The correct stability order of the following resonating structures is:
The correct option is D (III) > (I) > (IV) > (II)
Resonance is the phenomenon in which a molecule can move its π electrons in the system. These electrons delocalized themselves in the compound forming a conjugated system of π electrons. This movement of the electrons cannot be exhibited with the help of one lewis structure, hence more than one structure is drawn to explain the delocalization. These structures are called resonating structures.
Now, the stability of the resonating structures depends upon many factors. Now, we will discuss these factors and then arrange the given resonating structures according to their stability.
1. Structure with a greater number of covalent bonds contributes more towards the resonance hybrid(stability).
2. Structures that involve the separation of positive and negative charges are of higher energy and hence contribute little towards the resonance hybrid.
3. Lesser the charge separation of positive and negative charges, more stable is
the resonance structure.
4. When atoms of different electronegativities are involved, the structure with a
the negative charge on the more electronegative atom and positive charge on less
electronegative atom is of lower energy and hence contribute more towards the
resonance hybrid than the alternate structure in which the charges are reversed.
5. Structure having like charges on adjacent atoms are highly unstable and hence
contribute little towards the resonance hybrid.
6. Structures that help to delocalize the positive charge make important
contribution towards the resonance hybrid regardless of the fact whether the
a positive charge is on fewer or more electronegative atoms.
7. ) Resonance structure in which all the atoms have an octet of electrons makes a larger contribution towards the resonance hybrid than those structures in which one or more of the atoms do not have an octet of electrons.
Based on these observations, the correct order of stability will be (III) > (I) > (IV) > (II)