2. Alcohols
Structure
Alcohols are compounds of the general formula ROH, where R is any alkyl
or substituted alkyl group. The group may be primary, secondary, or tertiary;
it may be open-chain or cyclic; it may contain a double bond, a halogen
atom, or an aromatic ring. For example:
3. All alcohols- contain the hydroxyl (-OH) group, which, as the functional group, determines the
properties characteristic of this family. Variations in structure of the R group may affect the rate at
which the alcohol undergoes certain reactions, and even, in a few cases, may affect the kind of
reaction. Compounds in which the hydroxyl group is attached directly to an aromatic ring are not
alcohols; they are phenols, and differ so markedly from the alcohols that we shall consider them
in a separate chapter.
An alcohol is classified according to the kind of carbon that bears the OH group:
Nomenclature
Alcohols are named by three different systems. For the simpler alcohols the common names,
which we have already encountered, are most often used. These consist simply of the name of the
alkyl group followed by the word alcohol. For example:
4. We should notice that similar names do not always mean the same classification; for example,
isopropyl alcohol is a secondary alcohol, whereas isobutyl alcohol is a primary alcohol. It is
sometimes convenient to name alcohols by the carbinol system. According to this system,
alcohols are considered to be derived from methyl alcohol, CH3OH, by the replacement of one or
more hydrogen atoms by other groups. We simply name the groups attached to the carbon bearing
the OH and then add the suffix -carbinol to include the C-OH portion:
5. Finally, there is the most versatile system, the IUPAC. The rules are:
(1) Select as the parent structure the longest continuous carbon chain that contains the OH group
then consider the compound to have been derived from this structure by replacement of hydrogen
by various groups. The parent structure is known as ethanol, propanol, butanol, etc., depending
upon the number of carbon atoms; each name is derived by replacing the terminal -e of the
corresponding alkane name by -ol.
(2) Indicate by a number the position of the OH group in the parent chain, generally using the
lowest possible number for this purpose.
(3) Indicate by numbers the positions of other groups attached to the parent chain.`
Alcohols containing two hydroxyl groups are called glycols. They have both common names and
IUPAC names.
10. H.W/ Give structures of compounds A through D in the following industrially important synthesis.
Reactions
C-OH BOND CLEAVAGE
1. Reaction with hydrogen halides
12. O--H BOND CLEAVAGE
4. Reaction as acids: reaction with active metals
5. Ester formation
13. Alkyl Halides
alkyl halides are all compounds of the general formula R-X, where R is any
simple alkyl or substituted alkyl group. For example:
14. Physical properties
In spite of their polarity, alkyl halides are insoluble in water, probably because of their inability to
form hydrogen bonds. They are soluble in the typical organic solvents. lodo, bromo, and
polychloro compounds are more dense than water.
15. a. Industrial source
Preparation
Many fluorine compounds are not prepared by direct fluorination, but rather by replacement of
chlorine, using inorganic fluorides:
16. In the laboratory alkyl halides are most often prepared by the methods outlined below.
b. Laboratory
1. From alcohols
2. Halogenation of certain hydrocarbons.
Examples:
17. 3. Addition of hydrogen halides to alkenes
4. Addition of halogens to alkenes and alkynes
5. Halide exchange
19. Ethers and Epoxides
Structure and nomenclature of ethers
Ethers are compounds of the general formula R -O R, Ar O R, or Ar-O Ar.
To name ethers we usually name the two groups that are attached to oxygen,
and follow these names by the word ether:
20. If one group has no simple name, the compound may be named as an alkoxy derivative:
The simplest aryl alkyl ether has the special name of anisole
If the two groups are identical, the ether is said to be symmetrical (e.g., ethyl ether, phenyl ether),
if different, unsymmetrical (e.g., methyl tert-butyl ether, anisole).
21. Physical properties of ethers
a. Industrial sources of ethers. Dehydration of alcohols
Preparation
23. Reactions of ethers. Cleavage by acids
Ethers are comparatively un reactive compounds. The ether linkage is quite stable toward bases,
oxidizing agents, and reducing agents. In so far as the ether linkage itself is concerned, ethers
undergo just one kind of reaction, cleavage by acids :
24. Cyclic Ethers
In their preparation and properties, most cyclic ethers are just like the ethers we have already
studied: the chemistry of the ether linkage is essentially the same whether it forms part of an open
chain or part of an aliphatic ring.
EPOXIDES
Preparation of epoxides
Epoxides are compounds containing the three-membered ring:
