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NEET 2025 · ChemistryPrevious Year Question

The total number of possible isomers (both structural as well as stereoisomers) of cyclic ethers of molecular formula is:

Answer: (B) 11. \textbf{Answer:} (b) \textbf{Solution:} The cyclic ethers of comprise the four-membered oxetanes (oxetane, 2-methyloxetane, 3-methyloxetane), the five-membered oxolane (tetrahydrofuran) and the three-membered oxiranes bearing alkyl groups (2-ethyloxirane and 2,2- / 2,3-dimethyloxirane).

  1. A.10
  2. B.11✓
  3. C.6
  4. D.8

Correct Answer

(B) 11

Solution & Explanation

\textbf{Answer:} (b) \textbf{Solution:} The cyclic ethers of comprise the four-membered oxetanes (oxetane, 2-methyloxetane, 3-methyloxetane), the five-membered oxolane (tetrahydrofuran) and the three-membered oxiranes bearing alkyl groups (2-ethyloxirane and 2,2- / 2,3-dimethyloxirane). Several of these rings (e.g. 2-methyloxetane, 2-ethyloxirane and 2,3-dimethyloxirane) carry a stereocentre and exist as R/S enantiomers, and 2,3-dimethyloxirane also has cis/trans forms. Summing all constitutional isomers together with their stereoisomers gives 11.

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