Topscore ochem question

[Decan]

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Please look at question 97 on test 1 (rection of butadiene with HCl). I selected B (b/c of 1,2 addition of HCl) but the answer says that it can also be 1,4 addition. Is that because the resulting carbocation will be allylic?

Also, can someone explain why choice C on question 98 is not anti-aromatic? The explanation topscore provides is that it is not planar, but all the carbons are sp2 hybridized...

Any help would be greatly appreciated!

 

[whoaaitzkyle]

I don't know any better to explain 98...I think the answer is self explanatory.

#97:

It is B&C because when you put the reaction in low heat, it will add 1,2 addition because it is under kinetic control. If you were to do the reaction with high temperature it would add 1,4 addition because it is under thermodynamic control . Since heat is not mentioned in the question both structures are possible.

 

[Decan]

Ah, I understand 97...thanks!

Can anyone explain 98?

 

[TimeforDAT]

Ah, I understand 97...thanks!

Can anyone explain 98?

yeah just like the explanation says, it is not planar. Anti-aromaticity rules are the same as aromatic rules which states it must be planar, conjugated, all carbons must be sp2. but the differences lies in the number of delocalized pi electrons in which there are 4n electrons. Although the cyclooctatetraene has 4n electrons (this case being 8), the molecule itself is not planar but tub shaped. So the rule for being planar is broken,. The cyclooctatetraene's property is that it adds like alkenes by addition, whereas typically aromatic compounds react by electrophilic substitution.

http://en.wikipedia.org/wiki/Cyclooctatetraene

http://www.cem.msu.edu/~reusch/VirtualText/react3.htm

 

[Decan]

Awesome...that helps! I forgot that cyclooctatetraene is sp2 hybridized, but is non planar. Thanks!

 

[heywhatsup]

can anyone explain what exactly makes a molecule planar or non-planar?
i think this is what is confusing me most

can anyone explain topscore NS test 1 number 77 please?

helppppp 🙁