benzene and friends

[vixen]

can someone help me understand this?

from what I understand, for something to be aromatic, it has to have 3 things, 1) must follow the 4n+2 rule 2) be planar 3) have a closed loop (meaning all sp2 carbons)

How can you tell if something is going to be planar? Isn't that synonymous w/having sp2 carbons, or do anions and cations make a difference.

Also, if something is ANTIaromatic, it follows the same thing as aromatic except its 4n?

and nonaromatic is everything that doesn't follow these rules?

I really am lost as to how to draw molecular orbitals and then be able to tell if its aromatic or not...also, sometimes the answers will say, "its non aromatic because the internal H's prevent planarity"...how do you know if the H's are internal?

Ok, if anyone wants to help me out, I'd really appreciate it...mechanisms I understand, but this stuff I really don't

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[UCMonkey]

OK, its been a while since o-chem, but I seem to remember that things with SP2 carbons are pretty much always planar. That said, another way I spotted aromatic compounds is that they have conjugated double bonds. That is, the structure alternates: double bond - single bond, double bond etc.....

But like I said, its been 3 years, so take from that anything or nothing.

 

[brandonite]

Yes, if you have any sp3 carbons in the ring, then the ring is not planar. That's pretty much the only way you can tell.

I've never heard of antiaromatic.

I've never heard of internal H's in a ring structure. I suppose if it's sp3, you could have bonds to the inside... I think with sp2 carbons, you'll always have bonds to the outside of the ring.

And, trust me, you don't want me to start talking about MO's, because that will just confuse both of us.

 

[vixen]

damn youuuu canadians! J/K! :wink:

 

[imtiaz]

figure out if B3N3H6 [borazine] is aromatic and you will understand. alternate B's and N's in the 6 membered ring.

 

[vixen]

thanks imitiaz...now I'm def on the right track

 

[brandonite]

•••quote:•••Originally posted by simseema17:
•damn youuuu canadians! J/K! :wink: •••••Well, I did agree with you about the sp2 thing! And I was honest enough to admit that I didn't know anything about the rest of it! I could've made stuff up to confuse you, couldn't I? I think I deserve more gratitude! After all, you are my sister... :wink:

 

[vixen]

ok ok, thanks bro remember, I'm the insolent, bratty sister?! <img border="0" alt="[Laughy]" title="" src="graemlins/laughy.gif" /> what do you expect when my daddy, ucla2000, keeps spanking me?! <img border="0" alt="[Laughy]" title="" src="graemlins/laughy.gif" />

 

[brandonite]

•••quote:•••Originally posted by simseema17:
•ok ok, thanks bro remember, I'm the insolent, bratty sister?! <img border="0" alt="[Laughy]" title="" src="graemlins/laughy.gif" /> what do you expect when my daddy, ucla2000, keeps spanking me?! <img border="0" alt="[Laughy]" title="" src="graemlins/laughy.gif" /> •••••Hey, don't go blaming the parents. Perplexed and I are model children, remember? It's just you that turned out bad... <img border="0" title="" alt="[Frown]" src="frown.gif" />

 

[PlayaHata]

If I'm not mistaken sp2 carbons have bond angles of 120degrees which does not make them planar (sorry monkey runner).. sp carbons are planar. Something is aromatic if it is cyclic conjugated polyene that possess 4n+2 pi electrons.

 

[vixen]

no roger rabbit, sp2 are planar and sp are linear.

 

[PlayaHata]

your right my bad (actually orgo book bad schaum's)i looked in my college text your right