Chapter 24

Indicate whether each statement is true or false. (a) Butane contains carbons that are \(s p^{2}\) hybridized. (b) Cyclohexane is another name for benzene. (c) The isopropyl group contains three \(s p^{3}\) -hybridized carbons. (d) Olefin is another name for alkyne.

Indicate whether each statement is true or false. (a) Pentane has a higher molar mass than hexane. (b) The longer the linear alkyl chain for straight- chain hydrocarbons, the higher the boiling point. (c) The local geometry around the alkyne group is linear. (d) Propane has two structural isomers.

Predict the ideal values for the bond angles about each carbon atom in the following molecule. Indicate the hybridization of orbitals for each carbon. $$\mathrm{CH}_{3} \mathrm{CCCH}_{2} \mathrm{COOH}$$

For each of the following hydrocarbons, state how many carbon atoms are in each molecule: \begin{equation}\begin{array}{l}{\text { (a) methane }} \\ {\text { (b) decane }} \\ {\text { (c) } 2 \text { -methylhexane }} \\ {\text { (d) neopentane }} \\ {\text { (e) acetylene }}\end{array}\end{equation}

True or false: The weaker a single bond in a molecule, the greater the chance it will be the site of a reaction (compared to stronger single bonds in the molecule).

Indicate whether each statement is true or false. (a) Alkanes do not contain any carbon-carbon multiple bonds. (b) Cyclobutane contains a four-membered ring. (c) Alkenes contain carbon-carbon triple bonds. (d) Alkynes contain carbon-carbon double bonds. (e) Pentane is a saturated hydrocarbon but 1-pentene is an unsaturated hydrocarbon. (f) Cyclohexane is an aromatic hydrocarbon. (g) The methyl group contains one less hydrogen atom than methane.

What structural features help us identify a compound as (a) an alkane, (b) a cycloalkane, (c) an alkene, (d) an alkyne, (e) a saturated hydrocarbon, (f) an aromatic hydrocarbon?

What is the octane number of a mixture that is 35\(\%\) heptane and 65\(\%\) isooctane?

Describe two ways in which the octane number of a gasoline consisting of alkanes can be increased.

\begin{equation}\begin{array}{l}{\text { (a) Is } \mathrm{C}_{4} \mathrm{H}_{6} \text { a saturated or unsaturated hydrocarbon? }} \\ {\text { (b) Are all alkynes unsaturated? }}\end{array}\end{equation}

(a) Is the compound \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\) saturated or unsaturated? Explain. (b) What is wrong with the formula \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{3} ?\)

Give the molecular formula of a hydrocarbon containing five carbon atoms that is (a) an alkane, (b) a cycloalkane, (c) an alkene, (d) an alkyne.

Give the molecular formula of a hydrocarbon containing five carbon atoms that is (a) an alkane, (b) a cycloalkane, (c) an alkene, (d) an alkyne.

Enediynes are a class of compounds that include some antibiotic drugs. Draw the structure of an "enediyne" fragment that contains six carbons in a row.

Give the general formula for any cyclic alkene, that is, a cyclic hydrocarbon with one double bond.

Write the condensed structural formulas for two alkenes and one alkyne that all have the molecular formula \(\mathrm{C}_{6} \mathrm{H}_{10}\) .

Draw all the possible noncyclic structural isomers of \(\mathrm{C}_{5} \mathrm{H}_{10}\) . Name each compound.

Name or write the condensed structural formula for the following compounds: \begin{equation}\begin{array}{l}{\text { (a) } 4 \text { -methyl-2-pentene }} \\\ {\text { (b) } \text {cis}-2,5 \text { -dimethyl-3-hexene }} \\ {\text { (c) ortho-dimethylbenzene }}\\\\{\text { (d) } \mathrm{HC}=\mathrm{CCH}_{2} \mathrm{CH}_{3}} \\ {\text { (e) } \text {trans}-\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}}\end{array}\end{equation}

Indicate whether each statement is true or false. (a) Two geometric isomers of pentane are \(n\)-pentane and neopentane. (b) Alkenes can have cis and trans isomers around the CC double bond. (c) Alkynes can have cis and trans isomers around the CC triple bond.

Draw all structural and geometric isomers of butene and name them.

Indicate whether each of the following molecules is capable of geometrical isomerism. For those that are, draw the structures: (a) \(1,1\) -dichloro-1-butene, (b) \(2,4\) -dichloro-2-butene, (c) \(1,4\) -dichlorobenzene, (d)\(4,4\)-dimethyl-2-pentyne.

Draw the three distinct geometric isomers of \(2,4\)-hexadiene.

(a) True or false: Alkenes undergo addition reactions and aromatic hydrocarbons undergo substitution reactions. (b) Using condensed structural formulas, write the balanced equation for the reaction of 2 -pentene with Br\(_{2}\) and name the resulting compound. Is this an addition or a substitution reaction? (c) Write a balanced chemical equation for the reaction of \(\mathrm{Cl}_{2}\) with benzene to make paradichlorobenzene in the presence of \(\mathrm{FeCl}_{3}\) as a catalyst. Is this an addition or a substitution reaction?

(a) When cyclopropane is treated with HI, 1 -i-iodopropane is formed. A similar type of reaction does not occur with cyclopentane or cyclohexane. Suggest an explanation for cyclopropane's reactivity. (b) Suggest a method of preparing ethylbenzene, starting with benzene and ethylene as the only organic reagents.

(a) One test for the presence of an alkene is to add a small amount of bromine, which is a red-brown liquid, and look for the disappearance of the red-brown color. This test does not work for detecting the presence of an aromatic hydrocarbon. Explain. (b) Write a series of reactions leading to para-bromoethylbenzene, beginning with benzene and using other reagents as needed. What isomeric side products might also be formed?

