{g} \mathrm{CO}_{2}\). What is the empirical formula of this helicene? b. If a \(0.0938-g\) sample of this helicene is dissolved in \(12.5 \mathrm{g}\) of solvent to give a 0.0175 \(M\) solution, what is the molecular formula of this helicene? c. What is the balanced reaction for the combustion of this helicene?

Marathon Problems. These problems are designed to incorporate several concepts and techniques into one situation. For each of the following, fill in the blank with the correct response. All of these fill-in-the-blank problems pertain to material covered in the sections on alkanes, alkenes and alkynes, aromatic hydrocarbons, and hydrocarbon derivatives. a. The first "organic" compound to be synthesized in the laboratory, rather than being isolated from nature, was _____________which was prepared from____________. b. An organic compound whose carbon-carbon bonds are all single bonds is said to be______. c. The general orientation of the four pairs of electrons around the carbon atoms in alkanes is_______. d. Alkanes in which the carbon atoms form a single unbranched chain are said to be_______alkanes. e. Structural isomerism occurs when two molecules have the same number of each type of atom but exhibit different arrangements of the_______between those atoms. f. The systematic names of all saturated hydrocarbons have the ending_______ added to a root name that indicates the number of carbon atoms in the molecule. g. For a branched hydrocarbon, the root name for the hydrocarbon comes from the number of carbon atoms in the _________continuous chain in the molecule. h. The positions of substituents along the hydrocarbon framework of a molecule are indicated by the ________of the carbon atom to which the substituents are attached. i. The major use of alkanes has been in_______reactions,as a source of heat and light. J. With very reactive agents, such as the halogen elements, alkanes undergo _______reactions, whereby a new atom replaces one or more hydrogen atoms of the alkane. k. Alkenes and alkynes are characterized by their ability to undergo rapid, complete ______ reactions, by which other atoms attach themselves to the carbon atoms of the double or triple bond. 1\. Unsaturated fats may be converted to saturated fats by the process of ________ m. Benzene is the parent member of the group of hydrocarbons called ________ hydrocarbons. n. An atom or group of atoms that imparts new and characteristic properties to an organic molecule is called a ___________ group. 0.4 _________alcohol is one in which there is only one hydrocarbon group attached to the carbon atom holding the hydroxyl group. p. The simplest alcohol, methanol, is prepared industrially by the hydrogenation of ________ q. Ethanol is commonly prepared by the __________of certain sugars by yeast. r. Both aldehydes and ketones contain the _______group but they differ in where this group occurs along the hydrocarbon chain. s. Aldehydes and ketones can be prepared by _______ of the corresponding alcohol. t. Organic acids, which contain the __________ group, are typically weak acids. u. The typically sweet-smelling compounds called ____________ result from the condensation reaction of an organic acid with an___________.

Choose one of the following terms to match the description 1 given in statements \((1)-(17) .\) All of the following pertain to proteins or carbohydrates. a. aldohexose b. saliva c. cellulose d. \(\mathrm{CH}_{2} \mathrm{O}\) e. cysteine f. denaturation g. disaccharides h. disulfide i. globular j. glycogen k. glycoside linkage I. hydrophobic m. ketohexoses n. oxytocin o. pleated sheet p. polypeptide q. primary structure (1) polymer consisting of many amino acids (2) linkage that forms between two cysteine species (3) peptide hormone that triggers milk secretion (4) proteins with roughly spherical shape (5) sequence of amino acids in a protein (6) silk protein secondary structure (7) water-repelling amino acid side chain (8) amino acid responsible for permanent wave in hair (9) breakdown of a protein's tertiary and/or secondary structure (10) animal polymer of glucose (11) \(-\mathrm{C}-\mathrm{O}-\mathrm{C}-\) bond between rings in disaccharide sugars (12) empirical formula leading to the name carbohydrate (13) where enzymes catalyzing the breakdown of glycoside linkages are found (14) six-carbon ketone sugars (15) structural component of plants, polymer of glucose (16) sugars consisting of two monomer units (17) six-carbon aldehyde sugars

For each of the following, fill in the blank with the correct response(s). All of the following pertain to nucleic acids. a. The substance in the nucleus of the cell that stores and transmits genetic information is DNA, which stands for _________ b. The basic repeating monomer units of DNA and RNA are called _______ c. The pentose deoxyribose is found in DNA, whereas ________is found in RNA. d. The basic linkage in DNA or RNA between the sugar molecule and phosphoric acid is a phosphate _______ linkage. e. The bases on opposite strands of DNA are said to be __________ to each other, which means the bases fit together specifically by hydrogen bonding to one another. f. In a strand of normal DNA, the base__________is always always found paired with cytosine. g. A given segment of the DNA molecule, which contains the molecular coding for a specific protein to be synthesized, is referred to as a _______ h. During protein synthesis, ______RNA molecules attach to and transport specific amino acids to the appropriate position on the pattern provided by _______RNA molecules. i. The codes specified by ________are responsible for assembling the correct primary structure of proteins.