Chapter 19

List the different sets of hybrid orbitals (valence bond theory) used to describe bonding in organic compounds. What combination of single and multiple bonds is possible with each hybridized set?

What is the principal difference between an oligomer and a polymer formed from the same monomer?

Is the interstitial alloy tungsten carbide (WC) considered to be an organic compound?

If the average molar mass of a polyethylene sample \(\mathrm{A}\) is twice that of sample \(\mathrm{B},\) which sample begins to soften at a higher temperature? Explain why.

Which of the following properties of polyethylene increases as the number of monomer units per molecule of the polymer increases? (a) melting point; (b) viscosity; (c) density; (d) C:H ratio; (e) fuel value

Do linear and branched alkanes with the same number of carbon atoms all have the same empirical formula?

If an alkane and a cycloalkane have equal numbers of carbon atoms per molecule, do they have the same number of hydrogen atoms?

What is the hybridization of carbon in alkanes?

Why isn't cyclohexane a planar molecule?

Are cycloalkanes saturated hydrocarbons?

Do constitutional isomers always have the same molecular formula?

Do constitutional isomers always have the same chemical properties?

Are constitutional isomers members of a homologous series?

Draw and name all the constitutional isomers of \(\mathrm{C}_{5} \mathrm{H}_{12}\)

Draw and name all the constitutional isomers of \(\mathrm{C}_{6} \mathrm{H}_{14}\)

Crude Oil Place the following molecules, all of which are products of the distillation of crude oil, in order in which they would appear in the distillate during simple distillation: \(\mathbf{C}_{6} \mathrm{H}_{14}, \mathrm{C}_{18} \mathrm{H}_{38}, \mathrm{C}_{12} \mathrm{H}_{26}, \mathrm{C}_{9} \mathrm{H}_{20}\)

Which has a higher hydrogen-to-carbon ratio: hexane or cyclohexane?

Can combustion analysis distinguish between an alkene and a cycloalkane containing the same number of carbon atoms?

Can their reaction with hydrogen distinguish between an alkene and a cycloalkane containing the same number of carbon atoms?

Why don't alkynes have cis and trans isomers?

Ethylene reacts quickly with HBr at room temperature, but polyethylene is chemically unreactive toward HBr. Explain why these related substances have such different properties.

Polymerization of butadiene \(\left(\mathrm{CH}_{2}=\mathrm{CHCH}=\mathrm{CH}_{2}\right)\) does not yield the same polymer as polymerization of ethylene \(\left(\mathrm{CH}_{2}=\mathrm{CH}_{2}\right)\) a. How could we convert poly(butadiene) into poly(ethylene)? b. Predict the reactivity of poly(butadiene) with HBr.

Using the average bond strengths given in Appendix 4 estimate the molar heat of hydrogenation, \(\Delta H_{\text {hydrogenation }},\) for the conversion of \(\mathrm{C}_{2} \mathrm{H}_{4}\) to \(\mathrm{C}_{2} \mathrm{H}_{6}\) $$\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2}(g)+\mathrm{H}_{2}(g) \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{3}(g)$$

Using the average bond strengths given in Appendix 4 estimate the molar heat of hydrogenation, \(\Delta H_{\text {hydrogenation }},\) for the conversion of \(\mathrm{C}_{2} \mathrm{H}_{2}\) to \(\mathrm{C}_{2} \mathrm{H}_{6}\) $$\mathrm{CH} \equiv \mathrm{CH}(g)+2 \mathrm{H}_{2}(g) \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{3}(g)$$

Using data in Appendix \(4,\) calculate \(\Delta H_{\mathrm{rxn}}\) for the production of acetylene from the controlled combustion of methane: $$6 \mathrm{CH}_{4}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{C}_{2} \mathrm{H}_{2}(g)+2 \mathrm{CO}(g)+10 \mathrm{H}_{2}(g)$$ Is this an endothermic or an exothermic reaction?

Using data in Appendix \(4,\) calculate \(\Delta H_{\mathrm{rxn}}\) for the production of acetylene from the reaction between calcium carbide and water, given that the \(\Delta H_{f}^{\circ}\) of \(\mathrm{CaC}_{2}\) is \(-59.8 \mathrm{kJ} / / \mathrm{mol}\) $$\mathrm{CaC}_{2}(s)+2 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{C}_{2} \mathrm{H}_{2}(g)+\mathrm{Ca}(\mathrm{OH})_{2}(s)$$. Is this an endothermic or an exothermic reaction?

