Alcohols, alkyl halides and ethers

1. Alcohol, Alkyl Halides and Ethers

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:
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.`

5. Alcohols containing two hydroxyl groups are called glycols. They have both common names and IUPAC names.
Physical properties

6. a. Industrial source
Preparation
b. Laboratory
1. Oxymercuration-demercuration

7. 2. Hydroboration-oxidation
3. Grignard synthesis

8. 4. Hydrolysis of alkyl halides
5. Hydroxyiation of alkenes

9. H.W/ Give structures of compounds A through D in the following industrially importantsynthesis.
Reactions
C-OH BOND CLEAVAGE
1. Reaction with hydrogen halides

10. 2. Reaction with phosphorus trihalides
3. Dehydration

11. O--H BOND CLEAVAGE
4. Reaction as acids: reaction with active metals
5. Ester formation

12. 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:

13. 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.

14. a. Industrial source
Preparation
Many fluorine compounds are not prepared by direct fluorination, but rather by replacement of chlorine, using
inorganic fluorides:

15. b. Laboratory
In the laboratory alkyl halides are most often prepared by the methods outlined below.
1. From alcohols
Examples:
2. Halogenation of certain hydrocarbons.

16. 3. Addition of hydrogen halides to alkenes
4. Addition of halogens to alkenes and alkynes
5. Halide exchange

17. Reactions
2. Dehydrohalogenation: elimination
3. Preparation of Grignard reagent.
4. Reduction

18. 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:

19. 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).
Physical properties of ethers

20. Preparation
a. Industrial sources of ethers. Dehydration of alcohols
Preparation of ethers
1. Williamson synthesis
2. Alkoxymercuration-demercuration.

21. 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 :

22. 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: