Lecture on Alcohols

Overview

• Lecturer: Iman
• Topics Covered:
  • Description and properties of alcohols
  • Nomenclature and physical properties
  • Reactions of alcohols (oxidation, mesylates/tosylates, protecting groups)
  • Reactions of phenols, quinones, hydroxyquinones, ubiquinone

Alcohols: Description and Properties

General Formula and Functional Group

• General formula: R-OH
• Functional group: Hydroxy group (-OH)

Nomenclature

• **IUPAC System: **
  • Replace the -e ending of the root alkane with -ol
  • Provide the lowest possible number to the carbon bonded to -OH
  • Examples:
    • Propane → Propanol (2-propanol)
    • Hexane → Hexanol (4,5-dimethyl-2-hexanol)
  • Common Naming:
    • Name the alkyl group as a derivative followed by “alcohol”
    • Example: Ethane → Ethyl alcohol
  • When -OH is Not the Highest Priority
    • Named with the prefix “hydroxy”

Physical Properties

• Capable of intermolecular hydrogen bonding
• Higher melting and boiling points as compared to analogous hydrocarbons
• Boiling points increase significantly with more -OH groups
• Hydrogen bonding involves attraction between the partially positive hydrogen of one molecule and the partially negative oxygen of another
• Hydroxy hydrogen is weakly acidic; alcohols can dissociate into protons and alkoxide ions

Reactions of Alcohols

Oxidation Reactions

• Primary alcohols to aldehydes/ketones with PCC (pyridinium chlorochromate)
• Secondary alcohols to ketones with PCC or stronger oxidizing agents
• Primary alcohols to carboxylic acids with strong oxidizing agents (sodium/potassium dichromate, chromium trioxide)
• Tertiary alcohols cannot be oxidized without breaking carbon-carbon bonds

Mesylates and Tosylates

• Alcohols can be converted to better leaving groups for nucleophilic substitution
• Mesylate: SO3CH3
• Tosylate: SO3C6H4CH3
• Function as protecting groups in synthesis to prevent unwanted reactions

Protecting Groups

• Alcohols can protect aldehydes/ketones by forming acetals/ketals
• Example: Protecting an aldehyde with a diol, then removing the protection at the end of the synthesis

Reactions of Phenols

• Phenols: Aromatic rings with -OH groups
• Hydroxy hydrogen of phenols is particularly acidic due to resonance stabilization
• Naming conventions for substituted benzene rings: Ortho (adjacent), Meta (separated by one carbon), Para (opposite sides)

Quinones and Hydroxyquinones

• Quinones: Produced by oxidation of phenols, named by numerically indicating carbonyl positions
• Hydroxyquinones: Quinones with additional hydroxy groups
• Example: Ubiquinone (Coenzyme Q) in electron transport chain
• Quinones are electron acceptors biochemically in processes like photosynthesis and aerobic respiration

Ubiquinone (Coenzyme Q)

• Vital electron carrier in the electron transport chain
• Can be reduced to ubiquinol
• Participates in oxidation-reduction for electron transport

Conclusion

• Covered all required topics for this chapter on alcohols
• Practice problems to follow in the next video

Happy studying and good luck!