Draw the resonance structure indicated by the curved arrows. Assign formal charges, and evaluate which of the two structures is a larger contributor to the resonance hybrid.

Question

Resonance structure with curved arrows showing electron movement and formal charge assignment.

Accepted Answer

Welcome back everyone provide the residents structure, including formal charges denoted in the illustration below, which is the major contributor to the residents hybrid of the compound shown. So we're going to first recognize that we need to fill in any formal charges. So we want to recall bonding preference and we're going to recall that the bonding preference for an atom like oxygen is for itself to have two bonds and two lone pairs. And this will result in a formal charge equal to zero because oxygen will be stable that way, Whereas nitrogen prefers to have three bonds and one lone pair to be stable for a formal charge of zero and carbon will prefer to have four bonds. And so we're going to see that in the structure our carbon atoms do indeed have four bonds where our oxygen atom also has two bonds and two lone pairs as it prefers. And nitrogen will have its three bonds and one lone pair. So we have formal charges of zero, meaning we have a net formal charge of zero for our structure. So we have a pretty stable structure here, but now, based on those arrows denoting the bond moving to oxygen as a lone pair and the lone pair moving between carbon and nitrogen as a bond. We're now going to form our first president structure where we would have our molecule as follows where the second carbon is now singly bonded to oxygen, where oxygen has a total of three lone pairs on itself and nitrogen is doubly bonded to this second carbon and singly bonded to these other hydrogen atoms where now nitrogen does not have any lone pairs on itself. And to calculate its formal charge, we would count a total of 1234 directly attached valence electrons on this nitrogen atom. Where because nitrogen we would recall is in Group five A would prefer to have five directly attached valence electrons to itself. And so this nitrogen atom is missing one of its five valence electrons. And so it has a formal charge of plus one. Going to this oxygen atom, we would count a total of directly attached vance electrons to this oxygen atom, meaning that it has one more than it would prefer because we would recall that oxygen located in Group six A should have six valence electrons to be stable. And so this oxygen has one more than it needs. And so it has a formal charge of minus one. Our carbon atoms are still happy, they still have their four bonds. And so we don't need to give them any formal charges. So now we need to determine between which of these two resonance structures would be the major contributor to the resonance hybrid. So we're going to go ahead and also denote the fact that we have a net formal charge of zero for the structure for this second resonance structure, but we still individually have a formal charge on at least one of our atoms being minus one on oxygen and then plus one on our nitrogen atom. And due to these presence of formal charges, we still would say that this second resonance structure is therefore going to be a minor contributor, Whereas structure one we would want to label as a major contributor Because we would recognize that we have minimum formal charge of zero on or sorry, the maximum amount of formal charges of zero being on all of our atoms in this entire structure. We determined that based on bonding preferences and based on counting the directly attached valence electrons. And so because each atom in this first structure was bonded according to bonding preference, we have stable atoms which all have minimal formal charges. So all formal charges of zero, meaning that this structure is a major contributor. And so for our final answer, we're going to confirm that this first structure is our major contributor and the second structure is going to be our minor contributor and our second answer for the resonant structure here. So I hope that everything I explained was clear. What's boxed in yellow and highlighted is our final answers. If you have any questions, please leave them down below and I'll see everyone in the next practice video

Draw the resonance structure indicated by the curved arrows. Assign formal charges, and evaluate which of the two structures is a larger contributor to the resonance hybrid.

Verified Solution

Key Concepts

Resonance Structures

Formal Charge

Resonance Hybrid