Chapter 24

Which of these molecules is unsaturated? [Section 24.3\(]\)

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?

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?

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 the name or condensed structural formula, as appropriate:(c) 2 -methylheptane (d) 4 -ethyl- 2,3 -dimethyloctane (e) 1,2 -dimethylcyclohexane

Give the name or condensed structural formula, appropriate: (a) CCCCC(C)CC(C)C (b) 2,2 -dimethylpentane (c) 4 -ethyl-1,1-dimethylcyclohexane (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{3}\) (e) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{C}_{2} \mathrm{H}_{5}\right) \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\)

Give the name or condensed structural formula, as appropriate: (a) 3 -phenylpentane (b) 2,3 - dimethythexane (c) 2 -ethyl-2-methylhepane (d) CCCCCCCCCC(C)C(C)C (e) CC1CCC1

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

(a) Why are alkanes said to be saturated? (b) Is \(\mathrm{C}_{4} \mathrm{H}_{6}\) a saturated hydrocarbon? Why or why not?

(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. 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?

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.

Name or write the condensed structural formula for the fol- lowing compounds: (a) trans -2 -pentene (b) 2,5 -dimethyl-4-octene (c) CCC(C)=CCC(C)C (d) Brc1ccc(Br)cc1 (e) C#CC(C)(CC)CC

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

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 -dichloro-1-butene, (b) 2,4 -dichloro-2butene, (c) 1,4 -dichlorobenzene, \((\) d) 4,5 -dimethyl- 2 -pentyne.

(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 para-dichlorobenzene 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).

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 \(-a l\) 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) 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.

Would you expect pure acetic acid to be a strongly hydrogenbonded substance? How do the melting and boiling points of the substance \(\left(16.7^{\circ} \mathrm{C}\right.\) and \(\left.118^{\circ} \mathrm{C}\right)\) support your answer?

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) 2 -ethyl-1-hexanol, (b) methyl phenyl ketone, (c) para-bromobenzoic acid, (d) ethyl butyl 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 acids' 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) Draw the condensed structure of the tripeptide Gly-GlyHis. (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.

(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.