JEE Advanced 2019 · Paper 2 · Chemistry Q14

ChemistryNumerical+3Question 32 of 54

Total number of isomers, considering both structural and stereoisomers, of cyclic ethers with the molecular formula $\ce{C4H8O}$ is ______

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Answer and worked solution

Official answer: 10

Count the cyclic ethers of $\ce{C4H8O}$ by ring size, including stereoisomers.

Five-membered ring: tetrahydrofuran, 1.
Four-membered ring: 2-methyloxetane (chiral, 2) and 3-methyloxetane (1).
Three-membered ring:
- 2-ethyloxirane (chiral, 2);
- 2,2-dimethyloxirane (1);
- 2,3-dimethyloxirane: cis meso (1) plus a trans pair of enantiomers (2).

$1+2+1+2+1+3=10.$
Answer: 10

JEE Advanced 2019 · Paper 2, Chemistry question 14