Question

which of the following pairs are not resonance structures?

: \\( \ddot { o } = c = \ddot { o } : \\) and : \\( \ddot { o } = c - \underset { \ddot { o } } { \overset { \ominus } { - } } \\)

\\( h _ { 3 } c - \underset { \ddot { o } } { \ddot { o } } - n = \ddot { o } : \\) and \\( h _ { 3 } c - \underset { \underset { \ddot { o } } { \ddot { o } } } { \overset { \oplus } { n } } \\)

\\( h _ { 3 } c - \underset { \ddot { o } } { \ddot { o } } - n = \ddot { o } : \\) and \\( h _ { 3 } c - \underset { \ddot { o } } { \ddot { o } } = n - \underset { \ddot { o } } { \overset { \ominus } { - } } \\)

\\( h - \underset { \underset { : \ddot { o } : } { \ddot { o } } } { \overset { : \ddot { o } : } { p } } - \underset { \ddot { o } } { \ddot { o } } - h \\) and \\( h - \underset { \ddot { o } } { \ddot { o } } - p - \underset { \ddot { o } } { \ddot { o } } - h \\)

Explanation:

Step1: Recall the rules of resonance structures

Resonance structures have the same connectivity of atoms but different distribution of electrons.

Step2: Analyze each pair

• For the first pair: The connectivity of atoms is the same ($O - C - O$), and it is a valid resonance (electron shift from double - bond to single - bond with charge separation).
• For the second pair: The connectivity of atoms is the same ($C - O - N - O$), and it is a valid resonance (electron delocalization with charge separation).
• For the third pair: The connectivity of atoms is the same ($C - O - N - O$), and it is a valid resonance (electron shift).
• For the fourth pair: In the first structure, there is a $P = O$ double bond, and in the second structure, the double - bond $O$ atom has changed its position. Resonance structures must have the same connectivity of atoms. Here, the position of the double - bonded $O$ atom has changed, so these are not resonance structures.

Answer:

The pair \(H-\ddot{O}-\underset{\underset{\ddot{O}}{||}}{P}-\ddot{O}-H\) and \(H-\ddot{O}-P-\ddot{O}-H\) (with the double - bonded \(O\) in a different position) are not resonance structures.