IIT-JEE 2012 · Paper 1 · Chemistry Q33

ChemistryMultiple correct+4Question 33 of 60

Which of the following molecules, in pure form, is (are) unstable at room temperature?

Answer and worked solution

Official answer: B, C

(A) Cyclohexa-1,4-diene has two isolated double bonds; it is a stable liquid.
(B) Cyclobutadiene has 4 π electrons in a planar ring: antiaromatic, and it dimerises at once even at low temperature. Unstable.
(C) Cyclopentadienone: polarising the C=O puts a positive charge on a 4π-electron ring (antiaromatic character), and it dimerises rapidly. Unstable.
(D) Tropone: polarising the C=O gives a tropylium-like 6π aromatic ring. Stable.

(B), (C)

Topics:Aromaticity

IIT-JEE 2012 · Paper 1, Chemistry question 33