JEE Advanced · 2019 · 27 May 2019 · Paper 2 · Alcohols Phenols and Ethers

Total number of isomers, considering both structural and stereoisomers, of cyclic ethers with the molecular formula

C_{4} H_{8} O

is ____

Answer: 10

Solution

Cyclic ethers with formula

C_{4} H_{8} O

include:

2-Methyloxetane (4-membered ring with methyl): 1 chiral center → 2 enantiomers (R, S)

3-Methyloxetane (4-membered ring with methyl at position 3): 1 chiral center → 2 enantiomers (R, S)

2-Ethyloxirane (3-membered ring with ethyl): 1 chiral center → 2 enantiomers (R, S)

2,3-Dimethyloxirane (3-membered ring with two methyls): 3 stereoisomers (R,R), (S,S), and (R,S = meso)

2,2-Dimethyloxirane (3-membered ring with gem-dimethyl): 1 isomer (no chirality)

Total: 1 + 2 + 2 + 2 + 3 = 10 isomers

JEE Advanced · 2019 · 27 May 2019 · Paper 2 · Numerical answer