MOD3 Alcohols 1(1) 2

Module 3 – Alcohols and Ethers

I. Alcohols

• Structure and Polarity

  • General structure: R-OH

  • Polarity due to the hydroxyl group (OH) resulting in hydrogen bonding capabilities.

  • Common examples: Methanol (CH3OH), Ethanol, Butanol, Phenol.

• Nomenclature of Alcohols

  • Alcohols categorized as primary (1°), secondary (2°), and tertiary (3°) based on the carbon to which the OH is attached.

    • Example: Isopropanol (2-Propanol) as a secondary alcohol.

• Physical Properties

  • Alcohols have higher boiling points compared to hydrocarbons due to hydrogen bonding.

  • Increased molecular weight correlates with higher boiling points.

• Amphoteric Nature

  • Alcohols can function as both acids (donating protons) and bases (accepting protons).

II. Synthesis of Alcohols

• A. Substitution Reactions

  • Converting alkyl halides into alcohols via nucleophilic substitution.

    • Example: R-Br + NaOH -> R-OH + NaBr.

• B. Addition Reactions

  • Alkenes can react with water (hydration) to form alcohols.

    • Example: H2C=CH2 + H2O -> CH3CH2OH (Ethanol).

• C. Reduction and Oxidation Reactions

  • Reduction of carbonyl compounds (aldehydes, ketones) to form alcohols using reagents like LiAlH4 or NaBH4.

  • Oxidation of primary and secondary alcohols to aldehydes/ketones and carboxylic acids respectively.

III. Reduction Reagents for Alcohol Synthesis

• A. Carbon Nucleophiles

  • Use of Grignard reagents and organolithium reagents to synthesize alcohols.

• B. Mechanisms

  • Grignard Reagents (e.g., RMgBr) and organolithium (e.g., RLi) react with carbonyls to yield alcohols.

IV. Alcohol Chemistry

• A. Reactions with Alcohols

  • Alcohols as nucleophiles or electrophiles in substitution and elimination reactions.

• B. Converting Alcohols to Better Leaving Groups

  • Protonation with strong acids (e.g., HX) transforms -OH into -OTs or -OMs, enhancing ease of substitution reactions.

V. Ethers

• A. General Information

  • Ethers are characterized by the general structure R-O-R'.

  • They are less reactive than alcohols and are commonly used as solvents.

• B. Ethers Nomenclature

  • Named based on the alkyl groups attached to the ether oxygen.

• C. Ether Synthesis

  • Synthesized through reactions like SN1 and SN2.

    • Example: Nucleophilic attack on alkyl halides can yield ethers.

• D. Epoxides

  • Formed by addition of peracids to alkenes.

  • Involves mechanisms like SN2 where the ether becomes a cyclic structure.

VI. Epoxide Reactions

• A. Acid-Catalyzed Ring Opening

  • Weak nucleophiles can attack epoxides with inversion of stereochemistry.

• B. Base-Catalyzed Ring Opening

  • Similar mechanisms allow for nucleophilic attack and inversion.

VII. Reduction Techniques and Conditions

• Overview of reagents such as NaBH4 and LiAlH4 for synthesis of alcohols from carbonyl compounds.

• Impact of stereochemistry on product formation in reduction and substitution reactions.