Summary

This chapter covered three oxygen-containing families built on the same $-\text{C--O--}$ motif but

differing in what is attached to that oxygen.

Alcohols ($\text{R--OH}$, saturated carbon) are named with the '-ol' suffix and classed as

primary/secondary/tertiary by how many carbons attach to the $-\text{OH}$ carbon. They are made

from alkenes (acid-catalysed hydration, Markovnikov), from haloalkanes ($S_N2$ with aqueous

hydroxide, cleanest for primary halides) and from carbonyl compounds (hydride reduction: aldehyde

$\rightarrow$ primary alcohol, ketone $\rightarrow$ secondary alcohol). Hydrogen bonding gives

alcohols much higher boiling points and water-solubility than comparable hydrocarbons, though

solubility falls as the hydrocarbon chain grows. The Lucas test distinguishes the three classes

by how fast each forms a carbocation ($3° > 2° > 1°$, exactly the rate order that also governs

E1 dehydration, whose major product follows Zaitsev's rule and can involve carbocation

rearrangement to a more stable cation). Primary alcohols are additionally oxidised stepwise

(aldehyde, then acid), esterified with acids, and converted to haloalkanes. Methanol and

ethanol are the two commercially dominant alcohols; unlike ethanol, methanol is metabolised in

the body to toxic formaldehyde and then formic acid, causing severe acidosis and blindness.

Phenols ($\text{Ar--OH}$, aromatic carbon) are made industrially almost entirely by the

cumene process (benzene $+$ propene $\rightarrow$ cumene $\rightarrow$ cumene hydroperoxide

$\rightarrow$ phenol $+$ acetone), and also from diazonium salts or from haloarenes (the

high-pressure Dow fusion route). Phenol is a genuinely acidic compound

($\text{p}K_a \approx 10$, against $\approx 16$ for an alcohol) because its conjugate base, the

phenoxide ion, delocalises its negative charge onto the ring's ortho/para carbons by resonance --

a stabilisation an alkoxide ion cannot access, though phenol remains a much weaker acid than a

carboxylic acid, whose carboxylate delocalises equally over two equivalent oxygens. This same

resonance donation from oxygen into the ring, in the neutral molecule, also makes $-\text{OH}$ a

strongly activating, ortho/para-directing group, so phenol brominates instantly (to

2,4,6-tribromophenol) without any catalyst and nitrates readily to a mixture of ortho/para

mono-nitro products. Phenol's practical importance spans antisepsis (Lister's original 'carbolic

acid'), phenol-formaldehyde (Bakelite) resin manufacture, and further use in drug and dye

synthesis.

Ethers ($\text{R--O--R}'$, no oxygen-bound hydrogen) are best made by the Williamson synthesis (alkoxide $+$ primary halide, $S_N2$; a secondary/tertiary halide instead gives

elimination as the major pathway). Lacking an $-\text{OH}$ hydrogen, ethers cannot hydrogen-bond to

each other and so boil far lower than an isomeric alcohol, though they retain modest water …