91Ó°ÊÓ

Compounds containing two hydroxyl groups are called diols.

The two diols can be on adjacent carbon atoms, increasing the intramolecular hydrogen bonding in the compound. They are named by adding a suffix diol to the parent chain of the compound.

Diols can be straight-chain compounds or ring structures. The two hydroxyl groups in a ring can have cis or trans configuration, and the configuration is mentioned in the IUPAC name. 1,2- diols are called glycols.

Compounds containing a hydroxyl group on a benzene ring are called phenols.

Phenols are more acidic than alcohols as the negative charge in the conjugate base is stabilized by the ring.

The lone pair on the oxygen makes the phenol ortho-para directing, and therefore, substitution in phenols occur at the positions ortho and para to the hydroxyl group.

Phenol is the IUPAC name for a benzene ring containing one hydroxyl group. The other substituents are added as a prefix to phenol along with their positions.

(a)

The given compound is a diol. The longest carbon chain with the highest number of substituents is the six-carbon straight chain.

Two hydroxyl groups are present in the first and fifth positions in the chain. A phenyl group is also attached to the first carbon. The third carbon contains a chlorine group.

Therefore, the IUPAC name of the given compound is 3-chloro-1-phenylhexane-1,5-diol.

(b)

The given compound is a diol. The parent chain of the compound is a ring containing six carbon atoms. It is called cyclohexane.

The two hydroxyl groups are in the first position and second position. Both the hydroxyl groups are in the same direction from the ring, which is downwards. Therefore, the compound has cis-configuration.

Therefore, the IUPAC name of the compound is cis-cyclohexane-1,2-diol.

(c)

The given compound is a phenol as it has a hydroxyl group on the benzene ring.

A nitro group is present in the ortho position to the hydroxyl group, the second position.

Therefore, the IUPAC name of the compound is 2-nitrophenol.

(d)

The given compound is a phenol as it has a hydroxyl group attached to a benzene ring.

A chorine group is attached ortho to the hydroxyl group, and a bromine group meta. Therefore, the chlorine and bromine groups are in the second and third positions, respectively.

Therefore, the IUPAC name of the compound is 3-bromo-2-chlorophenol.