Alcohols, Phenols and Ethers - Primary, secondary and tertiary alcohols

Alcohols are classified as primary ($1^{\circ}$), secondary ($2^{\circ}$), and tertiary ($3^{\circ}$) based on the number of carbon atoms directly attached to the carbon bearing the hydroxyl ($-OH$) group.

Primary ($1^{\circ}$) Alcohols: The $-OH$ group is attached to a carbon atom which is further attached to only one alkyl group (or hydrogen in the case of methanol). General structure: $R-CH_2-OH$.

Secondary ($2^{\circ}$) Alcohols: The $-OH$ group is attached to a carbon atom which is further attached to two alkyl groups. General structure: $R_2CH-OH$.

Tertiary ($3^{\circ}$) Alcohols: The $-OH$ group is attached to a carbon atom which is further attached to three alkyl groups. General structure: $R_3C-OH$.

Lucas Test: Used to distinguish between the three types. It uses Lucas reagent (conc. $HCl$ + anhydrous $ZnCl_2$). $3^{\circ}$ alcohols give immediate turbidity, $2^{\circ}$ give turbidity within 5 minutes, and $1^{\circ}$ alcohols do not give turbidity at room temperature.

Oxidation: Primary alcohols oxidize to aldehydes ($RCHO$) and then to carboxylic acids ($RCOOH$); secondary alcohols oxidize to ketones ($R_2C=O$); tertiary alcohols are resistant to oxidation in neutral/alkaline conditions but undergo dehydration/oxidation in acidic conditions to give ketones/acids with fewer carbons.

Catalytic Dehydrogenation: Passing vapors over heated $Cu$ at $573 \, K$. $1^{\circ} \rightarrow$ Aldehyde, $2^{\circ} \rightarrow$ Ketone, $3^{\circ} \rightarrow$ Alkene (dehydration occurs instead of dehydrogenation).