Phenols are a family of orgnaic compounds having a hydroxyl group attached directly to a benzene ring. Compounds that have a hydroxyl group attached to a polycyclic benzenoid ring are chemically similar to phenols, but they are called napthols and phenanthrols.

Physical Properties :

∎ Phenol is a colorless, toxic, corrosive, needle shaped solid.

∎ Phenol soon liquifies due to high hygroscopic nature.

∎ Phenol is less soluble in water, but readily soluble in organic solvents.

∎ Simplest phenols, because of hydrogen bonding have quite high boiling points.

∎ o−nitrophenol is, steam volatile and also is less soluble in water because of intramolecular hydrogen bonding.

Illustration: Explain the lower boiling point and decreased water solubility of o−nitrophenol and o−hydroxybenzaldehyde as compared with their m-and p-isomers.

Solution : Intramolecular H−bonding (chelation) in the o−isomers inhibits intermolecular attraction, lowering the boiling point, and reduces H−bonding with H2O, decreasing water solubility. Intramolecular chelation cannot occur in m− and p−isomers.

Next Page » 

Leave a Reply