Aamc cbt 11 bs 145

[sudo]

I'm a little hazy on drawing chair conformations and after trying to refresh myself, I'm still having some issues with this. Can someone explain how to figure out what the chair conformations of each of these are supposed to look like?

I think I'm having trouble figuring out how cis/trans and axial/equatorial correlate.

Thank you

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[MedPR]

Reds are axial, blues are equatorial. In chair conformers, two up or two down = cis, one up one down = trans. Since bulky groups are always equatorial, the tert-butyl in all of your structures above will be equatorial.

For the sake of simplicity, let's use the top right carbon on the above chair conformer as Carbon 1 and count clockwise for carbons 2-6.

1. cis-1,2. So the tert-butyl is equatorial, and therefore is pointing down. In order for the methyl to be cis as shown, it must also be pointing down, so it must be axial on carbon 2.

2. cis-1,3. Again, the t-butyl is equatorial and pointing down, so the methyl must also be pointing down. Carbon 3 equatorial points down, so methyl will also be equatorial.

3. trans-1,4. t-butyl is equatorial/down. Methyl must be up, so it will be equatorial.

 

[sudo]

Reds are axial, blues are equatorial. In chair conformers, two up or two down = cis, one up one down = trans. Since bulky groups are always equatorial, the tert-butyl in all of your structures above will be equatorial.

For the sake of simplicity, let's use the top right carbon on the above chair conformer as Carbon 1 and count clockwise for carbons 2-6.

1. cis-1,2. So the tert-butyl is equatorial, and therefore is pointing down. In order for the methyl to be cis as shown, it must also be pointing down, so it must be axial on carbon 2.

2. cis-1,3. Again, the t-butyl is equatorial and pointing down, so the methyl must also be pointing down. Carbon 3 equatorial points down, so methyl will also be equatorial.

3. trans-1,4. t-butyl is equatorial/down. Methyl must be up, so it will be equatorial.

Thank you so much for that explanation!

 

[451617]

Thank you so much for that explanation!

bump

i wish the picture in the explanation was working - it may help.
i'd appreciate an updated explanation of this problem.

thank you very much!

 

[Jepstein30]

I'm a little hazy on drawing chair conformations and after trying to refresh myself, I'm still having some issues with this. Can someone explain how to figure out what the chair conformations of each of these are supposed to look like?

I think I'm having trouble figuring out how cis/trans and axial/equatorial correlate.

Thank you

Here's the trick I used:

1) Identify the bulkiest group which will be Equatorial (E)
2) Starting from that group, the neighboring substituent with the SAME orientation (as in, pointing up or pointing down) will be axial. The neighboring substituent with the OPPOSITE orientation will be equatorial.
3) This pattern repeats around the ring. For everything pointing UP, it switches between E and A as you go around.

So pretty much, just have to know which group is bulkiest and its following a simple pattern from there. Also watch out for 1-3 diaxial interactions.

For these examples, t-butyl will always be equatorial.

I. This is cis 1-2.. so if t-buytl is equatorial, the neighboring methyl group must be axial (next to it, same orientation).

II. This is cis 1-3.. so if t-butyl is equatorial, the methyl group will also be equatorial (two spots away, same orientation)

III. This is trans 1-4.. if t-butyl is equatorial, we'd expect the substituent with the same orientation at carbon 4 to be axial.. since this orientation is flipped, it will be equatorial.

 

[451617]

Here's the trick I used:

1) Identify the bulkiest group which will be Equatorial (E)
2) Starting from that group, the neighboring substituent with the SAME orientation (as in, pointing up or pointing down) will be axial. The neighboring substituent with the OPPOSITE orientation will be equatorial.
3) This pattern repeats around the ring. For everything pointing UP, it switches between E and A as you go around.

So pretty much, just have to know which group is bulkiest and its following a simple pattern from there. Also watch out for 1-3 diaxial interactions.

For these examples, t-butyl will always be equatorial.

I. This is cis 1-2.. so if t-buytl is equatorial, the neighboring methyl group must be axial (next to it, same orientation).

II. This is cis 1-3.. so if t-butyl is equatorial, the methyl group will also be equatorial (two spots away, same orientation)

III. This is trans 1-4.. if t-butyl is equatorial, we'd expect the substituent with the same orientation at carbon 4 to be axial.. since this orientation is flipped, it will be equatorial.

awesome. thanks so much!
help appreciated