Question

Alcohols containing two hydroxyl groups are known as _ _ _ _ _ _.
(A) alkanediols
(B) glycols
(C) dialcohol
(D) both A and B

Answer 1

Hint: In the alcohols, we have a hydroxyl group (-OH) attached to the carbon atom. In the aliphatic chain with the two-hydroxyl group attached to it, we have the name of the alkane chain along with the term ‘diol’.

Complete step by step solution:
The compounds which have two hydroxyl groups present in it are called diols. These hydroxyl groups can be present either on the same carbon atom or on the adjacent carbon atoms.
So, we have the geminal diols and the vicinal diols. In the geminal diols, the two hydroxyl groups are present on the same carbon atom, whereas in the vicinal diols, the hydroxyl groups are on adjacent atoms. These aliphatic diols are known as glycols.
And through the IUPAC nomenclature, the parent aliphatic chain is named after the alkane, followed by the term ‘diol’ is added. Thus, we have the name as alkane diols.
The position of the hydroxyl group is also mentioned in the naming. For example, a vicinal diol, like $HO-C{{H}_{2}}-C{{H}_{2}}-OH$, it is named as $\text{1,2-Ethanediol}\,\text{or}\,\text{Ethylene}\,\text{glycol}$.
In geminal diol, like $H{{C}_{3}}-C{{(OH)}_{2}}-C{{H}_{3}}$ , it is named as $\text{2,2-Propanediol}$.

Therefore, the alcohols containing two hydroxyl groups in it are known as option (D) both (A) and (B), that is, alkanediols or glycols.

Note: The diols are often used in antifreeze products, like the ethylene glycol and the propylene glycol. Also, due to being non-poisonous in nature, they are made use of in the food and medical field.
An alkanediols is a subgroup of the diols, in the absence of heteroatoms or multiple bonds, having a linear or branched aliphatic chain with only two hydroxyl groups.