(1)Introduction: The families alcohols, ethers, phenols, and thiols may be considered in the context of water as follows: water = H-O-H; alcohol = R-O-H, where one hydrogen atom of water is replaced by a hydrocarbon functional group;  ether = R-O-R, where both hydrogen atoms of water are replaced by a hydrocarbon functional group;  phenol = phenyl-O-H, where on hydrogen atom of water is replaced by a benzene ring;  thiol = H-S-H, where the oxygen atom of water is replaced by sulfur.  Note that R- designates any alkane functional group, for example CH₃- is methyl, etc.

(2) Properties: The oxygen atom in each family member is SP³ hybridized to form sigma bonds, and the difference in electronegativity between oxygen and hydrogen produces a delta charge on the oxygen and the hydrogen atoms.

• In alcohols this allows hydrogen bonding between the molecules and this will influence the physical properties just like we saw in water.

• In ethers there is the strong electronegative center (oxygen) , but no hydrogen atom. Thus ethers will not hydrogen bond among themselves, but with any other molecule where hydrogen is bonded to oxygen or another strong electronegative center.
• Thiols contain sulfur rather than oxygen and are considered sulfur analogs of water.

The difference in the value of electronegativity between hydrogen and sulfur is NOT large enough to make this functional group polar, and thiols do not form hydrogen bonds. The cells of the liver contain enzymes capable of adding a hydroxyl group to non-soluble, toxic molecules so that they become water soluble and can be carried in the blood to the kidneys for excretion.
 

(3) Nomenclature of alcohols and ethers.  In the IUPAC system for naming alcohols the ending (-ol) replaces the ( -e) of alkane.  In addition, primary, secondary, and tertiary denotes the presence of two, one, or no hydrogen atoms bonded to the carbon containing the hydroxyl group. Alcohols may also contain more than one hydroxyl group, a polyhydroxyl alcohol that you must learn is glycerol or 1,2,3-propanetriol.

Write the structural formula for this important building block of many lipids.

For naming ethers, select the longest carbon chain as the parent compound and name group as the alkoxy substituent, (-oxy) followed by name of the other alkane group in the molecule.   The common name uses the word ether after the two alkanes have been named, i.e. dimethyl ether.
 

(4) Some special ethers - the most important ethers among biological molecules are the heterocyclic ethers, such as furan and pyran. Furan contains four carbons with two double bonds and one oxygen in a five-member ring, and pyran contains five carbons with two double bonds and one oxygen in a six-member ring.

Write the structure of each of these ethers and commit them to memory.

Later we will see their importance in the structure of sugars, where the hydroxyl and carbonyl functional groups occur in the same molecule and an intramolecular nucleophilic addition reaction occurs to form the ring or cyclic structure of either pyran or furan.
 

(5) Phenols - these are highly stable enols via the gain in resonance stabilization of the ring structure that we saw in the benzene ring (remember the pi cloud?), and they differ from alcohols in being more acidic.
 

(6) Thiols - these are considered sulfur analogs of alcohols and their physical properties differ from alcohols because of the lack of polarity. Thus this functional group (-SH) does not engage in hydrogen bonding. Their most important bonding occurs in proteins where the presence of two or more amino acids containing this functional group allows the formation of a covalent sulfur-to-sulfur bond via the oxidation/reduction reaction of (-SH + HS-) to form the  (-S-S-) linkage. This important covalent linkage allows proteins to assume unique shapes, and is also used to covalently link together individual polypeptide chains when the protein consists of two or more of such subunits. A good example is the insulin molecule, and you should look up the structure of this important hormone.
 
(7) Chemical reactions of alcohols are: dehydration to alkene - similar to alkene hydration, but in the reverse; oxidation/reduction of primary alcohols to the corresponding aldehyde, secondary alcohols to the corresponding ketone, and tertiary alcohols without a hydrogen are not reactive (remember that biological oxidations involve the loss of electrons or hydrogen and are always coupled to reductions or the gain of electrons or hydrogen, the enzyme is termed a dehydrogenase and works with a coenzyme like NAD or NADP ). Thus if you oxidize an alcohol with a dehydrogenase enzyme, the coenzyme in the oxidized form is converted into the reduced form.