Question

Acylium cation has two resonating structures (I) and (II). Which statement is correct for (I) and (II)?

A) (I) is more stable than (II)
B) Stability of (II) is more then (I)
C) Both have same stability
D) None of these

Answer 1

Resonance structures are the structures that are representing the delocalization of polyatomic ions or a molecule’s electrons. Resonance structure will be stable if it has negative charges on the most electronegative atoms and will be unstable if positive charges on the least electronegative atoms.

Complete step by step answer:
There are few conditions which need to be followed to check the stability of any resonating structure. -The resonating structure which has less electronegative atom and has positive charge is more stable and if in the structure every atom has complete octet then it is more stable.
-The stability of acylium ion is achieved by the positive mesomeric effect of lone pairs of electrons on empty p-orbital of ${C^ + }$. This helps to achieve the octet completion of a carbon atom and increase its stability.
-Mostly weak inductive effects dominate in resonance effect therefore the destabilizing negative inductive effect of oxygen has very negligible role.
-Now in the given structures of Acylium Since carbon atoms have less electronegativity than oxygen atoms, the positive charge present on $C$ will make the resonating structure more stable. Therefore structure (I) may be more stable than (II). But in case of structure (II) the octet of every atom is complete and it dominates over the electronegative effect. Therefore structure (II) is more stable than (I).
Hence, option B is the correct answer.

Note:
Resonance: It is defined as the property of a compound in which a compound can be visualized in multiple structures only having difference in the distribution of their electrons.
Resonance structure: they are used to represent the delocalized electrons over an atom or molecules.