Question: 86. Total number of possible isomers (both structural as well as stereoisomers) of cyclic ethers of molecular formula \mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O} is:
(1) 6
(2) 8
(3) 10
(4) 11
Answer: Option (3)
Explanation:
The molecular formula \mathrm{C}_{4}\mathrm{H}_{8}\mathrm{O} has one degree of unsaturation, which corresponds to one ring.
Since only cyclic ethers are to be considered, the oxygen atom must be present in the ring.
First, consider three-membered cyclic ethers (epoxides).
Substituted oxiranes with four carbon atoms give structural isomers,
some of which show geometrical or optical isomerism, contributing a total of 4 isomers.
Next, consider four-membered cyclic ethers (oxetanes).
Substitution on the oxetane ring gives 3 distinct structural isomers.
Then, consider five-membered cyclic ethers (tetrahydrofurans).
Methyl-substituted tetrahydrofurans give 3 isomers due to different positions of substitution.
Thus, the total number of possible isomers is:
4 + 3 + 3 = 10Therefore, the total number of structural and stereoisomers of cyclic ethers with molecular formula \mathrm{C}_{4}\mathrm{H}_{8}\mathrm{O} is 10.