The physical, chemical and spectroscopic properties of alcohols are relative to it’s chemical structures. Alcohols are compounds of the general formula ROH, where R is any alkyl or substituted alkyl group. The simple ethers, ROR, do not have O-H bonds, and most of their reactions are limited to the substituent groups. Before turning to the specific chemistry of alcohols and ethers, we remind you that the naming alcohols and ethers is summarized in naming alcohols, phenols and Naming Ethers.
- 15.1: Prelude to Alcohols and Ethers
- All carbohydrates and their derivatives, including nucleic acids, have hydroxyl groups. Some amino acids, most steroids, many terpenes, and plant pigments have hydroxyl groups. These substances serve many diverse purposes for the support and maintenance of life. The reactions involving the hydrogens of alcoholic OH groups are expected to be similar to those of water, HOH, the simplest hydroxylic compound. Alcohols, ROH, can be regarded in this respect as substitution products of water.
- 15.2: Physical Properties of Alcohols; Hydrogen Bonding
- Comparison of the physical properties of alcohols with those of hydrocarbons of comparable molecular weight shows several striking differences, especially for those with just a few carbons. Alcohols are substantially less volatile, have higher melting points, and greater water solubility than the corresponding hydrocarbons, although the differences become progressively smaller as molecular weight increases.
- 15.3: Spectroscopic Properties of Alcohols
- The hydrogen-oxygen bond of a hydroxyl group gives a characteristic absorption band in the infrared that is considerably influenced by hydrogen bonding. For example, in the vapor state (in which there is essentially no hydrogen bonding), ethanol gives an infrared spectrum with a fairly sharp absorption band at 3700 cm−1, owing to a free or unassociated hydroxyl group.
- 15.4: Preparation of Alcohols
- Many of the common laboratory methods for the preparation of alcohols have been discussed in previous post or will be considered later; thus to avoid undue repetition we shall not consider them in detail at this time. Included among these methods are hydration and hydroboration, addition of hypohalous acids to alkenes , hydrolysis of alkyl halides and of allylic and benzylic halides, addition of Grignard reagents to carbonyl compounds, and the reduction of carbonyl compounds.
- 15.5: Chemical Reactions of Alcohols. Reactions Involving the O-H Bond
- Several important chemical reactions of alcohols involve only the oxygen-hydrogen bond and leave the carbon-oxygen bond intact. An important example is salt formation with acids and bases. Alcohols, like water, are both weak bases and weak acids. The acid ionization constant of ethanol is slightly less than that of water.
- 15.6: Reactions Involving the C-O Bond of Alcohols
- Alkyl halide formation from an alcohol and a hydrogen halide affords an important example of a reaction wherein the C−O bond of the alcohol is broken.
- 15.7: Oxidation of Alcohols
- According to the scale of oxidation levels established for carbon, primary alcohols are at a lower oxidation level than either aldehydes or carboxylic acids. With suitable oxidizing agents, primary alcohols in fact can be oxidized first to aldehydes and then to carboxylic acids.
- 15.8: Polyhydric Alcohols
- Polyhydric alcohols in which the hydroxyl groups are situated on different carbons are relatively stable, and, as we might expect for substances with multiple polar groups, they have high boiling points and considerable water solubility, but low solubility in nonpolar solvents.
- 15.9: Unsaturated Alcohols - Alkenols
- The simplest unsaturated alcohols, ethenol (vinyl alcohol), is unstable with respect to ethanal and has never been isolated. Other simple unsaturated alkenols (enols) also rearrange to carbonyl compounds. However, ether and ester derivatives of enols are known and can be prepared by the addition of alcohols and carboxylic acids to alkynes. The esters are used to make many commercially important polymers.
- 15.10: Protection of Hydroxyl Groups
- By now it should be apparent that hydroxyl groups are very reactive to many reagents. This is both an advantage and a disadvantage in synthesis. To avoid interference by hydroxyl groups, it often is necessary to protect (or mask) them by conversion to less reactive functions. In the case of alcohols the hydroxyl group may be protected by formation of an ether, an ester, or an acetal.
- 15.11: Types and Reactions of Simple Ethers
- Substitution of the hydroxyl hydrogens of alcohols by hydrocarbon groups gives compounds known as ethers. These compounds may be classified further as open-chain, cyclic, saturated, unsaturated, aromatic, and so on.
- 15.12: Cyclic Ethers
- Ring compounds containing nitrogen, oxygen, sulfur, or other elements as ring atoms generally are known as heterocyclic compounds, and the ring atoms other than carbon are the hetero atoms.
- 15.E: Alcohols and Ethers (Exercises)
- These are the homework exercises to accompany Chapter 15 of the Textmap for Basic Principles of Organic Chemistry (Roberts and Caserio).
Contributors and Attributions
John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."