When an ether is protonated by a strong acid such as concentrated HI, what is the ion formed called?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Oxonium ion
The oxygen atom of an ether uses one lone pair to accept a proton from HI. The ion formed has a positively charged oxygen carrying three groups, an oxonium ion; for ethoxyethane:
\( \displaystyle \ce{C2H5-O-C2H5 + HI -> (C2H5)2OH^+ + I^-} \)
NCERT (2026-27 edition):
7.6.3 Chemical Reactions – “The reaction of an ether with concentrated HI starts with protonation of ether molecule.”
“Iodide is a good nucleophile. It attacks the least substituted carbon of the oxonium ion formed in step 1 and displaces an alcohol molecule by SN2 mechanism.”