DAT Destroyer OChem question

[JCLewis90]

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The answer to number 22 is D. I understand it, but at the same time, I feel like I would have chosen C. Why can't they both be equatorial? One up, one down..

 

[SafetyDog]

If you draw it out, it wouldn't be trans to eachother.

 

[Minion]

Remember that whenever you are doing trans, that they both have to be going up or down.

Also, whenever you are doing these problems. Recall that whenever you put one group and pretend to label the biggest group, the group that takes up the biggest space as oppose to bigger atomic mass (R,S) as equatorial. If you go down the next carbon, it just switches its position up and down. I usually associate with front as in up, and dash as in down. So in order for to be stable the most would be two equatorial positions, but in this case we notice that if we go around the circle and try to place both as equatorial then it would be impossible because that would corresponds to a CIS.

 

[LazyP]

Remember that whenever you are doing trans, that they both have to be going up or down.

Also, whenever you are doing these problems. Recall that whenever you put one group and pretend to label the biggest group, the group that takes up the biggest space as oppose to bigger atomic mass (R,S) as equatorial. If you go down the next carbon, it just switches its position up and down. I usually associate with front as in up, and dash as in down. So in order for to be stable the most would be two equatorial positions, but in this case we notice that if we go around the circle and try to place both as equatorial then it would be impossible because that would corresponds to a CIS.

should be one up, one down

 

[Minion]

Oops, you are right. Was typing faster than thinking.

 

[LazyP]

i do it all time! i knew exactly what u meant haha

 

[jnaz]

to be trans one has to be up and the other down. since they're 1,3 only one of them can be equitoral. Ethyl is bigger so that has the equitorial priority... hope this helps

 

[JCLewis90]

to be trans one has to be up and the other down. since they're 1,3 only one of them can be equitoral. Ethyl is bigger so that has the equitorial priority... hope this helps

So if they were 1,4 they could both be equatorial right?

 

[Soleus715]

So if they were 1,4 they could both be equatorial right?

yup! btw if you have chad's, he explains it really well. OC 2.3 I think.

easy way to think about it is to assign equa/axial on one of the two trans and then the up/down state alternates as you go down the carbons. so if 1 is equa/up, then 2 is equa/down, 3 equa/up, 4 equa/down

So as you can see 1,4 are both equa but 1 is up and 4 is down so it's trans 😀

 

[JCLewis90]

Sweet. Thanks guys. I've got it straight now

 

[lyates93]

Can anyone help with an explanation to why number 3 is C?

 

[StumpMT]

I drew up the structure using paint to help explain. All the circled carbons are places where Br can attach. All of the red circles are equivalent meaning that if Br attached to the top right all you have to do is rotate and/or flip the structure and it would appear to have attached at any one of the other red circles. All of the blue circles are equivalent and both of the purple circles are equivalent. So while there are many places where Br can attach, only 3 are structurally different.

 

[lyates93]

Thank you very much stump! Super helpful!