JEE Main Chemistry question

Amongst the given compounds, the one(s) in which all the atoms are in one plane in all possible conformations is(are)

(A)H₂C=C=C=CH₂ (butatriene)Correct
(B)H–C≡C–CH=C=CH₂ (an enyne-allene)
(C)H₂C=C=O (ketene)Correct
(D)CH₃–CH=C=CH–CH₃ (a cumulated diene with methyl termini)

Answer: (A),(C)

Solution

In a system of N cumulated double bonds, successive π-systems are mutually perpendicular, rotating the plane of each terminal substituent set by 90° per double bond. When N is odd (as in butatriene, N=3), the two terminal CH₂ planes end up parallel/coplanar with the rest of the molecule — the whole molecule is planar.

See the full step-by-step solution

Create a free account to read the complete working, and practise questions like this in a timed test.

Create a free account

Question ID VK-139108