# 2.E: Structural Organic Chemistry (Exercises)

Exercise 2-1 Draw the Lewis electron-pair structure of 2-propanone (acetone) clearly showing the bonding and nonbonding electron pairs in the valence shell of each atom. Draw structural formulas for other compounds having the composition $$\ce{C_3H_6O}$$ that possess

a. an aldehyde function.
b. an ether function in a ring.
c. an alcohol function and a double bond.
d. an alcohol function and a ring.

Exercise 2-2 Classify each of the following reactions as a substitution, addition, elimination, rearrangement, oxidation-reduction, or acid-base proton-transfer reaction:

a. $$\ce{CH_3COOH} + \ce{CH_3NH_2} \rightarrow \ce{CH_3CO} \overset{\ominus}{\ce{O}} + \ce{CH_3} \overset{\oplus}{\ce{N}} \ce{H_3}$$
b. $$\ce{C_6H_6} + \ce{Br_2} \rightarrow \ce{C_6H_5Br} + \ce{HBr}$$
c. $$\ce{CH_2=CH_2} + \ce{H_2O_2} \rightarrow \ce{HOCH_2CH_2OH}$$
d. $$\ce{CH_3COOCH_3} + \ce{NH_3} \rightarrow \ce{CH_3CONH_2} + \ce{CH_3OH}$$
e. $$\ce{CH_2=CH-CH_2-CH=CH_2} \rightarrow \ce{CH_3-CH=CH-CH=CH_2}$$
f.
g. $$\ce{ClCH_2CH_2Cl} + \ce{KOH} \rightarrow \ce{CH_2=CHCl} + \ce{KCl} + \ce{H_2O}$$
h. $$\ce{CH_3C \equiv} \overset{\ominus}{\ce{C}} \colon \overset{\oplus}{\ce{Na}} + \ce{CH_3OH} \rightarrow \ce{CH_3C \equiv CH} + \overset{\oplus}{\ce{Na}} \overset{\ominus}{\ce{O}} \ce{CH_3}$$
i. $$\ce{CH_3Cl} + \overset{\oplus}{\ce{Na}} \overset{\ominus}{\ce{O}} \ce{CH_3} \rightarrow \ce{CH_3OCH_3} + \overset{\oplus}{\ce{Na}} \overset{\ominus}{\ce{Cl}}$$

Exercise 2-3 Write a balanced equation for the complete combustion of benzene, $$\ce{C_6H_6}$$, to $$\ce{CO_2}$$ and $$\ce{H_2O}$$, and for the incomplete combustion of benzene to $$\ce{CO}$$ and $$\ce{H_2O}$$.

Exercise 2-4 How many grams of bromine will react by addition with (a) $$20 \: \text{g}$$ of ethene (b) $$20 \: \text{g}$$ of ethyne?

Exercise 2-5 Write balanced equations for the reactions of (a) metallic sodium with water, (b) metallic sodium with methanol, (c) sodium hydride with water, and (d) sodium hydride with ethanol.

Exercise 2-6 Write balanced equations for the reactions of (a) ammonia with sulfuric acid, (b) $$\ce{CH_3CH_2NH_2}$$ with sulfuric acid, (c) sodium hydroxide with ammonium chloride, and (d) sodium hydroxide with $$\ce{CH_3CH_2} \overset{\oplus}{\ce{N}} \ce{H_3} \overset{\ominus}{\ce{Cl}}$$.

Exercise 2-7 Draw structural formulas of the type

representing each of the required number of isomers for the following formulas. Be sure to use the normal valences for all of the atoms. Table 2-2 will be helpful to indicate possible structural types of various isomers.

a. $$\ce{C_5H_{12}}$$ (three)
b. $$\ce{C_3H_4Br_2}$$ (four)
c. $$\ce{C_2H_4O}$$ (three)
d. $$\ce{C_4H_8}$$ (four)
e. $$\ce{C_3H_9N}$$ (four)
f. $$\ce{C_3H_5Cl}$$ (at least three)
g. $$\ce{C_6H_6}$$ (at least five; more than 100 can be written!)
h. $$\ce{C_2H_4O_2}$$ (at least four)
i. $$\ce{C_3H_4O}$$ (at least three)
j. $$\ce{C_2H_3N}$$ (at least three)

