Chapter 25

Which of the following compounds is capable of possessing isomerism? In each case where isomerism is possible, identify the type or types of isomerism.

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

Are carbon monoxide or ammonia considered organic molecules? Why or why not?

(a) What is the difference between a straight-chain and branched-chain alkane? (b) What is the difference between an alkane and an alkyl group? (c) Why are alkanes said to be saturated? (d) Give an example of an unsaturated molecule.

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?

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. Which are saturated and which are unsaturated hydrocarbons?

Give the molecular formula of a cyclic alkane, a cyclic alkene, a linear alkyne, and an aromatic hydrocarbon that in each case contains six carbon atoms. Which are saturated and which are unsaturated hydrocarbons?

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. (Hint: "di" means "two".)

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

Write the condensed structural formulas for as many alkenes and alkynes as you can think of that 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.

What are the characteristic hybrid orbitals employed by (a) carbon in an alkane, (b) carbon in a double bond in an alkene, (c) carbon in the benzene ring, (d) carbon in a triple bond in an alkyne?

What are the approximate bond angles (a) about carbon in an alkane, \((b)\) about a doubly bonded carbon atom in an alkene, (c) about a triply bonded carbon atom in an alkyne?

Why is geometric isomerism possible for alkenes, but not for alkanes and alkynes?

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

Indicate whether each of the following molecules is capable of geometrical (cis-trans) isomerism. For those that are, draw the structures: (a) 1,1-dichloro1-butene, (b) 2,4 -dichloro-2-butene, (c) 1,4 -dichlorobenzene, (d) 4,5-dimethyl-2-pentyne.

Draw all the distinct geometric isomers of 2,4 -hexadiene.

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

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

(a) What is the difference between a substitution reaction and an addition reaction? Which one is commonly observed with alkenes, and which one with aromatic hydrocarbons? (b) Using condensed structural formulas, write the balanced equation for the addition reaction of 2 -pentene with \(\mathrm{Br}_{2}\) and name the resulting compound. (c) Write a balanced chemical equation for the substitution reaction of \(\mathrm{Cl}_{2}\) with benzene to make paradichlorobenzene in the presence of \(\mathrm{FeCl}_{3}\) as a catalyst.

Using condensed structural formulas, write a balanced chemical equation for each of the following reactions: (a) hydrogenation of cyclohexene; (b) addition of \(\mathrm{H}_{2} \mathrm{O}\) to trans-2-pentene using \(\mathrm{H}_{2} \mathrm{SO}_{4}\) as a catalyst (two products); (c) reaction of 2-chloropropane with benzene in the presence of \(\mathrm{AlCl}_{3}\).

(a) When cyclopropane is treated with HI, 1-iodopropane is formed. A similar type of reaction does not occur with cyclopentane or cyclohexane. How do you account for the reactivity of cyclopropane? (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, 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.

Give the structural formula 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).

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-pentanone, (c) 3methyl-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.

Acetic anhydride is formed from acetic acid in a condensation reaction that involves the removal of a molecule of water from between two acetic acid molecules. 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) 3,3-dichlorobutyraldehyde, (b) methyl phenyl ketone, (c) para-bromobenzoic acid, (d) methyl-trans-2-butenyl ether, (e) \(N, N\) -dimethylbenzamide.

Draw the structure for 2-bromo-2-chloro-3-methylpentane, and indicate any chiral carbons in the molecule.

Does 3-chloro-3-methylhexane have optical isomers? Why or why not?

(a) What is an \(\alpha\) -amino acid? (b) How do amino acids react to form proteins? (c) Draw the bond that links amino acids together in proteins. What is this called?

What properties of the side chains (R groups) of amino acids are important in affecting the amino acid's overall biochemical behavior? Give examples to illustrate your reply.

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

(a) Describe the primary, secondary, and tertiary structures of proteins. (b) Quaternary structures of proteins arise if two or more smaller polypeptides or proteins associate with each other to make an overall much larger protein structure. The association is due to the same hydrogen bonding, electrostatic, and dispersion forces we have seen before. Hemoglobin, the protein used to transport oxygen molecules in our blood, is an example of a protein that has quaternary structure. Hemoglobin is a tetramer; it is made of four smaller polypeptides, two "alphas" and two "betas." (These names do not imply anything about the number of alpha helices or beta sheets in the individual polypeptides.) What kind of experiments would provide sound evidence that hemoglobin exists as a tetramer and not as one enormous polypeptide chain? You may need to look into the chemical literature to discover techniques that chemists and biochemists use to make these decisions.

What is the difference between the \(\alpha\) helix and \(\beta\) sheet secondary structures in proteins?

In your own words, define the following terms: (a) carbohydrate, (b) monosaccharide, (c) disaccharide, (d) polysaccharide.

What is the difference between \(\alpha\) -glucose and \(\beta\) -glucose? Show the condensation of two glucose molecules to form a disaccharide with an \(\alpha\) linkage; with a \(\beta\) linkage.

What is the empirical formula of glycogen? What is the unit that forms the basis of the glycogen polymer? What form of linkage joins these monomeric units?

The structural formula for the linear form of D-mannose is: (a) How many chiral carbons are present in the molecule? (b) Draw the structure of the six-member-ring form of this sugar.

The structural formula for the linear form of galactose is: (a) How many chiral carbons are present in the molecule? (b) Draw the structure of the six-member-ring form of this sugar.

Describe the chemical structures of lipids and phospholipids. Why can phospholipids form a bilayer in water?

Adenine and guanine are members of a class of molecules known as purines; they have two rings in their structure. Thymine and cytosine, on the other hand, are pyrimidines, and have only one ring in their structure. Predict which have larger dispersion forces in aqueous solution, the purines or the pyrimidines.

When samples of double-stranded DNA are analyzed, the quantity of adenine present equals that of thymine. Similarly, the quantity of guanine equals that of cytosine. Explain the significance of these observations.