MORISSON   Organic Chemistry

MORISSON Organic Chemistry


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ether the structure represented b t 11. As we shall see, the differences 
in physical and chemical properties of thesb two compounds can readily be 
accounted for on the basis of the difference in structure. 
I I 
H H 
I I 
H H 
I I I 
Ethyl alcoho! Dimethyljether 
Dijkrmt compounds that have the same molecular formula are called isomers 
(Greek: isos, equal; metos, part). They contain the same numbers of the same 
kinds of atoms, but the atoms are attached to one another in different ways. 
Isomers are different compounds because they have different moleculdr structures. 
CHAP. 1 PROBLEMS 37 
This difference in molecular structure gives rise to a difference in properties; 
it is the difference 41 propprties which tells us that we .are dealing with different 
compounds. In some case? the difference in structure-and hence the difference 
in properties-is so marked that the isomers are assigned to different chemical 
families, as, for example, ethyl alcohol and dimethyl ether. In other cases the 
difference in structure is so subtle that it can be described only in terms of three- 
dimensional models. Other kinds of isomerism fall between these two extremes. 
PROBLEMS 
1. Which of the following would you expect to be ionic, and which non-ionic? Give a 
simple electronic structure (Sec. 1.3) for each, showing only valence shell electrons. 
(a) MgCIz (c) ICl (e) KClO, (g) Bas04 
(b) CH2Cl2 (d) NaOCl (f) SiCl, (h) CH3NH2 
2. Give a likely simple electronic structure (Sec. 1.3) for each of the following, assuming 
them to be completely covalent. Assume that every atom (except hydrogen, of course) has a 
complete octet, and that two atoms may share more than one pair of electrons. 
(a) N2H4 (d) COCI, (g) co32" (3 CH20 
(b) H2S04 (e) HONO (h) C2H4 (k) CH202 
(c) HS0,- (f) NO2- (9 C2H2 (1) c3Hs 
3. What shape would you expect each of the following to have? 
(a) (CH3)3B (e) tha amide ion, NH2- 
(b) the methyl aniofi, CH3: - (f) dimethyl ether 
(c) the methyl cation, CH3+ .(g) the fluoroborate ion, BF,- 
( 4 HIS (h) (CH3)3N 
4. In many complex ions, e.g., CO(NH~),~+, the bonds to the central atom can be 
pictured as utilizing six equivalent sp3d2 (ord2sp3) hybrid orbitals. On the basis of maximum 
separation of orbitals, what geometry would you expect these complexes to have? 
5. Indicate the direction of the dipole hnoment, ifany, th'at you would expect for each 
of the following: 
(a) HBr ( 4 CH2C12 (g) dimethyl ether 
(b) IC1 (e) CHCI, (h), (CH3)3N 
(c) 12 (f) CH30H (i) CF2C12 
About Working Problems 
Working problems is a necessary part of your work for two reasons: it will 
guide your study i d the right direction, and, after you have studied a particular 
chapter, it will show whether or not you have reached your destination. 
You should work all the problems that you can; you should get help with the 
ones you cannot work yourself. The first problems in each set are easy, but provide 
the drill in drawing formulas, naming compounds, and using reactions that even 
the best student needs. The later problems in each set are the kind encountered by 
practicing chemists, a1:d test your ability to use what you have learned. 
You can check your answers to many of the problems in the answer section in 
the back of the book, and by use of the index. You will find more complete answers 
to all the problems, together with suggestions about how to approach each type of 
problem, in the-study Guide. 
38 STRUCTURE AND PROPERTIES CHAP. 1 
6. (a) Although HCl (1.27 A) is a longgr molecule than HF (0.92 A), it has a smaller 
dipole moment (1.03 debye compared to 1.75 debye). How do you account for this fact? 
(b) The dipole moment of CH3F is 1.847 debyq, and of CD3F, 1.858 debye. (D is 'H, 
deuterium.) Compared with the C-H bond, what is the direction of the C-D dipole? 
7. What do the differences in properties between lithium acetylacetonate (m.p. very 
high, insoluble in chloroform) and beryllium atetylacetonate (m.p. 108 OC, b.p. 270 OC, 
soluble in chloroform) suggest about their structures? 
