Chapter 22

The average molar mass of one base pair of nucleotides in DNA is approximately $600\mathrm{g}/\mathrm{mol}$. 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?

In glycine, the carboxylic acid group has $K_{\mathrm{a}}=4.3\times {10}^{-3}$ and the amino group has $K_{\mathrm{b}}=6.0\times {10}^{-5}$. Use these equilibrium constant values to calculate the equilibrium 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. ${}^{+}{\mathrm{H}}_3{\mathrm{NCH}}_2{\mathrm{CO}}_2\mathrm{H}\rightleftharpoons 2{\mathrm{H}}^{+}+{\mathrm{H}}_2{\mathrm{NCH}}_2{\mathrm{CO}}_2^{-}$

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 Exercise $62.$ 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 ${\mathrm{C}}_4{\mathrm{H}}_8$ is reacted with ${\mathrm{H}}_2\mathrm{O}$, 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 $\mathrm{HCl}$, 1 -chloro-1-methylcyclohexane 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?

Polycarbonates are a class of thermoplastic polymers that are used in the plastic lenses of eyeglasses and in the shells of bicycle helmets. A polycarbonate is made from the reaction of bisphenol A (BPA) with phosgene $\left({\mathrm{COCl}}_2\right)$ : polycarbonate $+2n\mathrm{HCl}$ Phenol $\left({\mathrm{C}}_6{\mathrm{H}}_5\mathrm{OH}\right)$ is used to terminate the polymer (stop its growth). a. Draw the structure of the polycarbonate chain formed from the above reaction. b. Is this reaction a condensation or an addition polymerization?

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 $\left({\mathrm{C}}_8{\mathrm{H}}_8\right)$. a. Draw two repeating units of $\mathrm{ABS}$ 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 $8.80\mathrm{\%}\mathrm{N}$ by mass. It took $0.605\mathrm{g}{\mathrm{Br}}_2$ to react completely with a $1.20-\mathrm{g}$ sample of $\mathrm{ABS}$ 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 $\mathrm{\Delta }S$ and $\mathrm{\Delta }G$ for stretching the rubber band? e. Give the molecular explanation for the sign of $\mathrm{\Delta }S$ 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 $⟶$ butane b. 1-butanol $⟶2$ -butanone

A chemical "breathalyzer" test works because ethanol in the breath is oxidized by the dichromate ion (orange) to form acetic acid and chromium(III) ion (green). The balanced reaction is $3{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(aq)+2{\mathrm{Cr}}_2{\mathrm{O}}_7{}^{2-}(aq)+2{\mathrm{H}}^{+}(aq)⟶$ $3{\mathrm{HC}}_2{\mathrm{H}}_3{\mathrm{O}}_2(aq)+4{\mathrm{Cr}}^{3+}(aq)+11{\mathrm{H}}_2\mathrm{O}(l)$ You analyze a breathalyzer test in which $4.2\mathrm{mg}{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ was reduced. Assuming the volume of the breath was $0.500\mathrm{L}$ at $30.{}^{\circ }\mathrm{C}$ and $750.\mathrm{mm}\mathrm{Hg}$, what was the mole percent alcohol of the breath?

Helicenes are extended fused polyaromatic hydrocarbons that have a helical or screw-shaped structure. a. A $0.1450-\mathrm{g}$ 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 $0.0938-\mathrm{g}$ sample of this helicene is dissolved in $12.5\mathrm{g}$ of solvent to give a $0.0175\mathrm{m}$ solution, what is the molecular formula of this helicene? c. What is the balanced reaction for the combustion of this helicene?