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Alcohol, Phenol and Ether
In organic chemistry, alcohols, phenols, and ethers are among the most important functional groups. They are frequently tested in JEE Main and JEE Advanced because they combine concepts of structure, reactivity, preparation, and mechanisms.
- Alcohols: Organic compounds containing a hydroxyl group (–OH) attached to a saturated carbon atom.
- Phenols: Aromatic compounds where the hydroxyl group (–OH) is directly attached to a benzene ring.
- Ethers: Organic compounds with an oxygen atom bonded to two alkyl or aryl groups (R–O–R').
These compounds are highly relevant in both industrial applications (fuels, pharmaceuticals, solvents) and in understanding reaction mechanisms, making them vital for JEE preparation.
1.0What are Alcohols?
Alcohols are organic compounds that contain a hydroxyl (−OH) functional group bonded to a saturated, aliphatic carbon atom. The simplest alcohol is methanol (CH_3OH).
Classification of Alcohols
Depending on the number of hydroxyl groups attached, alcohols can be classified into three types.
- Monohydric alcohols: They contain one -OH group. Example, CH3CH2-OH
- Dihydric alcohols: They contain two -OH groups. Example, 1,2-Ethandiol.
- Trihydric alcohols: They contain three -OH groups. Example 1,2,3-Propantriol.
Depending on the number of carbon atoms which are directly attached to the carbon that is bonded with the -OH group, alcohols can be classified into three types.
- Primary The carbon with the −OH group is bonded to only one other carbon atom (e.g., ethanol).
- Secondary (2^∘): The carbon with the −OH group is bonded to two other carbon atoms (e.g., isopropanol).
- Tertiary (3^∘): The carbon with the −OH group is bonded to three other carbon atoms (e.g., tert-butyl alcohol).
Nomenclature of Alcohols
Alcohols (IUPAC rules):
- Longest carbon chain containing –OH group is selected.
- The –OH group gets the lowest possible number.
- The suffix –ol is used.
- Example: CH₃CH₂OH → Ethanol.
Preparation of Alcohols
- Hydration of Alkenes:
- Ethene + H₂O → Ethanol (using H₂SO₄ catalyst).
- Mechanism follows Markovnikov’s rule.
- Hydrolysis of Alkyl Halides:
- R–X + NaOH (aq) → R–OH.
- Reduction of Carbonyl Compounds:
- Aldehydes + H₂/Ni → Primary Alcohols.
- Ketones + H₂/Ni → Secondary Alcohols.
- Fermentation of Sugars:
- Glucose → Ethanol (using yeast enzyme).