8. n-Butyl alcohol (b.p. 118 OC) has a much higher boiling point than its isomer diethyl 
ether (b.p. 35 "C), yet both compounds show the same solubility (8 g per 100 g) in water. 
H H H H H H H H 
I I I L 
H-C-C-C- -0-H 
I I I I 
H-C-C-0-C-C-H 
I I I I 
H H H H 
I I I I 
H H H H 
n-Butyl alcohol Diethyl ether 
How do you account for these facts? 
9. Rewrite the following equations to show the Lowry-Brmsted acids and bases 
actually involved. Label each as stronger or weaker, as in Sec. 1.22. 
(a) HCl(aq) + NaHC03(aq) t- H2C03 + NaCl 
(b) NaOH(aq) + NaHC03(aq) c- NazC03 + HzO 
( 4 NH3(aq) + HN03(aq) t- NH4N03(aq) 
(d) NaCN(aq) .-f HCN(aq) + NaOH(aq) 
(e) NaH + H 2 0 - Hz + NaOH 
(f) CaC2 + HzO - Ca(OH)2 + C2Hz 
Calcium Acetylene 
carbide 
10. What is the Lowry-Brmsted acid in (a) HCl dissolved in water; (b) HCI (un- 
ionized) dissolved in benzene? (c) Which solution is the more strongly acidic? 
11. Account for the fact that nearly every organic compound containing oxygen 
dissolves in cold concentrated sulfuric acid to yield a solution from which the compound 
can be recovered by dilution with water. 
12. How might you account for the following orders of acidity? Be as specific as you 
can. 
HC104 > HC102 > HC10 a'nd H2SO4 > H2S03 
13. For each of the following molecular formulas, draw structures like those in Sec. 
1.23 (a line for each shared pair, of electrons) for all the isomers you can think of. Assume 
that every atom (except hydrogen) has a complete octet, and that two atoms may share more 
than one pair of electrons. 
(a) C2H7N c4Hl0 (e) C3H8O 
@I C3H8 ( 4 C3H7C1 (f) C2H40 
14. In ordinary distillation, a liquid is placed in a flask and heated, at ordinary or 
reduced pressure, until distillation is complete. In the modification calledjlash distillation, 
the liquid is dripped into a heated flask at the same rate that it distills out, so that there is 
little liquid in the flask at any time. What advantage might flash distillation have, and under 
what conditions might you use it? 
Chapter
Methane
Energy of Activation.
Transition State
2.1 Hydrocarbons
Certain organic compounds contain only two elements, hydrogen and carbon,
and hence are known as hydrocarbons. On the basis of structure, hydrocarbons
are divided into two main classes, aliphatic and aromatic. Aliphatic hydrocarbons
are further divided into families: alkanes, alkenes, alkynes, and their cyclic ana-
logs (cycloalkanes, etc.). We shall take up these families in the order given.
Hydrocarbons
Aliphatic Aromatic
Alkanes Alkenes Alkynes Cyclic
aliphatic
The simplest member of the alkane family and, indeed, one of the simplest of
all organic compounds is methane, CH4 . We shall sUidy this single compound at
some length, since most of what we learn about it can be carried over with minor
modifications to any alkane.
2.2 Structure of methane
As we discussed in the previous chapter (Sec. 1.11), each of the four hydrogen
atoms is bonded to the carbon atom by a covalent bond, that is, by the sharing of a
pair of electrons. When carbon is bonded to four other atoms, its bonding orbitals
(sp* orbitals, formed by the mixing of one s and three/? orbitals) are directed to the
corners of a tetrahedron (Fig. 2. la). This tetrahedral arrangement is the one that
permits the orbitals to be as far apart as possible. For each of these orbitals to
40 METHANE CHAP. 2 
2.2 structure of methane 
As we discussed in the previous chapter (Sec. 1.1 l), each of the four hydrogen 
atoms is bonded to the carbon atom by a covalent bond, that is, by the sharing of 
a pair of electrons. When carbon is bonded to four other atoms, its bonding orbitals 
(sp3 orbitals, formed by the mixing of ones and threep orbitals)