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  • Chemistry, WM Revision Notes

    Abstract

    WM1

    Alcohols

    Physical Properties of Alcohols

    • Polar due to \(O\)-\(H\) bond

    • Able to hydrogen bond

      • Explains why alcohols have higher MBP’s than corresponding alkanes

      • Also explains why alcohol and water mix

    • \(O\)-\(H\) bond becomes less influential in longer chains

      • Solubility in water decreases

      • Other properties more similar to those of corresponding alkanes

    Reactions of Alcohols

    Types of alcohols

    Primary alcohols:

    • -\(O\)-\(H\) carbon bonded to one other

    Secondary alcohols:

    • -\(O\)-\(H\) carbon bonded to two others

    Tertiary alcohols:

    • -\(O\)-\(H\) carbon bonded to three others

    Oxidation

    • The \(O\)-\(H\) group is oxidised by strong oxidising agents

      • Acidified Potassium Dichromate(VI), \(K_2Cr_2O_7\)

        • Orange dichromate ion reduced to green chromate(III) ion

        • \(Cr_2O_7^{2-}\Rightarrow Cr^{3+}\)

    • \(O\)-\(H\) group converted to carbonyl \(C\)=\(O\) group

    • Will not take place if there is no hydrogen attached to the carbon

    • Carbonyl formed depends on reacting alcohol and conditions

      • Aldehyde or ketone

    Heating under Reflux

    • Safer when using volatile compounds

    • Prevents loss of solvent, reagent, or product

    Oxidation of Primary alcohols

    • Initially oxidised to an Aldehyde

    • Can be further oxidised to a Carboxylic Acid

      • Excess oxidising agent

      • Under reflux

    • If the Aldehyde is required:

      • Distilled in situ

        • Prevents further oxidation

      • Excess Alcohol

      • No reflux

    Oxidation of Primary Alcohols

    Oxidation of Secondary alcohols

    • Oxidised to ketones

      • Excess oxidising agent

      • Under reflux

    • No further oxidation

      • Due to strong \(C\)-\(C\) bond