Class 12 Chemistry Chapter 18 – Alcohol, Phenol and Ether

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Chapter 18: Alcohols, Phenols, and Ethers

Chapter 18 in the Class 12 Chemistry syllabus covers three important classes of organic compounds: alcohols, phenols, and ethers. These compounds are characterized by the presence of hydroxyl (-OH) and ether (R-O-R’) functional groups. Understanding their structure, properties, and reactions is crucial for a deeper insight into organic chemistry.

Alcohols

  1. Introduction
  • Alcohols are organic compounds containing one or more hydroxyl (-OH) groups attached to a carbon atom.
  • The general formula for alcohols is R-OH, where R represents an alkyl group.
  1. Nomenclature
  • IUPAC Naming: Alcohols are named by replacing the -e ending of the corresponding alkane with -ol. The position of the -OH group is indicated by a number (e.g., methanol, ethanol, propan-2-ol).
  • Common Naming: Often involves naming the alkyl group followed by the word “alcohol” (e.g., methyl alcohol, ethyl alcohol).
  1. Classification
  • Primary (1°) Alcohols: The carbon atom holding the -OH group is bonded to only one other carbon atom.
  • Secondary (2°) Alcohols: The carbon atom holding the -OH group is bonded to two other carbon atoms.
  • Tertiary (3°) Alcohols: The carbon atom holding the -OH group is bonded to three other carbon atoms.
  1. Physical Properties
  • Alcohols are generally colorless liquids with characteristic odors.
  • They have higher boiling points than corresponding alkanes due to hydrogen bonding.
  • Lower alcohols are miscible with water, while solubility decreases with increasing carbon chain length.
  1. Chemical Properties
  • Acidity: Alcohols are weakly acidic; they can donate a proton to form alkoxide ions.
  • Dehydration: Alcohols can lose water to form alkenes.
  • Oxidation: Primary alcohols can be oxidized to aldehydes and then to carboxylic acids, while secondary alcohols are oxidized to ketones.
  • Esterification: Alcohols react with carboxylic acids to form esters.
  1. Uses
  • Alcohols are used as solvents, antifreeze, fuels, and in the manufacture of beverages and pharmaceuticals.

Phenols

  1. Introduction
  • Phenols are aromatic compounds in which one or more hydroxyl groups are directly attached to an aromatic ring.
  • The simplest phenol is phenol itself (C₆H₅OH).
  1. Nomenclature
  • Named by indicating the position of the -OH group relative to other substituents on the aromatic ring.
  1. Physical Properties
  • Phenols are generally solid or liquid at room temperature and have a distinct, medicinal odor.
  • They have higher boiling points than similar aromatic hydrocarbons due to hydrogen bonding.
  1. Chemical Properties
  • Acidity: Phenols are more acidic than alcohols due to resonance stabilization of the phenoxide ion.
  • Electrophilic Substitution Reactions: The -OH group is activating, directing electrophiles to ortho and para positions.
  • Reactions with Bases: Phenols can react with strong bases to form phenoxide ions.
  1. Uses
  • Phenols are used in the production of plastics, dyes, pharmaceuticals, and as disinfectants.

Ethers

  1. Introduction
  • Ethers are compounds with an oxygen atom connected to two alkyl or aryl groups (R-O-R’).
  • They are generally represented as R-O-R’, where R and R’ can be the same or different.
  1. Nomenclature
  • IUPAC Naming: The smaller alkyl group is named as an alkoxy group, followed by the name of the larger alkyl group (e.g., methoxyethane).
  • Common Naming: Involves naming the two alkyl groups followed by “ether” (e.g., diethyl ether).
  1. Physical Properties
  • Ethers are relatively inert and have lower boiling points than alcohols of comparable molecular weight due to the absence of hydrogen bonding.
  • They are good solvents for nonpolar and slightly polar compounds.
  1. Chemical Properties
  • Low Reactivity: Ethers are generally resistant to chemical reactions, making them useful as solvents.
  • Cleavage by Acids: Under strong acidic conditions, ethers can be cleaved to form alkyl halides and alcohols.
  1. Uses
  • Ethers are used as solvents, anesthetics, and in the synthesis of other organic compounds.

Conclusion

Alcohols, phenols, and ethers are fundamental organic compounds with diverse applications in industry, medicine, and everyday life. Understanding their properties, reactions, and uses is essential for studying organic chemistry and its practical applications.

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