Alcohols and phenols – A Level Chemistry WJEC Revision

Classification and Structure of Alcohols and Phenols

Alcohols are organic compounds that contain a hydroxyl (-OH) functional group attached to a carbon atom.
Depending on the number of hydroxyl groups attached, alcohols can be classified as primary (1°), secondary (2°), or tertiary (3°).
Phenols are a type of alcohol where the hydroxyl group is associated directly with a benzene ring.
Phenols often exhibit different physical and chemical properties than alcohols due to the aromatic benzene ring.

Alcohols demonstrate hydrogen bonding leading to higher boiling points when compared to hydrocarbons with similar relative molecular mass.
Unlike alcohols, phenols are weakly acidic due to the stabilisation of the negative charge in the phenoxide ion by the benzene ring.
Alcohols and Phenols are soluble in water to an extent that decreases with the length of the hydrocarbon chain.

Alcohols undergo dehydration reactions to form alkenes in presence of an acid.
They also react with a variety of carboxylic acids to form esters in a process known as esterification.
Phenols are more reactive than alcohols due to the electron-rich nature of the benzene ring. They undergo electrophilic substitution reactions with ease.
Alcohols can be oxidised to form aldehydes, ketones or carboxylic acids depending on the type of alcohol and reaction conditions.
Both alcohols and phenols can be converted to halogenoalkanes through a nucleophilic substitution reaction with a halogen.

Alcohols are important solvents and intermediates in the synthesis of other organic compounds such as pharmaceuticals and polymers.
Methanol and ethanol are useful fuels; ethanol is also used in alcoholic beverages.
Phenols are used in the manufacture of phenolic resins, plastics and disinfectants.

Qualitative tests like the Lucas test or the iodoform test identify different types of alcohols.
Spectral methods, such as infrared spectroscopy and mass spectrometry, provide information about the structure of the alcohol or phenol.
Titration with a standard solution of a strong base enables determination of the amount of phenol in a sample due to its weakly acidic nature.
For quantitative analysis, Gas chromatography can be used to determine the concentration of alcohols in a sample.