For each of the following compounds, draw the important resona...

Question

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.

(e) [CH₃C(OH)₂]⁺

(f) [CH₂CHNH]^–

Accepted Answer

Welcome back everyone to another video, draw the significant resonance structures for the following label. The major and minor contributors, we're given two structures and we can begin with the first one specifically, it is an aide. And we have to recall that nitrogen would have we bonds and a long pair of electrons in a neutral form and oxygen has two bonds and two long pairs, right? So essentially, we have to recall that whenever resonance is considered, we have to demonstrate the electron flow from a high electron density to the low electron density. Now, in this case, specifically, what we notice is that if we take the low pair of electrons on nitrogen, this lump pair is actually delocalized, it's part of the conjugate P system, right. So we can essentially form a pi bond out of it by breaking the adjacent pi bond and moving those electrons onto oxygen, which essentially gives us our second resonance form. So we're going to draw nitrogen with two hydrogens bonded to it. Now, nitrogen is bonded to carbon and carbon now is bonded to oxygen. Oxygen gets an extra long pair. And this means that it gets a formal negative charge. Now, carbon is double bonded to nitrogen and nitrogen gets a form of positive charge because it forms a total of four bonds. And of course, we're going to add the remaining metal group. This is it now essentially between the two forms we have to consider which one is major and which one is minor, all of the atoms have an octet. So we are essentially going to label the first one as the major one because all of the atoms have a formal charge of zero, right, the second resonance form has two formal charges. So apparently the major one is the first one and the minor one is the second one. If we consider the second example, once again, we have to start with a high electron density. We're going to add the loan pairs for oxygen, oxygen with a negative charge would have wheel on pairs, neutral oxygen would have two long pairs and carbon with a positive charge only has three bonds. So we're starting with a long pair of electrons and we're going to delocalized that long pair into the formation of a pi bond by breaking the adjacent pi bond. And this would give us our second resonance form. So we end up with carbon, we can add those two hydros, we have carbon carbon, single bond, carbon oxygen, single bond. Now oxygen gets an extra long pair which provides it with a formal negative charge. And now we are going to add the double bonded oxygen with two long pairs remaining from here, we can draw another resonance form. Let's not forget to add the original positive charge on carbon. And essentially to draw the next form, we are simply going to shift our pi bond from oxygen towards carbon. Right. That makes sense. Since carbon is electron deficient, we can break the pi bond and shift it between the two carbons. This gives us our next resonance form. Let's introduce the double bond between two carbons. And now the metal carbon is bonded to two oxygens in each oxygen gets a formal negative charge. Now, on top, we have oxygen with three loan pairs and a formal negative charge to be more accurate. Since we are shifting the pi bond from oxygen towards carbon oxygen with two lone pairs and one bond would actually have a formal positive charge, right. So we have our resonance forms and now we want to consider our major and minor contributors. So let's go ahead and do that. If we look at the first structure, it doesn't have an octet on carbon, right? Carbon only has three bonds, a total of six valence electrons. So octet is incomplete. That's the first rule that we want to check when it comes to the second resin form, we notice that we still have that same incomplete octet on carbon. And now for the last structure, we also don't have a complete attack on oxygen. So none of the structures has a complete octet, meaning we have to consider all of the other aspects. And the second aspect that we are considering is the formal positive charge. And the formal negative charge, more electron atoms prefer to carry a formal negative charge. So we can clearly see that a formal negative charge is present on oxygen or the second structure in the third structure, right, the formal positive charge is preferred on carbon. So we can essentially state that the first structure has a formal positive charge on carbon. And the second structure has a formal positive charge on carbon. Now, from here, we can essentially state that the metal resins form will be the major contributor. Now, why is it the major contributor? Considering the formal charges, the formal negative charge is on a more electron oxygen and the formal positive charge is on a less electron carbon. That's exactly what we want. While the first structure also has a formal positive charge on carbon and a formal negative charge on oxygen. So it would also be a major contributor. And we can clearly see that because the first and the second structures, they're very similar. Right now, the third structure would be the minor contributor because there is a formal positive charge on oxygen and oxygen is more electron than carbon. So we essentially have our final answers. Let's label them. That would be it for today. And thank you for watching.

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.
(e) [CH₃C(OH)₂]⁺
(f) [CH₂CHNH]^–

Key Concepts

Resonance Structures

Major and Minor Contributors

Charge Distribution in Resonance

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