Welcome Guest Search | Active Topics |

Tag as favorite
Aromaticity
Options
Previous Topic Next Topic
Aida_5230
#1 Posted : Sunday, July 05, 2020 5:44:18 PM
Rank: Newbie

Groups: Registered
Joined: 6/5/2020
Posts: 2

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
Hi, I just have a few questions about aromaticity. Firstly, why is a cyclopentadienyl anion considered aromatic? I understand that the pi electrons fit huckel's rule, however isn't the carbanion sp3 hybridized because it is attached to 4 electrons groups (the lone pair, the hydrogen, and both carbons)? However, online sources tell me it is sp2 hybridized and I don't understand why...

As well, I'm having trouble understanding why bases are aromatic or not... For example, for cytosine, the internet tells me it has 6 pi electrons because you include the ones on the NH, however why doesn't it count the lone pair electrons on the double bonded N (shouldn't it be 8 pi electrons using that logic)?

Thanks
Back to top
Report?
INSTR_Katerina_102
#2 Posted : Sunday, July 05, 2020 6:00:38 PM
Rank: Advanced Member

Groups: Registered
Joined: 6/24/2019
Posts: 250

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
Firstly, why is a cyclopentadienyl anion considered aromatic? I understand that the pi electrons fit huckel's rule, however isn't the carbanion sp3 hybridized because it is attached to 4 electrons groups (the lone pair, the hydrogen, and both carbons)? However, online sources tell me it is sp2 hybridized and I don't understand why...

Recall that a lone pair that participates in resonance must be in a p orbital - that forces your geometry to be sp2 as a result. Without this resonance, you are correct and a carbanion would a tetrahedral parent shape. This is very similar to the amide bond, where the nitrogen may look like an sp3 hybridized atom, but has in fact significant sp2 character.


As well, I'm having trouble understanding why bases are aromatic or not... For example, for cytosine, the internet tells me it has 6 pi electrons because you include the ones on the NH, however why doesn't it count the lone pair electrons on the double bonded N (shouldn't it be 8 pi electrons using that logic)?


https://ibb.co/dgWrwWZ

I've drawn the main tautomers where you can clearly see the aromaticity of nucleotides. This is what you'd look at when you are considering what to leave in and leave out for counting aromaticity.

Please let know if this is unclear.
Back to top
Report?
Users browsing this topic
Guest
Tag as favorite
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.

Clean Slate theme by Jaben Cargman (Tiny Gecko)
Powered by YAF | YAF © 2003-2009, Yet Another Forum.NET
This page was generated in 0.091 seconds.