AIIMS 2010 Chemistry Resonance in Organic Chemistry MCQ Question

Resonating structures are different ways to represent a molecule that cannot be adequately described by a single Lewis structure. Let's analyze the options:

A) The contributing structures must have the same number of unpaired electrons. This is correct because the resonance structures should maintain the same number of unpaired electrons to ensure that they represent the same overall electronic configuration.

B) The contributing structures should have similar energies. This is also correct, as resonance structures that are significantly different in energy will not contribute equally to the resonance hybrid.

C) The contributing structures should be so written that unlike charges reside on atoms that are far apart. This is the incorrect statement. In resonance structures, it is preferable for unlike charges to be as far apart as possible to minimize repulsion, but this is not a strict requirement. The key is that the structures should be valid Lewis structures, and charge separation is often not ideal.

D) The positive charge should be present on the electropositive element and the negative charge on the electronegative element. This statement is correct because it reflects the stability of charge distribution in resonance structures, aligning with the periodic trends of electronegativity.

Thus, option C is not a correct condition for resonance structures.