Question

Glycerine contains which type of one hydroxyl group?
A. Secondary
B. Primary
C. Tertiary
D. None of these

Answer 1

Hint: Glycerine is known to be a polyol compound, which means it has more than one hydroxyl group. It has a total of three hydroxyl groups attached to it.

Complete step by step solution:
- Glycerine is known as glycerol as it contains three hydroxyl groups in its molecular formula.
- It is a sweet tasting compound that is odorless.
- Glycerine is a non-toxic, viscous liquid that is used in pharmaceutical formulations.
- The three hydroxyl groups in the glycerine makes it soluble in water and has a hygroscopic nature.
- It is a non-volatile liquid.
- The chemical formula of glycerine is ${C}_{3}{H}_{8}{O}_{3}$.
- And since it contains 3 carbon atoms and 3 hydroxyl groups, its chemical name according to IUPAC is propane-1, 2, 3-triol.
- The expanded molecular formula of glycerol can be written as $C{H}_{2}OH-CH OH-C{H}_{2}OH$.
- The hydroxyl groups in glycerol are attached to each carbon atom.
- The molecular structure of glycerine is given below.

- We know that a primary carbon is a carbon atom which is attached to only one other carbon atom and the hydroxyl group attached to this carbon is known as a primary hydroxyl group.
- Similarly, a secondary carbon is a carbon atom which is attached to two other carbon atoms and the hydroxyl group attached to this carbon is known as a secondary hydroxyl group.
- And a tertiary carbon is a carbon atom which is attached to three other carbon atoms and the hydroxyl group attached to this carbon is known as a tertiary hydroxyl group.
- Here, 2 primary hydroxyl groups are present and 1 secondary hydroxyl group is present.
- Therefore, glycerine contains one secondary type of hydroxyl group. Hence, the correct answer is option (A).

Note: Glycerol is mainly used in the food industry as well as in personal care products. The hygroscopic nature of glycerine makes it readily retain or take up the water. It is denser and has a higher boiling point than water.