Chapter 13. Summary.

Nomenclature of alcohols and phenols. Alcohols are aliphatic compounds that contain the hydroxyl functional group (-OH). Aromatic compounds with an -OH group attached to the ring are called phenols. Several alcohols are well known by common names. In the lUPAC system, the characteristic ending -ol is used to designate alcohols. Phenols are named as derivatives of the parent compound phenol.

Classification of Alcohols. Alcohols are classified on the basis of the number of carbon atoms which are bonded directly to the carbon which is attached to the OH group. In. primary alcohols the OH- bonded carbon is bonded to one other carbon. In secondary alcohols the OH-bonded carbon is bonded to two other carbons. In tertiary alcohols the OH-bonded carbon Is bonded to three other carbons.

Physical properties of Alcohols. Hydrogen bonding can occur between alcohol molecules, and between alcohol molecules and water. As a result, alcohols have higher boiling points than hydrocarbons of similar molecular weight, and low molecular weight alcohols are soluble in water.

Reactions of Alcohols. Two important reactions of alcohols are dehydration and oxidation. Alcohols may be dehydrated in two different ways depending upon the reaction temperature. With sulfuric acid at 180 C an alkene is produced, while at 140 C an ether is the product. he oxidation products obtained from the alcohols depend upon the class of alcohol being oxidized. A primary alcohol produces an aldehyde which is further oxidized to a carboxylic acid. A secondary alcohol produces a ketone. A tertiary alcohol does not react with oxidizing agents.

Important Alcohols. Some simple alcohols with commercial value are methanol (a solvent and fuel), ethanol (present in alcoholic beverages), isopropyl alcohol (rubbing alcohol), ethylene glycol (antifreeze), and glycerol (a moistening agent). Ethanol intended for industrial or research uses is often denatured to prevent its use in alcoholic beverages which are produced by fermentation processes and heavily taxed.

Characteristics and Uses of phenols. Phenols are weak acids which are widely used for their antiseptic and disinfectant properties. Some phenols are used as antioxidants in foods and a variety of other materials.

Ethers. Ethers contain an oxygen attached to two carbons as the characteristic functional group. In the lUPAC system, ethers are named as alkoxy derivatives of alkanes. The -O-R group is the alkoxy group which may have names such as methoxy (-O-CH3) or ethoxy (-O-CH2CH3). The simplest and most important compound of this class is ethyIene oxide.

Properties of Ethers. Like the alkanes, ethers are very unreactive substances. Pure ethers cannot form hydrogen bonds. As a result, their boiling points are comparable to those of hydrocarbons and lower than those of alcohols of similar molecular weight. Ethers are much less polar than alcohols but are still slightly soluble in water due to the

limited formation of hydrogen bonds.

Thiols. Thiols contain an -SH group which often imparts a strong, disagreeable odor to the compound. Two reactions of thiols that are important in protein chemistry are their oxidation to produce a disulfide and their reaction with heavy metals, such as mercury. Disulfides may be converted back to thiols by a reducing agent.