Stupid OChem Question

[Parietal Lobe]

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I know this is very basic but it's not making sense to me. I'm working on aromaticity and how to tell if a compound is aromatic or anti-aromatic. I got the 4n + 2 rule, but here's a problem I don't understand.

If you have a cyclopentane with two double bonds on either side and a + at the top, how is that 4 pi electrons?

 

[medking]

I know this is very basic but it's not making sense to me. I'm working on aromaticity and how to tell if a compound is aromatic or anti-aromatic. I got the 4n + 2 rule, but here's a problem I don't understand.

If you have a cyclopentane with two double bonds on either side and a + at the top, how is that 4 pi electrons?

Every double bond is 2 pi electrons. You have 2 double bonds.

 

[Parietal Lobe]

Every double bond is 2 pi electrons. You have 2 double bonds.

So wouldn't that be a total of 4 for just the double bonds? How is it that you still have 4 with the + charge on top?

 

[medking]

So wouldn't that be a total of 4 for just the double bonds? How is it that you still have 4 with the + charge on top?

The plus charge means that there is a lack of electron/s. If you take a negative charge away from something, what is left? Yes, a positive charge. I guess if you can picture a neutron being made up of an electron and proton, it makes sense.

So the 4 pi electrons in the 2 double bonds are the only electrons you count when determining aromaticity.

 

[Parietal Lobe]

The plus charge means that there is a lack of electron/s. If you take a negative charge away from something, what is left? Yes, a positive charge. I guess if you can picture a neutron being made up of an electron and proton, it makes sense.

So the 4 pi electrons in the 2 double bonds are the only electrons you count when determining aromaticity.

I'm sorry to be trouble, but I'm still confused. If you only count the double bonds then why is it that when there's a negative charge instead of the + on the top of the same cyclopentane, it's 6 pi electrons? You add electrons for the - but ignore the +?

 

[medking]

I'm sorry to be trouble, but I'm still confused. If you only count the double bonds then why is it that when there's a negative charge instead of the + on the top of the same cyclopentane, it's 6 pi electrons? You add electrons for the - but ignore the +?

Well, technically I didn't ignore the positive at the top. It's just that there are no pi electrons there. So, total number of pi electrons for that compound would be, 2 + 2 + 0 = 4

Now if there was a negative sign instead of a positive sign, that means that there are 2 pi electrons there, and thus the total number of pi electrons would be, 2 + 2 + 2 = 6

BTW, the negative and positive signs are determined by oxidation number so if you're confused about that, go over that. For carbon, if there is a positive, it means that there are no pi electrons and if there is a negative, it means that there are two pi electrons.

 

[Parietal Lobe]

Well, technically I didn't ignore the positive at the top. It's just that there are no pi electrons there. So, total number of pi electrons for that compound would be, 2 + 2 + 0 = 4

Now if there was a negative sign instead of a positive sign, that means that there are 2 pi electrons there, and thus the total number of pi electrons would be, 2 + 2 + 2 = 6

BTW, the negative and positive signs are determined by oxidation number so if you're confused about that, go over that. For carbon, if there is a positive, it means that there are no pi electrons and if there is a negative, it means that there are two pi electrons.

OK, now that makes sense. Thank you so much!!