Key Points

Alcohols have a hydroxyl (-OH) group attached to a saturated, $sp^3$-hybridized carbon atom. Phenols have a hydroxyl group directly attached to an $sp^2$-hybridized carbon of an aromatic ring. Ethers feature an oxygen atom connected to two alkyl or aryl groups (R-O-R').

Alcohols are classified as primary (1^\\circ), secondary (2^\\circ), or tertiary (3^\\circ) based on the number of carbon atoms bonded to the carbon bearing the -OH group. They are also classified as mono-, di-, or trihydric based on the number of -OH groups present.

Alcohols can be prepared by the acid-catalyzed hydration of alkenes, a reaction that follows Markovnikov's rule. Alternatively, the hydroboration-oxidation of alkenes yields an alcohol with anti-Markovnikov regioselectivity.

Aldehydes are reduced to primary alcohols, and ketones are reduced to secondary alcohols using reducing agents like sodium borohydride ($\\text{NaBH}_4$) or lithium aluminium hydride ($\\text{LiAlH}_4$). Carboxylic acids and esters are reduced to primary alcohols using $\\text{LiAlH}_4$.

Grignard reagents (R-MgX) react with carbonyl compounds to produce alcohols. Reaction with methanal (HCHO) yields a primary alcohol, other aldehydes yield secondary alcohols, and ketones yield tertiary alcohols.

Phenol is commercially manufactured from cumene (isopropylbenzene). Cumene is oxidized in air to form cumene hydroperoxide, which is then treated with dilute acid to produce phenol and acetone as a by-product.

This method is used to prepare both symmetrical and unsymmetrical ethers. It involves an $S_N2$ reaction between a sodium alkoxide (R-ONa) and a primary alkyl halide (R'-X), yielding an ether (R-O-R'). Tertiary alkyl halides lead to elimination.

Alcohols and phenols have much higher boiling points than ethers and hydrocarbons of similar molecular masses. This is due to the presence of strong intermolecular hydrogen bonding between the -OH groups.

Phenols are significantly more acidic than alcohols. The higher acidity of phenols is due to the resonance stabilization of the resulting phenoxide ion, which delocalizes the negative charge over the benzene ring.

The Lucas test, using a mixture of concentrated HCl and anhydrous $\\text{ZnCl}_2$, distinguishes between primary, secondary, and tertiary alcohols. Tertiary alcohols react instantly to form turbidity, secondary alcohols react within minutes, and primary alcohols do not react at room temperature.

Alcohols undergo dehydration to form alkenes when heated with a protic acid like concentrated $\\text{H}_2\\text{SO}_4$. The ease of dehydration follows the order: Tertiary > Secondary > Primary, based on carbocation stability.

Primary alcohols are oxidized to aldehydes using mild agents like PCC, or to carboxylic acids using strong agents like $\\text{KMnO}_4$. Secondary alcohols are oxidized to ketones. Tertiary alcohols are resistant to oxidation.

The -OH group in phenol is a strongly activating, ortho-para directing group for electrophilic aromatic substitution. Common reactions include nitration (forming o- and p-nitrophenol) and halogenation (forming 2,4,6-tribromophenol with bromine water).

When phenol is treated with chloroform ($\\text{CHCl}_3$) in the presence of aqueous sodium hydroxide, an aldehyde group (-CHO) is introduced onto the aromatic ring, primarily at the ortho position, forming salicylaldehyde.

Phenol is converted to sodium phenoxide with NaOH, which then reacts with carbon dioxide ($\\text{CO}_2$) under pressure. Subsequent acidification yields salicylic acid (2-hydroxybenzoic acid), an important precursor for aspirin.

Ethers are cleaved by strong hydrogen halides (HX) under drastic conditions. The reaction is $R-O-R' + HX \\rightarrow RX + R'OH$. The order of reactivity of hydrogen halides is $\\text{HI} > \\text{HBr} > \\text{HCl}$.