E2 reactant question

[virtualmaster999]

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Hi all!

I got really thrown up on this question. I'm trying to find the fastest way to be able to figure this out, and the only way I can do this is by drawing the newmann projection to see how the stereochem will lay out, and thus, I can see if it is E or Z. I feel like that would be too long on the actual. Is there an easier way??

Thanks in advance!!

 

[ThunderSplash]

Hi all!

I got really thrown up on this question. I'm trying to find the fastest way to be able to figure this out, and the only way I can do this is by drawing the newmann projection to see how the stereochem will lay out, and thus, I can see if it is E or Z. I feel like that would be too long on the actual. Is there an easier way??

Thanks in advance!!

There is a much more helpful explanation under me. 🙂

 

[510586]

Hi all!

I got really thrown up on this question. I'm trying to find the fastest way to be able to figure this out, and the only way I can do this is by drawing the newmann projection to see how the stereochem will lay out, and thus, I can see if it is E or Z. I feel like that would be too long on the actual. Is there an easier way??

Thanks in advance!!

We know it is E2 so it must use the antiperi planar. With B, it has the antiperiplanar H as a wedge so it maintains its conformation and would result in the ethyls on opposite sides. However in C, you must rotate the compound around the single bond until the Br has an antiperiplanar H. If they are on opposite sides what you can do is just add the double bond like normal but then switch one of the sides. I did a question just like this and asked orgoman if the shortcut was ok and he said it was. But newman will still be safer (in case you make a careless mistake on the shortcut).

E2 causes an inversion of stereo chemistry. Knowing this, and the fact that Z means "Z Zame Zide" (the same side), it should be easy to see that C is the correct answer.

I think you are thinking of sn2 .

 

[ThunderSplash]

We know it is E2 so it must use the antiperi planar. With B, it has the antiperiplanar H as a wedge so it maintains its conformation and would result in the ethyls on opposite sides. However in C, you must rotate the compound around the single bond until the Br has an antiperiplanar H. If they are on opposite sides what you can do is just add the double bond like normal but then switch one of the sides. I did a question just like this and asked orgoman if the shortcut was ok and he said it was. But newman will still be safer (in case you make a careless mistake on the shortcut).


I think you are thinking of sn2 .

Yes I was, sorry about that. I've been working on ochem all night and it's starting to mess with my head. Great explanation by the way!

 

[510586]

Yes I was, sorry about that. I've been working on ochem all night and it's starting to mess with my head. Great explanation by the way!

No problem! Honestly I'm just glad I'm finally able to help other people. I've been posting so many questions in the Destroyer threads and new threads, so it feels pretty good when I know the answer to other people's questions

 

[virtualmaster999]

Thanks guys!

 

[virtualmaster999]

We know it is E2 so it must use the antiperi planar. With B, it has the antiperiplanar H as a wedge so it maintains its conformation and would result in the ethyls on opposite sides. However in C, you must rotate the compound around the single bond until the Br has an antiperiplanar H. If they are on opposite sides what you can do is just add the double bond like normal but then switch one of the sides. I did a question just like this and asked orgoman if the shortcut was ok and he said it was. But newman will still be safer (in case you make a careless mistake on the shortcut).


I think you are thinking of sn2 .

Wait could you explain this shortcut in a different way? I just got confused on when you said switching the sides.

 

[510586]

Wait could you explain this shortcut in a different way? I just got confused on when you said switching the sides.

http://forums.studentdoctor.net/threads/rotating-structure-for-e2-question.1146931/ This should be it

 

[510586]

Wait could you explain this shortcut in a different way? I just got confused on when you said switching the sides.

Just did it again here u go.

 

[Typical Average Student]

Sorry if it's not clear...

 

[virtualmaster999]

Sorry if it's not clear...
View attachment 193834

Great pic! How'd you go about knowing which side to put the substituent on the newmann? I think that's what is messing me up.

 

[Typical Average Student]

Great pic! How'd you go about knowing which side to put the substituent on the newmann? I think that's what is messing me up.

Its a little difficult to picture with new projections but what you do is angle your vision so that hydrogen is behind the carbon of interest and figure out the R and S from there.