Among the compounds A and B with molecular formula C₉H₁₈O₃ , A is having higher boiling point the B. The possible structures of A and B are :

Solution

Chemistry ma’am · 3 steps

First check both structures are really C₉H₁₈O₃, then let the O–H groups decide who boils higher.

1. Check the formula. A trisubstituted cyclohexane ring is C₆H₉. Three OCH₃ groups or three CH₂OH groups bring 3 C, 9 H and 3 O, giving C₉H₁₈O₃. Two CH₂OH groups plus one OH bring only 2 C, giving C₈H₁₆O₃, which is not an isomer.
2. Compare boiling points. An alcohol has O–H bonds, so its molecules hydrogen bond to each other strongly. An ether has no O–H bond, so it has only weaker dipole and dispersion forces. Among isomers, the triol boils much higher than the triether.

   Option	A	B	Verdict
   (a)	triether, C₉H₁₈O₃	C₈H₁₆O₃	B is not an isomer
   (b)	triether, C₉H₁₈O₃	triol, C₉H₁₈O₃	B boils higher, order reversed
   (c)	triol, C₉H₁₈O₃	triol, C₉H₁₈O₃	both have three O–H, no definite reason for A to be higher
   (d)	triol, C₉H₁₈O₃	triether, C₉H₁₈O₃	A hydrogen bonds, so A boils higher

3. So. In (d), A is cyclohexane-1,3,5-triyltrimethanol and B is 1,3,5-trimethoxycyclohexane. They are isomers, and only A can hydrogen bond, so A has the higher boiling point. The answer is (d).

The idea to keep. For isomers, look for O–H or N–H first. An alcohol always outboils an ether of the same formula because ether molecules cannot hydrogen bond to each other.

Answer from the NTA final answer key. Solution by PrepWiser.