Chemistry Reference
In-Depth Information
Because the hydrocarbon portion of an alkane or aromatic hydrocarbon is rel-
atively inert, the atoms of the other elements form the centers of reaction. The
hydrocarbon portion is termed a
radical
and is often represented by the symbol
R. The radical is essentially the parent hydrocarbon with a hydrogen atom
removed. The reactive portion of the molecule, containing the other element(s), is
called the
functional group.
Radicals are named just like side chains (see Section
20.2): The name of the parent hydrocarbon has its ending changed to
-yl.
How-
ever, the radical derived from benzene, is called the
phenyl rad-
ical.
Radicals derived from alkanes are called
alkyl radicals.
(A radical may be a
hydrogen atom in some classes containing carbon atoms in the functional group.)
Table 20.3
Total Bond
Orders of Atoms in Uncharged
Organic Molecules
Atom
Total Bond Order
C
4
H
1
C
6
H
5
¬
,
C
6
H
6
,
O
2
S
2
N
3
P
3
EXAMPLE 20.12
X*
1
*X refers to any halogen atom: F, Cl, Br,
or I. Except for hydrogen, the total bond
order of each element in the table is
8 minus its group number.
What are the names of the radicals formed when a hydrogen atom is removed
from one end of each of the first four unbranched alkanes? (See Table 20.1 if
necessary.)
Solution
The names are methyl, ethyl, propyl, and butyl, respectively.
Practice Problem 20.12
What are the names of the radicals formed
from the unbranched alkanes with nine and ten carbon atoms?
The subsections that follow briefly describe nine different classes of organic
compounds: organic halides, alcohols, ethers, aldehydes, ketones, acids, esters,
amines, and amides.
Organic Halides
Organic halide
is a general term that refers to any fluoride, chloride, bromide,
or iodide of a hydrocarbon. The halogen atom is bonded with a single covalent
bond to one carbon atom. The symbol X is often used to represent any one of
the halogen atoms: F, Cl, Br, or I. Organic halides may be produced by the reac-
tion of the elemental halogen and a hydrocarbon or by the reaction of a hydro-
gen halide and an unsaturated hydrocarbon, among other methods:
Heat
X
2
CH
4
¡
CH
3
X
HX
(X
F, Cl, Br, or I)
HX
CH
2
“
CH
2
¡
CH
3
CH
2
X
Reaction of excess halogen with an alkane can result in replacement of
more than one hydrogen atom:
2 X
2
CH
4
£ CH
2
X
2
2 HX
3 X
2
CH
4
£ CHX
3
3 HX
4 X
2
CH
4
£ CX
4
4 HX
Chloroform, and carbon tetrachloride, are familiar products of the
chlorination of methane. Halogenated hydrocarbons are intermediates in the
production of many other types of organic compounds.
CHCl
3
,
CCl
4
,
