Why is glucose soluble in water but cyclohexane is not?

Glucose is soluble in water, while cyclohexane is not, due to their differences in molecular structure and the nature of their intermolecular forces.

Molecular Structure:

Glucose (C6H12O6) is a polar molecule. It contains numerous hydroxyl (-OH) groups, which have polar covalent bonds. These polar groups interact favorably with water molecules through hydrogen bonding.
Cyclohexane (C6H12), on the other hand, is a nonpolar molecule. It consists of carbon and hydrogen atoms arranged in a cyclic structure, with no electronegative elements like oxygen or nitrogen. It lacks polar bonds and, as a result, does not form strong interactions with water.
Intermolecular Forces:

Water (H2O) is a polar molecule that exhibits hydrogen bonding. The positively charged hydrogen atoms in water are attracted to the negatively charged oxygen atoms in neighboring water molecules. This gives rise to strong intermolecular forces between water molecules, making it an excellent solvent for polar and ionic substances.
Glucose can form hydrogen bonds with water because of its polar hydroxyl groups. These hydrogen bonds facilitate its dissolution in water, as the water molecules can surround and solvate the glucose molecules.
Cyclohexane, being nonpolar, lacks the ability to form strong hydrogen bonds with water. The forces of attraction between cyclohexane molecules are primarily London dispersion forces (Van der Waals forces), which are much weaker than hydrogen bonds. Consequently, cyclohexane does not mix well with water, and the two substances tend to separate into distinct phases.
In summary, the polar nature of glucose, its ability to form hydrogen bonds with water, and the nonpolar nature of cyclohexane, which lacks such interactions, are the key reasons why glucose is soluble in water while cyclohexane is not.