orgo antiaromatic compounds

[UnimaasMED]

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I picked C because 4n rule for antiaromatic is valid and it looks to me as it is planar (all carbons are sp2 hybridized)
Topscore says right answer is D. Can someone please explain?

The funny thing is that KBB also lists compound C as a "typical antiaromatic compound". WTF???

 

[RUpremed]

i'm pretty sure it comes down to C not being planar

 

[Kobebucsfan]

yeah its not planar, and it has 8 sides

 

[UnimaasMED]

how could you tell its not planar though? My teacher told me whenever all the carbons are sp2 hybridized you can assume it is planar.
Can someone please explain?

 

[glo1984]

A good rule of thumb for cyclic structures is that if the ring has 7 carbons or less and all are sp2 hybridized, it is considered planar. If either one of those aren't met, it isn't planar.

As someone stated above, there are 8 carbons.

 

[27Teeth]

I picked C because 4n rule for antiaromatic is valid and it looks to me as it is planar (all carbons are sp2 hybridized)
Topscore says right answer is D. Can someone please explain?

The funny thing is that KBB also lists compound C as a "typical antiaromatic compound". WTF???

This is a matter of a few simple rules:

In order to be aromatic a compound must be 1) fully conjugated (so the double bonds need to alternate perfectly), 2) a ring and 3) 4n+2 pi electrons.

A compound is ANTI- aromatic if t meets rules 1 and 2 but NOT 3

The answer is C here because the compound is not 4n+2 pi electrons

Answer D the cyclobutene with the free electron pair is non-aromatic. because it is not fully conjugated (recall that cyclopropene with the free electron pair IS aromatic)

 

[UnimaasMED]

This is a matter of a few simple rules:

In order to be aromatic a compound must be 1) fully conjugated (so the double bonds need to alternate perfectly), 2) a ring and 3) 4n+2 pi electrons.

A compound is ANTI- aromatic if t meets rules 1 and 2 but NOT 3

The answer is C here because the compound is not 4n+2 pi electrons

Answer D the cyclobutene with the free electron pair is non-aromatic. because it is not fully conjugated (recall that cyclopropene with the free electron pair IS aromatic)

27 teeth, the answer here is D. I picked the wrong answer. In fact answer D is anti-aromatic.

 

[UnimaasMED]

A good rule of thumb for cyclic structures is that if the ring has 7 carbons or less and all are sp2 hybridized, it is considered planar. If either one of those aren't met, it isn't planar.

As someone stated above, there are 8 carbons.

Thank you glo. If you don't mind could you explain why choice D is antiaromatic?

 

[Kobebucsfan]

Thank you glo. If you don't mind could you explain why choice D is antiaromatic?

D is antiaromatic b/c there are only 4

and 4 is not part of 4n+2 rule

 

[loveoforganic]

The rule for antiaromatic isn't "not 4n+2" - it's "4n" electrons.

 

[Kobebucsfan]

The rule for antiaromatic isn't "not 4n+2" - it's "4n" electrons.

isn't that what i said?

if its not 4n+2, it cant be aromatic

 

[loveoforganic]

Antiaromatic and nonaromatic are different

 

[orgohacks]

Antiaromatic and nonaromatic are different

To repeat what a bunch of people have said, for something to be antiaromatic is has to:

1) be cyclic
2) be flat
3) have 4n pi electrons

Cyclooctatetraene satisfies 1) and 3) but it is tub-shaped, not flat.

D) has 4 pi electrons and is flat.

Kind of a silly nitpicky question though. Cyclooctatetraene *would* be antiaromatic except for the fact that it is big and flexible enough to adopt a tub shape.