Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:
(c) Not all of the C—C bond lengths in naphthalene are equivalent. Based on your resonance structures, how many C—C bonds in the molecule do you expect to be shorter than the others?

Question

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:

(c) Not all of the C—C bond lengths in naphthalene are equivalent. Based on your resonance structures, how many C—C bonds in the molecule do you expect to be shorter than the others?

Accepted Answer

welcome back everyone in this example. We have the molecule financially and given by the molecular formula C 14 H. 10. It's a 36 member ring of carbon with edges fused together and it has the following incomplete lewis structure. So we can see the expanded skeletal form of the molecule below. And we need to determine how many residents structures this molecule financially has and we need to also draw all of the resonant structures. But our first step is going to be completing this lower structure and so we should recognize that the carbons in this molecule are all unstable because they only have three bonds. And we want to recall that carbons bonding preferences to have four bonds so that it's fully stable and has a full octet. So the carbon would just have a total of four bonds and we want to go ahead and mend this by recalling that we can add pi bonds to our molecule to stabilize these carbons, recall that pi bonds are also known as double bonds. So let's go ahead and add some pi bonds to our molecule. But before we do so we'll go ahead and label each ring in our molecules. So this would be ring one. This would be ring to and then this would be ring three. So beginning with ring one, we can add a pi bond between these two carbons, these two carbons and these two carbons to give each carbon and ring one a full octet so that it's stable with four bonds. Now in regard to the hydrogen in this molecule, we should recall that hydrogen only has one electron. And so it's only able to form one co valent bond to the carbon atoms in our molecule. So our hydrogen are already stable and that's why we're just focusing on the carbons here. So moving on to ring to to stabilize the carbons in ring two, we would add a double bond between these two carbons and these two carbons and that would give each carbon in ring to a total of four bonds for its stability to be verified. So moving on to ring three, we can go ahead and also add a double bond between these two carbons and a pi bond between these two carbons. And with these bonds added, we can see that each carbon and ring three will have a total of four bonds to be stable with philoctetes. So the this is actually going to complete our Lewis structure and represent our first resonance form of finance three. So now we want to go ahead and move into our second residence form. So we'll draw a resonance arrow and in order to draw our second residence structure, we need to shift these pi bonds to different locations. And so we'll do so by doing that with ring one where we can shift this pi bond to this location, we can shift this pi bond to this location and we can shift this pi bond over here, we can also shift the pi bonds in ring to where this one can go over here once this one moves to this location and then with this one shifting over here, we would have to shift this pi bond over here. So now we'll go ahead and draw out our new structure. And because we understand that our hydrogen are implied in the skeletal structure of finance three. And we're just going to draw in our rings. So beginning with ring one, we have our ring that we draw in, its bonded to ring to hear. And sorry about that. And then we have ring three above. So beginning with our pi bonds in ring one, we have shifted so that we now have a pi bond in this location, a pi bond in this location. And we now have a pi bond here as well as here and then here. And so these were our new placements for our pi bonds. And we still have those two original placements of our pi bonds in ring three. Now, we want to go ahead and draw another resident structure by manipulating again the positions of these pi bonds. So let's go ahead and draw another resonance arrow and focusing on ring two. We can shift the locations of the pi bonds here. So we can shift this pipe on here, which would then in turn cause this pipe on to shift to this location, which would then also allow this pipe on to shift to this location. And so now we produce a third resident structure. So we'll draw out our finance three rings. So we have the first ring and let's draw that better first string, our second ring And then our 3rd ring. So beginning with our first ring, we didn't change any of our pi bonds here. They maintained their position. But now in ring two we have a pi bond that is now at this location, a pi bond at this location and now a pi bond at this location. And then we still have our original placements of these two pi bonds in ring three. So now we're going to make 1/4 resonant structure by again alternating our bonds. Now we'll focus on alternating the bonds between ring two and ring three. So we can actually shift this bond to this location which would then in turn cause this pi bond to shift over here, which would then in turn cause this pi bond to have to shift over here. And so this would create our fourth resonant structure. So we'll draw an arrow And we'll draw the fourth resident structure below. So beginning with ring one which is bonded to ring to And then ring three above that. So bring one. We also did not change the placement of the pi bond, so they have maintained their locations moving on to ring to. We now have a pi bond that has shifted over to this location. We still have our pi bond here and here that we did not move. And then we have a pi bond now in this location and a pi bond in this location. So this would be our fourth resident structure and we can draw our fifth resonance structure by shifting our bonds in ring one, so we can shift this pi bond to this location, which would cause this pi bond to shift here, and then this pi bond would have to shift here. And so this would result in our fifth and final resonance structure where it will actually drill us below, so that we have enough room. So we'll draw that here. So beginning with ring one connected to ring to. Sorry about that. And then we have ring three. So looking at our previous resident structure, we've maintained the positions of our pi bonds in ring three and two. So we have these sigma or pi bonds that maintained the same position and we have these two. Or sorry, this one shifted, but this pi bond remained the same in ring two. But now in ring one, we now have a pi bond in this location. We have a pi bond now in this location and now we have a pi bond in this location And this would be our fifth and final resonance structure. And so we would be able to say that our finance during c. 14 h 10 has five. So it has five resident structures total. So this would be our first answer. and then all of the five residents structures that we've drawn in would be the answers as far as our illustrations of these residents structures. So that would include our diagram that we completed the LeWIS structure for that was also one of our resident structures here, so everything boxed around in yellow as well as our five resident structures here, are our final answers to complete this example, and this will correspond to choice a in the multiple choice. So I hope that everything I reviewed was clear. If you have any questions, please leave them down below and I will see everyone in the next practice video.

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:(a) Draw all of the resonance structures of naphthalene. How many are there?

Verified Solution

Key Concepts

Resonance Structures

Lewis Structures

Delocalization of Electrons