Among the compounds A and B with molecular formula C9H18O3, A has a higher boiling point than B. The possible…

🧠 Two isomers with formula $\mathrm{C_9H_{18}O_3}$: one has –OCH₃ ether groups (no O–H), the other has –CH₂OH groups (with O–H). The one with O–H has much higher boiling point due to H-bonding.

🗺️ Identify the structures:

1,3,5-trimethoxycyclohexane: Three –OCH₃ ether groups

• No O–H bonds → no H-bond donor capability
• Only van der Waals and weak dipole–dipole forces
• Lower boiling point → this is B

1,3,5-tris(hydroxymethyl)cyclohexane: Three –CH₂OH groups

• Three O–H bonds → extensive intermolecular H-bonding (three donors per molecule)
• Much stronger intermolecular association
• Higher boiling point → this is A

⚡ The molecule with O–H groups always has a significantly higher boiling point than its ether isomer — H-bonds (20–40 kJ/mol per bond) are far stronger than dipole–dipole forces (2–5 kJ/mol).

$\boxed{\text{Answer: A = 1,3,5-tris(hydroxymethyl)cyclohexane; B = 1,3,5-trimethoxycyclohexane}}$