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    Comprehensive NEET Chemistry Notes for Alcohols, Phenols, and Ethers

    Alcohols, Phenols, and Ethers

    1. Introduction to Alcohols, Phenols, and Ethers

    Alcohols, phenols, and ethers are classes of organic compounds containing hydroxyl (-OH) and alkoxy (-OR) functional groups. Alcohols have an -OH group attached to an aliphatic carbon atom, phenols have an -OH group attached to an aromatic ring, and ethers have two alkyl or aryl groups bonded to an oxygen atom.

    Did You Know?

    Alcohols and phenols are important in various industrial applications, including the production of perfumes, dyes, and pharmaceuticals.

    2. Nomenclature and Structure

    2.1 Nomenclature of Alcohols

    • Common Names: Derived from the names of the alkyl group followed by the word 'alcohol' (e.g., methyl alcohol, ethyl alcohol).
    • IUPAC Names: Named by replacing the -e ending of the parent alkane with -ol (e.g., methanol, ethanol).

    2.2 Nomenclature of Phenols

    • Named as derivatives of the simplest phenol, benzene with an -OH group (e.g., phenol, 2-methylphenol).

    2.3 Nomenclature of Ethers

    • Common Names: Named by listing the alkyl groups in alphabetical order followed by the word 'ether' (e.g., diethyl ether).
    • IUPAC Names: Named as alkoxy derivatives of alkanes (e.g., methoxyethane).

    NEET Tip:

    For dihydric alcohols (glycols) and trihydric alcohols (glycerols), use the prefixes di-, tri-, etc., before the -ol suffix.

    3. Preparation Methods

    3.1 Preparation of Alcohols

    • From Alkenes:
      • Hydration: Addition of water to alkenes in the presence of an acid catalyst.
        • Example: C2​H4​+H2​O→C2​H5​OH
      • Hydroboration-Oxidation: Addition of borane followed by oxidation.
        • Example: BH3​⋅THF+H2​O2​/OH−→R2​CHOH

    3.2 Preparation of Phenols

    • From Haloarenes: Dow process involves the reaction of chlorobenzene with NaOH at high temperature and pressure.
      • Example: C6​H5​Cl+NaOH→C6​H5​OH+NaCl

    3.3 Preparation of Ethers

    • Williamson Synthesis: Reaction of an alkoxide ion with a primary alkyl halide.
      • Example: R−O−+R′−X→R−O−R′+X−

    Common Misconception:

    Students often confuse the preparation methods of alcohols and phenols. Remember that phenols cannot be prepared by simple hydration of alkenes.

    4. Physical Properties

    4.1 Boiling Points

    • Alcohols have higher boiling points than ethers and hydrocarbons of similar molecular mass due to hydrogen bonding.

    4.2 Solubility

    • Lower alcohols are soluble in water due to hydrogen bonding. Solubility decreases with increasing molecular weight.

    4.3 Acidity

    • Phenols are more acidic than alcohols due to the resonance stabilization of the phenoxide ion.

    NEET Tip:

    In phenols, the presence of electron-withdrawing groups (e.g., -NO_2) increases acidity, while electron-donating groups (e.g., -CH_3) decrease acidity.

    5. Chemical Reactions

    5.1 Reactions of Alcohols

    • Dehydration: Alcohols can be dehydrated to form alkenes using acid catalysts.
      • Example: C2​H5​OHH2​SO4​​C2​H4​+H2​O
    • Oxidation: Primary alcohols oxidize to aldehydes and then to carboxylic acids; secondary alcohols oxidize to ketones.
      • Example: C2​H5​OH[O]​CH3​CHO[O]​CH3​COOH

    5.2 Reactions of Phenols

    • Electrophilic Substitution: Phenols undergo electrophilic substitution reactions like nitration, halogenation, and sulfonation.
      • Example: C6​H5​OH+Br2​→C6​H4​BrOH+HBr

    5.3 Reactions of Ethers

    • Cleavage: Ethers are cleaved by strong acids to form alkyl halides.
      • Example: R−O−R′+HI→R−I+R′−OH

    Mnemonic:

    "Oxidation of alcohols: Primary to carboxylic, Secondary to ketone, Tertiary no reaction."

    6. Uses and Applications

    • Alcohols: Used in the manufacture of perfumes, pharmaceuticals, and as solvents.
    • Phenols: Used in the production of plastics, explosives, and antiseptics.
    • Ethers: Commonly used as solvents and in anesthesia (e.g., diethyl ether).

    Real-life Application:

    Ethanol is used as a biofuel and in hand sanitizers due to its antiseptic properties.

    Quick Recap

    • Alcohols: Named by replacing -e with -ol, prepared from alkenes, higher boiling points due to hydrogen bonding.
    • Phenols: More acidic than alcohols, undergo electrophilic substitution, used in antiseptics.
    • Ethers: Named by alkyl groups followed by ether, lower boiling points, cleaved by strong acids.

    Practice Questions

    1. Explain the mechanism of dehydration of ethanol to form ethene.
    2. How does the presence of electron-withdrawing groups affect the acidity of phenols?
    3. Describe the Williamson synthesis of ethers with an example.
    4. Predict the products of the oxidation of 2-propanol.
    5. Compare the boiling points of ethanol, dimethyl ether, and propane.

    Answers to Practice Questions

    1. Mechanism of Dehydration: Formation of carbocation intermediate, followed by elimination of water.
    2. Acidity of Phenols: Electron-withdrawing groups stabilize the phenoxide ion, increasing acidity.
    3. Williamson Synthesis: Alkoxide ion reacts with alkyl halide (e.g., CH3​ONa+CH3​I→CH3​OCH3​+NaI).
    4. Oxidation of 2-Propanol: Forms acetone (ketone) - CH3​CHOHCH3​[O]​CH3​COCH3​.
    5. Boiling Points Comparison: Ethanol > Dimethyl ether > Propane, due to hydrogen bonding in ethanol.

    Glossary

    • Dehydration: Loss of water from a molecule.
    • Hydration: Addition of water to a molecule.
    • Electrophilic Substitution: Replacement of a hydrogen atom in an aromatic ring with an electrophile.
    • Williamson Synthesis: Formation of an ether from an alkoxide and an alkyl halide.