Exercise 2-8 Draw Lewis electron-pair structures for the following substances whose structural formulas are given. Use distinct, correctly placed dots for the electrons and show both the bonding and nonbonding pairs. Mark all atoms that are not neutral with charges of the proper sign.

a. propane, $$\ce{CH_3CH_2CH_3}$$
b. methylcyclopropane, $$\ce{(CH_2)_2CHCH_3}$$
c. propadiene, $$\ce{CH_2=C=CH_2}$$
d. propyne, $$\ce{HC \equiv CCH_3}$$
e. benzene, $$\ce{C_6H_6}$$
f. tetrafluoroethene, $$\ce{F_2C=CF_2}$$
g. methoxymethane, $$\ce{CH_3OCH_3}$$
h. ethanal, $$\ce{CH_3CHO}$$
i. ethanoic acid, $$\ce{CH_3CO_2H}$$
j. benzenamine, $$\ce{C_6H_5NH_2}$$
k. nitromethane, $$\ce{CH_3NO_2}$$
l. benzenecarbonitrile, $$\ce{C_6H_5C \equiv N}$$

Exercise 2-9 Write an expanded structural formula with a line for each bond for each of the following substances which are represented by a condensed formula:

a. $$\ce{CH_3CH(CH_3)_2}$$
b. $$\ce{CH_3CCCH_3}$$
c. $$\ce{(CH_2)_4}$$
d. $$\ce{CH_2CHCCH}$$
e. $$\ce{CH_3CONHCH_3}$$
f. $$\ce{CH_3CO_2C_2H_5}$$
g. $$\ce{CH_2CHCHO}$$
h. $$\ce{C_6H_5NO_2}$$
i. $$\ce{C_2H_5CN}$$
j. $$\ce{(CH_3O)_2CO}$$

Exercise 2-10 Free rotation generally occurs around $$\ce{C-C}$$ single bonds (see Section 1-1E). Thus the following structural formulas are of the same compound, 2,3-dimethylbutane, because rotation about the central $$\ce{C-C}$$ bond makes the structures identical:

For the following structural formulas, determine which represent the same compound and which do not.

a.

b.

c.

d.

e.

Exercise 2-11 Write all the structural formulas you can for the different covalent isomers of the following molecular formulas. All the atoms should have their normal valences (i.e., monovalent for hydrogen and halogens, divalent for oxygen, trivalent for nitrogen, and tetravalent for carbon).

a. $$\ce{C_3H_6}$$ (two)
b. $$\ce{C_3H_4}$$ (three)
c. $$\ce{C_2H_4O}$$ (three)
d. $$\ce{C_2H_4ClF}$$ (two)
e. $$\ce{C_3H_9N}$$ (four)
f. $$\ce{C_4H_9Cl}$$ (four)

Exercise 2-12 With reference to Table 2-2 in necessary, draw structural formulas that satisfy the following descriptions:

a. three position isomers of $$\ce{C_2H_4O_2}$$ with a carbonyl group $$\left( \ce{-C=O} \right)$$.
b. four position isomers of $$\ce{C_4H_{10}O}$$ with a hydroxyl group $$\left( \ce{-OH} \right)$$.
c. a compound of formula $$\ce{C_5H_{12}}$$ that would have all its hydrogens located in chemically identical positions. (Chemically identical means that if one were to substitute a bromine for any one of the hydrogens, the same monobromo compound would be formed.)
d. a compound of formula $$\ce{C_3H_7ON}$$ with two chemically different methyl groups and an amide function.
e. two compounds of formula $$\ce{C_4H_8O}$$, one of which is an aldehyde, the other a ketone.
f. two compounds of formula $$\ce{C_3H_6O_2}$$, one of which is a carboxylic acid, the other a carboxylic ester.
g. two compounds of formula $$\ce{C_3H_4O}$$, both with $$\ce{C=O}$$ groups.
h. a compound of formula $$\ce{C_9H_{12}N_2}$$ in which all the hydrogens are located in chemically identical positions and both nitrogens are present as nitrile functions.

## Contributors

• John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."