Alcohols, Phenols and Ethers Alcohols and phenols are formed when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively, is replaced by -OH group. These classes of compounds find wide applications in industry as well as in day-to-day life. For instance, have you ever noticed that ordinary spirit used for polishing wooden furniture is chiefly a compound containing hydroxyl group, ethanol. The sugar we eat, the cotton used for fabrics, the paper we use for writing, are all made up of compounds containing -OH groups. The common name of an alcohol is derived from the common name of the alkyl group and adding the word alcohol to it. For example, \(\mathrm{CH_3OH}\) is methyl alcohol. The simplest hydroxy derivative of benzene is phenol. It is its common name and also an accepted IUPAC name. As structure of phenol involves a benzene ring, in its substituted compounds the terms ortho (1,2-disubstituted), meta (1,3-disubstituted) and para (1,4-disubstituted) are often used in the common names. In ethers, the four electron pairs, i.e., the two bond pairs and two lone pairs of electrons on oxygen are arranged approximately in a tetrahedral arrangement. The bond angle is slightly greater than the tetrahedral angle due to the repulsive interaction between the two bulky (-R) groups.
What is the common name for the following structure given below?
Show Hint
Find the relative positions of the two OH groups: they are para (1,4).
Step 1: Count the substituents: The ring carries two -OH groups and nothing else. So it cannot be a cresol, which has one -OH and one methyl group. This removes option 4.
Step 2: Find the positions: Number the ring from the top carbon as 1. Going round the ring, the bottom carbon is number 4. So the groups are at 1 and 4.
Step 3: Match each name: Catechol is 1,2. Resorcinol is 1,3. Hydroquinone is 1,4. Only the third name has the groups across from each other.
Step 4: Conclude: The compound drawn is para-dihydroxybenzene, commonly called hydroquinone.
Final Answer: Two -OH groups at the para positions of benzene mean the compound is hydroquinone.\[ \boxed{\text{Hydroquinone}} \]