Describe the intermediate that is thought to form in the addition of a hydrogen halide to an alkene, using cyclohexene as the alkene in your description.

The molar heat of combustion of gaseous cyclopropane is \(-2089 \mathrm{kJ} / \mathrm{mol};\) that for gaseous cyclopentane is \(-3317 \mathrm{kJ} / \mathrm{mol} .\) Calculate the heat of combustion per \(\mathrm{CH}_{2}\) group in the two cases, and account for the difference.

Draw the molecular structure for (a) an aldehyde that is an isomer of acetone, (b) an ether that is an isomer of 1-propanol.

(a) Give the empirical formula and structural formula for a cyclic ether containing four carbon atoms in the ring. (b) Write the structural formula for a straight-chain compound that is a structural isomer of your answer to part (a).

The IUPAC name for a carboxylic acid is based on the name of the hydrocarbon with the same number of carbon atoms. The ending-oic is appended, as in ethanoic acid, which is the IUPAC name for acetic acid. Draw the structure of the following acids: (a) methanoic acid, (b) pentanoic acid, (c) 2-chloro-3-methyldecanoic acid.

Aldehydes and ketones can be named in a systematic way by counting the number of carbon atoms (including the carbonyl carbon) that they contain. The name of the aldehyde or ketone is based on the hydrocarbon with the same number of carbon atoms. The ending -al for aldehyde or -one for ketone is added as appropriate. Draw the structural formulas for the following aldehydes or ketones: (a) propanal, (b) 2-penta-none, (c) 3-methyl-2-butanone, (d) 2-methylbutanal.

Draw the condensed structure of the compounds formed by condensation reactions between (a) benzoic acid and ethanol, (b) ethanoic acid and methylamine, (c) acetic acid and phenol. Name the compound in each case.

Draw the condensed structures of the compounds formed from (a) butanoic acid and methanol, ( b) benzoic acid and 2-propanol, (c) propanoic acid and dimethylamine. Name the compound in each case.

Write a balanced chemical equation using condensed structural formulas for the saponification (base hydrolysis) of (a) methyl propionate, (b) phenyl acetate.

Write a balanced chemical equation using condensed structural formulas for (a) the formation of butyl propionate from the appropriate acid and alcohol, (b) the saponification (base hydrolysis) of methyl benzoate.

Pure acetic acid is a viscous liquid, with high melting and boiling points (\(16.7^{\circ} \mathrm{C}\) and \(118^{\circ} \mathrm{C}\)) compared to compounds of similar molecular weight. Suggest an explanation.

Acetic anhydride is formed from two acetic acid molecules, in a condensation reaction that involves the removal of a molecule of water. Write the chemical equation for this process, and show the structure of acetic anhydride.

Write the condensed structural formula for each of the following compounds: (a) 2-pentanol, (b) \(1,2\)-propanediol,(c) ethyl acetate, (d) diphenyl ketone, (e) methyl ethyl ether.

Write the condensed structural formula for each of the following compounds: (a) 2 -ethyl-1-hexanol, (b) methyl phenyl ketone, (c) para-bromobenzoic acid, (d) butyl ethyl ether, (e) \(N,N\)-dimethylbenzamide.

How many chiral carbons are in 2 -bromo-2-chloro-3-methylpentane? (a) \(0,(\mathbf{b}) 1,(\mathbf{c}) 2,(\mathbf{d}) 3,(\mathbf{e}) 4\) or more.

Is 3 -chloro-3-methylhexane chiral?

(a) Draw the chemical structure of a generic amino acid, using \(R\) for the side chain. (b) When amino acids react to form proteins, do they do so via substitution, addition, or condensation reactions? (c) Draw the bond that links amino acids together in proteins. What is this called?

Indicate whether each statement is true or false. (a) Tryptophan is an aromatic amino acid. (b) Lysine is positively charged at pH \(7 .(\mathbf{c})\) Asparagine has two amide bonds. (d) Isoleucine and leucine are enantiomers. (e) Valine is probably more water-soluble than arginine.

Write a chemical equation for the formation of methionyl-glycine from the constituent amino acids.

(a) Draw the condensed structure of the tripeptide Gly-Gly-His. (b) How many different tripeptides can be made from the amino acids glycine and histidine? Give the abbreviations for each of these tripeptides, using the three-letter and one-letter codes for the amino acids.

Indicate whether each statement is true or false. (a) The sequence of amino acids in a protein, from the amine end to the acid end, is called the primary structure of the protein. (b) Alpha helix and beta sheet structures are examples of quaternary protein structure. (c) It is impossible for more than one protein to bind to another and make a higher order structure.

Indicate whether each statement is true or false: (a) Disaccharides are a type of carbohydrate. (b) Sucrose is a monosaccharide. (c) All carbohydrates have the formula \(\mathrm{C}_{n} \mathrm{H}_{2 m} \mathrm{O}_{m} .\)

(a) Are \(\alpha\) -glucose and \(\beta\) -glucose enantiomers? (b) Show the condensation of two glucose molecules to form a disaccharide with an \(\alpha\) linkage. (c) Repeat part (b) but with a \(\beta\) linkage.

(a) What is the empirical formula of cellulose? (b) What is the monomer that forms the basis of the cellulose polymer? (c) What bond connects the monomer units in cellulose: amide, acid, ether, ester, or alcohol?

(a) What is the empirical formula of starch? (b) What is the monomer that forms the basis of the starch polymer? (c) What bond connects the monomer units in starch: amide, acid, ether, ester, or alcohol?