Chemistry Reference
In-Depth Information
Table 2.6
Selected Common Alkyl Halides
Formula
Common Name
IUPAC Name
B.P. (°C)
CH
3
Cl
Methyl chloride
Chloromethane
−24
CH
3
Br
Methyl bromide
Bromomethane
5
CH
3
I
Methyl iodide
Iodomethane
42
CH
2
Cl
2
Methylene chloride
Dichloromethane
40
(CH
3
)
2
CHBr
Isopropyl bromide
2-Bromopropane
60
(CH
3
)
3
CCl
tert
-Butyl chloride
2-Chloro-2-methylpropane
51
IUPAC, International Union of Pure and Applied Chemistry.
This is the first functional class that has a heteroatom. The relatively high elec-
tronegativity of the halogens gives a highly polar covalent bond (Inductive
effect, Chapter 1). This does not change the
sp
3
hybrid state or tetrahedral shape
of the carbon, but it does give a reactive site that controls the chemistry of alkyl
halides.
Table 2.6
shows the IUPAC naming of alkyl halides that come from the
hydrocarbon parents, with the halogen atom treated as a substituent.
FIGURE 2.7
Classification of 1°, 2°, and 3° alkyl halides.
Figure 2.7
shows that, similar to alkanes, alkyl halides and alcohols can be clas-
sified as 1° (primary), 2° (secondary), and 3° (tertiary). Note that the nominal
oxidation number of the carbon bonded to the halogen changes from −1 in pri-
mary to +1 in tertiary. This change explains why there is a difference in reactivity
across the range of alkyl halides.
2.6 ALCOHOLS, PHENOLS, ETHERS, AND THEIR
SULFUR EQUIVALENTS (THIOLS AND
THIOETHERS)
Figure 2.8
shows that all of these functional classes have a general structure in
which carbon is connected by a single bond to one electronegative heteroatom.
This gives a polar single bond between the heteroatom and the saturated
sp
3
-
hybridized carbon. The nominal oxidation numbers are the same as for alkyl
halides.
The heteroatom is also
sp
3
-hybridized and the tetrahedral shape of the func-
tional group is well defined. It is common not to show the two lone pairs of
electrons on the oxygen and sulfur. However, we must not forget the lone pairs,
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