Question

The resonance structures of carbon monoxide are shown below. Show how each structure can be converted into the other using the curved-arrow notation. To draw an arrow, click on the structure to enter the edit mode, then click on the curved arrow icon.

Answer 1

Concepts and reason

It is the curved-arrow notation that shows how to attain one resonance structure from another. In other words, it shows how the electrons move in the structure of the compound. The movement of electrons always takes place in pairs. The electrons always move from tail to head as shown:

The tail must have the ability to donate electrons (lone pair or bond pair) and the head must have the ability to accept the electrons in accordance with the octet rule. The three possible movements for the curved arrow are:

Bond pair to lone pair

Lone pair to bond pair

Bond pair to bond pair

The formal charge also changes with each arrow by factor of 1. Since the tail donates the electrons, therefore it attains a positive charge. And since the head gains the electrons, therefore it attains a negative charge.

Fundamentals

When a single Lewis structure is unable to represent the structure of a compound, then the resonance structures come into play. It is the movement of electrons that distinguish each resonance structure from the other.

The Lewis dot structure of ${\rm{CO}}$ is:

$:c=0 $

Another Lewis structure of ${\rm{CO}}$ obtained using the curved arrow-notation and showing the movement of electrons from ${\rm{O}}$ to ${\rm{C}}$ is:

The octet of carbon is not complete. Therefore, to complete the octet of ${\rm{C}}$ , the lone pair on ${\rm{O}}$ atom shifts to the ${\rm{C}}$ atom thereby forming a new bond between the two.

Another Lewis structure obtained using the curved arrow-notation and showing the movement of $\Pi$ -electrons from ${\rm{C}} - {\rm{O}}$ triple bond to ${\rm{O}}$ is:

There will be a shift from $\Pi$ -electrons of the ${\rm{C}} - {\rm{O}}$ triple bond to ${\rm{O}}$ atom. Since the ${\rm{C}}$ loses an electron and ${\rm{O}}$ gains an electron, thus they get a neutral charge.

Finally, the curved arrow representation is:

Ans:

The interconversion between the structures using the curved-arrow notation is: