Chemistry · Ch 7 — Alcohols, Phenols and Ethers

Summary

Classification: Alcohols ( $\text{R-OH}$ ), phenols ( $\text{Ar-OH}$ ), and ethers ( $\text{R-O-R'}$ ) are classified by the number of alkyl/aryl groups attached to the oxygen.
Nomenclature: IUPAC names use suffix -ol for alcohols, -phenol for phenols, and -oxy (or alkoxy) for ethers; common names use alcohol, phenol, and ether.
Preparation of alcohols: Hydration of alkenes (Markovnikov addition), reduction of carbonyl compounds ( $\text{RCHO} \xrightarrow{\text{NaBH}_4} \text{RCH}_2\text{OH}$ ), and Grignard reaction ( $\text{RMgX} + \text{HCHO} \rightarrow \text{RCH}_2\text{OH}$ ).
Preparation of phenols: From diazonium salts ( $\text{ArN}_2^+ \xrightarrow{\text{H}_2\text{O}} \text{ArOH}$ ), or from cumene (isopropylbenzene) via hydroperoxide rearrangement.
Preparation of ethers: Williamson synthesis ( $\text{R-O}^- + \text{R'X} \rightarrow \text{R-O-R'}$ ) and dehydration of alcohols ( $2\text{ROH} \xrightarrow{\text{H}_2\text{SO}_4, 140^\circ\text{C}} \text{R-O-R} + \text{H}_2\text{O}$ ).
Physical properties: Alcohols and phenols have higher boiling points than ethers due to intermolecular $\text{O-H}\cdots\text{O}$ hydrogen bonding; ethers have lower boiling points and are less polar.
Acidity: Phenols ( $\text{p}K_a \approx 10$ ) are more acidic than alcohols ( $\text{p}K_a \approx 16$ ) due to resonance stabilization of phenoxide ion; electron-withdrawing groups increase acidity, electron-donating groups decrease it.
Reactions of alcohols: Dehydration to alkenes (E1/E2), oxidation to aldehydes/ketones (using $\text{PCC}$ or $\text{K}_2\text{Cr}_2\text{O}_7$ ), and esterification with carboxylic acids.
Reactions of phenols: Electrophilic substitution (bromination, nitration, Friedel-Crafts) occurs at ortho and para positions due to $\text{-OH}$ activation; also form coloured complexes with $\text{FeCl}_3$ . …

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