Which of the following compounds will produce a precipitate with AgNO3 ?
(A)(see structure)
(B)(see structure)✓ Correct
(C)(see structure)
(D)(see structure)
Answer: (B)
Solution
A halide gives a precipitate with silver nitrate only if it can ionise to release the halide ion, and that turns on how stable the resulting cation is. Cycloheptatrienyl bromide ionises to the tropylium cation, a seven-membered ring with six π electrons that is aromatic and therefore very stable, so the C−Br bond breaks readily and AgBr precipitates. The other compounds have aromatic or vinylic C−Br bonds that resist ionisation, or give far less stable cations, and so give no precipitate.
JEE Main · 2019 · 11 Jan 2019 · Shift 2 · Single correct option