Given the following two reactions and thermodynamic data from Appendix 4, estimate \(\Delta H_{\mathrm{m}}\) for the hydrogenation of acetylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)\) with one mole of hydrogen gas to make ethylene \(\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)\) \(\mathrm{HC}=\mathrm{CH}(g)+2 \mathrm{H}_{2}(g) \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{3}(g)\) Acetylene Ethane \(\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}_{2}(g)+\mathrm{H}_{2}(g) \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{3}(g)\) Ethylene Ethane

The 2000 Nobel Prize in Chemistry was awarded for research on the electrically conductive polymer polyacetylene. a. Draw the carbon-skeleton structure of three monomeric units of the addition polymer that results from the polymerization of acetylene, \(\mathrm{HC} \equiv \mathrm{CH}\). *b. There are two possible stereoisomers of polyacetylene. Describe the two isomeric forms.

Why is benzene a planar molecule?

Why are aromatic molecules stable?

Do tetramethylbenzene and pentamethylbenzene have constitutional isomers?

Draw all the constitutional isomers of trimethylbenzene.

Calculate the fuel values of gaseous benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) and ethylene gas \(\left(\mathrm{C}_{2} \mathrm{H}_{4}\right) .\) Does one mole of benzene have a higher or lower fuel value than three moles of ethylene?

Does one mole of gaseous benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) have a higher or lower fuel value than three moles of acetylene gas \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right) ?\)

Explain why methylamine (CH \(_{3} \mathrm{NH}_{2}\) ) is more soluble in water than butylamine \(\left[\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{NH}_{2}\right]\)

Renewable Energy Bacteria of the genus Metbanosarcina convert amines to methane. Their action helps make methane a renewable energy source. Determine the estandard enthalpy of the following reaction from the appropriate standard enthalpies of formation $$\left(\Delta H_{\mathrm{f}, \mathrm{CH}, \mathrm{NH}_{2}}^{\circ}=-23.0 \mathrm{kJ} / \mathrm{mol}\right)$$ $$4 \mathrm{CH}_{3} \mathrm{NH}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow 3 \mathrm{CH}_{4}(g)+\mathrm{CO}_{2}(g)+4 \mathrm{NH}_{3}(g)$$

Methylamine is a weak base. a. Use information in Appendix 5 to sketch the titration curve for the titration of \(125 \mathrm{mL}\) of a \(0.015 M\) solution of methylamine with \(0.100 M\) HCl. b. Label the curve with the \(\mathrm{pH}\) of the analyte solution, the \(\mathrm{p} K_{\mathrm{a}}\) of the analyte, and with the \(\mathrm{pH}\) and titrant volumes halfway to the equivalence point and at the equivalence point. c. Draw the structures of the species present in the solution at the equivalence point.

The \(p K_{b}\) values in Appendix 5 tell us that methylamine is a stronger base than ammonia and that dimethylamine is even stronger. Use the differences in their molecular structures to explain this trend in the strengths of these three bases.

Would you expect the fuel value of alcohols to increase or decrease as the number of carbon atoms in the alcohol increases?

Why do ethers typically boil at lower temperatures than alcohols with the same molecular formula?

Clean Skin Disposable wipes used to clean the skin prior to getting an immunization shot contain ethanol. After wiping your arm, your skin feels cold. Why?

Explain why carboxylic acids tend to be more soluble in water than aldehydes with the same number of carbon

Can we use combustion analysis to distinguish between ketones and aldehydes with the same number of carbon atoms?

Can we use combustion analysis to distinguish between ethers and ketones with the same number of carbon atoms?

What distinguishes an amine from an amide?

Explain why nylon reacts with acid, whereas polyethylene is inert toward acid.

Consult tables of thermochemical data in Appendix 4 for any values you may need to solve Problems 19.111 through 19.114 Calculate \(\Delta H_{\mathrm{mn}}^{\circ}\) for the following reactions of methanogenic bacteria, given $$\Delta H_{f, \mathrm{HCOOH}}^{\circ}=-425.0 \mathrm{kJ} / \mathrm{mol}$$ (1) \(\quad \mathrm{CH}_{3} \mathrm{COOH}(\ell) \rightarrow \mathrm{CH}_{4}(g)+\mathrm{CO}_{2}(g)\) (2) \(4 \mathrm{HCOOH}(\ell) \rightarrow \mathrm{CH}_{4}(g)+3 \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(\ell)\)

Consult tables of thermochemical data in Appendix 4 for any values you may need to solve Problems 19.111 through 19.114 Calculate \(\Delta H_{\mathrm{mn}}^{\circ}\) for the following reactions of methanogenic bacteria: (1) \(4 \mathrm{H}_{2}(g)+\mathrm{CO}_{2}(g) \rightarrow \mathrm{CH}_{4}(g)+2 \mathrm{H}_{2} \mathrm{O}(\ell)\) (2) \(\quad 4 \mathrm{CH}_{3} \mathrm{OH}(\ell) \rightarrow 3 \mathrm{CH}_{4}(g)+\mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(\ell)\)

Can all of the terms enantiomer, achiral, and optically active be used to describe a single compound? Explain.

Could a racemic mixture be distinguished from an achiral compound based on optical activity? Explain your answer.